Web API with Entity Framework inheritance - entity-framework

Question

Suppose I have the following entities:
abstract class User
{
string Id
string Name
}
class UserA : User
{
List<UserB> Bs
}
class UserB : User
{
string UserAId
[ForeignKey("UserAId"), JsonIgnore]
UserA UserA
}
I want to load all of them in one query and get only the id of the collection. For example, if return
[HttpGet]
public IEnumerable<Usuario> Get()
{
return _context.Users.ToList();
}
The response include all data from "Bs" collection
[
{
"id": "0",
"name": "User A",
"Bs": [
{
"id": "1",
"name" : ....
"aId": ....
},
{
"id": "2",
"name" : ....
"aId": ....
}
]
},
{
"aId": "0",
"id": "1",
"name": "User B 1"
},
{
"aId": "0",
"id": "2",
"name": "User B 2"
}
]
How to get the collection without the extra properties?
[
{
"id": "0",
"name": "User A",
"Bs": [
{
"id": "1"
},
{
"id": "2"
}
]
},
{
"aId": "0",
"id": "1",
"name": "User B 1"
},
{
"aId": "0",
"id": "2",
"name": "User B 2"
}
]
And return this json without "aId" and "name" from the "Bs" collection

Answer 1

I think you can use a select statement to project the id like:
_context.Users.Select(user => user.id)
You will have to change the return type
Reference:
https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/method-based-query-syntax-examples-projection

Answer 2

I resolved this issue with this method:
[HttpGet]
public IEnumerable<dynamic> Get()
{
IEnumerable<dynamic> res = _context.Users.OfType<UserA>()
.Select(u => new {Id = u.Id, Name = u.Name, Users = u.Users.Select(ui => new { Id = ui.Id }) })
.ToArray();
res = res.Concat<dynamic>(_context.Users.OfType<UserB>());
return res;
}

Answer 3

To return the ids from the type UserA's Bs collection, you need to filter out the values based on the type and then use SelectMany on the Bs collection
[HttpGet]
public IEnumerable<int> Get()
{
return _context.Where(e => (e is UserA))
.Select(u => (UserA)u)
.SelectMany(b => b.Bs)
.ToList();
}