現在我們在SQL Server數據庫中有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
語句中有一個外鍵FK_Person_Person，關系是[Person].[ParentCode]指向[Person].[Code]，這是一個典型的父子關系表，[Person]表的一行數據屬於另一行數據，關系可以無限遞歸。
現在我們使用EF Core的Scaffold-DbContext指令自動生成實體和DbContext，生成Person實體代碼如下：
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; } } }
我們可以看到Person實體中的屬性public Person ParentCodeNavigation { get; set; }表示的是實體的父級Person。
Person實體中的屬性public ICollection<Person> InverseParentCodeNavigation { get; set; }表示的是實體的所有子級Person。
再來看看Scaffold-DbContext指令自動生成的DbContext類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"); //設置了Person實體ParentCodeNavigation屬性和InverseParentCodeNavigation屬性的父子關系（一對多關系，一個Person對多個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類的OnModelCreating方法中，已經用Fluent API設置了Person實體ParentCodeNavigation屬性和InverseParentCodeNavigation屬性的父子關系（一對多關系，一個Person對多個Person）。
然后我們在.NET Core控制台項目的Program類中定義了兩個靜態方法：
- AddPersonFromParentNavigation通過Person實體的ParentCodeNavigation屬性插入父子關系數據到Person表
- AddPersonFromChildrenNavigation通過Person實體的InverseParentCodeNavigation集合屬性插入父子關系數據到Person表
還有個DeleteAllPersons靜態方法，用於清除Person表的數據。在Main方法中我們還通過循環逐層顯示了Person數據的父子關系。
我們先調用AddPersonFromParentNavigation方法通過Person實體的ParentCodeNavigation屬性插入父子關系數據到Person表：
using FFCoreView.Entities; using Microsoft.EntityFrameworkCore; using System; using System.Collections.Generic; using System.Linq; namespace FFCoreView { class Program { /// <summary> /// 通過Person實體的ParentCodeNavigation屬性插入父子關系數據到Person表 /// </summary> static void AddPersonFromParentNavigation() { //通過ParentCodeNavigation屬性插入父子關系數據：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//通過ParentCodeNavigation屬性指定Tom的父級是James }; Person sam = new Person() { Code = "P003", Name = "Sam", ParentCodeNavigation = tom//通過ParentCodeNavigation屬性指定Sam的父級是Tom }; dbContext.Person.Add(james); dbContext.Person.Add(tom); dbContext.Person.Add(sam); dbContext.SaveChanges(); } } /// <summary> /// 通過Person實體的InverseParentCodeNavigation集合屬性插入父子關系數據到Person表 /// </summary> static void AddPersonFromChildrenNavigation() { //通過InverseParentCodeNavigation集合屬性插入父子關系數據：James<-Tom<-Sam using (TestDBContext dbContext = new TestDBContext()) { Person james = new Person() { Code = "P001", Name = "James", InverseParentCodeNavigation = new List<Person>()//通過InverseParentCodeNavigation集合屬性指定James的子級是Tom { new Person() { Code = "P002", Name = "Tom", InverseParentCodeNavigation = new List<Person>()//通過InverseParentCodeNavigation集合屬性指定Tom的子級是Sam { new Person() { Code = "P003", Name = "Sam" } } } } }; dbContext.Person.Add(james); dbContext.SaveChanges(); } } /// <summary> /// 刪除數據庫Person表的所有數據 /// </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方法調用一個就可以了 //AddPersonFromChildrenNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法調用一個就可以了 Person rootPerson; using (TestDBContext dbContext = new TestDBContext()) { //查詢根級的Person "James"，並使用EF Core中EagerLoading的Include方法查詢下兩級Person的InverseParentCodeNavigation集合 rootPerson = dbContext.Person.Where(p => p.Name == "James").Include("InverseParentCodeNavigation.InverseParentCodeNavigation").First(); } int