Convert collections of database entities to collections of view models - asp.net-web-api

Question

I am working on a .NET Core Web API
So far I used to return anonymous types in my controllers but now I want to start using the full power of swagger with auto documentation of the return types.
Which lead me to start using view models.
But I am struggling with converting between the auto-generated database model classes
and the auto-generated swagger view model classes.
It works for a single instance (see GetPerson method in the controller below) but fails when I want to return lists.
So my questions:
How do I cast/convert collections/lists of objects between view models and database models
Is the code in the controller correct? Are there easier/shorter/better ways to do the conversion? (I read about using the implicit operator)
Error message I get:
Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Collections.Generic.List'. An explicit conversion exists (are you missing a cast?)
It gives me an InvalidCastException if I cast them explicitly like
List result = (List)_dbContext.Person....
there seems to be a problem with generics in the display of stackoverflow
Assume I used the generic lists with giving a type PersonView
My code looks like:
Database models
public partial class Person
{
public Person()
{
}
public int Id { get; set; }
public string Firstname { get; set; }
public string Lastname { get; set; }
public int? MainAdressId { get; set; }
public virtual Adress MainAdress { get; set; }
}
public partial class Adress
{
public Adress()
{
Person = new HashSet();
}
public int Id { get; set; }
public string CityName { get; set; }
public int CityPostalCode { get; set; }
public string StreetName { get; set; }
public string HouseNumber { get; set; }
public string FloorNumber { get; set; }
public string DoorNumber { get; set; }
public virtual ICollection Person { get; set; }
}
View models
public class City
{
public string Name { get; set; }
public int PostalCode { get; set; }
}
public class Street
{
public string Name { get; set; }
public string HouseNumber { get; set; }
public string FloorNumber { get; set; }
public string DoorNumber { get; set; }
}
public class AdressView
{
public Street Street { get; set; }
public City City { get; set; }
}
public class PersonView
{
public string FirstName { get; set; }
public string Lastname { get; set; }
public AdressView Adress { get; set; }
}
The controller class which is working for a single instance but not for lists
using System.Collections.Generic;
using System.Linq;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using Swashbuckle.SwaggerGen.Annotations;
using PersonExample.ModelsPersonDB;
using PersonExample.ModelsViewPerson;
namespace PersonExample.Controllers
{
[Route("api/[controller]")]
public class PersonViewTestController : Controller
{
private readonly PersonDBContext _dbContext;
private readonly ILogger _logger;
public PersonViewTestController(PersonDBContext dbContext, ILogger logger)
{
_dbContext = dbContext;
_logger = logger;
_logger.LogDebug("{0} > new instance created", GetType().Name);
}
[HttpGet("{id:int}", Name = "GetPerson")]
[ProducesResponseType(typeof(PersonView), 200)]
[SwaggerOperation("GetPerson")]
public virtual IActionResult GetPerson([FromRoute]int id)
{
PersonView result = _dbContext.Person
.Include(p => p.MainAdress)
.Where(p => p.Id == id)
.Select(p => new PersonView()
{
FirstName = p.Firstname,
Lastname = p.Lastname,
Adress = (p.MainAdress == null) ? null :
new AdressView()
{
Street = new Street()
{
Name = p.MainAdress.StreetName,
HouseNumber = p.MainAdress.HouseNumber,
FloorNumber = p.MainAdress.FloorNumber,
DoorNumber = p.MainAdress.DoorNumber
},
City = new City()
{
Name = p.MainAdress.CityName,
PostalCode = p.MainAdress.CityPostalCode
}
}
}
)
.FirstOrDefault();
return new ObjectResult(result);
}
[HttpGet(Name = "GetPersonList")]
[ProducesResponseType(typeof(List), 200)]
[SwaggerOperation("GetPersonList")]
public virtual IActionResult GetPersonList()
{
List result = _dbContext.Person
.Include(p => p.MainAdress)
.Select(p => new PersonView()
{
FirstName = p.Firstname,
Lastname = p.Lastname,
Adress = (p.MainAdress == null) ? null :
new AdressView()
{
Street = new Street()
{
Name = p.MainAdress.StreetName,
HouseNumber = p.MainAdress.HouseNumber,
FloorNumber = p.MainAdress.FloorNumber,
DoorNumber = p.MainAdress.DoorNumber
},
City = new City()
{
Name = p.MainAdress.CityName,
PostalCode = p.MainAdress.CityPostalCode
}
}
}
);
return new ObjectResult(result);
}
}
}

Answer 1

you can use AutoMapper https://github.com/AutoMapper/AutoMapper/wiki/Getting-started
here some examples: Simple Automapper Example
example with EF core and ASP.NET WebApi: https://github.com/chsakell/aspnet5-angular2-typescript

Answer 2

I missed the .ToList() at the end of the query.
The full controller know looks like:
[HttpGet(Name = "GetPersonList")]
[ProducesResponseType(typeof(List), 200)]
[SwaggerOperation("GetPersonList")]
public virtual IActionResult GetPersonList()
{
List result = _dbContext.Person
.Include(p => p.MainAdress)
.Select(p => new PersonView()
{
FirstName = p.Firstname,
Lastname = p.Lastname,
Adress = (p.MainAdress == null) ? null :
new AdressView()
{
Street = new Street()
{
Name = p.MainAdress.StreetName,
HouseNumber = p.MainAdress.HouseNumber,
FloorNumber = p.MainAdress.FloorNumber,
DoorNumber = p.MainAdress.DoorNumber
},
City = new City()
{
Name = p.MainAdress.CityName,
PostalCode = p.MainAdress.CityPostalCode
}
}
}
).ToList(); //missed that line
return new ObjectResult(result);
}