Linq use variable in where clause. May 8, 2014 · If you were using Linq then you could use the let keyword to define an inline variable (the code posted in the question isn't actually using Linq). May 14, 2025 · Learn how to use the LINQ 'let' clause in C# to create intermediate variables within queries. l is the range variable. var ext = from file in files let idx = f. Jul 11, 2025 · You can provide a condition to where clause using lambda expression or by using Func delegate type. This article explain how to use the if condition to add additional Where constraints based on a condition. Experiment with different conditions and scenarios to master the art of filtering collections using C# Where Contains with LINQ. So, in SQL where I would do something like "where OrganizationId = '12' or OrganizationId = '13' or OrganizatonId = '17'. Microsoft Visual C# LINQ: Letting New Values in LINQ . This is usually done in order to store the results of intermediate sub-queries, for example: Jul 13, 2020 · a composable filter for LINQ is something like an Expression<Func<YourRowType, bool>> - then it would be simply return query. Basically in the first loop with the DateClause's ends up returning nothing if I have two date clauses, works great with one date clause. After that we use this variable in where clause to compare each element is greater than 150 or not and last we print those elements which Feb 1, 2013 · I would also make an extra variable to change the closure's capture type to be explicitly of DataContext (since the Linq statement is like a lambda, and delayed evaluated. Earlier I stated that everything in your Linq must have an equivalent in SQL. Sep 21, 2022 · A query expression must begin with a from clause. In a LINQ query, the from clause comes first in order to introduce the data source (students) and the range variable (student). Aug 20, 2024 · The 'Where' clause in C# is commonly used in LINQ queries to filter elements that satisfy a specific condition. Methods like . In a LINQ query, you're always working with objects. But here in Linq I can only think of using an IF condition where I will write the same query thrice, with each IF block having an additional condition. Where(c => previousPredicates || c. Having said that, in most cases, I think it's easier to maintain multiple, separate queries than it is to deal with one big query. And I have a question regarding the conversion. Update - my where clause is predefined and will be based on user input so I don't think this will work for me. Sep 15, 2021 · In LINQ to Entities queries, expressions can contain anything allowed by the types within the System. The For Each loop displays the company name for each customer in the query result. PredicateBuilder has been released in the LINQKit NuGet package LINQKit is a free set of extensions for LINQ to SQL and Entity Framework power users. Where comes under the Filtering Operators category? Jul 10, 2015 · I am trying to make a LINQ statement where the where clause is a string variable. We already discussed how many LINQ methods can use a Lambda Expression to performs its task Sep 15, 2021 · The where clause is used in a query expression to specify which elements from the data source will be returned in the query expression. Now here's Sep 15, 2021 · You can use the IsMatch method in the where clause of a LINQ query. Both the range variable and the data source are strongly typed. Sep 10, 2010 · With Linq, can I use a conditional statement inside of a Where extension method? Mar 30, 2016 · Using DateTime Variable In Where Clause March 30, 2016 Andy DBA Stack Exchange 0 Aug 30, 2018 · the translation looked easy to understand as the LINQ version matches with SQL statement 👍. Linq' allows to predicates from strings. Categories where category. Because Where is producing an IQueryable, the execution is deferred Discover how to add `or` conditions in LINQ queries using the `Where` clause. The expressions that can be used in LINQ to Entities queries are a superset of the expressions that can be used to query the Entity Framework. Jul 3, 2014 · The problem is in joinExpression. Using EntityFramework Core and SQL Server to create a dynamic IQueryable filtering that is not susceptible to SQL injection attacks Jan 7, 2012 · 2 If you need to compose your queries dynamically on the fly, you can use the LINQ Dynamic Query library, a sample from Microsoft: This sample shows a technique for composing LINQ statements on the fly, dynamically, at run time. The data Aug 29, 2015 · The problem being, that I can't dynamically generate a list of "OR" clauses for linq to sql, because they are set at compile time. Field3 == X) or how to solve that Nov 29, 2019 · Explanation: In the above example, the result is the query variable which stores the result of the given query expression. GetFileUrl twice. In a1, we store the result of the s + 100 expressions. Aug 29, 2024 · What is the LINQ Where Clause? The Where clause in LINQ is used to filter a sequence of values based on a predicate—a function that defines the conditions the elements must satisfy to be included in the result set. A