A Join extension method for the dynamic Linq

http://social.msdn.microsoft.com/Forums/en-US/linqtosql/thread/4482b083-72bd-4415-82be-8cccbd9eabba

         

         public static IQueryable Join(this IQueryable outer, IEnumerable inner, string outerSelector, string innerSelector, string resultsSelector, params object[] values)
        {
            if (inner == null) throw new ArgumentNullException("inner");
            if (outerSelector == null) throw new ArgumentNullException("outerSelector");
            if (innerSelector == null) throw new ArgumentNullException("innerSelector");
            if (resultsSelector == null) throw new ArgumentNullException("resultsSelctor");

            LambdaExpression outerSelectorLambda = DynamicExpression.ParseLambda(outer.ElementType, null, outerSelector, values);
            LambdaExpression innerSelectorLambda = DynamicExpression.ParseLambda(inner.AsQueryable().ElementType, null, innerSelector, values);

            ParameterExpression[] parameters = new ParameterExpression[] {
            Expression.Parameter(outer.ElementType, "outer"), Expression.Parameter(inner.AsQueryable().ElementType, "inner") };
            LambdaExpression resultsSelectorLambda = DynamicExpression.ParseLambda(parameters, null, resultsSelector, values);

            return outer.Provider.CreateQuery(
                Expression.Call(
                    typeof(Queryable), "Join",
                    new Type[] { outer.ElementType, inner.AsQueryable().ElementType, outerSelectorLambda.Body.Type, resultsSelectorLambda.Body.Type },
                    outer.Expression, inner.AsQueryable().Expression, Expression.Quote(outerSelectorLambda), Expression.Quote(innerSelectorLambda), Expression.Quote(resultsSelectorLambda)));
        }


        //The generic overload.
        public static IQueryable<T> Join<T>(this IQueryable<T> outer, IEnumerable<T> inner, string outerSelector, string innerSelector, string resultsSelector, params object[] values)
        {
            return (IQueryable<T>)Join((IQueryable)outer, (IEnumerable)inner, outerSelector, innerSelector, resultsSelector, values);
        }

 应用

var aaa = context.Dict.Where(p=>p.DictionaryId >3).Select(p => p.DictionaryId);

var bbb = context.Dict.Join(aaa, "DictionaryId", "it", "outer");