实体框架核心 - ForeingKey显示空值

Question

I'm developing a Entity Framework with ASP.NET Core and i'm building a database in SQL Express 2017 and a REST API using C#.

I have two models (Usuario and Alimento): This is my Alimento model:

public class Alimento{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public int codAl { get; set; }

[Required(ErrorMessage = "Se requiere de una denominacion")]
[StringLength(50, MinimumLength = 2)]
public string Descripcion { get; set; }

public string Cantidad { get; set; }

[Required(ErrorMessage = "Calorias es imprescindible")]
[DataType(DataType.Currency)]
[Range(1, 999, ErrorMessage = "El rango debe estar entre 1 y 999")]
public int Calorias { get; set; }
    }

and this is my Usuario model:

public class Usuario{
public int Id { get; set; }
public string email { get; set; }

[Required(ErrorMessage = "Se requiere de una denominacion")]
[StringLength(50, MinimumLength = 2)]
public string nombre { get; set; }

public Alimento alimento { get; set; }
}

When i migrate the solution and update the database, i can see the attribute "alimento" in USUARIO table like "alimentocodAl".

I'm trying to modelize "A food(ALIMENTO) has been eaten by an user(USUARIO)" I have a controller that i get all entries from a specific user, but when I use the API, my foreing key in USUARIO table (Usuario foreing key to Alimento by codAl) show null values, for example:

[{"id":1,"email":"mail","nombre":"nombre","alimento":null}, 
{"id":2,"email":"mail","nombre":"nombre","alimento":null}, 
{"id":3,"email":"mail","nombre":"nombre","alimento":null}]

This isn't correct because I have values in this colum inside my table.

The code that execute the controller is:

public IEnumerable<Usuario> GetInfoUsuario(string email)
{
    var user = ctx.usuarios.ToList().Where(b => b.email == email);
    return user;
}

What i have wrong?

this is for an REST APi developed with ASP.NET and Entity Framework Core running in Windows 7.

Answer 1

您可以尝试将Alimanto包括在内

ctx.usuarios.Include(b => b.alimento)

Answer 2

You are retrieving only Usuario from database. If you want to get any additional info you need to use Include .

Instead of line var user = ctx.usuarios.ToList().Where(b => b.email == email);

You need to have var user = ctx.usuarios.Where(b => b.email == email).Include(usr => usr.alimento).ToList();

Ps

I moved ToList() as the last operation because it evaluates expression. Now it will filter table before retrieving data instead of downloading all users and filtering afterwards.

Answer 3

Try to map with this example:

public class Usuario{
public int Id { get; set; }
public string email { get; set; }

[Required(ErrorMessage = "Se requiere de una denominacion")]
[StringLength(50, MinimumLength = 2)]
public string nombre { get; set; }

[ForeignKey("alimento")]
public int AlimentoId {get; set;}

public virtual Alimento alimento { get; set; }
}


public class Alimento{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public int codAl { get; set; }

[Required(ErrorMessage = "Se requiere de una denominacion")]
[StringLength(50, MinimumLength = 2)]
public string Descripcion { get; set; }

public string Cantidad { get; set; }

[Required(ErrorMessage = "Calorias es imprescindible")]
[DataType(DataType.Currency)]
[Range(1, 999, ErrorMessage = "El rango debe estar entre 1 y 999")]
public int Calorias { get; set; }

public virtual ICollection<Usario> Users {get; set;}
    }

Right one to many mapping should be created with code above. Something like this should be received from Usario table.

[{"id":1,"email":"mail","nombre":"nombre","AlimentoId":1}] 

Answer 4

Make Foreign Key Field "virtual". Change

public Alimento alimento { get; set; }

to the following

public virtual Alimento alimento { get; set; }