Conventions.Remove （）EF Core？

Question

在我的常规.NET Framework应用程序中，我使用的是EF 6.x并且还使用了一些继承，具体来说：

采购Order.cs和Sales Order.vs都从Order.cs继承

在继承自OnModelCreating()的上下文类的IdentityDbContext中，我正在做：

modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();

这曾经工作，但现在我将我的应用程序移动到.NET Core 2.0，我正在使用EF Core。什么在EF Core中实现了同样的目的？因为现在我收到错误：

System.Data.SqlClient.SqlException（0x80131904）：在表'Order'上引入FOREIGN KEY约束'FK_Order_Business_CustomerId'可能会导致循环或多个级联路径。指定ON DELETE NO ACTION或ON UPDATE NO ACTION，或修改其他FOREIGN KEY约束。

UPDATE

这是Ahmar回答后的代码。在我的上下文课中，我有：

protected override void OnModelCreating(ModelBuilder builder)
{
  base.OnModelCreating(builder);
  builder.HasDefaultSchema("PD");

  builder.Entity<Customer>()
    .HasMany(c => c.SaleOrders)
    .WithOne(e => e.Customer)
    .OnDelete(DeleteBehavior.SetNull);

  builder.Entity<Supplier>()
    .HasMany(po => po.PurchaseOrders)
    .WithOne(e => e.Supplier)
    .OnDelete(DeleteBehavior.SetNull);

  builder.Entity<PurchaseOrder>()
    .HasMany(li => li.LineItems)
    .WithOne(po => po.PurchaseOrder)
    .OnDelete(DeleteBehavior.SetNull);

  builder.Entity<SaleOrder>()
    .HasMany(li => li.LineItems)
    .WithOne(po => po.SaleOrder)
    .OnDelete(DeleteBehavior.SetNull);
}

就实体而言，它们是：

public abstract class Business : IEntity
{
  protected Business()
  {
    CreatedOn = DateTime.UtcNow;
  }

  public int Id { get; set; }
  public string Name { get; set; }
  public string TaxNumber { get; set; }
  public string Description { get; set; }
  public string Phone { get; set; }
  public string Website { get; set; }
  public string Email { get; set; }
  public bool IsDeleted { get; set; }
  public DateTime CreatedOn { get; set; }
  public DateTime? ModifiedOn { get; set; }
  public ICollection<Address> Addresses { get; set; } = new List<Address>();
  public ICollection<Contact> Contacts { get; set; } = new List<Contact>();
}

[Table("Customers")]
public class Customer : Business
{
  public decimal AllowedCredit { get; set; }
  public decimal CreditUsed { get; set; }
  public int NumberOfDaysAllowedToBeOnMaxedOutCredit { get; set; }
  public ICollection<SaleOrder> SaleOrders { get; set; }
}

[Table("Suppliers")]
public class Supplier : Business
{
  public ICollection<PurchaseOrder> PurchaseOrders { get; set; }
}

public abstract class Order : IEntity
{
  protected Order()
  {
    Date = DateTime.UtcNow;
    CreatedOn = DateTime.UtcNow;
  }

  public int Id { get; set; }
  public DateTime Date { get; set; }
  public decimal ShippingCost { get; set; }
  public Currency ShippingCurrency { get; set; }
  public decimal ShippingConversionRate { get; set; }
  public bool IsDeleted { get; set; }
  public DateTime CreatedOn { get; set; }
  public DateTime? ModifiedOn { get; set; }
  public ICollection<Invoice> Invoices { get; set; }
  public ICollection<Note> Notes { get; set; }
}

[Table("PurchaseOrders")]
public class PurchaseOrder : Order
{
  public int SupplierOrderNumber { get; set; }
  public PurchaseOrderStatus Status { get; set; }
  public decimal Vat { get; set; }
  public decimal ImportDuty { get; set; }
  public int SupplierId { get; set; }
  public Supplier Supplier { get; set; }
  public ICollection<PurchaseOrderLineItem> LineItems { get; set; }
}

[Table("SaleOrders")]
public class SaleOrder : Order
{
  public decimal AmountToBePaidOnCredit { get; set; }
  public SaleOrderStatus Status { get; set; }
  public ICollection<SaleOrderLineItem> LineItems { get; set; }
  public int CustomerId { get; set; }
  public Customer Customer { get; set; }
}

所以在做了艾哈迈尔建议之后，当我做update-database时，我仍然得到同样的错误。

Answer 1

您需要在.Net Core EF中的每个实体上配置级联删除行为。

实体框架Core Fluent API OnDelete方法用于指定删除主体时应在关系中的依赖实体上发生的操作。

OnDelete方法将DeleteBehavior枚举作为参数：

• 应删除级联 - 家属
• 限制 - 家属不受影响
• SetNull - 从属行中的外键值应更新为NULL

例：

public class Company
{
    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<Employee> Employees { get; set; }
}

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int? CompanyId { get; set; }
    public Company Company { get; set; }
}

protected override void OnModelCreating(Modelbuilder modelBuilder)
{
    modelBuilder.Entity<Company>()
        .HasMany(c => c.Employees)
        .WithOne(e => e.Company).
        .OnDelete(DeleteBehavior.SetNull);
}

删除公司时，它会将Employee表中的CompanyId属性设置为null。

在Configuring One To Many Relationships获取更多细节

PS。请确保您的所有引用属性都应为null，因此，EF Core可以在删除时将它们设置为null。就像CompanyId一样。