How to Build Dynamic WHERE Clauses with OR Logic in LINQ to Entities?

Use OR logic to build dynamic WHERE clauses in LINQ to Entities

LINQ to Entities uses delayed execution to build dynamic queries. However, these queries usually use AND to connect WHERE conditions. To implement OR logic, consider using a predicate builder library like LINQKit.

Use LINQKit’s PredicateBuilder

With LINQKit, predicates can be built dynamically using its PredicateBuilder. Here is a modified version of the code provided:

<code class="language-c#">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 replaces the calling expression with a simpler structure that Entity Framework understands. Without it, exceptions will occur during query execution.

Other predicate builders

Alternatively, consider using Peter Montgomery's universal predicate builder: https://www.php.cn/link/cfaedf8d25fee6179bfc4bcb64bbbfbd()`.

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