EF4 CTP5 - LINQ Dynamic Query Library throws InvalidCastException

问题

With the upgrade to EF4 CTP5, the previously working (with CTP4) LINQ Dynamic Query Library throws the following exception

Unable to cast object of type 'System.Data.Entity.Infrastructure.DbQuery' to type 'System.Linq.IQueryable`1[KIT.TAM.Core.Entities.TravelAgent]'.

on the return statement below:

namespace System.Linq.Dynamic
{
    public static class DynamicQueryable
    {
        public static IQueryable<T> Where<T>(this IQueryable<T> source, string predicate, params object[] values)
        {
            return (IQueryable<T>)Where((IQueryable)source, predicate, values);
        }
    }
}

Is there an updated version of the library that works with EF4 CTP5?

Thanks folks.

回答1:

Solved this one. In DynamicLibrary.cs:

I replaced

public static IQueryable<T> Where<T>(this IQueryable<T> source, string predicate, params object[] values)
{    
    return (IQueryable<T>)Where((IQueryable)source, predicate, values);
}

with

public static IQueryable<T> Where<T>(this IQueryable<T> source, string predicate, params object[] values)
{
    if (source == null) throw new ArgumentNullException("source");
    if (predicate == null) throw new ArgumentNullException("predicate");
    LambdaExpression lambda = DynamicExpression.ParseLambda(source.ElementType, typeof(bool), predicate, values);
    return source.Provider.CreateQuery<T>(
        Expression.Call(
            typeof(Queryable), "Where",
            new Type[] { source.ElementType },
            source.Expression, Expression.Quote(lambda)));
}

This is the basically the same code in

public static IQueryable Where(this IQueryable source, string predicate, params object[] values)

but changed source.Provider.CreateQuery() to source.Provider.CreateQuery<T>.

You will also have to do this for the static method OrderBy<T>.

来源：https://stackoverflow.com/questions/4431869/ef4-ctp5-linq-dynamic-query-library-throws-invalidcastexception

标签

linq

entity-framework-4