local range variable that represents each element in the source sequence. Mar 29, 2023 · I often use LINQ query in my projects, and I sometime needs to pass the lambda expression at the run Tagged with csharp, linq, lambda. Condition; to work filter. It applies a Boolean condition (predicate) to each source element (referenced by the range variable) and returns those for which the specified condition is true. May 1, 2012 · I am using Linq to Entities and have added the using stmt of using System. Here's one example, and here's another. Dynamic; Your query would look like this: Aug 19, 2025 · Learn how to use LINQ Dynamic query to execute methods such as Select, OrderBy, or Where clause dynamically. e, my_list, where clause applies the filter, i. Question yourself: How could I pass this function call in a SQL Statement? Nov 24, 2016 · The problem is that using Linq expressions on an Entity Framework uses a backend Linq to Entities mapper and every linq extension method used can only work if a supporting translation to TSQL (or language for whichever DBMS is in use) exists. Jan 18, 2025 · The compiler does this composition when you write queries using query syntax. Usage of C# (C Sharp) Query Keywords – select, from, where, in This article will help you in understanding the usage of keywords select, from and where in framing LINQ Query Expression. Aug 20, 2024 · By mastering the where clause in C# with LINQ, you can enhance the efficiency and readability of your code. Jan 17, 2017 · Using the let keyword in . How do I let them execute with Parenthese and add a simple OR now using the API? Is there a way to save the predicate in some variables so I can make something like: Query = Query. You need to refactor your Filter expression to be the thing that LINQ wants. Dynamic. 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) { If this were to be done using sql queries I would have used string builder to have them appended to the main strSQL query. Aug 20, 2025 · Query operators In a LINQ query, the first step is to specify the data source. Using the single-clause form will help performance here. Where expects a Func<T, bool> (i. Consider this example: var l Sep 28, 2009 · Since my article on using parameters for Preventing SQL Injection In ASP. Dec 29, 2019 · In my example, I first show a working LINQ Query which is hard coded. foreach (var name in names) { query = query. In the above figure, we have used "where" operator (aka clause) followed by a condition. Where(Filter()). AsQueryable: The AsQueryable method can be used to convert a variable containing a list to an IQueryable object, which allows Using variable in sql WHERE clause for Operation Asked 9 years, 11 months ago Modified 9 years, 11 months ago Viewed 9k times Feb 20, 2015 · There is an alternative syntax when using LINQ queries, which is more like SQL. You can just use row. Dynamic; My goal is to pass in the whereClause variable into the emailList query (see screen shot). But apart from filtering I also want to update a global variable inside Where. 8 I'm trying to write an some Linq where the Where clause contains items meeting certain criteria - but excludes a subset of those items meeting some other conditions. The code above is correct, but you may find this version more concise: int categoryId = 4 IArticleRepository articleRepo = unitOfWork. e. The reason you have to convert your collection to a List is because the only thing you know about the collection returned by LINQ's Where clause is that it produces a collection that implements the IEnumerable interface. Multiple Where clause You can call the Where () extension method more than one time in a single LINQ query. CategoryId == categoryId where article. net Framework 4. Referreds where May 2, 2023 · While linq is a poor tool choice for this requirement, you should change the select to return all columns. 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. May 2, 2021 · A quick guide on how to use the Where LINQ operator, using both method and query syntax. There are around 50 Standard Query Operators available in LINQ. You might filter items using a where clause, sort the output collection using orderby, group items, or perform some computation. NET LINQ to store variables within a statement January 17, 2017 Leave a comment It happens that we have a LINQ statement where we want to refer to partial results by variable names while expressing some computation. By combining multiple conditions with logical operators, you can build complex filters that adjust at runtime. FirstActivityTime == myDate in your filter and EF will generate the correct SQL query, incorporating an is null check along with the equality check. Once initialized with a value, the range variable can't be used to store another value. Learn to filter data based on multiple criteria easily!