LinqKit versus 'Method cannot be translated into a store expression' exception

Question

I am using LinqKit and I want to write a predicate in which the code has to call a plain boolean method, like this :

var predicate = PredicateBuilder.False<MyEntity>();

var predicate = predicate.And(myEntity => this.EntityMatches(myEntity));

this.ObjectSet.AsExpandable().Where(predicate).ToList();

Here is (part of) the EntityMatches method :

private bool EntityMatches(MyEntity myEntity)
{
    bool isMatch;

    // I make a call to another library boolean method here.
    isMatch = otherLib.IsEntityMatch(myEntity);

    // I perform some other checks right after.
    isMatch &= // some other conditions ...

    return isMatch;
}

I get this exception when running deferred execution :

LINQ to Entities does not recognize the method 'Boolean EntityMatches(MyEntity)' method, and this method cannot be translated into a store expression.

How can I rewrite the EntityMatches method so it is understandable by the store provider ?

Problem not related with *linqkit*. Your function is work with IEnumerable list, but not IQueryable, because Linq cannot convert custom methods — Khurshid, May 01 '13 at 14:09
Where do you see IEnumerable or IQueryable types ? The predicate variable is of type `Expression>`. — , May 01 '13 at 14:24

score 0 · Accepted Answer · answered May 01 '13 at 14:31

0

LinqKit is not magic, it can't see inside EntityMatches() or otherLib.IsEntityMatch(), so there is no way it can help you translated those into SQL.

What LinqKit can do is to create a complicated condition out of simple parts. But each simple part has to be translatable into SQl by itself and I don't see a way how to do that in your case, especially since you're using some external library.

answered May 01 '13 at 14:31

svick

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So, I guess that the only way to get it done is to filter as much as I can from the database, and then filter the in-memory results using these custom methods ? – May 01 '13 at 15:10
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@JoanLeaven Yeah, probably. But if you know what the custom methods do, maybe you could create an expression that does the same thing, which means you could do it using the database completely. – svick May 01 '13 at 15:56
The libary method is far too complex to rewrite as a linq Expression. I ended up filtering the most I can directly from the database, and filtering the resulting in-memory results using the libary method. – May 01 '13 at 20:05

score 0 · Answer 2 · edited May 23 '17 at 11:43

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You should convert your method to Linq Expression. Please read this maybe it will help IQueryable extension method for linq2entities

edited May 23 '17 at 11:43

Community

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answered May 01 '13 at 15:45

Khurshid

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Good advice, but the library method is huge and very complex. It would be to much work to rewrite it as a linq expression. I ended up using the library method as a filter to in-memory objects. – May 01 '13 at 20:06

LinqKit versus 'Method cannot be translated into a store expression' exception

2 Answers2