[英]Entity framework: When adding to new entities, how to use autogen ID from entity B as foreign key in entity A?
我有兩個實體,其中實體A具有到實體B的外鍵。實體PK在DB中自動生成。 當我為每個實體創建一個新對象並將實體A鏈接到B時,我希望SaveChanges()在保存實體B之后並在保存實體A之前更新實體A中的外鍵,但這不會發生-我期望太多了? 我必須使用兩次SaveChanges()調用嗎?
碼:
public class Product
{
[Key]
public int ProductId { get; set; }
[Required]
public int ProductTypeId { get; set; }
[ForeignKey("ProductTypeId")]
public virtual ProductType ProductTypeRef { get; set; }
}
public class ProductType
{
[Key]
public int ProductTypeId { get; set; }
}
Product product = new Product();
product.ProductTypeRef = new ProductType();
_context.Products.Add(product);
_context.SaveChanges(); // leads to exception telling foreign key constraint not met
這對我來說很好:
using System;
using System.Linq;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity;
using System.Data;
using System.Diagnostics;
using System.Threading.Tasks;
namespace Ef6Test
{
public class Product
{
[Key]
public int ProductId { get; set; }
[Required]
public int ProductTypeId { get; set; }
[ForeignKey("ProductTypeId")]
public virtual ProductType ProductType { get; set; }
}
public class ProductType
{
[Key]
public int ProductTypeId { get; set; }
}
class Db : DbContext
{
public DbSet<Product> Products { get; set; }
public DbSet<ProductType> ProductTypes { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
}
}
class Program
{
static void Main(string[] args)
{
Database.SetInitializer(new DropCreateDatabaseAlways<Db>());
using (var db = new Db())
{
Product product = new Product();
product.ProductType = new ProductType();
db.Products.Add(product);
db.SaveChanges(); // works fine
}
Console.WriteLine("Hit any key to exit");
Console.ReadKey();
}
}
}
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