手动创建表达式树

Question

I have the classes

public class MyModel
{
    public MyModel()
    {
        this.Map = new MyMap();
    }
    public MyMap Map { get; set; }
}

public class MyMap
{
    public string MyProperty1 { get; set; }
    public int MyProperty2 { get; set; }
}

How can I construct this lambda

Expression<Func<MyModel, string>> exp = m => m.Map.MyProperty1;

manually using Expression Tree?

Answer 1

Like this:

var parameter = Expression.Parameter(typeof (MyModel));
var mapProperty = Expression.Property(parameter, "Map");
var myProperty1 = Expression.Property(mapProperty, "MyProperty1");

var exp = Expression.Lambda<Func<MyModel, string>>(myProperty1, parameter);

Answer 2

You can do this using the PropertyOrField method of Expression, here is a quick example I cooked up using your objects:

var model = new MyModel();

var mapExpr = Expression.PropertyOrField(Expression.Constant(model), "Map");
var propExpr = Expression.PropertyOrField(mapExpr, "MyProperty1");

Expression.Lambda<Func<string>>(propExpr).Compile()(); //Outputs the value of MyProperty1 on the variable called model.