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POHowto use predicates in LINQ to Entities for Entity Framework objects
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2013-10-27T09:49:13.553
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2017-05-23T12:17:56.830
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I'm using LINQ to Entities for Entity Framework objects in my Data Access Layer. My goal is to filter as much as I can from the database, without applying filtering logic to in-memory results. For that purpose Business Logic Layer passes a predicate to Data Access Layer. I mean <pre><code>Func<MyEntity, bool> </code></pre> So, if I use this predicate directly, like <pre><code>public IQueryable<MyEntity> GetAllMatchedEntities(Func<MyEntity, Boolean> isMatched) { return qry = _Context.MyEntities.Where(x => isMatched(x)); } </code></pre> I'm getting the exception <blockquote> [System.NotSupportedException] --- {"The LINQ expression node type 'Invoke' is not supported in LINQ to Entities."} </blockquote> Solution in <a href="https://stackoverflow.com/questions/8741667/the-linq-expression-node-type-invoke-is-not-supported-in-linq-to-entities-in-e">that question</a> suggests to use AsExpandable() method from <a href="http://www.albahari.com/nutshell/linqkit.aspx" rel="nofollow noreferrer">LINQKit</a> library. But again, using <pre><code>public IQueryable<MyEntity> GetAllMatchedEntities(Func<MyEntity, Boolean> isMatched) { return qry = _Context.MyEntities.AsExpandable().Where(x => isMatched(x)); } </code></pre> I'm getting the exception <blockquote> Unable to cast object of type 'System.Linq.Expressions.FieldExpression' to type 'System.Linq.Expressions.LambdaExpression' </blockquote> Is there way to use predicate in LINQ to Entities query for Entity Framework objects, so that it is correctly transformed it into a SQL statement. Thank you.
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<c#><entity-framework><linq-to-entities><predicate><linqkit>
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Howto use predicates in LINQ to Entities for Entity Framework objects
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1. COI don't want to interfere, but exposing `IQueryable` and expression parameters is generally considered to be a bad idea. It's better to add specification parameters to `GetAllMatchedEntities` (like `int minimumAge`) and build the query inside the method.
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