---This video is based o Jan 26, 2021 · Using the . Where("Name=@0 And UserName=@1", name, name); } return query; 'System. This condition is generally expressed using lambda expression. Jun 5, 2013 · I have the linq query working to get the logged in users location (s) (yes a user can have multiple locations) and now I am trying to write what I have a variable that is sometimes a list, sometimes a single value, but never null (it's a list of location codes). Jul 23, 2024 · Creating Dynamic Where Clauses To create dynamic where clauses using lambda expressions, you can leverage the Where method provided by LINQ. Aug 20, 2024 · Conclusion In this blog post, we've explored how you can utilize the Where method with LINQ to filter collections in C# based on specific conditions. For example: string whereClause = "(Code = '12') AND (Name = 'a')" ; var referreds = from r in _db. Net languages. Your code might provide parameters for the filter, or the sort key, or other expressions that are part of the query. In the above example, the from clause specifies that the source data for the query is the Employees table in the db database, and the in keyword specifies that each row in the table will be assigned to a variable named e. Reference the library in your code: using System. Jan 16, 2025 · Query variable In LINQ, a query variable is any variable that stores a query instead of the results of a query. Step 4: Last step is to execute the query by using a foreach Feb 8, 2022 · Linq Conditional where clause when parameter can be null Ask Question Asked 3 years, 8 months ago Modified 3 years, 6 months ago Aug 10, 2019 · Make use of LINQ expressions to produce a Lambda expression dynamically. When the underlying provider translates it into a SQL statement, the chances are good that both variants will create the same statement. From the DataTable, I want to use the Where clause to return a particular row. Apr 25, 2024 · In most LINQ queries, the general shape of the query is set in code. Apr 8, 2011 · I had to construct the predicate for the 'Where' clause dynamically based on User Interface selections. ". After the query is executed, the result variable will contain a collection of Sep 15, 2021 · The following query expression uses a From clause to declare a range variable cust for each Customer object in the customers collection. Switch vs. NET, I have had a few emails asking how to do the same with an IN clause expression. Here's a summary of the situation and I will provide full… Sep 5, 2016 · System. Because a query variable doesn't store the results of the query, you can modify it or use it as the basis for a new query at any time, even after you execute it. The “let” keyword lets us do that. The Where clause uses the range variable to restrict the output to customers from the specified region. Is there a better way to do this? Jan 17, 2017 · A note about chaining the . Query operators select and shape the result based on the type of the source. Mar 27, 2013 · As @DarenThomas says, if the Variable is actually external to the Linq statement the entire statement becomes defunct because Variable won't potentially change on each iteration. I looked at "How can I select a row from a datatable using two va Aug 28, 2012 · I've found examples of how to "dynamically" add more where clauses to a linq query, but I'm not sure how to make it work with my specific query. Jul 23, 2024 · One common scenario is using lambda expressions with the Where clause to filter data based on specific criteria. MoveNext () method. ArticleRepository; var articlesQuery = from article in articleRepo. Thanks linq linq-to-sql where-clause asked Nov 12, 2009 at 2:19 Zeus 3,397 6 51 64 Apr 1, 2025 · This tutorial explains the Var, LINQ and Ternary Operator in C# with syntax, usage and programming examples. The benefit of using "Let" is that it makes the query very readable and using this we can create a variable and assign a calculated value in that variable. How does one accomplish a where clause that checks a column is in a dynamic list of values using Linq to Sql? In this tutorial, you'll learn how to use the LINQ Where() method to filter a sequence of values based on a predicate function. Where() methods: You can chain together all the LINQ methods you want. In the TextClause's loop it seems to ignore every text clause after the first one. However, if the Dec 17, 2009 · I am using Linq to Entity in case that matters. Let's check out a few examples. The Language Integrated Query (LINQ) syntax is arguably one of the most powerful features of . Then after the list is built, using reflection and dynamic objects build a new list of just the columns you want. Apr 26, 2019 · I want to filter a list using LINQ with Where extension method. GetAll() from category in article. Use variable in where clause only if NOT empty? A kind of dynamic where clause? Asked 14 years, 11 months ago Modified 9 years, 10 months ago Viewed 10k times In this article, I am going to discuss LINQ Where Filtering Method in C# with Examples. For more information, see How to: Generate XML from CSV Files. May 11, 2009 · What is the best way to assemble a dynamic WHERE clause to a LINQ statement? I have several dozen checkboxes on a form and am passing them back as: Dictionary<string, List<string>> ( In this tutorial, you'll learn how to use the EF Core Where() method to filter data based on one or more conditions. Sep 