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POHow to do a subquery in LINQ?
 

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    <p>Here's an example of the query I'm trying to convert to LINQ:</p> <pre><code>SELECT * FROM Users WHERE Users.lastname LIKE '%fra%' AND Users.Id IN ( SELECT UserId FROM CompanyRolesToUsers WHERE CompanyRoleId in (2,3,4) ) </code></pre> <p>There is a FK relationship between <code>CompanyRolesToUsers</code> and <code>Users</code>, but it's a many to many relationship and <code>CompanyRolesToUsers</code> is the junction table.</p> <p>We already have most of our site built, and we already have most of the filtering working by building Expressions using a PredicateExtensions class.</p> <p>The code for the straightforward filters looks something like this:</p> <pre><code> if (!string.IsNullOrEmpty(TextBoxLastName.Text)) { predicateAnd = predicateAnd.And(c =&gt; c.LastName.Contains( TextBoxLastName.Text.Trim())); } e.Result = context.Users.Where(predicateAnd); </code></pre> <p>I'm trying to add a predicate for a subselect in another table. (<code>CompanyRolesToUsers</code>)</p> <p>What I'd like to be able to add is something that does this:</p> <pre><code>int[] selectedRoles = GetSelectedRoles(); if( selectedRoles.Length &gt; 0 ) { //somehow only select the userid from here ???: var subquery = from u in CompanyRolesToUsers where u.RoleID in selectedRoles select u.UserId; //somehow transform this into an Expression ???: var subExpression = Expression.Invoke(subquery); //and add it on to the existing expressions ???: predicateAnd = predicateAnd.And(subExpression); } </code></pre> <p>Is there any way to do this? It's frustrating because I can write the stored procedure easily, but I'm new to this LINQ thing and I have a deadline. I haven't been able to find an example that matches up, but I'm sure it's there somewhere.</p>
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