Search through Where clause in LINQ, using dynamic properties

Question

I\'m basically trying to construct a query, and I don\'t know why microsoft made this so difficult in Entity Framework and LINQ. I have various parameter STRINGS. So if you

Answer 1

You'll have to build an expression tree to pass to the Where method. Here's a loose adaptation of some code I have lying about:

string searchfield, value; // Your inputs
var param = Expression.Parameter(typeof(User), "user");

return Expression.Lambda>(
    Expression.Call(
        Expression.Property(
            param,
            typeof(User).GetProperty(searchfield)),
        typeof(string).GetMethod("Contains"),
        Expression.Constant(value)),
    param);

That will generate an appropriate expression to use as the parameter to Where.

EDIT: FYI, the resultant expression will look something like user => user.Foo.Contains(bar).

EDIT: To sort, something like this (ripped from my DynamicOrderList class):

private IQueryable OrderQuery(IQueryable query, OrderParameter orderBy)
{
    string orderMethodName = orderBy.Direction == SortDirection.Ascending ? "OrderBy" : "OrderByDescending";
    Type t = typeof(T);

    var param = Expression.Parameter(t, "user");
    var property = t.GetProperty(orderBy.Attribute);

    return query.Provider.CreateQuery(
        Expression.Call(
            typeof(Queryable),
            orderMethodName,
            new Type[] { t, typeof(string) },
            query.Expression,
            Expression.Quote(
                Expression.Lambda(
                    Expression.Property(param, property),
                    param))
        ));
}