如何在EF6与EF Core中设置删除Division时不级联删除Worker？

实体关系定义 #

public class Company 
{
    public int Id { get; set; }
    public string CompanyName { get; set; }
    [InverseProperty("Round")]
    public ICollection<Division> Divisions { get; set; }
}

public class Industry
{
    public int Id { get; set; }
    public string IndustryName { get; set; }
    [InverseProperty("Industry")]
    public ICollection<Division> Divisions { get; set; }
}

public class Division
{
    [Column(Order = 1), Key, ForeignKey("Company")]
    public int CompanyId { get; set; }
    [Column(Order = 1), Key, ForeignKey("Industry")]
    public int IndustryId { get; set; }
    public string DivisionName { get; set; }
    public ICollection<Worker> Workers { get; set; }
}

public class Worker
{
    [Key]
    public int WorkerId { get; set; }
    [Column(Order = 2), ForeignKey("Division")]
    public int CompanyId { get; set; }
    [Column(Order = 2), ForeignKey("Division")]
    public int IndustryId { get; set; }
    public string WorkerName { get; set; }
}

需求：删除Division实体时，不能同时删除关联的Worker实体，下面分别给出EF6和EF Core的配置方案。

EF6实现方案 #

首先要明确：当前Worker的CompanyId和IndustryId是非可空的int类型，要是直接禁用级联删除，删除Division时数据库会因为外键约束报错。所以要么把这两个外键改成可空类型，要么删除Division前手动把关联Worker的外键设为null。

1. 调整Worker实体（可选，根据业务需求） #

如果允许Worker不关联任何Division，把外键改成可空：

public class Worker
{
    [Key]
    public int WorkerId { get; set; }
    [Column(Order = 2), ForeignKey("Division")]
    public int? CompanyId { get; set; }
    [Column(Order = 2), ForeignKey("Division")]
    public int? IndustryId { get; set; }
    public string WorkerName { get; set; }
}

2. 用Fluent API配置级联行为 #

在你的DbContext重写OnModelCreating方法，添加以下配置：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Worker>()
        .HasRequired(w => w.Division) // 要是外键改成可空了，就换成HasOptional
        .WithMany(d => d.Workers)
        .HasForeignKey(w => new { w.CompanyId, w.IndustryId })
        .WillCascadeOnDelete(false); // 禁用级联删除，相当于Restrict
}

配置后，EF6生成的外键约束不会带级联删除逻辑：如果外键可空，删除Division时Worker会被保留且外键值变为null；如果外键非空，必须提前处理Worker的关联，否则数据库会报错。

EF Core实现方案 #

EF Core的级联行为配置更灵活，同样要先处理外键的可空性问题，再选合适的删除行为。

方案1：允许Worker外键为空（推荐） #

先修改Worker实体的外键为可空类型，同时建议显式添加导航属性（方便EF Core识别关系）：

public class Worker
{
    [Key]
    public int WorkerId { get; set; }
    [Column(Order = 2), ForeignKey("Division")]
    public int? CompanyId { get; set; }
    [Column(Order = 2), ForeignKey("Division")]
    public int? IndustryId { get; set; }
    public string WorkerName { get; set; }
    public Division Division { get; set; } // 显式添加导航属性
}

然后在DbContext的OnModelCreating里配置删除行为：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Worker>()
        .HasOne(w => w.Division)
        .WithMany(d => d.Workers)
        .HasForeignKey(w => new { w.CompanyId, w.IndustryId })
        .OnDelete(DeleteBehavior.SetNull); // 删除Division时自动把Worker的外键设为null
}

方案2：Worker外键必须非空 #

如果业务要求Worker必须关联某个Division，那就配置DeleteBehavior.Restrict，但删除Division前必须手动把关联Worker分配到其他Division，不然数据库会抛外键约束异常：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Worker>()
        .HasOne(w => w.Division)
        .WithMany(d => d.Workers)
        .HasForeignKey(w => new { w.CompanyId, w.IndustryId })
        .OnDelete(DeleteBehavior.Restrict); // 禁止级联删除，有未处理的关联Worker时删除Division会报错
}

简单总结：SetNull适合外键可空的场景，删除Division自动清空Worker的关联；Restrict则是完全禁止级联，靠数据库约束阻止违规删除。

内容的提问来源于stack exchange，提问作者Mateusz Kaleta