I needed a classic “where guid in” type of query to do (though i’m not sure if i should be thinking in that way when using linq:) so i poked around a bit, but couldn’t find anything good. So here it is:

        public static IQueryable<T> WhereIn<T,TMember>(this IQueryable<T> query, Expression<Func<T, TMember>> member, IList<TMember> inList) where T : BaseEntity
        {
            if (inList.Count() == 0) return query.Where(x => false);
            Expression<Func<TMember, bool>> expr = x => Enumerable.Contains(inList,x);
            var method = ((MethodCallExpression)expr.Body).Method;
            var expression = Expression.Call(null, method, ((MethodCallExpression)expr.Body).Arguments[0], member.Body);
            var lambda = Expression.Lambda<Func<T, bool>>(expression, "inLambda", member.Parameters);
            return inList.Count() > 0 ? query.Where(lambda) : query.Where(x => false);
        }

A classic example of usage would be something like this

Repository.Query<Partner>().WhereIn(x => x.Guid, partnerGuidList))

We are basically selecting partners by partnerguid, it’s very useful for paging and such.

An ispiration for this type of solution came from the this blog post for catching future values. Hope this helps!