Linq handle null ienumerable. You must check first if StreetAdditional is null.

• Linq handle null ienumerable One of my pet peeves with the LINQ extension methods is their inability to handle null source lists. Name == strRegion This answer is wrong. domainmaps. Contains (value. Select(x => x). Amount)" returns double and it doesn't allow you to use "??" operator to set 0 for empty collection. OfType<T>() will remove null values and return a list of the type T. IsPositive). One way would be to create a singleton-sequence out of the item (such as an array), and then Concat it onto the original:. studentTypes. public static class AddressExtensions { public static Address DeliveryAddress(this IEnumerable<Address> addresses) { return addresses. 24. Empty<T> (or any other "empty" enumerable of that type). Except(chqList, MyEqualityComparer<MyClass>); Here is the IComparer: I have a linq query in which i am getting the user list and after that we are getting the record by userid filter. It doesn't tell them how many times you wish to enumerate. AsEnumerable (). If the source is null then it just returns null-coalescing of the value parameter. Empty<T>() can be seen as more efficient than returning null. Data. var results = from t in All() where t. Rather easy, isn't it? Considering the following: private const string LISTSEPARATOR = "; "; album. 4, The foreach statement). FirstName?. Empty, and a null IEnumerable<T> is not the same as Enumerable. if string, replace null by string. StreetAdditional. handling null values of datetime. But if a program is null, it throws an System. searchResults = (from i in SearchList where ( i. How can I check for null values on IEnumerable<T> where T can be either a reference type or Nullable<T> type?. int score = dbContext. MyTable. . This way I don't have to repeat null checks all over the place, and I don't get an IEnumerable back that I have to cast. LINQ, "Value cannot be null", yet query evaluates. Enumerable, including Count, ToArray and OfType. mkfs. IsNullOrEmpty(searchText) || x. With Linq2Objects, Sum always returns 0 even if all input elements were null or there were no input elements at all. Follow edited Jan 1, 2011 at 17:44. @mrhands I'm 100% sure that ListMetadataKor is null. 8. If you insist on doing it the hard way ;p. – This is the problem: listOfA. ToList(); If you are using the C# 6. Where (extension) Enumerable. Name); PropertyInfo[] props = typeof(T). I have been trying to figure out a way to accomplish the same task in a Linq statement. It's a fairly common use case for us ( e. Empty<SASF>() or throw an ArgumentException, depending on what you need. Instance); foreach (var prop in I'm writing a simple console application that compares two instances of a custom class object. Try this. However, I would like to check that it is not "null" or An enumerable containing some nulls is not empty. tags == null) instead. Entity Framework – linq and null values. ShouldBeFalse(); } Now the question comes, how do we use LINQ to IEnumerable to handle such case, how to use LINQ to remove those items from Others entity? but we need to keep other2 and other3 not to be null (keep it count is 0). Public | BindingFlags. [name] = @p__linq__1 Make sure that you first turn your DbSet, IEnumerable, ICollection, or List into an IQueryable otherwise c# will not be able to find the WhereIf extension method. Thats the reason for the exception. Then, use it in the same way, i. Title } creates an instance of an anonymous type with two fields - Description and Title) You should remove the Select part to make it work. Related. Value. Try. Empty<T>(); } If both are null, you will get a non-null, empty enumerable. Repeat(item, 1); This will create a new IEnumerable that only contains your item. AnswerRows ?? Enumerable. Empty : l) If you Here the benefits are already noticeable, we avoid one null check. ArgumentNullException: Value cannot be null. Unless you have a really good reason, anything that generates an iterable collection should return an empty collection instead of null. Should i check the length of the string and then null the relevant vars and then check this in my linq statement or can i do something Assuming that Person is a class Contains seems to be method of this class. First(); @novaterata: Creating (for example) a Queue from an IEnumerable will copy the references in the IEnumerable. var user = UserDal. Street. The compiler will stop asking for a return in that case. Any() check if the collection/sequence contains any elements (they do not check if it's null and will throw an exception if it is). Handling null values inside a WHERE with ANY Condition in linq. Follow edited Mar 15, 2022 at 15:24. I have a function that returns an IQueryable<MyObject> object from a LINQ-to-SQL query. The || operator plus the String. If "F00" and "n10" are the only valid values that commSubGp can have, you should throw an ArgumentException, for this parameter. ) and that means I don't need where clause in the query as selecting none on checkboxlist means selecting all. – andreim. When you explicitly check for "field == NULL", LINQ probably converts that to "field IS NULL". Where(x => x != null) . You should start from Tools. I can see that every other extension method always must throw an ArgumentNullException for the exact reason you're saying. Changes: how you obtain countMethodInfo for a generic method; the arguments to Invoke; Code (note obj is my instance of When dealing with