LINQ Expression> equavalent of .Contains()

Question

Has anybody got an idea of how to create a .Contains(string) function using Linq Expressions, or even create a predicate to accomplish this

public static Express         


        

Answer 1

I use something similiar, where I add filters to a query.

public static Expression> PropertyStartsWith(PropertyInfo property, TypeOfPropery value)
{
     var parent = Expression.Parameter(typeof(TypeOfParent));
     MethodInfo method = typeof(string).GetMethod("StartsWith",new Type[] { typeof(TypeOfPropery) });
     var expressionBody = Expression.Call(Expression.Property(parent, property), method, Expression.Constant(value));
     return Expression.Lambda>(expressionBody, parent);
}

Usage, to apply filter against a property whose name matches Key, and using supplied value, Value.

public static IQueryable ApplyParameters(this IQueryable query, List gridParameters)
{

   // Foreach Parameter in List
   // If Filter Operation is StartsWith
    var propertyInfo = typeof(T).GetProperty(parameter.Key);
    query = query.Where(PropertyStartsWith(propertyInfo, parameter.Value));
}

And yes, this method works with contains:

        public static Expression> PropertyContains(PropertyInfo property, TypeOfPropery value)
    {
        var parent = Expression.Parameter(typeof(TypeOfParent));
        MethodInfo method = typeof(string).GetMethod("Contains", new Type[] { typeof(TypeOfPropery) });
        var expressionBody = Expression.Call(Expression.Property(parent, property), method, Expression.Constant(value));
        return Expression.Lambda>(expressionBody, parent);
    }

By having those 2 examples, you can more easily understand how we can call various different methods by name.