Construct LambdaExpression for nested property from string

.net c# expression-trees lambda linq

Question

I am trying to create a lambda expression for a nested property at run-time from the name of the propert. Basically I am trying to create the lambda expression specified by:

var expression = CreateExpression<Foo, object>(foo => foo.myBar.name);

private static Expression CreateExpression<TEntity, TReturn>(Expression<Func<TEntity, TReturn>> expression)
{
    return (expression as Expression);
}

With the classes:

class Foo
{
    public Bar myBar { get; set; }
}
class Bar
{
    public string name { get; set; }
}

However all I am given is the type of Foo and the string "myBar.name"

If it were a normal property such as just needing the value "myBar" then I could use the following:

private static LambdaExpression GetPropertyAccessLambda(Type type, string propertyName)
{
    ParameterExpression odataItParameter = Expression.Parameter(type, "$it");
    MemberExpression propertyAccess = Expression.Property(odataItParameter, propertyName);
    return Expression.Lambda(propertyAccess, odataItParameter);
}

However this code does not work for nested properties and I'm not sure how to create the LambdaExpression to do the work of foo.myBar.name.

I think it's going to be something like this:

GetExpression(Expression.Call(GetExpression(Foo, "myBar"), "name"))

But I can't seem to work out how to get it all working, or if there's a better way to do this at run-time.

Accepted Answer

Do you mean:

static LambdaExpression CreateExpression(Type type, string propertyName) {
    var param = Expression.Parameter(type, "x");
    Expression body = param;
    foreach (var member in propertyName.Split('.')) {
        body = Expression.PropertyOrField(body, member);
    }
    return Expression.Lambda(body, param);
}

For example:

class Foo {
    public Bar myBar { get; set; }
}
class Bar {
    public string name { get; set; }
}
static void Main() {
    var expression = CreateExpression(typeof(Foo), "myBar.name");
    // x => x.myBar.name
}

?



Licensed under: CC-BY-SA with attribution
Not affiliated with Stack Overflow
Is this KB legal? Yes, learn why
Licensed under: CC-BY-SA with attribution
Not affiliated with Stack Overflow
Is this KB legal? Yes, learn why