IQueryable<T> queries, the lambda expressions are converted into expression trees and expression trees don't support the null conditional operator. If you are using a Linq to SQL context and querying in the fashion of . MyRegisteredItems ?? Enumerable. SelectMany(x => x. MyProperty). public static IEnumerable<Game> GameByMatchingName(this IRepositoryAsync<Game> repository, string searchCriteria, string countryId = null) { return repository . Besides LINQ, are there any other solutions? I tried to use the following, but failed, var others = ((MyVM)DataContext). List<Foo> MethodReturningFooList() { I'm not quite sure about the use case. Contains(SearchTerm) orderby r I've modified it to handle a specific separator and it works great, but sometimes, some of the properties for a given object will contain a null value and I'm wondering if it is possible to expand this code to handle the null and replace it by a default value based on the property type i. Where(ans => !string. Value for Non-Nullable System. Is there an elegant way to handle We have a list of modules for a page and want to get the maximum value of the column "Sort". You can do: (mIds ?? Enumerable. ) throws on null, but works correctly with empty sequence. It can be further tracked to the design of SQL and the principles three-state logic. DisplayName) . ToolConvert. Append(image. Usage: SingleOrDefaultAsync() does exactly what's in the method name, it tries to find a single entry and returns the default if nothing is found. – juharr. Because of that behavior, null-values can be handled and you don't get a NullReferenceException. c#; linq; Share. ToList();. When you use foreach, internally, this is calling the IEnumerable's GetEnumerator() method. Queryable() . One answer posted there exhibited best performance and was extremely consise, with the relevant coding snippet repeated here for posterity:. ToArray(); In this case, if null passed to searchTerm you can check the null expression like below. We can write one small extension method for IEnumerable<T> with name Match, which takes two How to handle null values in LINQ Select statement. e. Count > 0; } Share. Even in F#, which does not really use nulls except for interoperability with other . GetProperties(BindingFlags. I know this makes no sense since empty sets and nullable types are not the same thing at all. The expression check for null of the source parameter then concatenate a null-coalescing of the value parameter. GroupBy(x => x. How can I set a zero-value instead of null in LINQ Select Sum. ID > 0). Books. However, it is perfectly valid to have an empty IEnumerable or IEnumerable<T>. For each property, I'm writing True or False to the console window to show whether each of the objects' properties match. There is no absolute right approach, it depends. CSharpNoob. My linq query is returning values with which I'm populating a new instance of a class. Select, nor Enumerable. IEnumerable<Student> studentTypes = this. Count prior to returning the object. This happens because it is an extension method, which is just syntactic sugar. Layers. And then you are trying to do a ToLower() on a null value. ToLower ToLower doesn't have any parameters, so it can be ruled out. Check if list is null before using linq. subitems) You can easily return an empty enumerable instead of null. After this I am trying to loop through the result set. You have multiple options, first is to do an explicit check against null and the other option is to use Null propagation operator. ) != null simply checks that the object isn't null (it could still be empty). NestedCollection) Your second NestedA instance doesn't have a NestedCollection, so it's trying to find "all the items in a null reference". Commented Apr 21, 2017 at 9:08. Union(yourIds ?? Enumerable. Some queries must be expressed as method calls. public static class Extension { public static IEnumerable<T> WhereNotNull<T>(this Alternatively you can do this if you like to start from null: IEnumerable<Book> books = null; var moreBooks = context. ListarItens(null, null, null). Select. 379. Description, t. SingleAsync() instead, which will throw My Linq query is some thing like this: IEnumerable&lt;Results&gt; subResult = from query in datatable. Empty<ClassRegisteredItems>(); myCollection. Why does this statement throw a null reference exception? 2. Possible InvalidOperationException The problem is really in whatever is creating these enumerables. In LINQ to Entities this is converted and executed as SQL. – Matt Howells. Captain Kenpachi. But if you use LINQ it expects that the "Sum(l => l. Chances are you will not have a null object, and having no or less rows is not the same (I am sure you understand the semantics). Contains(streetAdditional)) This works because && is a shortcut-operator and if a != null yields false, the second expression with the null-value won't be evaluated since the result will be false anyway. Consider this code with and without the commented line:. question_group) . Example: You can use the OfType operator. SQL has no issues with expression like subASSRED. Failing that, a NullReferenceException in this code likely means that you a fetching the entire table and filtering on the client, which in turn means you are using an outdated version of EF where this happens silently (newer versions raise an exception if the filter cannot be translated to SQL), so remove that ToLower() so that Enumerable. Union(results2); You can create an extension method similar to ToDictionary() with the difference being that it allows duplicates. I can change the objects parameter to be List and then avoid the possible multiple enumeration but then I don't get the highest object that I can handle. This is a tweaked version of the original source that only applies the filter if shouldApplyFilter returns true, comments are also removed for brevity. 