How to build an IEnumerable<int>.Contains() Expression?

问题

I'm currently working with ASP Dynamic Data for the first time and I'm trying to build a filter. Our users have a need to locate items in a list based upon whether or not the item is a child of a selected parent (our items can have more than one parent).

The items in question are Segments and each Segment has a property called RouteIds, of type IEnumerable, which is a collection of all of the Segment's parent Ids.

I've gotten to this point in overriding the GetQueryable method in my filter, but I keep getting exceptions thrown on the last line shown:

ConstantExpression ce = Expression.Constant(int.Parse(this.ddlRouteNames.SelectedValue));
ParameterExpression pe = Expression.Parameter(source.ElementType);
MemberExpression me = Expression.Property(pe, this.Column.Name);
var callExpression = Expression.Call(typeof(Enumerable), "Contains", new Type[] { me.Type }, ce, me);

The thought is that a user would select the appropriate Route from a DropDownList and then I'd check to see if the Segment's RouteIds property contains that Route's Id.

Any pointers on how to get this working?

Edit - Here is the exception:

No generic method 'Contains' on type 'System.Linq.Enumerable' is compatible with the supplied type arguments and arguments. No type arguments should be provided if the method is non-generic.

回答1:

There are two problems in your code:

1. Your parameters are backwards. The first parameter has to be the collection, the second the item you're searching for.
2. Your type argument is IEnumerable<int>, when it should be just int.

So, the fixed code is:

var callExpression = Expression.Call(
    typeof(Enumerable), "Contains", new[] { typeof(int) }, me, ce);

But it seems all the parts of your expression are not actually dynamic, so maybe something like that following would work too:

Expression<Func<Segment, bool>> expression =
    s => s.RouteIds.Contains(int.Parse(this.ddlRouteNames.SelectedValue));

来源：https://stackoverflow.com/questions/16347794/how-to-build-an-ienumerableint-contains-expression