Linq list null check. You can write an extension method for List<>, which will check for null and otherwise it will call ForEach on its this parameter. My extension method first checks to see if the enumeration is null and if so creates an empty list. Obviously, there are many factors at play here, so let's rest LINQ is a technology for extracting data using an idiom derived from the C# programming language. 0 and later). List<string> MyList = (List<string>)Session["MyList "]; if(MyList !=null || MyList != "") { } MyList != "" does not work if string has more space so How can i check my list string is "" or null by using linq in c# ? That condition is neatly represented in a null-vs-not-null check. Is there a concise way to return a list - or null if the list is empty? var list = new List<int>{ 1, 2, 2, 4, 4 }; return list. ToString ()). Then your dictionary is probably null, or you have keys stored for a null value. Yes, works for the original question, because when Empty they wanted Empty, but not a general solution for IsNullOrEmpty. Learn about join methods in the LINQ framework in C#. Any[TSource](IEnumerable`1 source) at Program. 0 can tidy some of the if-not-null clutter. foreach(var item in myObject. (aka Elvis operator) is not allowed in a queryable (LINQ-to-SQL or LINQ-to-Entities) collection. Select (p => p. I would assume there's a simple LINQ query to do this, I'm just not exactly sure how. It returns a boolean value indicating whether the element exists in the sequence. Often times, returning an empty list or array is often a better choice than returning null. All I want is a list of answerRows that are not null, but Questions can sometimes be null too. MoveNext() at System. AsEnumerable (). In this article, we will explore various methods to determine if an array is empty in C#. This blog post demonstrates how to dynamically build a LINQ expression tree with multiple nested conditions, use the compiled query to filter an in-memory list, then reuse the expression query a relational database. Where(x => x. 2 of these arguments are optional and I wanted to write a LINQ query that knows to exclude or include certain parts of the query depending on if an argument is null or not. StatusID comes null i. But if you use LINQ it expects that the " Sum (l => l. Call it ForEachWithNullCheck or something like this and you will be fine. Why does C# behave this How can I query this list using Linq to create two lists the first list should contain the minimum required to ship an item to the customer (addressline1, city state and zip). Avoiding that check while also ensuring that the enumerable is not null is impossible. e. When should you use the LINQ Contains Method in C#? What is LINQ Contains Method in C#? The LINQ Contains Method in C# checks if a sequence (like a list or array) contains a specific element using the default equality comparer or a specified compare. We use LINQ extension methods Where to filter out null values and Select to convert nullable strings to non-nullable strings (string! indicates a non-nullable reference type in C# 8. In this article, we'll explore various techniques to handle null values and exceptions in C# LINQ queries. Name FROM Jan 11, 2016 · LINQ Where with AND OR condition Asked 16 years, 3 months ago Modified 6 years, 7 months ago Viewed 200k times Mar 22, 2009 · I love using LINQ in . StatusID is null first. If so, Exists is an instance method which functions very similar to Any. How can I conditionally add Jan 11, 2016 · LINQ Where with AND OR condition Asked 16 years, 3 months ago Modified 6 years, 7 months ago Viewed 200k times Mar 21, 2011 · Is there any way to compare strings in a C# LINQ expression similar to SQL's LIKE operator? Suppose I have a string list. MyOtherObject. ] at System. Where(x => x == 3). . Furthermore, the 'Safe Navigation' operator in C# 6. NET, but I want to know how that works internally? Aug 14, 2008 · We're working on a Log Viewer. In the Sql days I'd add to the query string, but I want to do it with Linq. On this list I want to search a string. The query was something like that: SELECT Members. Jun 6, 2009 · How to make a where in clause similar to one in SQL Server? I made one by myself but can anyone please improve this? public List<State> Wherein(string listofcountrycodes) { Feb 1, 2013 · I am trying to convert an old raw Sql query in Linq with Entity Framework here. I would like to request adding the ? null check before a foreach loop. However, the compiler is unaware of this EF Core guarantee, and produces warnings as if the LINQ query were executed in memory, with LINQ to Objects. My guess is that col1 in your example is of type List<T>. The Length property, Count() extension method of LINQ or the IsNullOrEmpty() method can be used to check if the array is empty. 94 list will never be null with LINQ; it will simply represent an "empty collection" if need be. If the object is null, there definitely aren't 'any', and it should probably return false. The Ultimate K-12 Nutrition Program Checklist Is your nutrition program checking all the right boxes? This comprehensive checklist is designed so your team is set up for success year-round. As a result, it is necessary to use the null-forgiving operator (!) to inform the compiler that an actual null value isn't possible: Hi meJustAndrew and Bilal- I want to check if list has any items in it specifically it shouldn’t be an empty list like []. 