EF核心-创建没有主键/外键的关系

Question

我试图将EF配置为在检索用户或产品时包含文档。实体文档有一个ReferenceId属性，该属性应存储UserId或ProductId。这样，当我为用户或产品保存文档时，UserId或ProductId将保存为document.referenceID。

实体:

public class User
{
    public string Id { get; set; }
    public ICollection<Document> Documents { get; set; }
}

public class Product
{
    public string Id { get; set; }
    public ICollection<Document> Documents { get; set; }
}

public class Document
{
    public string Id { get; set; }
    public string ReferenceId { get; set; }
}

正在配置:

builder.Entity<User>(e =>
{
    e.HasKey(e => e.Id);
    e.Property(p => p.Id).ValueGeneratedOnAdd();
    e.HasMany(e => e.Documents)
     .WithOne()
     .OnDelete(DeleteBehavior.Cascade);
});

builder.Entity<Product>(e =>
{
    e.HasKey(e => e.Id);
    e.Property(p => p.Id).ValueGeneratedOnAdd();
    e.HasMany(e => e.Documents)
     .WithOne()
     .OnDelete(DeleteBehavior.Cascade);
});

builder.Entity<Document>(e =>
{
    e.HasKey(e => e.Id);
    e.Property(p => p.Id).ValueGeneratedOnAdd();
    e.ToTable("Documents");
});

保存:

var user = new User { };
var userDocument = new Document { ReferenceId = user.Id };

var product = new Product { };
var productDocument = new Document { ReferenceId = product.Id };

_context.Users.Add(user);
_context.Products.Add(product);
_context.Add(userDocument);
_context.Add(productDocument);
_context.SaveChanges();

迁移:

migrationBuilder.CreateTable(
    name: "Documents",
    columns: table => new
    {
        Id = table.Column<string>(nullable: false),
        ReferenceId = table.Column<string>(nullable: true),
        ProductId = table.Column<string>(nullable: true),
        UserId = table.Column<string>(nullable: true)
    },
    constraints: table =>
    {
        table.PrimaryKey("PK_Documents", x => x.Id);
        table.ForeignKey(
            name: "FK_Documents_Products_ProductId",
            column: x => x.ProductId,
            principalTable: "Products",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);
        table.ForeignKey(
            name: "FK_Documents_Users_UserId",
            column: x => x.UserId,
            principalTable: "Users",
            principalColumn: "Id",
            onDelete: ReferentialAction.Cascade);
    });

我不希望在Documents表上创建2个外键（ProductId和UserId）。有没有办法让EF自动将UserId和ProductId链接到referenceid？

Answer 1

您可以创建多对多表:

public class Product
{
  public string Id { get; set; }
  public ICollection<ProductDocument> ProductDocuments{ get; set; }
}

public class Document
{
  public string ReferenceId { get; set; }
}

public class ProductDocument
{
  public ICollection<Product> Products{ get; set; }
  public ICollection<Document> Documents { get; set; }
}

您必须使用相同的模式为用户表ieUserDocumentes创建一个单独的表。

Answer 2

解决这个问题的正确方法是让User和Product继承一个基类，并将Id和Documents属性移到该类中。

public class BaseObject
{
    public string Id { get; set; }
    public ICollection<Document> Documents { get; set; }
}

public class User : BaseObject
{
}

public class Product : BaseObject
{
}

public class Document
{
    public string BaseObjectId { get; set; }
}