Error using Code First From Database

Question

I’m trying to use the Entity Framework with a Sqlserver database that I created outside of Visual Studio. The problem is that when I add the ADO.NET Entity data Model to the project to do the relation, it is failing to create one of the classes to reference with the table in the database.

My bank has these tables:

After choosing ADO.NET Entity data Model, I choose Code First From Database and select to import all tables:

However the Productovenda table is not imported along with the others. It is only imported if I select just it. What may be happening?

Answer 1

If your relationship entity has only the references to the primary tables, then the RU will only treat it as a collection:

Note that the properties are virtual (virtual), that is, the RU maps them as navigation property (recommended reading).

In this case, the navigation property only signals to the EF that a related record can be found in the specified entity. In the examples below it has been indicated that a Product may (or may not) be associated with several SALES or a Sale may (or may not) have several PRODUCTS.

Product
See in this template there is a collection of SALE.

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

[Table("Produto")]
public partial class Produto
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public Produto()
    {
        Venda = new HashSet<Venda>();
    }

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

    [StringLength(10)]
    public string descricao { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Venda> Venda { get; set; }
}

Sale
And in this model, a collection of PRODUCT.

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

[Table("Venda")]
public partial class Venda
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public Venda()
    {
        Produto = new HashSet<Produto>();
    }

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

    public DateTime? referencia { get; set; }

    public int? qtd { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Produto> Produto { get; set; }
}

To create the model - A justification

If you notice, there is no reason for EF to create a template since all fields will be automatically filled in when you link a product to sale or vice versa.

If at random, your Sales Tableproduct has other fields (besides foreign fields), EF will create a template for it, so you can design your application and provide the user with a means to fill these fields.

Note that I simply created the Discount field and the template was created:

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

[Table("ProdutoVenda")]
public partial class ProdutoVenda
{
    [Key]
    [Column(Order = 0)]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int idProduto { get; set; }

    [Key]
    [Column(Order = 1)]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int idVenda { get; set; }

    public double? desconto { get; set; }

    public virtual Produto Produto { get; set; }

    public virtual Venda Venda { get; set; }
}

Other readings
Many Relationship for Many Entity Framework 6
List, virtual and Entity Framework