3. CSharpNoob Enumerable<Guid>. With both extensions, one for strings, one It might be nicer if the process object was something that processed just one item in the list at a time (if that's even possible), that way you could collect each individual exception and return an AggregateException just like the Task Parallel library does. The Overflow Blog WBIT #2: Memories of persistence and the state of state Since NULL means undefined, you can't say that two null values are equal, since by definition you don't know what they are. Where(a => a. But really it's better to filter the nulls first like Rob's answer. Should a reference to a null variable Converting linq result to hashset. It was a Tuesday. Consider the following example: Well, in my opinion the empty enumerable should be distinguishable from null enumerable object, so the two should not behave in the same way. In particular, the whole LINQ world What is null? First off let's assume that null means unknown. Contains(searchString) == true But I would suggest you to use Is there a way to make the FirstOrDefault on a list of integers return a null value when the list is empty? c#. Linq, exclude SQL Nulls. IsNullOrEmpty(SearchTerm) ||r. If the value is null then it's used in the where statement. List<string> list = {"a"}; // is the result null or something else? @omega default(T) returns the default value of a type. Select(ii => props[ii] != null ? props[ii]. AsEnumerable() select new Results LINQ query operators and null lists 8 December, 2009. it returns either the first element from the enumerable, or if none exists, the result of default(T). Advantage is that Enumerable. You might want to try something like this instead: var questionGroups = questions. studentID== studentId)); return studentTypes. Eric Lippert's Null Is Not Empty provides a great reasoning for that. FirstName. OfType<T>(); Another option is make your own DistinctBy that behaves the way you want. Where(t => t. Enumerable. Sort). GetMetadata method and check when it returns null. Contains(searchText)) or Where(x => string. Key == col select new { ColumnName = col, FieldValue = field. Summaries = (from r in Summaries where string. Just use the same type as MyProperty and it won't filter out anything else. Checking for nulls in Linq Query. ToArray(); In this case, if null passed to searchTerm you can check the null expression like below I'd be inclined to write both of these as extension methods on IEnumerable<Address>. Contains(SearchTerm) orderby r select r). So you just have to check for null first: You can use a combination of other LINQ methods to handle not matching condition: var res = dictionary. Empty<IAnswerRow>()); In both the OP's code and the above code, questions and answerRows will never be null, so the null checks are not required (you may wish to put . ToList return null. FirstName != null && x. c# foreach I have a question about LINQ query. I receive an object parameter in an method that can be IEnumerable<string> or IEnumerable<bool?> or IEnumerable<int?> or IEnumerable<Guid?> and so on (it can also be non collection types hence the object type). I also think (I haven't tested this yet) that the generated SQL would use an extra subselect query by doing that, while mine would just deal with an empty set by returning null. calling . where a. Range(0, 1000000). But instead an InvalidOperationException is being thrown, stating that the "Sequence contains no elements". AsEnumerable(). ParentLayer } ) If you're doing this really often, consider writing an Append (or similar) extension-method, such as the one listed here, which would let you do:. Linq sorting with nullable object. Contains(searchText)) where x is a Person won't work at all with LINQ to Entities, even with a simple class like . Attributes["itemprop"] instead of p. If Any were not an extension method, calling it on null would result in NullReferenceException. your handleNullProps method is not even reached - the exception is thrown before that. An expression like Where(x => x. Select(t => t. 1 Where is the best place to handle it ? In the GetById method or in the caller ? in enumerable item Otherwise Null Exception from . Max(); I have a method returning IEnumerable object, but I found that sometimes (on error) the method returns null value of IEnumerable. If it was something I needed to do regularly in a loop I'd find another way. For me, if the project use Linq most, please use all Linq. Most queries in the introductory Language Integrated Query (LINQ) documentation are written b Query syntax and method syntax are semantically identical, but query syntax is often simpler and easier to read. Score ?? 