How to construct LambdaExpression with conversion
- by nerijus
I need to sort in ajax response grid by column name. Column value is number stored as a string.
Let's say some trivial class (in real-life situation there is no possibility to modify this class):
class TestObject
{
public TestObject(string v)
{
this.Value = v;
}
public string Value { get; set; }
}
then simple test:
[Test]
public void LambdaConstructionTest()
{
var queryable = new List<TestObject>
{
new TestObject("5"),
new TestObject("55"),
new TestObject("90"),
new TestObject("9"),
new TestObject("09"),
new TestObject("900"),
}.AsQueryable();
var sortingColumn = "Value";
ParameterExpression parameter = Expression.Parameter(queryable.ElementType);
MemberExpression property = Expression.Property(parameter, sortingColumn);
//// tried this one: var c = Expression.Convert(property, typeof(double));
LambdaExpression lambda = Expression.Lambda(property, parameter); //// constructs: o=>o.Value
var callExpression = Expression.Call(typeof (Double), "Parse", null, property);
var methodCallExpression = Expression.Call(
typeof(Queryable),
"OrderBy",
new[] { queryable.ElementType, property.Type },
queryable.Expression,
Expression.Quote(lambda)); // works, but sorts by string values.
//Expression.Quote(callExpression)); // getting: System.ArgumentException {"Quoted expression must be a lambda"}
var querable = queryable.Provider.CreateQuery<TestObject>(methodCallExpression);
// return querable; // <- this is the return of what I need.
}
Sorry for not being clear in my first post as @SLaks answer was correct but I do not know how to construct correct lambda expression in this case.
