I have a method that takes Expression type parameter, in my method i want to get values of this expression but cant find out hot to do that.

private User GetUser(Expression<Func<User, bool>> query)
{
  User user = Context.User.Where(query).FirstOrDefault();
  return user;
}

I am calling this method with different parameters like

GetUser(u => u.Username == username);

GetUser(u=> u.Email == email);

I want to change GetUser method to work with stored procedures but i need to find what is inside query parameter

I want to check if query is u.Username == username I will call GetUserByUsername SP if query is u.Email == email I will call GetuserByEmail SP

The expression can be reduced to several expressions.

 var body = query.Body as BinaryExpression;
 if (body != null)
 {
    var left = body.Left as MemberExpression;
    if (left != null)
    {
        Console.WriteLine(left.Member.Name);
         // You can get "Username" or "Email" here
    }
 }

By the way I think you are in a wrong direction. Think about this situation: Some other developer see your GetUser method, using it in this way:

var result = GetUser(u => u.Email.Equals("[email protected]")); //or
var another = GetUser(u => u.Username.Contains("bar"));

He would think he is correct, but in fact your method won't give his ideal result! Well you can say "never mind, I will inform them this change", but what about the days after you quitted this team/company? It's a nightmare if a method doesn't behave like its declaration.