EF Core 2.0 已经支持自动生成父子关系表的实体
现在我们在SQL Server数据库中有Person表如下：
CREATE TABLE [dbo].[Person]( [ID] [int] IDENTITY(1,1) NOT NULL, [Code] [nvarchar](50) NULL, [Name] [nvarchar](50) NULL, [ParentCode] [nvarchar](50) NULL, [CreateTime] [datetime] NULL, [UpdateTime] [datetime] NULL, CONSTRAINT [PK_Person] PRIMARY KEY CLUSTERED ( [ID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO ALTER TABLE [dbo].[Person] ADD CONSTRAINT [DF_Person_CreateTime] DEFAULT (getdate()) FOR [CreateTime] GO ALTER TABLE [dbo].[Person] ADD CONSTRAINT [IX_Person] UNIQUE NONCLUSTERED ( [Code] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO ALTER TABLE [dbo].[Person] WITH CHECK ADD CONSTRAINT [FK_Person_Person] FOREIGN KEY([ParentCode]) REFERENCES [dbo].[Person] ([Code]) GO ALTER TABLE [dbo].[Person] CHECK CONSTRAINT [FK_Person_Person] GO
语句中有一个外键FK_Person_Person，关系是[Person].[ParentCode]指向[Person].[Code]，这是一个典型的父子关系表，[Person]表的一行数据属于另一行数据，关系可以无限递归。
现在我们使用EF Core的Scaffold-DbContext指令自动生成实体和DbContext，生成Person实体代码如下：
using System; using System.Collections.Generic; namespace FFCoreView.Entities { public partial class Person { public Person() { InverseParentCodeNavigation = new HashSet<Person>(); } public int Id { get; set; } public string Code { get; set; } public string Name { get; set; } public string ParentCode { get; set; } public DateTime? CreateTime { get; set; } public DateTime? UpdateTime { get; set; } public Person ParentCodeNavigation { get; set; } public ICollection<Person> InverseParentCodeNavigation { get; set; } } }
我们可以看到Person实体中的属性public Person ParentCodeNavigation { get; set; }表示的是实体的父级Person。
Person实体中的属性public ICollection<Person> InverseParentCodeNavigation { get; set; }表示的是实体的所有子级Person。
再来看看Scaffold-DbContext指令自动生成的DbContext类TestDBContext：
using System; using Microsoft.EntityFrameworkCore; using Microsoft.EntityFrameworkCore.Metadata; namespace FFCoreView.Entities { public partial class TestDBContext : DbContext { public TestDBContext() { } public TestDBContext(DbContextOptions<TestDBContext> options) : base(options) { } public virtual DbSet<Person> Person { get; set; } protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { if (!optionsBuilder.IsConfigured) { optionsBuilder.UseSqlServer("Server=localhost;User Id=sa;Password=Dtt!123456;Database=TestDB"); } } protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity<Person>(entity => { entity.HasIndex(e => e.Code) .HasName("IX_Person") .IsUnique(); entity.Property(e => e.Id).HasColumnName("ID"); entity.Property(e => e.Code) .IsRequired() .HasMaxLength(50); entity.Property(e => e.CreateTime) .HasColumnType("datetime") .HasDefaultValueSql("(getdate())"); entity.Property(e => e.Name).HasMaxLength(50); entity.Property(e => e.ParentCode).HasMaxLength(50); entity.Property(e => e.UpdateTime).HasColumnType("datetime"); //设置了Person实体ParentCodeNavigation属性和InverseParentCodeNavigation属性的父子关系（一对多关系，一个Person对多个Person） entity.HasOne(d => d.ParentCodeNavigation) .WithMany(p => p.InverseParentCodeNavigation) .HasPrincipalKey(p => p.Code) .HasForeignKey(d => d.ParentCode) .HasConstraintName("FK_Person_Person"); }); } } }
可以看到TestDBContext类的OnModelCreating方法中，已经用Fluent API设置了Person实体ParentCodeNavigation属性和InverseParentCodeNavigation属性的父子关系（一对多关系，一个Person对多个Person）。
然后我们在.NET Core控制台项目的Program类中定义了两个静态方法：
- AddPersonFromParentNavigation通过Person实体的ParentCodeNavigation属性插入父子关系数据到Person表
- AddPersonFromChildrenNavigation通过Person实体的InverseParentCodeNavigation集合属性插入父子关系数据到Person表
还有个DeleteAllPersons静态方法，用于清除Person表的数据。在Main方法中我们还通过循环逐层显示了Person数据的父子关系。
我们先调用AddPersonFromParentNavigation方法通过Person实体的ParentCodeNavigation属性插入父子关系数据到Person表：