0); where domainstatement can be null and score also can be null My initial feeling is no, you don't but it certainly can't hurt. Exception: @PhillipScottGivens no, there is an additional requirement that the GetEnumerator method return an instance of a type that has an appropriate MoveNext method and Current property (ecma spec 15. The result of FirstOrDefault() in this case will be a default instance of an ValueTuple<int,int,int> - all fields will be set to their default value, 0. Handling Exceptions in LINQ Queries. Casting to (int?) before summing makes sense in the context of Linq2Sql, where Sum can return null (directly from the SQL query) even when the compiler infers non-nullable result which leads to an exception. ToLower (). The method looks something like this. var userlist = (from Users in _context. Answer) . If a source collection is null or contains an When dealing with reference types, a null value is semantically different from an "empty" value. TraceTimer+TimerInstance, TracePerfWorker') is not itself marked as serializable. But the issue is while looping through the results, at the end I am getting the below exception on the for each statement: I have a List which holds > 10. Its not an object. var max = db. public IEnumerable<Test> GetTest() { return GetTestForMe() ?? Enumerable. TypeId == avoid the argument null exception in linq like below. How to handle null values with where clause in LINQ? 0. Linq: When object is null an exception is thrown. Check null var postCode = // this gives address or null, if either person is null or its address person. If the return is empty, not sure if it is null or not. As Dmitry shows, you can cheat by initialising as an empty list of objects, which means it won't loop, but to me it seems pointless to initialise something in memory just to save a line of code I have two queries which return a collection of the same kind of object, after these two queries are done, I want to union them. if most are Reactive, please use Reactive for all. subitems == null ? new List<item>() : i. Products where p. Id). We were surprised that the order returned was not the same as when doing the Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Well, in my opinion the empty enumerable should be distinguishable from null enumerable object, so the two should not behave in the same way. Linq. UsersID == 1); But what should The reason you are getting null is because you are trying to convert an IQueryable based on an an anonymous type to IEnumerable<TimelineItem> (new { t. You could take a different approach and turn nulls into empties: I'm writing two LINQ queries where I use my first query's result set in my second query. string Qtyvalues = dtQty. An object collection such as an Each LINQ operator returns an IEnumerable<T> which only when iterating throught it, retrieve its result. SingleOrDefault() will return the single matching object or the default value (which is null for reference types). IsNullOrEmpty(ans)); Checking for nulls in Linq Query. It ignores null values in the source sequence. Well, in my opinion the empty enumerable should be distinguishable from null enumerable object, so the two should not behave in the same way. Categories; return cat; } } here is the interface: Gotcha. IsNullOrWhiteSpace (i. var values = Enumerable. The EF Sum() function can only deal with empty sets if its dealing with nullable data. The goal of taking the highest object is noble, but it leaves There is a big difference between an empty collection and a null reference to a collection. g. With(x=>x. if the project like for, then please do all in for. Empty<T>() to handle the special case of an empty source, but again I'd suggest throwing if source is null. Sometimes the jobname or jobnumber could be empty. False "Sequence contains no elements" exception when using Single() 1. – Marc Gravell. The old Tuple type was a reference type. If you want to go change the type of the collection from nullable type IEnumerable<T?> to non-null type IEnumerable<T> you can use . Making enumerating null a special case would create inconsistency between the I think I can handle the except method ok with my own IComparer but the Range method I can't figure out because it only excepts int so this doesn't compile: Enumerable. Max<TSource>(System The problem is NOT that the 'Price' data type is nullable. During that enumeration, a null reference exception is occuring due to code you have not posted in the question. As a side note, you should use . Checkboxlist can return Null (or empty string in the e. HasValue descending orderby p. Any() instead of . Filter out null values in Linq. C# LINQ NULL check. Since it is an Still - what is the type of v. (params T[] items) which means the compiler would handle the conversion from a single item to an array. 2. I am doing a LINQ query on this IEnumerable&lt;Term&gt; terms = from t in regionCollection where t. SelectMany(f => f. Linq Enumerable. Empty) Likewise, to avoid null when you expect a list, you can add a 2nd extension as overload from this answer. Name. This would align with the Null-Object-Pattern, hence the benefits are the same. If the lists could be null, then you have to check for null. location and wsdetails. FirstOrDefault() which does the same - returns the first item, or null if the result is empty. LINQ orderBy with possible null values. Questions == question) . I am struggling on how I modify this to return 0 if that occurs. ColumnName));`. How to handle NULL object property with FirstOrDefault using Linq. SQL Data Reader - IEnumerable<string> answerValues = fillings . Below is the Linq code I have now. The expectation seems to be that you won't be passing undefined values for something that is expected to exist, so it's still an exception when you have a null. 13. So the null values will effectively be ignored in Min or Max calculation unless all the values are null . . AsEnumerable() select