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(); entity.Property(e => e.CreateTime)
.HasColumnType("datetime")
.HasDefaultValueSql("(getdate())"); entity.Property(e => e.Name).HasMaxLength(); entity.Property(e => e.ParentCode).HasMaxLength(); 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 = ;//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==)
{
//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(); entity.Property(e => e.CreateTime)
.HasColumnType("datetime")
.HasDefaultValueSql("(getdate())"); entity.Property(e => e.Name).HasMaxLength(); entity.Property(e => e.ParentCode).HasMaxLength(); 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。