using FFCoreView.Entities; using Microsoft.EntityFrameworkCore; using System; using System.Collections.Generic; using System.Linq; namespace FFCoreView { class Program { /// <summary> /// 通过Person实体的ParentCodeNavigation属性插入父子关系数据到Person表 /// </summary> static void AddPersonFromParentNavigation() { //通过ParentCodeNavigation属性插入父子关系数据：James<-Tom<-Sam using (TestDBContext dbContext = new TestDBContext()) { Person james = new Person() { Code = "P001", Name = "James" }; Person tom = new Person() { Code = "P002", Name = "Tom", ParentCodeNavigation = james//通过ParentCodeNavigation属性指定Tom的父级是James }; Person sam = new Person() { Code = "P003", Name = "Sam", ParentCodeNavigation = tom//通过ParentCodeNavigation属性指定Sam的父级是Tom }; dbContext.Person.Add(james); dbContext.Person.Add(tom); dbContext.Person.Add(sam); dbContext.SaveChanges(); } } /// <summary> /// 通过Person实体的InverseParentCodeNavigation集合属性插入父子关系数据到Person表 /// </summary> static void AddPersonFromChildrenNavigation() { //通过InverseParentCodeNavigation集合属性插入父子关系数据：James<-Tom<-Sam using (TestDBContext dbContext = new TestDBContext()) { Person james = new Person() { Code = "P001", Name = "James", InverseParentCodeNavigation = new List<Person>()//通过InverseParentCodeNavigation集合属性指定James的子级是Tom { new Person() { Code = "P002", Name = "Tom", InverseParentCodeNavigation = new List<Person>()//通过InverseParentCodeNavigation集合属性指定Tom的子级是Sam { new Person() { Code = "P003", Name = "Sam" } } } } }; dbContext.Person.Add(james); dbContext.SaveChanges(); } } /// <summary> /// 删除数据库Person表的所有数据 /// </summary> static void DeleteAllPersons() { using (TestDBContext dbContext = new TestDBContext()) { dbContext.Database.ExecuteSqlCommand("DELETE FROM [dbo].[Person]"); } } static void Main(string[] args) { DeleteAllPersons(); AddPersonFromParentNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法调用一个就可以了 //AddPersonFromChildrenNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法调用一个就可以了 Person rootPerson; using (TestDBContext dbContext = new TestDBContext()) { //查询根级的Person "James"，并使用EF Core中EagerLoading的Include方法查询下两级Person的InverseParentCodeNavigation集合 rootPerson = dbContext.Person.Where(p => p.Name == "James").Include("InverseParentCodeNavigation.InverseParentCodeNavigation").First(); } int level = 1;//用于计算当前显示到第几级的Person实体了 //从rootPerson开始，通过Person实体的集合属性InverseParentCodeNavigation逐层遍历所有子Person集合，来显示Person的Name while (true) { //显示当前Person的层级数和Name Console.WriteLine($"Person level {level.ToString()} : {rootPerson.Name}"); if(rootPerson.InverseParentCodeNavigation.Count==0) { //如果rootPerson.InverseParentCodeNavigation.Count为0表示父子关系已经循环完毕，没有子级的Person了，跳出循环 break; } //设置rootPerson为子级Person，以便在循环中继续遍历 rootPerson = rootPerson.InverseParentCodeNavigation.First(); level++;//当前Person实体的层级数加1 } Console.WriteLine("Press any key to quit..."); Console.ReadKey(); } } }
执行上面代码后，数据库Person表的数据如下所示：
控制台输出的内容如下：
如果我们在Main方法中注释掉AddPersonFromParentNavigation方法，改为使用AddPersonFromChildrenNavigation方法插入数据，会得到相同的结果。
使用EF Core删除父子关系数据
我们现在更改Program类Main方法的逻辑，来尝试删除父子关系的根级Person "James"，代码如下：
static void Main(string[] args) { DeleteAllPersons(); AddPersonFromParentNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法调用一个就可以了 //AddPersonFromChildrenNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法调用一个就可以了 using (TestDBContext dbContext = new TestDBContext()) { //查询根级的Person "James"，不使用EF Core中EagerLoading的Include方法查询子级InverseParentCodeNavigation集合 Person james = dbContext.Person.Where(p => p.Name == "James").First(); dbContext.Person.Remove(james); dbContext.SaveChanges();//尝试删除Person "James"，结果报错：The DELETE statement conflicted with the SAME TABLE REFERENCE constraint "FK_Person_Person". 违反了外键的强制约束 } Console.WriteLine("Press any key to quit..."); Console.ReadKey(); }
执行上面代码，会在DbContext.SaveChanges方法调用时抛出异常，如下所示：
使用EF Core的日志功能我们可以看到在执行DbContext.SaveChanges方法时，EF Core执行的SQL语句如下：
=============================== EF Core log started =============================== Failed executing DbCommand (29ms) [Parameters=[@p0='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; DELETE FROM [Person] WHERE [ID] = @p0; SELECT @@ROWCOUNT; =============================== EF Core log finished ===============================
该SQL语句相当于是执行了：