dataRow. And if JobTitle were null, you would get a NullReferenceException . GroupBy() but actually is treated as GroupBy(listWithNulls). Where(x => (x. LINQ SelectMany and Where extension method ignoring nulls. First(n =&gt; n. Whats the best way to handle this. Attributes["itemprop"]. SUM() on SQL which returns NULL when no value is provided. DateOfBirth is a Nullable < DateTime > Source is Entity Framework 4 // using System. Points? int int? IEnumerable – Rashack. Generic { public static class ExtensionMethods { public static Maybe you can just use Where(q => q != null), to filter out the nulls? Or, it it is "List of things or null", you can use something like Select(l => l == null ? Iterable. Where(x => x. Count > 0 and . FirstOrDefault (extension) String. Both . I think what you probably want to do is to remove all the question groups that are null and then check to see if the enumerable is empty. AsNotNull(). Min(o => o. Sum(v => v. Use First when you know that there is one or more items in the collection. ToLower(). Concat(new[] { image. But you probably have a bug here: First() indicates you might have multiple items and want to select the first item - but since there is no ordering involved it means you will get a random item. Hot Network Questions You could use the null coalescing operator to ensure you have a non-null collection: var myCollection = RegisteredItems. Partials. ToString One of my pet peeves with the LINQ extension methods is their inability to handle null source lists. update your select to something like this. Address) // this gives post code or returns null, // if previous value in chain is null or post code is null . worklocation are null causing an exception. ToLower()?. Take(2); This example shows how to handle possible null values in source collections. If you try this with something other than a basic list, I expect you'll see significantly different (slower) results. Or if you have access to the code exposing this collection, you could ensure that MyRegisteredItems is never null. Exceptions can occur during I am using a LINQ query to find sum of a column and there is a slight chance that the value might be null in few cases . Something like: public static Dictionary<TKey, TElement> SafeToDictionary<TSource, TKey, TElement>( this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, var termsList = _actList == null ? null : _actList. The query is not realized until ToList enumerates it. 000 items. In particular, the whole LINQ world (. A null collection is not empty same as a null int? is not zero. Field<string> ("KEYMATERIALS"). LowestPrice select p; Descendants can't return null it always return IEnumerable<T> Where can't return null it return IEnumerable<T> Attributes might Be null yes but you can avoid using Value you can use (string)p. Then you just have to handle nulls being returned and converting them to 0 for your not-nullable I think I get what this is telling me - the implicit class that the enumerator has apparently generated ('System. For example, you must use a method call to express a query that retrieves the number of elements that match a specified con One way to handle null values in LINQ queries is to use the null coalescing operator ??, which returns the left-hand operand if it’s not null, and the right-hand operand otherwise. 0 nullable references, retaining only non-nulls?. in other words, I could do this: from si in (i. I know that IQueryable objects utilize lazy evaluation, so I don't want to enumerate it by using . If you would like to select only Description and Title, The GroupBy-method is an extension-method, which means it is a static method which accepts your date as a parameter. Enumerable. I am using the below code and trying to group by Currency and Code. Not a big deal really. Empty<Test>(); } Using Enumerable. Of course I could use Any or the query syntax (as in here). You can use the null-coalesing operator to return a new instance if the SingleOrDefault() call returns null. The function SUM in SQL returns null if there are no items in the collection, but the signature of Enumerable. Context. Count<T>() has special handling for ICollection<T>. How can I write this LINQ phrase using IEnumerable/List Extension methods // get only rows of ID var query = from i in items select i. Any(). An empty IEnumerable<T> The null check inside WhereNotNull() can look like this: namespace System. Aggregate() method to concatenate a list of strings separated by a semicolon. – Simon Belanger. My datatable is being created generically and being populated with a generically created datarow. Thanks for the upvote and feedback! I'm returning a null in my code: (the var cat line) public class CategoryItemsViewModel { public ICategoriesRepository categoriesRepository; public IEnumerable<Categories> GetCategories() { var cat = categoriesRepository. The default for a reference type, your object Pie in this case, is null hence the warning. It turns out that. domainstatement. In this case, foreach I am trying to see if there is any better way of writing the query below when there is an optional parameter (CountryId) which can be NULL. Use methods that do something else, like FirstOrDefault(), SingleOrDefault() and so on. Any(num => num < 0). Select (p => p. It's as expensive as there are items in the sequence. DateTime. An object collection such as an IEnumerable<T> can contain elements whose value is null. I am not sure if the following ToList() will throw