12, 2025 · Here res is the query variable which stores the result of the query expression. How can I tell LINQ to not process it in case it's null or to r In my experience for reasonably complex queries, the way you write linq queries makes a difference sql server 2005 sometimes doesn't produce an optimal query plan for queries with deep levels of subquery nesting Jul 8, 2013 · I have a DataTable that I am pulling from a DataSet. Jun 25, 2012 · I want to add in the where clause a way to select only the users with the OrganizationId's in the array. Nov 1, 2018 · By the way, for the on clause in this example it's essential that the range variable that you're using in the join (osub, in my example) be on the right-hand side of the keyword equals. In this entry, I explore a couple of ways to do this. The Where Linq operator, probably the most commonly used, allows you to filter or find things where a certain boolean condition is met. Where() don't actually execute against the database (yet). The from clause specifies the following: The data source on which the query or sub-query will be run. GetExtension instead of parsing the string yourself (for example, your code will May 5, 2017 · Null value in linq where clause Asked 8 years, 6 months ago Modified 7 years, 6 months ago Viewed 26k times Oct 12, 2025 · The range variable introduced by the into clause (groups in Listing 16. The from clause is used to specify the data source, i. e, a1. Sep 14, 2021 · A LINQ query, often referred to as a query expression, consists of a combination of query clauses that identify the data sources and iteration variables for the query. I want to pass it to the WHERE clause, but it is different for different concrete types T (it is dependent on the entity variable), for example for a specific entity it could be Sep 15, 2021 · 4 IF you were using Linq To Objects that should work but you are doing Linq To SQL and in this case you must think on how you would translate this function into a valid SQL statement. Jul 17, 2017 · Why don't you want to use var? List<KeyValuePair<int,string>> looks ugly Also Groups is just local variable, it is common that name starts with lowercase letter in this case. StatusCode) I do not want to use switch or If condition. 'System. Dynamic LINQ: Using a switch statement may be more feasible if you have a limited number of possible where clause conditions. Mar 25, 2015 · Is there a way for me to declare a variable within the select that I can the reuse within the LINQ select? And I don't want to call _storageService. You can do this with the let keyword, which creates a new range variable and initializes it with the result of the expression you supply. A single query expression may contain multiple where clauses and a single clause may contain Apr 27, 2015 · When this is a linq-to-object call, multiple where clauses will lead to a chain of IEnumerables that read from each other. See LINQ Query Syntax versus Method Syntax (C#) for more information. Where() calls are building a Linq Query that is connected with AND, which is fine. When it comes to handling null values, you can use the 'Where' clause to exclude or manipulate items that are null. Ya know, similar to how SQL statements can use an IN clause in the WHERE clause like this: SELECT city FROM Customers WHERE state Explore how to combine Join and Where clauses in LINQ queries and Lambda expressions in C# for filtering and joining data efficiently. ') + 1 select file. Enumerable. Let's dive into how you can leverage C# lambda expressions with the Where clause effectively. Aug 21, 2022 · Describes various techniques your code can use to query dynamically depending on runtime state, by varying either LINQ method calls or the expression trees passed into those methods. Linq' is available as a nuget package. Expressions namespace, including lambda expressions. e, l. Mar 12, 2012 · The Where clause in thisw code snippet shows how you create a where clause using a parameterised string and then dynamically inject values for the parameters at run time, for example, based on user input. Additionally, a query expression can contain sub-queries, which also begin with a from clause. Sep 15, 2021 · In a LINQ query, the first step is to specify the data source that you want to query. NET. May 10, 2008 · That's easy to do with a normal SQL statement since you can use the "WHERE IN (Value1,Value2)" clause to find what you need. May 4, 2023 · In LinQ, a query starts with the from clause, which specifies the data source you’re working with and introduces a query variable as a range variable. The next example uses a list that is built at runtime, all i need to figure out is how to insert the string variable (whereClause) into the LINQ Query without compile errors? Working example (hard coded) Jan 11, 2016 · select item; Here I would like to check if listStatus and listMerchants are not null only then put them inside WHERE clause. quick summary in the analysisObjectRepository object, there are certain o Since you're using LINQ to Entities rather than LINQ to SQL, the question you're referencing doesn't apply. 