Question

How can I get all types participating in a linq expression? I actually need this to be able to cache the query results.

In this example it is easy:

var Query = (from x in DataContext.Current.ContractDurations select x);

as
the type i need is provided in

Query.ElementType

But what happens when I do this:

var Query = (from x in DataContext.Current.ContractDurations select x.ID);

The ElementType will be int. The same problem will exist with joins where the ElementType will be some random anonymous type.

Answer 1

 public class QueryExpressionVisitor : ExpressionVisitor
{
    public List<Type> Types
    {
        get;
        private set;
    }


    public QueryExpressionVisitor()
    {
        Types = new List<Type>();

    }
    public override Expression Visit(Expression node)
    {
        return base.Visit(node);
    }

    protected override Expression VisitConstant(ConstantExpression node)
    {
        if (node.Type.IsGenericTypeDefinition && node.Type.GetGenericTypeDefinition() == typeof(IQueryable<>))
            CheckType(node.Type.GetGenericArguments()[0]);
        return base.VisitConstant(node);
    }

    protected override Expression VisitMember(MemberExpression node)
    {
        CheckType(node.Member.DeclaringType);
        return base.VisitMember(node);
    }



    private void CheckType(Type t)
    {
        if (!Types.Contains(t))
        {
            Types.Add(t);
        }
    }
}