an exception or just a empty List<string> if nothing found in IEnumerable result?. Handling null values @vladd commented on Fri Nov 06 2015. But in some cases when there is no data in the database table my first query returns null, and because of this my second query fails since wsdetails. So won't copy the objects pointed to by the IEnumerable, but it will copy references to those objects. Empty() because SelectMany expects an IEnumerable to flatten, so you can replace it with an empty one when it's null. Max(); Console. Follow answered Apr 11, 2019 at 12:55. But speaking generally, I agree that it's annoying EF limitation, especially the reasoning behind the structurally incompatible initializations requirement, which forces us to use an ugly workaround I'm going to propose you. You must check first if StreetAdditional is null. Concat(moreBooks); although I have several question as to why you want / need to do things this way. IsPositive) does not contains elements. Empty<IQuestion>()); IEnumerable<IAnswerRow> answerRows = questions. DefaultIfEmpty("Unknown") . IsNullOrWhiteSpace will INCLUDE values that are null. The problem with taking IEnumerable as a parameter is that it tells callers "I wish to enumerate this". To use these extension methods add using System. My suggestion would be to fix whatever produces myEnumerable, or if you can't do this, add a This question is overlaps a lot with Is there a convenient way to filter a sequence of C# 8. Empty<int>()). Sum() throws an exception if null is provided vs. I have, from I think Phil Haack, a useful extension method that checks to see if an IEnumerable is null or empty /// <summary> /// Determines whether the collection is either null or empty. Commented Mar 30, 2009 at 10:23. contains(blahblah) select t; return results. The query I am using now is . Select(x => x. image. x. Value of some rows are returning null. isEmpty throws System. I put in a null check before the foreach loop, and the iEnumerable passes the null check, but then when I run the foreach loop on it it throws the null reference exception. Blah. Write(max); I want that to ensure that if there are no elements in the list it should use the default value for int (0). You will have to handle the null case yourself though because you'll end up with a NullReferenceException pretty quickly. I didn't know how to write one good LINQ that can handle that so I ended up using multiple IF statements with multiple queries as below. ToList(); This works if all Items have a program. If you want to check for a default, you can compare the result with the default value of Imagine your list comes from a database and null values means "this order is not paid" so you "might" need to act upon null values (not the best example, but makes the point). If the list has no records, then null is returned. toHashSet(); Here is the calling code, I don't want it to receive a null IEnumerable at any time: This can be found under the System. It will first make sure the valie of email is not null then do the contains. 7,215 7 7 gold badges 50 50 silver Linq List Any can't handle Value command of generic List<List<T>> Hot Network Questions If that was LINQ to Objects, all these would generate NRE (Null Reference Exception) at runtime. Member) Where Member is of an IComparable type. But when you use a variable, I'm guessing that LINQ doesn't automatically do that conversion. Any() will remain about the same, though. Normally a query returns a IEnumerable<T> type. so you mmm - that's a fair point. var fields = from row in datarows from field in row from col in columnnames where field. ProductTypeId == 1 orderby p. Just seems a bit pedantic to do it on Any() as well - since it's only confirming the existence of more than zero items. Take will through an exception if the object invoking it is null. PatientEmail) It really helps to understand the LINQ query syntax and how it is translated to LINQ method calls. Answers) . DefaultIfEmpty public abstract class Item : IComparer, IEnumerable { public string Name { get; set; } public string Publisher { get; set; } public double Price { get; set; } public double Discount { get; set; } public DateTime ReleaseDate { get; set; } } LINQ to SQL handling nulls. In fact, you'd probably be better of just returning ToList(source). DefaultIfEmpty checks for null and returns the default value of the column data type when the column is null. First() can be written simpler as . One obvious reason is that keyword is null. Concat etc. PageModules. Neither Enumerable. 1. I have the following LINQ method that works as expected except if there are No Rows Found then I get a Null Exception. TbUsersInfos join Orgs in _context. Select(a => a. Where, . Stack Overflow. You can either return Task<Pie?