使用像Func这样的表达式

Question

I need to get selector using expression which has source and destination, like mapper (I need it for EF).

public class Region
{
    public int RegionId { get; set; }
    public string RegionName { get; set; }
}

var country = new List<Region> { new Region { RegionId = 21, RegionName = "MyRegion" } };
Expression<Func<Region, string>> exp = (x => x.RegionName);
country.Select(s => exp(s));
// exp(s) gives compilation error (Method name expected)

Is it possible to get it?

Answer 1

Imagine this:

var items = new List<int>();
Expression<Func<int, int>> selector = (x => x);

You cannot do this because it is an Expression :

selector(x); // will not work

But this will work because you are compiling the expression so now you can call the Func<int, int> :

selector.Compile()(1);

And if you want to use the expression in a IQueryable , you can do this:

items.AsQueryable().Select(x => selector);
// Or simply
items.AsQueryable().Select(selector);

So in your case, it should be:

country.Select(exp);