How Can I Create a Dynamic OR Query with LINQ to Entities?

Build dynamic OR queries using LINQ to Entities

In LINQ to Entities, it is very common to create dynamic queries using delayed execution. However, these queries usually use AND to connect WHERE conditions.

To implement OR logic, i.e. search for multiple properties using a single identifier, you can leverage LINQKit's PredicateBuilder. This allows you to build predicates dynamically:

<code class="language-csharp">var query = from u in context.Users select u;
var pred = Predicate.False<user>();

if (type.HasFlag(IdentifierType.Username))
    pred = pred.Or(u => u.Username == identifier);

if (type.HasFlag(IdentifierType.Windows))
    pred = pred.Or(u => u.WindowsUsername == identifier);

return query.Where(pred.Expand()).FirstOrDefault();</code>

The

Expand() method is crucial because Entity Framework cannot handle call expressions. By calling it, you activate LINQKit's expression accessor class, which replaces these expressions with simpler structures that Entity Framework understands.

Without Expand(), the expression is invoked, resulting in the exception: "LINQ expression node type 'Invoke' is not supported in LINQ to Entities."

Another Predicate Builder

Later, a general predicate builder was developed that can perform the same task without Expand():

https://www.php.cn/link/451e10de8e2fb18a9f795679b52dc9f6

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