DELETE FROM [Person] WHERE [Name]=N'James'
很明显这个删除操作违反了我们在数据库中Person表上定义的外键[FK_Person_Person]的强制约束，[FK_Person_Person]的外键定义如下：
--注意下面写了关键字WITH CHECK表示该外键是强制约束 ALTER TABLE [dbo].[Person] WITH CHECK ADD CONSTRAINT [FK_Person_Person] FOREIGN KEY([ParentCode]) REFERENCES [dbo].[Person] ([Code]) GO
所以很明显我们如果直接使用Delete语句删除Person表中父子关系的根级Person “Jame”，SQL Server会报错，当然有人可能会说如果我们设置外键不强制约束就不会报错了，但是这并不是一个好办法，我们来看看在强制约束下如何使用EF Core来删除Person表的根级Person。
下面我们继续更改Program类Main方法的逻辑，现在我们在读取Person表的根级Person “Jame”时，加上EF Core中EagerLoading的Include方法将Person "James"的子节点Person "Tom"也查询出来：
static void Main(string[] args) { DeleteAllPersons(); AddPersonFromParentNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法调用一个就可以了 //AddPersonFromChildrenNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法调用一个就可以了 using (TestDBContext dbContext = new TestDBContext()) { //查询根级的Person "James"，使用EF Core中EagerLoading的Include方法，将Person "James"的子节点Person "Tom"也查询出来 Person james = dbContext.Person.Where(p => p.Name == "James").Include("InverseParentCodeNavigation").First(); dbContext.Person.Remove(james); dbContext.SaveChanges();//尝试删除Person "James"，现在就不会报错了，数据在数据库中被成功删除 } Console.WriteLine("Press any key to quit..."); Console.ReadKey(); }
我们看到这一次删除成功执行了，没有报错，那么为什么这次没有违反数据库外键 [FK_Person_Person]的强制约束呢？我们查看EF Core生成的后台日志如下：
=============================== EF Core log started =============================== An 'Person' entity tracked by 'TestDBContext' changed from 'Unchanged' to 'Deleted'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== SaveChanges starting for 'TestDBContext'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== DetectChanges starting for 'TestDBContext'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== DetectChanges completed for 'TestDBContext'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== An 'Person' entity tracked by 'TestDBContext' changed from 'Unchanged' to 'Modified'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Foreign key property 'Person.ParentCode' detected as changed. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see property values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Opening connection to database 'TestDB' on server 'CNGDCAAITSQL01'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Opened connection to database 'TestDB' on server 'CNGDCAAITSQL01'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Beginning transaction with isolation level 'ReadCommitted'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executing DbCommand [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; UPDATE [Person] SET [ParentCode] = @p0 WHERE [ID] = @p1; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executed DbCommand (23ms) [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; UPDATE [Person] SET [ParentCode] = @p0 WHERE [ID] = @p1; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== A data reader was disposed. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executing DbCommand [Parameters=[@p2='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; DELETE FROM [Person] WHERE [ID] = @p2; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executed DbCommand (25ms) [Parameters=[@p2='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; DELETE FROM [Person] WHERE [ID] = @p2; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== A data reader was disposed. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Committing transaction. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Closing connection to database 'TestDB' on server 'CNGDCAAITSQL01'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Closed connection to database 'TestDB' on server 'CNGDCAAITSQL01'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Disposing transaction. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== An 'Person' entity tracked by 'TestDBContext' changed from 'Deleted' to 'Detached'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== An 'Person' entity tracked by 'TestDBContext' changed from 'Modified' to 'Unchanged'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== SaveChanges completed for 'TestDBContext' with 2 entities written to the database. =============================== EF Core log finished ===============================