level = 1;//用於計算當前顯示到第幾級的Person實體了 //從rootPerson開始，通過Person實體的集合屬性InverseParentCodeNavigation逐層遍歷所有子Person集合，來顯示Person的Name while (true) { //顯示當前Person的層級數和Name Console.WriteLine($"Person level {level.ToString()} : {rootPerson.Name}"); if(rootPerson.InverseParentCodeNavigation.Count==0) { //如果rootPerson.InverseParentCodeNavigation.Count為0表示父子關系已經循環完畢，沒有子級的Person了，跳出循環 break; } //設置rootPerson為子級Person，以便在循環中繼續遍歷 rootPerson = rootPerson.InverseParentCodeNavigation.First(); level++;//當前Person實體的層級數加1 } Console.WriteLine("Press any key to quit..."); Console.ReadKey(); } } }
執行上面代碼后，數據庫Person表的數據如下所示：
控制台輸出的內容如下：
如果我們在Main方法中注釋掉AddPersonFromParentNavigation方法，改為使用AddPersonFromChildrenNavigation方法插入數據，會得到相同的結果。
使用EF Core刪除父子關系數據
我們現在更改Program類Main方法的邏輯，來嘗試刪除父子關系的根級Person "James"，代碼如下：
static void Main(string[] args) { DeleteAllPersons(); AddPersonFromParentNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法調用一個就可以了 //AddPersonFromChildrenNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法調用一個就可以了 using (TestDBContext dbContext = new TestDBContext()) { //查詢根級的Person "James"，不使用EF Core中EagerLoading的Include方法查詢子級InverseParentCodeNavigation集合 Person james = dbContext.Person.Where(p => p.Name == "James").First(); dbContext.Person.Remove(james); dbContext.SaveChanges();//嘗試刪除Person "James"，結果報錯：The DELETE statement conflicted with the SAME TABLE REFERENCE constraint "FK_Person_Person". 違反了外鍵的強制約束 } Console.WriteLine("Press any key to quit..."); Console.ReadKey(); }
執行上面代碼，會在DbContext.SaveChanges方法調用時拋出異常，如下所示：
使用EF Core的日志功能我們可以看到在執行DbContext.SaveChanges方法時，EF Core執行的SQL語句如下：
=============================== 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 ===============================
該SQL語句相當於是執行了：
DELETE FROM [Person] WHERE [Name]=N'James'
很明顯這個刪除操作違反了我們在數據庫中Person表上定義的外鍵[FK_Person_Person]的強制約束，[FK_Person_Person]的外鍵定義如下：
--注意下面寫了關鍵字WITH CHECK表示該外鍵是強制約束 ALTER TABLE [dbo].[Person] WITH CHECK ADD CONSTRAINT [FK_Person_Person] FOREIGN KEY([ParentCode]) REFERENCES [dbo].[Person] ([Code]) GO
所以很明顯我們如果直接使用Delete語句刪除Person表中父子關系的根級Person “Jame”，SQL Server會報錯，當然有人可能會說如果我們設置外鍵不強制約束就不會報錯了，但是這並不是一個好辦法，我們來看看在強制約束下如何使用EF Core來刪除Person表的根級Person。
下面我們繼續更改Program類Main方法的邏輯，現在我們在讀取Person表的根級Person “Jame”時，加上EF Core中EagerLoading的Include方法將Person "James"的子節點Person "Tom"也查詢出來：
static void Main(string[] args) { DeleteAllPersons(); AddPersonFromParentNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法調用一個就可以了 //AddPersonFromChildrenNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法調用一個就可以了 using (TestDBContext dbContext = new TestDBContext()) { //查詢根級的Person "James"，使用EF Core中EagerLoading的Include方法，將Person "James"的子節點Person "Tom"也查詢出來 Person james = dbContext.Person.Where(p => p.Name == "James").Include("InverseParentCodeNavigation").First(); dbContext.Person.Remove(james); dbContext.SaveChanges();//嘗試刪除Person "James"，現在就不會報錯了，數據在數據庫中被成功刪除 } Console.WriteLine("Press any key to quit..."); Console.ReadKey(); }
我們看到這一次刪除成功執行了，沒有報錯，那么為什么這次沒有違反數據庫外鍵 [FK_Person_Person]的強制約束呢？我們查看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 ===============================