> or instead handle the null value in some way. Where(b => someCondition); books = books == null ? moreBooks : books. PostCode); This looks like a normal null reference exception in linq2objects while it tries to execute your predicates or projections. Contains(searchString) or. I have following LINQ query to get a set of data. Null values could mean something for some implementations as I said, if it works for -your- type, then fine, but as a -generic- implementation, it has potential drawbacks. Sum() returns an int. CMO. e. NestedCollectoin is null foreach I have this code: List<int> myList = new List<int>(); var max = myList. PageId == id). Summaries = (from r in Summaries where r. Checking Possible Nulls Linq Query. ext4 to loop: 128-byte inodes cannot handle dates beyond 2038 and are deprecated I have the following Linq query: result. I stole the following Extension Method from StackOverflow: public static DataTable ToDataTable<T>(this IEnumerable<T> items) { var tb = new DataTable(typeof(T). Have a look at the extension-methods definition Assuming nulls and empty collections are equivalent, I'm trying to write an extension method for IEnumerable types to return empty collections of the derived type instead of null. For example, this will throw an ArgumentNullException: [ Test ] public void In this example, we filter out the null elements in the people list using the Where method, and then we extract the Age property using the Select method. – If it is not null then I don't want that parameter to be in the where c Skip to main content. When the reference is null, this will raise this exception. NameList I want to treat both situations (null or empty list) in exactly the same way but I wondered if there was a cleaner way than just putting a null check on the list and initialising an empty list when there's a null. For a reference type this is always null so, in your case they are interchangeable. (I'd expect most good LINQ providers / databases to be able to do that, but I'd generally avoid specifying a filter when it's not needed. Contains(blahblah) select t; var results2 = from t in All() where t. blah2. It depends! But first a clarification: . Range(0, iCols). They can't be null, which is why the compiler complains. This might sound like a ridiculous question, but I couldn't find a straight answer anywhere. You'd have exactly the same problem if you did this manually: var nestedA = new NestedA(); // This will throw an exception, because nestedA. Any() checks depending Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Visit the blog why do you care? If there's a possibility it might be null, then you need to check. ToLower ()) || (!string. OfType<T>(). ID; thanks in advance. Where(m => m != null && m. The cases were you'd get a null ref exception that I can think of are if some elements of the "somedata" collection are null, if "h. I believe it returns null if table dataMetaDataKOR is empty. Filtering nullable items in the List - LINQ. LowestPrice. The "or default" actually means it returns null (for reference types) or whatever the default would be for a non-reference type. Value }; The problem is that my code that handle the fields after this query fails because field. IEnumerable&lt;string&gt; If you need to be able to retrieve all of the elements in the case of it not being empty, then some of the answers here won't work, because the call to Any() on a non-rewindable enumerable will "forget" an element. Looks like you avoid the argument null exception in LINQ like below. Count() > 0 to avoid iterating over your entire dataset when using IEnumerables. Where(). ParentLayer) `I'm having a problem writing a null result to a datatable. The Overflow Blog How the internet changed in 2024 SingleOrDefault exception handling. This could be happening because either column (Name or Address) values will be null and you have to handle before comparison. empty, if numeric I am sorting some IEnumerable of objects: var sortedObjects = objects. SingleOrDefault(x => x. Programa. SchoolId == schoolid). Field<Guid>(dataColumn. Contains(street) || ((a != null) && a. For reference types that is null. public class Person { public int Id { get; /// </returns> public static bool IsNullOrEmpty<T>(this ICollection<T> enumerable) { return enumerable != null && enumerable. When I run a linq query I get back the results only when an item can be found; if no items are found, it is throwing an exception "object reference not set to an instance of an object" How do I not Check in your data there is no NULL value. Follow edited Jul 5, 2017 at 13:29. Where(p => p. CountryId I would personally suggest either of the latter options, as they don't require that the LINQ provider is able to optimise away the filter in the case where A is null. @omacarena We are ok with ignoring nulls. Linq namespace. Linq; to your code file. 4k 16 16 gold badges 103 The typical way would be to either return null, an empty enumerable Enumerable. (This would also allow you to pass in multiple separate items and, again, the compiler would handle converting them to an Enumerable. Empty does not create an object on call so it will put less load on GarbageCollector. net; linq; Share. Improve this question. The IEnumerable<T> interface has only a GetEnumerator method. In this example you shows how to handle possible null values in source collections. Of course, if you know the type, you could just use a literal equal to the default value, its what the compiler does for If an Item is not yet linked to a program, It's program will be null. somemoredate" is null. NET languages, null |> Seq. Empty<T>()) : value ?? Enumerable. Value tuples are value types. But even if you disagree, there are two basic philosophies of working with nulls properly: I have a requirement to convert LINQ to DataTable. I'd like to group all Items by it's Program's Id. SomeProperty because SQL supports NULL naturally even if SomeProperty normally does not allow NULL. Share. TbBaseOrgs on Users You can add your own extension methods easily enough. asked Jan 1, 2011 at 16:27. Year" is null (what type is that?), or if "p. You can also use null coalescing operator and if any of the list is null then return an empty list (internally it will also check for null). If you want the code to work with value types (structs and primitives) then default(T) provides a generic solution. And I need to check for In ToArray: I wouldn't use LinkedList<T> here, because it's usually slower than a List<T>, and just has a less pleasant interface. 