I have those methods:
public int count(
Guid companyId, Expression<Func<T, bool>> isMatch)
{
var filters = new Expression<Func<T, bool>>[]{
x => x.PriceDefinition.CompanyId == companyId,
isMatch
};
return GetCount(filters);
}
public virtual int GetCount(
IEnumerable<Expression<Func<T, bool>>> filters)
{
IQueryable<T> _query = ObjectSet;
if (filters != null)
{
foreach (var filter in filters)
{
_query = _query.Where(filter);
}
}
return _query.Count();
}
When using:
count(some_guid, x => x.IsMatch(entityId, inviterId, routeId, luggageTypeId));
I get the following exception:
LINQ to Entities does not recognize the method 'Boolean IsMatch(System.Nullable`1[System.Int64], System.Nullable`1[System.Int64], System.Nullable`1[System.Int64], System.Nullable`1[System.Int64])' method, and this method cannot be translated into a store expression.
What is the reason for this?
How can I solve it?
When using linq-to-entities you cannot use arbitrary .NET methods in query. Each method used in the query must be translatable to SQL. It will not help you to return Expession<Func<entityType, bool>>
because where condition must be evaluated for each record on the database server.
For EF your code means something like:
SELECT COUNT(*)
FROM ...
LEFT JOIN ...
WHERE IsMatch(....)
Because EF validates function names passed to the query it will throw exception because it doesn't know IsMatch equivalent on SQL server.
The only possible functions which can be used in Linq-to-entities are:
EdmFunctions
EdmFunctions are methods marked with EdmFunctionAttribute
which maps .NET function to SQL counterpart. Those functions usually cannot be executed in common .NET code because they do nothing or throw exception. They are only function place holder for Linq-to-entities. Available EdmFunctions are:
System.Data.Objects.EntityFunctions
System.Data.Objects.SqlClient.SqlFunctions
EdmFunction
attribute to the SQL function imported to designer.I have already described how to create model defined function in another answer. Creating mapped SQL function is pretty similar. Instead of manually creating Function
element in EDMX you will map EdmFunctionAttribute
properties to imported SQL function.
You're passing an expression that calls a function named IsMatch
.
LINQ to Entities doesn't know what to do with this function.