问题
Without using Automapper, I'm trying to map a list of DTO's into each element of a list of DTO's. Specfically in this example, I want the API to return a list of parents where each parent contains it's list of children and list of pets.
I have an EF Core project with the models below (which use fully defined relationships) and exist within a larger database.
There is a Parent object, which has many Pet objects and many Child objects, like so:
EF Core Models
public class Parent
{
public int ParentId { get; set; }
public string Name { get; set; }
public List<Child> Children { get; set; }
public List<Pet> Pets { get; set; }
}
public class Child
{
public int ChildId { get; set; }
public string Name { get; set; }
public int ParentId { get; set; }
public Parent Parent { get; set; }
}
public class Pet
{
public int PetId { get; set; }
public string Name { get; set; }
public int ParentId { get; set; }
public Parent Parent { get; set; }
}
Without using Automapper I'm trying to use DTOs in a controller to send the data out.
I've setup the DTOs as follows:
DTOs
public class ParentDTO
{
public int ParentId { get; set; }
public string Name { get; set; }
//Should these be List<> or IEnumerable<>?
public IEnumerable<ChildDTO> Children { get; set; }
public IEnumerable<PetDTO> Pets { get; set; }
}
public class ChildDTO
{
public int ChildId { get; set; }
public string Name { get; set; }
}
public class PetDTO
{
public int PetId { get; set; }
public string Name { get; set; }
}
Currently my controller looks like this:
Controller Attempt 1
// GET: api/Parents/
[HttpGet]
public IEnumerable<ParentDTO> GetParents()
{
var parents = from pa in _context.Parents
select new ParentDTO()
{
Name = pa.Name
};
return parents;
}
// GET: api/Parents/GetParentsWith
[HttpGet("[action]")]
public IEnumerable<ParentDTO> GetParentsWith()
{
var parents = from pa in _context.Parents
select new ParentDTO()
{
Name = pa.Name,
//Not sure how to correctly do this below...
Children = (from c in _context.Children.Where(c => c.ParentId == pa.ParentId)
select new ChildDTO()
{
Name = c.Name
}),
Pets = (from pe in _context.Pets.Where(pet => pet.ParentId == pa.ParentId)
select new PetDTO()
{
Name = pe.Name
})
};
return parents;
}
My GET: api/Parents/ works just fine (because I'm not trying to make the nested list), but how do I add the related child and pet items to the parents DTO like I'm trying to do in GET: api/Parents/GetParentsWith?
Trying this gives the error:
Microsoft.Data.SqlClient.SqlException (0x80131904): Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.
....
...
I've also tried:
Controller Attempt 2
// GET: api/Parents/GetParentsWith
[HttpGet("[action]")]
public IEnumerable<ParentDTO> GetParentsWith()
{
var parents = from pa in _context.Parents
select new ParentDTO()
{
Name = pa.Name,
Children = (from c in pa.Children
select new ChildDTO()
{
Name = c.Name
}),
Pets = (from pe in pa.Pets
select new PetDTO()
{
Name = pe.Name
})
};
return parents;
}
This also gives the error:
Microsoft.Data.SqlClient.SqlException (0x80131904): Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.
....
...
I've also tried:
Controller Attempt 3
// GET: api/Parents/GetParentsWith
[HttpGet("[action]")]
public IEnumerable<ParentDTO> GetParentsWith()
{
var parents = from pa in _context.Parents
select new ParentDTO()
{
ParentId = pa.ParentId,
Name = pa.Name
};
foreach (ParentDTO parent in parents)
{
var children = from child in _context.Children where child.ParentId == parent.ParentId
select new ChildDTO()
{
ChildId = child.ChildId,
Name = child.Name
};
var pets = from pet in _context.Pets
where pet.ParentId == parent.ParentId
select new PetDTO()
{
PetId = pet.PetId,
Name = pet.Name
};
parent.Children = children;
parent.Pets = pets;
return parents;
}
Which doesn't throw any errors so maybe I'm on the right track here, unfortunately it just returns null where I would expect an array of children or pets:
[
{
"parentId": 1,
"name": "Ronald",
"children": null,
"pets": null
},
{
"parentId": 2,
"name": "Benjamin",
"children": null,
"pets": null
},
{
"parentId": 3,
"name": "Sally",
"children": null,
"pets": null
},
{
"parentId": 4,
"name": "Foobar",
"children": null,
"pets": null
}
]
Solved! But did I do it right?
I noticed parents was an IQueryable, and so the assignment within the foreach was not working as I expected... I think I've got a bit to learn about IQueryable, IEnumerable etc. etc.
// GET: api/Parents/GetParentsWith
[HttpGet("[action]")]
public ask<ActionResult<IEnumerable<ParentDTO>>> GetParentsWith()
{
var parents = (from pa in _context.Parents
select new ParentDTO()
{
ParentId = pa.ParentId,
Name = pa.Name
}).ToListAsync();
foreach (ParentDTO parent in await parents)
{
var children = from child in _context.Children where child.ParentId == parent.ParentId
select new ChildDTO()
{
ChildId = child.ChildId,
Name = child.Name
};
var pets = from pet in _context.Pets
where pet.ParentId == parent.ParentId
select new PetDTO()
{
PetId = pet.PetId,
Name = pet.Name
};
parent.Children = children;
parent.Pets = pets;
}
return parents;
}
来源：https://stackoverflow.com/questions/57104588/solved-maybe-how-to-return-list-of-dto-with-nested-lists-of-related-dto