我們看到這次EF Core在執行DbContext.SaveChanges方法時執行了兩個SQL語句，在執行Delete語句前還執行了一個Update語句，這個Update語句就是關鍵所在，它會先更新Person表中父子關系根級Person "James"的子節點Person "Tom"的ParentCode列為NULL，相當於下面的SQL語句：
UPDATE [Person] SET [ParentCode] = NULL WHERE [Name] = N'Tom'
這樣后面再用Delete語句刪除Person "James"時，就不會違反數據庫外鍵 [FK_Person_Person]的強制約束了，所以我們看到這次執行完Program類Main方法的代碼后，數據庫Person表的數據如下所示：
我們可以看到Person "Tom"的ParentCode列為NULL，這就是Update語句的效果。
那么有沒有辦法在刪除Person表中父子關系的根級Person "James"時，讓EF Core也刪除"James"所有的子孫節點呢（也就是將Tom和Sam也同時刪除掉）？
首先我們更改Scaffold-DbContext指令自動生成的DbContext類TestDBContext，將其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"); //設置了Person實體ParentCodeNavigation屬性和InverseParentCodeNavigation屬性的父子關系（一對多關系，一個Person對多個Person） entity.HasOne(d => d.ParentCodeNavigation) .WithMany(p => p.InverseParentCodeNavigation) .HasPrincipalKey(p => p.Code) .HasForeignKey(d => d.ParentCode) .OnDelete(DeleteBehavior.Cascade)//設置父子表的級聯刪除 .HasConstraintName("FK_Person_Person"); }); }
和前面不一樣的地方用綠色高亮標記出來了，這次我們使用了Fluent API的OnDelete方法聲明Person實體的父子外鍵關系是DeleteBehavior.Cascade級聯刪除的。
現在我們再將Program類Main方法改為如下，我們這次在查詢Person表父子關系的根級節點Person "James"時，用EF Core中EagerLoading的Include方法查詢了下兩級Person的InverseParentCodeNavigation集合，相當於還查詢出了Person "Tom"和Person "Sam"，然后刪除Person "James：
static void Main(string[] args) { DeleteAllPersons(); AddPersonFromParentNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法調用一個就可以了 //AddPersonFromChildrenNavigation();//AddPersonFromParentNavigation和AddPersonFromChildrenNavigation方法調用一個就可以了 using (TestDBContext dbContext = new TestDBContext()) { //查詢根級的Person "James"，並使用EF Core中EagerLoading的Include方法查詢下兩級Person的InverseParentCodeNavigation集合，相當於還查詢出了Person "Tom"和Person "Sam" Person james = dbContext.Person.Where(p => p.Name == "James").Include("InverseParentCodeNavigation.InverseParentCodeNavigation").First(); dbContext.Person.Remove(james); dbContext.SaveChanges();//這次，父子關系的根級Person "James"及子孫級Person "Tom"和Person "Sam"被一起刪除了 } Console.WriteLine("Press any key to quit..."); Console.ReadKey(); }
我們看看在執行DbContext.SaveChanges方法時，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 ===============================
我們看到由於我們在DbContext類TestDBContext的OnModelCreating方法中開啟了級聯刪除，這次在執行DbContext.SaveChanges方法時，EF Core后台生成了三個Delete語句，其相當於如下SQL語句的效果：
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”連同其子孫節點Person “Tom”和Person “Sam”被一起從數據庫中刪除了，最后數據庫中Person表的數據如下所示：
因此我們看到在EF Core級聯刪除父子表的數據是可以的，但是有個最大的缺點，那就是必須先用EF Core中EagerLoading的Include方法查詢出所有要刪除的子孫節點，試想一下我們怎么知道Person表中的父子關系有多少級呢，在本例中因為我們知道Person表只有三級數據:James<-Tom<-Sam，所以我們在Program類Main方法中是這么寫的查詢：
//查詢根級的Person "James"，並使用EF Core中EagerLoading的Include方法查詢下兩級Person的InverseParentCodeNavigation集合，相當於還查詢出了Person "Tom"和Person "Sam" Person james = dbContext.Person.Where(p => p.Name == "James").Include("InverseParentCodeNavigation.InverseParentCodeNavigation").First();
但是實際場景中，我們很有可能不知道Person表的父子關系到底有多少級，所以我們無法知道上面的Include("InverseParentCodeNavigation.InverseParentCodeNavigation")中InverseParentCodeNavigation集合屬性該寫多少次。所以刪除父子關系表數據最好的辦法還是使用EF Core調用SQL Server中的存儲過程，在存儲過程中用遞歸算法刪除父子關系數據。