我们看到这次EF Core在执行DbContext.SaveChanges方法时执行了两个SQL语句，在执行Delete语句前还执行了一个Update语句，这个Update语句就是关键所在，它会先更新Person表中父子关系根级Person "James"的子节点Person "Tom"的ParentCode列为NULL，相当于下面的SQL语句：
UPDATE [Person] SET [ParentCode] = NULL WHERE [Name] = N'Tom'
这样后面再用Delete语句删除Person "James"时，就不会违反数据库外键 [FK_Person_Person]的强制约束了，所以我们看到这次执行完Program类Main方法的代码后，数据库Person表的数据如下所示：
我们可以看到Person "Tom"的ParentCode列为NULL，这就是Update语句的效果。
那么有没有办法在删除Person表中父子关系的根级Person "James"时，让EF Core也删除"James"所有的子孙节点呢（也就是将Tom和Sam也同时删除掉）？
首先我们更改Scaffold-DbContext指令自动生成的DbContext类TestDBContext，将其OnModelCreating方法更改如下：
protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity<Person>(entity => { entity.HasIndex(e => e.Code) .HasName("IX_Person") .IsUnique(); entity.Property(e => e.Id).HasColumnName("ID"); entity.Property(e => e.Code) .IsRequired() .HasMaxLength(50); entity.Property(e => e.CreateTime) .HasColumnType("datetime") .HasDefaultValueSql("(getdate())"); entity.Property(e => e.Name).HasMaxLength(50); entity.Property(e => e.ParentCode).HasMaxLength(50); entity.Property(e => e.UpdateTime).HasColumnType("datetime"); //设置了Person实体ParentCodeNavigation属性和InverseParentCodeNavigation属性的父子关系（一对多关系，一个Person对多个Person） entity.HasOne(d => d.ParentCodeNavigation) .WithMany(p => p.InverseParentCodeNavigation) .HasPrincipalKey(p => p.Code) .HasForeignKey(d => d.ParentCode) .OnDelete(DeleteBehavior.Cascade)//设置父子表的级联删除 .HasConstraintName("FK_Person_Person"); }); }
和前面不一样的地方用绿色高亮标记出来了，这次我们使用了Fluent API的OnDelete方法声明Person实体的父子外键关系是DeleteBehavior.Cascade级联删除的。
现在我们再将Program类Main方法改为如下，我们这次在查询Person表父子关系的根级节点Person "James"时，用EF Core中EagerLoading的Include方法查询了下两级Person的InverseParentCodeNavigation集合，相当于还查询出了Person "Tom"和Person "Sam"，然后删除Person "James：
static void Main(string[] args) { DeleteAllPersons(); AddPersonFromParentNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法调用一个就可以了 //AddPersonFromChildrenNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法调用一个就可以了 using (TestDBContext dbContext = new TestDBContext()) { //查询根级的Person "James"，并使用EF Core中EagerLoading的Include方法查询下两级Person的InverseParentCodeNavigation集合，相当于还查询出了Person "Tom"和Person "Sam" Person james = dbContext.Person.Where(p => p.Name == "James").Include("InverseParentCodeNavigation.InverseParentCodeNavigation").First(); dbContext.Person.Remove(james); dbContext.SaveChanges();//这次，父子关系的根级Person "James"及子孙级Person "Tom"和Person "Sam"被一起删除了 } Console.WriteLine("Press any key to quit..."); Console.ReadKey(); }
我们看看在执行DbContext.SaveChanges方法时，EF Core生成的后台日志：
=============================== EF Core log started =============================== SaveChanges starting for 'TestDBContext'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== DetectChanges starting for 'TestDBContext'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== DetectChanges completed for 'TestDBContext'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Cascade state change of 'Person' entity to 'Deleted' due to deletion of parent 'Person' entity. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== An 'Person' entity tracked by 'TestDBContext' changed from 'Unchanged' to 'Deleted'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Cascade state change of 'Person' entity to 'Deleted' due to deletion of parent 'Person' entity. