EF extension method: "This function can only be invoked from LINQ to Entities."
asp.net c# entity-framework lambda
Question
I have made an extension method to EF entities:
public static IEnumerable<T> WildcardSearch<T>(this IEnumerable<T> entity,
string param, Func<T,
string> selector)
{
return entity.Where(l => SqlFunctions.PatIndex(param, selector(l)) > 0);
}
//exception: This function can only be invoked from LINQ to Entities.
result = context.FOO.WildcardSearch(id, x => x.Id).ToList();
I get the exception above if I try to use it.
However, if I run (what I assume) the very same code directly on my collection, it works as intented.
Why do I get the exception, and is there any way to fix this?
Similar threads suggest changing the type to IQueryable, but it doesn't seem to help.
//this works
result = context.FOO.Where(x =>
SqlFunctions.PatIndex(id, x.Id) > 0).ToList();
Accepted Answer
It needs to be IQueryable<T> and Expression<Func<...>>; unfortunately this means rebuilding the expression tree - for example:
public static IQueryable<T> WildcardSearch<T>(this IQueryable<T> entity,
string param, Expression<Func<T, string>> selector)
{
var lambda = Expression.Lambda<Func<T, bool>>(
Expression.GreaterThan(
Expression.Call(
typeof(SqlFunctions), "PatIndex", null,
Expression.Constant(param, typeof(string)),
selector.Body),
Expression.Constant(0)),
selector.Parameters);
return entity.Where(lambda);
}
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