1) modify GetAttendanceListOf to return an empty list if no attendance (good idea in general, as null object pattern is very often a life saver, and for collection, an empty collection is often semantically similar to null) 2) if you don't control that method, write a safe extension method which will return empty list in case of null, e. NullReferenceException: Object reference not set to an instance of an object. However, it works fine for a LINQ-to-Objects collection. In short, the methods are essentially the same. From menu planning to production records, point-of-service efficiency, family communications, and proactive meal debt strategies, this all-in-one guide helps you streamline operations and support student If you want to master Language Integrated Query (LINQ), you first need to understand the expressions it is based on. That's kind of a general question (but I'm using C#), what's the best way (best practice), do you return null or empty collection for a method that has a collection as a return type ? By the way, if your sequence contains default(T) elements (e. It was using the IN operator with a collection of items. In C#, developers face the dilemma of whether to return null or an empty list or array when a method is not able to return values. Equals() and return false. This allows you to do a foreach on it without explicitly having to check for null. In order to avoid this situation you need to make LINQ expect " double? ". In SQL, I could write: SELECT * F Apr 25, 2017 · Wide range of operators provided by default, and others can easily be added for LINQ to Objects Language features introduced primarily for LINQ are widely applicable elsewhere (yay for lambdas) Cons: Query expressions aren't understood well enough, and are overused. 48 I have the below example code, and I am interested to know how I can make this any cleaner, possibly through better use of SelectMany(). One is more var nonNullOptions = GetNonNullOptions(Option1, Option2, Option3, Option4); Notice that I only check for null value items, as an empty string and a null value are two different things. null) and you need to distinguish between being empty and the first element being null, you can't use FirstOrDefault. LINQ has its origins in functional programming, which emphasises immutability of objects, so it doesn't provide a built-in way to update the original list in-place. Often simple method invocation is shorter and simpler. Amount ". You are also using a dictionary wrong, to retrieve values it's most common to use the index: [] Are you using the dictionary by choice? In the case that it does I want to create a linq query to check for nulls in a where clause while also checking for other values in the list and adding them to the where clause as well. Linq. Exists does not appear to be an extension method. 25 I have an list of objects that contains another object in it. User does not select any value then this query fails with an exception. ToList(); //returns 0 if empty - want to 27 I'm constructing a linq query that will check is a string in the DB contains any of the strings in a list of strings. Amount) " returns double and it doesn't allow you to use "?? " operator to set 0 for empty collection. FirstOrDefault (); The null-propagating operator ?. Main() :line 15 Conclusion Filtering out null values in C# using LINQ is a valuable technique to ensure data integrity and streamline data processing workflows. Field<string> ("KEYMATERIALS"). The use will have the option to filter by user, severity, etc. If every element of the list is equal and present in the same location in the opposite list then I would consider them to be equal. LINQ is a technology for extracting data using an idiom derived from the C# programming language. The query " SELECT SUM ( [Amount]) " will return NULL for empty list. Enumerable. The Problem with Null The main issue with null is that it can lead to the infamous NullReferenceException. One is more Oct 5, 2014 · I've recently started using LINQ quite a bit, and I haven't really seen any mention of run-time complexity for any of the LINQ methods. The way to test is with the Any extension method: A join of two data sources associates objects with objects that share an attribute across data sources. This returns records without any problem, but if this smodel. Something like. I'm building a query in LINQ using Entity Framework Core and I have a method that takes 3 arguments. The difference is that Any is an extension method for any IEnumerable<T> defined in System. null check is already validated before in the code. @Tom aside from one null check there's no penalty for the cases where the enumerator is not null. Basically, I am looking for the option similar to SQL "IN" Mar 21, 2011 · Is there any way to compare strings in a C# LINQ expression similar to SQL's LIKE operator? Suppose I have a string list. When calling Any() on a null object, it throws an ArgumentNullException in C#. You can do it by casting " (double?)l. List<MyClass> myClass = new List<MyClass>(); I want to do some linq like this myClass. If list is null, then the foreach iterates over an empty collection -- so zero iterations are performed. I'm aware there are a few other ways to handl In that second example, if list is non-null, then the foreach iterates over it as normal. Obviously List == List will use Object. ToList(); Thing is sometimes "MyOtherObject" is null. Name = "Name"). so check if smodel. At this point the QuestionList property will not be null. g. We'll discuss how to avoid common pitfalls, and A Json based Rules Engine with extensive Dynamic expression support How to handle null values in LINQ Select statement string Qtyvalues = dtQty. If any of these methods return 0 or the array is null, it can be determined that the array is empty. Name FROM Mar 22, 2009 · I love using LINQ in . <SelectManyIterator>d__16`2. While it owes much in functional design to SQL, it is fundamentally its own data querying language. How do I check for this? False Stack Trace: [System. By leveraging LINQ's powerful querying capabilities, developers can easily exclude null entries from collections and focus on working with meaningful data. It can be used on any IEnumerable<T> instance. MyNullableCollection?) { } Notice the ? at the end. Given this piece of code: class Program { static void Main(string[] args) { List<Person> It replaces null, but won't replace an Empty string with myDefault. How can I conditionally add Dec 11, 2025 · I am new to LINQ query and trying figure out how to filter list of records based on the list of IDs found in the sub-query inside. cuco, rotb, wwwxi, duu8h, 5x0q, hnmr4, 5tk4, uo7kn, nc9f, inqwsw,