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== An 'Person' entity tracked by 'TestDBContext' changed from 'Unchanged' to 'Deleted'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Opening connection to database 'TestDB' on server 'CNGDCAAITSQL01'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Opened connection to database 'TestDB' on server 'CNGDCAAITSQL01'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Beginning transaction with isolation level 'ReadCommitted'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executing DbCommand [Parameters=[@p0='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; DELETE FROM [Person] WHERE [ID] = @p0; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executed DbCommand (27ms) [Parameters=[@p0='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; DELETE FROM [Person] WHERE [ID] = @p0; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== A data reader was disposed. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executing DbCommand [Parameters=[@p1='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; DELETE FROM [Person] WHERE [ID] = @p1; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executed DbCommand (26ms) [Parameters=[@p1='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; DELETE FROM [Person] WHERE [ID] = @p1; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== A data reader was disposed. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executing DbCommand [Parameters=[@p2='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; DELETE FROM [Person] WHERE [ID] = @p2; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Executed DbCommand (25ms) [Parameters=[@p2='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30'] SET NOCOUNT ON; DELETE FROM [Person] WHERE [ID] = @p2; SELECT @@ROWCOUNT; =============================== EF Core log finished =============================== =============================== EF Core log started =============================== A data reader was disposed. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Committing transaction. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Closing connection to database 'TestDB' on server 'CNGDCAAITSQL01'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Closed connection to database 'TestDB' on server 'CNGDCAAITSQL01'. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== Disposing transaction. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== An 'Person' entity tracked by 'TestDBContext' changed from 'Deleted' to 'Detached'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== An 'Person' entity tracked by 'TestDBContext' changed from 'Deleted' to 'Detached'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== An 'Person' entity tracked by 'TestDBContext' changed from 'Deleted' to 'Detached'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values. =============================== EF Core log finished =============================== =============================== EF Core log started =============================== SaveChanges completed for 'TestDBContext' with 3 entities written to the database. =============================== EF Core log finished ===============================
我们看到由于我们在DbContext类TestDBContext的OnModelCreating方法中开启了级联删除，这次在执行DbContext.SaveChanges方法时，EF Core后台生成了三个Delete语句，其相当于如下SQL语句的效果：
DELETE FROM [Person] WHERE [Name]=N'Sam' DELETE FROM [Person] WHERE [Name]=N'Tom' DELETE FROM [Person] WHERE [Name]=N'James'
所以Person “James”连同其子孙节点Person “Tom”和Person “Sam”被一起从数据库中删除了，最后数据库中Person表的数据如下所示：
因此我们看到在EF Core级联删除父子表的数据是可以的，但是有个最大的缺点，那就是必须先用EF Core中EagerLoading的Include方法查询出所有要删除的子孙节点，试想一下我们怎么知道Person表中的父子关系有多少级呢，在本例中因为我们知道Person表只有三级数据:James<-Tom<-Sam，所以我们在Program类Main方法中是这么写的查询：
//查询根级的Person "James"，并使用EF Core中EagerLoading的Include方法查询下两级Person的InverseParentCodeNavigation集合，相当于还查询出了Person "Tom"和Person "Sam" Person james = dbContext.Person.Where(p => p.Name == "James").Include("InverseParentCodeNavigation.InverseParentCodeNavigation").First();
但是实际场景中，我们很有可能不知道Person表的父子关系到底有多少级，所以我们无法知道上面的Include("InverseParentCodeNavigation.InverseParentCodeNavigation")中InverseParentCodeNavigation集合属性该写多少次。所以删除父子关系表数据最好的办法还是使用EF Core调用SQL Server中的存储过程，在存储过程中用递归算法删除父子关系数据。
