EF Core 连接结果的通用类型 class

Question

Trying to come up with a dynamically typed class for storing results from querying my EF Core dbcontext. What I'm trying to avoid is creating a new class for every join combination I might need. For example, I have these 2 entities that I want to join in a query:

List<Person> People = new List<Person>(){ new Person(){ Id = 1, Name = "John Doe"}};
List<Address> Addresses = new List<Address>(){ new Address(){ Id = 1, City = "Anonland"}};

What I have tried is:

a) Creating a generic type class that just contains one each of the provided type params

public class QueryResult<T1, T2> {
        public T1 t1;
        public T2 t2;

        public QueryResult(T1 t1, T2 t2) {
            this.t1 = t1;
            this.t2 = t2;
        }
    }

then

List<QueryResult<Person, Address> res = 
            People.Join(
                Addresses,
                p => p.Id,
                a => a.Id,
                (p,a) => new QueryResult<Person, Address>(p, a))
            .ToList();

foreach (var x in res){
    Console.WriteLine($"{x.t1.Name} - {x.t2.City}");
}

I can live with this, but I would prefer to have more descriptive var names than t1 / t2, which I don't think I can accomplish using this method.

and b) using an implementation of Dictionary<string,object> :

public class QueryResult<T1, T2> : Dictionary<string, object> {
    public QueryResult(T1 a, T2 b){
        this.Add(typeof(T1).ToString(), a);
        this.Add(typeof(T2).ToString(), b);        
    }
}

then

List<QueryResult<Person, Address> res = 
            People.Join(
                Addresses,
                p => p.Id,
                a => a.Id,
                (p,a) => new QueryResult<Person, Address>(p, a))
            .ToList();

foreach (var x in res){
            Console.WriteLine(((Person)x["Person"]).Name + " - " + ((Address)x["Address"]).City);
        }

This also works and is more descriptive, but then accessing and casting the objects is long-winded and redundant.

Is there some sort of middle ground here that I'm missing? Or maybe just going about this entirely the wrong way?

Answer 1

Why not just use value tuples available since C# 7 which allow to specify field names ?

List<(Person Person, Address Address)> res = 
            People.Join(
                Addresses,
                p => p.Id,
                a => a.Id,
                (p,a) => (p, a))
            .ToList();

Or using var :

var res = People.Join(
                Addresses,
                p => p.Id,
                a => a.Id,
                (p,a) => (Person: p, Address: a))
            .ToList();
 
foreach (var x in res){
        Console.WriteLine(x.Person.Name + " - " + x.Address.City);
    }

Answer 2

So for future reference, 'tuple literals' are not supported in expression trees, so I was getting compiler errors with this. What I ended up having to do is instantiate a tuple explicitly

List<Tuple<Person, Address>> res = 
            People.Join(
                Addresses,
                p => p.Id,
                a => a.Id,
                (p,a) => new Tuple<Person, Address>(p, a))
            .ToList();

foreach (var x in res){
    // x.Item1.Name, etc
}

which still introduces the less descriptive Item1...ItemN, but at least avoids creating a custom class.