[英]composite key as foreign key
我在 MVC 3 应用程序中使用实体框架 4.1。 我有一个实体,其中我的主键由两列(复合键)组成。 这在另一个实体中用作外键。 如何建立关系? 在正常场景中,我们使用:
public class Category
{
public string CategoryId { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
public int ProductId { get; set; }
public string Name { get; set; }
public string CategoryId { get; set; }
public virtual Category Category { get; set; }
}
但是如果类别有两列键怎么办?
您可以使用任何一种流畅的API:
public class Category
{
public int CategoryId1 { get; set; }
public int CategoryId2 { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
public int ProductId { get; set; }
public string Name { get; set; }
public int CategoryId1 { get; set; }
public int CategoryId2 { get; set; }
public virtual Category Category { get; set; }
}
public class Context : DbContext
{
public DbSet<Category> Categories { get; set; }
public DbSet<Product> Products { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Category>()
.HasKey(c => new {c.CategoryId1, c.CategoryId2});
modelBuilder.Entity<Product>()
.HasRequired(p => p.Category)
.WithMany(c => c.Products)
.HasForeignKey(p => new {p.CategoryId1, p.CategoryId2});
}
}
或数据注释:
public class Category
{
[Key, Column(Order = 0)]
public int CategoryId2 { get; set; }
[Key, Column(Order = 1)]
public int CategoryId3 { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
[Key]
public int ProductId { get; set; }
public string Name { get; set; }
[ForeignKey("Category"), Column(Order = 0)]
public int CategoryId2 { get; set; }
[ForeignKey("Category"), Column(Order = 1)]
public int CategoryId3 { get; set; }
public virtual Category Category { get; set; }
}
我相信最简单的方法是在Navigation属性上使用Data Annotation,如下所示: [ForeignKey("CategoryId1, CategoryId2")]
public class Category
{
[Key, Column(Order = 0)]
public int CategoryId1 { get; set; }
[Key, Column(Order = 1)]
public int CategoryId2 { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
[Key]
public int ProductId { get; set; }
public string Name { get; set; }
public int CategoryId1 { get; set; }
public int CategoryId2 { get; set; }
[ForeignKey("CategoryId1, CategoryId2")]
public virtual Category Category { get; set; }
}
在.NET Core
和.NET 5 <
文档中只显示了Data annotations (simple key)
。
但是使用来自@LadislavMrnka 的示例,您将收到如下错误消息:
System.InvalidOperationException:有多个 [ForeignKey] 属性指向导航“”的属性。 要使用数据注释定义复合外键,请在导航中使用 [ForeignKey] 属性。
使用该错误消息,您可以编写如下代码:
public class Product
{
[Key]
public int ProductId { get; set; }
public string Name { get; set; }
public int CategoryId2 { get; set; }
public int CategoryId3 { get; set; }
[ForeignKey("CategoryId2,CategoryId3")]
public virtual Category Category { get; set; }
}
来自 Microsoft 的Fluent API (composite key)
示例:
internal class MyContext : DbContext
{
public DbSet<Car> Cars { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Car>()
.HasKey(c => new { c.State, c.LicensePlate });
modelBuilder.Entity<RecordOfSale>()
.HasOne(s => s.Car)
.WithMany(c => c.SaleHistory)
.HasForeignKey(s => new { s.CarState, s.CarLicensePlate });
}
}
public class Car
{
public string State { get; set; }
public string LicensePlate { get; set; }
public string Make { get; set; }
public string Model { get; set; }
public List<RecordOfSale> SaleHistory { get; set; }
}
public class RecordOfSale
{
public int RecordOfSaleId { get; set; }
public DateTime DateSold { get; set; }
public decimal Price { get; set; }
public string CarState { get; set; }
public string CarLicensePlate { get; set; }
public Car Car { get; set; }
}
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