11) becomes the range variable for the remainder of the query; any previous range variables are logically a part of the earlier query and cannot be used in the query continuation. Like if listMerchants is null then query will be like where listStatus. Title In T-SQL you could have a query like: SELECT * FROM Users WHERE User_Rights IN ("Admin", "User", "Limited") How would you replicate that in a LINQ to Entities query? Is it even possible? Mar 24, 2025 · LINQ offers a consistent model for queries on data across various kinds of data sources and formats. Contains(item. We already saw a glimpse of what you can do with the Where () method in the LINQ introduction article, but in this article, we'll dig a bit deeper. The following examples demonstrate some basic LINQ queries by using each approach listed previously. Basically whereClause is not constructed in the method, it is a parameter of the method which does the LINQ. After that, you can chain query operators like where, select, group, and order to define filters, transformations, and other operations. Build an expression for Entity Framework with the following clauses: And, Or, Any Mar 16, 2011 · the problem in short we have a lambda expression used in the Where clause, which is not returning the "expected" result. You can use the PredicateBuilder class. Aug 7, 2019 · The ForEach method doesn't return a value so I don't need a variable to catch anything. Jan 10, 2013 · I'm trying to get a property from an array of object that can be null (the array) and I'm always getting a null reference exception. Condition should be C# code. Mar 30, 2024 · let clause - C# ReferenceIn a query expression, it's sometimes useful to store the result of a subexpression in order to use it in subsequent clauses. This tutorial covers efficient data transformation, improving readability, and optimizing LINQ expressions. Where clause supports query syntax in both C# and VB. However, I wanted to do it with LINQ in this case. The select clause specifies that the query will return the value of each row in the table. The ability to express queries over different data sources declaratively has made the . However I cannot do it. a function that takes T as input and returns bool) meaning for your line whereClause = test => filter. In order to define a variable inside a linq expression, you can use the let keyword. More specifically, a query variable is always an enumerable type that produces a sequence of elements when iterated over in a foreach statement or a direct call to its IEnumerator. NET ecosystem more productive. Dynamic LINQ: Dynamic LINQ can be a good option if you have a complex where clause that is generated dynamically based on user input. You can also use the techniques described in this section to transform semi-structured text data to XML. This tutorial explains LINQ query syntax. Contains ("my") and select clause provides the type of the returned items. Substring(idx); However for the specific scenario you've posted I'd recommend using Path. Therefore, the From clause in a query always comes first. Linq. In the query expression, we created a range variable using let keyword, i. Understanding Lambda Expressions In C#, a lambda expression is a concise way to define an anonymous function. Filtering data: the Where () method One of the most basic (but also most powerful) operations you can perform on a set of data is to filter some of it out. Just use the Where extension method. Would the LINQ version fetch all data from database first and filter (using Where clause) in memory? or would the query create an optimal syntax to send to the database and fetch only filtered records? Mar 20, 2011 · SQL ‘IN’ clause when using Linq to Entities (use it the right way!) 20 March 2011 on SQL We all know what ‘IN’ clause is about – we want records where a field value matches one of the specified variants. Any thoughts? + Introduction LINQ has one operator called "Let" that allows us to create / declare variables inside the LINQ query. And you can use LINQ to query or modify the MatchCollection results returned by a regular expression. It will need to take the whole of the Master variable. Jun 3, 2020 · If you want to master Language Integrated Query (LINQ), you first need to understand the expressions it is based on. LastIndexOf('. In query expression syntax, a where (C#) or Where (Visual Basic) clause translates to an invocation of Where<TSource> (IEnumerable<TSource>, Func<TSource,Boolean>). Check out Scott Guthrie's introduction to the topic here. By combining the power of Where and Contains, you can efficiently query and manipulate data in your C# applications. Experiment with different scenarios and leverage the power of LINQ to streamline your data querying processes. May 19, 2008 · A colleague and I were talking about some LINQ features yesterday and one of the topics that came up was how to implement an IN clause. May 18, 2019 · All these . 1 That's a built-in Feature of LINQ. After the From clause, you can use different Standard Query Operators to filter, group, join elements of the collection. 8e5 8u2ts t8 2c0mfkzp mdo mf g2q hw 5f xyoggh