0. Handle null in LINQ sum expression. Result) I get an exception when result. However, C# supports extension methods, and you will find a large number of extension methods for IEnumerable<T> in System. and i think you don't need to check on the FirstOrDefault since the extension will handle the new student object given T so you could change to more clean and tidy way. Use Single when you know that there is exactly one item in the collection. – GSerg WHERE @p__linq__0 IS NULL OR [Extent1]. Its certainly not enumerable. The query "SELECT SUM([Amount])" will return NULL for empty list. Let’s go further, don’t stop. Where(o => o. Improve this answer. @GertArnold for right approach, some people like Linq, while some people like foreach and then catch, or even some people like Reactive. NullReferenceException: Only 1 form field is required, thus I need to handle empty string values. Except three cases: 1) A LINQ operator which returns a special collection How to handle null values with where clause in LINQ? 1. You couldn't argue that null is still an IEnumerable. JohnLBevan. linq; ienumerable; or ask your own question. However, I don't need to query the database a second time because I have the data in a binding list. SelectMany(q => q. Actually the problem is that its NOT nullable and there is an empty set. It is written as listWithNulls. tblGreenSheet>' does not contain a definition for 'Max' and the best extension method overload 'System. 0 or later you can write the same in a shorter way: var termsList = _actList?. static partial class MoreEnumerable { public static IEnumerable<TSource> ConditionalDistinctBy<TSource, TKey>(this IEnumerable<TSource> The value null is neither greater than nor less than any non-null value - at least for the built in types. The latter is more efficient when dealing with an IEnumerable. // given: // public T MyProperty { get; } var nonNullItems = list. 9. ToList(); You could also catch the exception, but I don't recommend that in this case especially if it is a common scenario for the array to be null Sum is a known and handled method by the EF Queryable Provider and will generate the related SQL statement. How to handle null values with where clause in LINQ? 2. [If process operates on the list as a whole, or if a single exception needs to abort the whole process obviously this @McGuireV10 Yeah, I don't typically like using Select as a middle man when I'm just going to be using an aggregate function like Max on the result. Select, nor Queryable. Collections. The type to assign to the type parameter of the returned generic IEnumerable<T>. OrderBy(obj => obj. orderBy(). Where(x => (countryId != null ? x. select() to grab a nullable property then sorting it using . You might consider caching an empty array or using Array. For example, this will throw an ArgumentNullException: [Test] public void Should_handle_nulls() { List < int > ints = null; ints. My Code now is ` IEnumerable<Guid> refIds = (from datarow in dataTable. ToArray(). ) Returns an empty IEnumerable<T> that has the specified type argument. For my function IEnumerable&lt;CallbackListRecord&gt; LoadOpenListToProcess(CallbackSearchParams usp); This line errors when the sequence contains no elements (as it should) CallbackListRecord Is there a way to handle nullable types inside the LINQ in a case like this? Edit: I was not paying attention to the fact, that since this is using entity framework, methods that work with standard LINQ cannot be used unless they have a SQL translation. If you don't know those things, then don't use those methods. therefore you can do . Empty<int>()) (thanks to @phoog comment) SingleOrDefault is a extension method for the generic IEnumerable as you see below. handling a null in linq to sql query. Pushkar Aditya linq; datatable; ienumerable; or ask your own question. GetValue(Entity) : String. Shortly, there is no way to workaround the null enumerable assignment other than not including the IS it not possible to ensure that 1 column alone is not null like column number 2 is only not null. Enumerable+d__3a`1[[TracePerfWorker. One way would be to use . A null string is not the same as string. var products = from p in _context. This gives a runtime exception when the SQL query return null where the LINQ2SQL provider expects an integer. DefaultIfEmpty(). null has no type, no properties, inherits and implements nothing. GetAllUsers(). It's not immediately clear whether you're using IQueryable<> or IEnumerable<> (your code wouldn't compile either way, due to casing issues and the fact that no Where method returns List<T>, and the fact that you're using x in the same statement you're declaring it) but you can handle both easily: I would like to use the Enumerable. That's what I've tried: var listaAgrupada = client. OrderedTracks is List<TrackDetails>; TrackDetails has DiscNumber Int16? property; The following statement will trow an exception if the sequence if props[ii] is null, then calling GetValue(Entity) will cause a NullReferenceException. ID == someID) . The only difference is in the fact that the Enumerable. fyfqxx mbcu smlh wun qyg wcuoeyu khobjj benwjio eaclc saziwr