外键约束违规问题

10

我确定了3种情况。

  1. 没有入学的学生。
  2. 有入学但没有成绩的学生。
  3. 具有入学和成绩的学生。

注册表上有一个触发器来计算GPA。如果学生有成绩，它将更新或在GPA表中插入一个条目；没有成绩，没有GPA表条目。

我可以删除没有注册的学生（＃1）。我可以删除具有入学和成绩的学生（以上＃3）。但是我不能删除没有注册但没有成绩的学生（＃2）。我收到了参考约束违规。

DELETE语句与REFERENCE约束“ FK_dbo.GPA_dbo.Student_StudentID”冲突。在数据库“”，表“ dbo.GPA”的“ StudentID”列中发生了冲突。

如果我无法删除没有注册（也没有GPA条目）的新学生，那么我会理解违反约束的条件，但是我可以删除该学生。这是一个学生，没有注册并且没有成绩（我也没有GPA条目），我无法删除。

我已修补好扳机，因此可以继续前进。现在，如果您已注册，则无论如何触发器都会将您插入GPA表。但是我不理解潜在的问题。任何解释将不胜感激。

物有所值：

  1. Visual Studio 2013专业版。
  2. IIS Express（VS2013内部）。
  3. 使用EntityFramework 6.1.1的ASP.NET Web App。
  4. MS SQL Server 2014企业版。
  5. GPA.Value可为空。
  6. Enrollment.GradeID为空。

这是数据库的一个片段：

数据库映像

- 编辑 -

这些表都是由EntityFramework创建的，我使用SQL Server Management Studio生成了这些表。

这是带有约束的创建表语句：

GPA 表：

CREATE TABLE [dbo].[GPA](
    [StudentID] [int] NOT NULL,
    [Value] [float] NULL,
  CONSTRAINT [PK_dbo.GPA] PRIMARY KEY CLUSTERED 
  (
    [StudentID] ASC
  )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, 
         ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

ALTER TABLE [dbo].[GPA]  WITH CHECK 
  ADD  CONSTRAINT [FK_dbo.GPA_dbo.Student_StudentID] 
  FOREIGN KEY([StudentID])
  REFERENCES [dbo].[Student] ([ID])

ALTER TABLE [dbo].[GPA] 
  CHECK CONSTRAINT [FK_dbo.GPA_dbo.Student_StudentID]

Enrollment 表：

CREATE TABLE [dbo].[Enrollment](
    [EnrollmentID] [int] IDENTITY(1,1) NOT NULL,
    [CourseID] [int] NOT NULL,
    [StudentID] [int] NOT NULL,
    [GradeID] [int] NULL,
  CONSTRAINT [PK_dbo.Enrollment] PRIMARY KEY CLUSTERED 
  (
    [EnrollmentID] ASC
  )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, 
         ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

ALTER TABLE [dbo].[Enrollment]  WITH CHECK 
  ADD  CONSTRAINT [FK_dbo.Enrollment_dbo.Course_CourseID] 
  FOREIGN KEY([CourseID])
  REFERENCES [dbo].[Course] ([CourseID])
  ON DELETE CASCADE

ALTER TABLE [dbo].[Enrollment] 
  CHECK CONSTRAINT [FK_dbo.Enrollment_dbo.Course_CourseID]

ALTER TABLE [dbo].[Enrollment]  WITH CHECK 
  ADD  CONSTRAINT [FK_dbo.Enrollment_dbo.Grade_GradeID] 
  FOREIGN KEY([GradeID])
  REFERENCES [dbo].[Grade] ([GradeID])

ALTER TABLE [dbo].[Enrollment] 
  CHECK CONSTRAINT [FK_dbo.Enrollment_dbo.Grade_GradeID]

ALTER TABLE [dbo].[Enrollment]  WITH CHECK 
  ADD  CONSTRAINT [FK_dbo.Enrollment_dbo.Student_StudentID] 
  FOREIGN KEY([StudentID])
  REFERENCES [dbo].[Student] ([ID])
  ON DELETE CASCADE

ALTER TABLE [dbo].[Enrollment] 
  CHECK CONSTRAINT [FK_dbo.Enrollment_dbo.Student_StudentID]

Student 表：

CREATE TABLE [dbo].[Student](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [EnrollmentDate] [datetime] NOT NULL,
    [LastName] [nvarchar](50) NOT NULL,
    [FirstName] [nvarchar](50) NOT NULL,
  CONSTRAINT [PK_dbo.Student] 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]

这是触发器：

CREATE TRIGGER UpdateGPAFromUpdateDelete
ON Enrollment
AFTER UPDATE, DELETE AS
BEGIN
    DECLARE @UpdatedStudentID AS int
    SELECT @UpdatedStudentID = StudentID FROM DELETED
    EXEC MergeGPA @UpdatedStudentID
END

CREATE TRIGGER UpdateGPAFromInsert
ON Enrollment
AFTER INSERT AS
--DECLARE @InsertedGradeID AS int
--SELECT @InsertedGradeID = GradeID FROM INSERTED
--IF @InsertedGradeID IS NOT NULL
    BEGIN
        DECLARE @InsertedStudentID AS int
        SELECT @InsertedStudentID = StudentID FROM INSERTED
        EXEC MergeGPA @InsertedStudentID
    END

前进的补丁是在AFTER INSERT触发器中注释掉这些行。

这是存储过程：

CREATE PROCEDURE MergeGPA @StudentID int AS
MERGE GPA AS TARGET
USING (SELECT @StudentID) as SOURCE (StudentID)
ON (TARGET.StudentID = SOURCE.StudentID)
WHEN MATCHED THEN
    UPDATE
        SET Value = (SELECT Value FROM GetGPA(@StudentID))
WHEN NOT MATCHED THEN
INSERT (StudentID, Value)
    VALUES(SOURCE.StudentID, (SELECT Value FROM GetGPA(@StudentID)));

这是数据库功能：

CREATE FUNCTION GetGPA (@StudentID int) 
RETURNS TABLE
AS RETURN
SELECT ROUND(SUM (StudentTotal.TotalCredits) / SUM (StudentTotal.Credits), 2) Value
    FROM (
        SELECT 
            CAST(Credits as float) Credits
            , CAST(SUM(Value * Credits) as float) TotalCredits
        FROM 
            Enrollment e 
            JOIN Course c ON c.CourseID = e.CourseID
            JOIN Grade g  ON e.GradeID = g.GradeID
        WHERE
            e.StudentID = @StudentID AND
            e.GradeID IS NOT NULL
        GROUP BY
            StudentID
            , Value
            , e.courseID
            , Credits
    ) StudentTotal

这是控制器的delete方法的调试输出，select语句是查询要删除内容的方法。该学生有3个注册，REFERENCE删除第3个注册时会发生约束问题。我认为EF正在使用事务，因为未删除注册。

iisexpress.exe Information: 0 : Component:SQL Database;Method:SchoolInterceptor.ReaderExecuted;Timespan:00:00:00.0004945;Properties:
Command: SELECT 
    [Project2].[StudentID] AS [StudentID], 
    [Project2].[ID] AS [ID], 
    [Project2].[EnrollmentDate] AS [EnrollmentDate], 
    [Project2].[LastName] AS [LastName], 
    [Project2].[FirstName] AS [FirstName], 
    [Project2].[Value] AS [Value], 
    [Project2].[C1] AS [C1], 
    [Project2].[EnrollmentID] AS [EnrollmentID], 
    [Project2].[CourseID] AS [CourseID], 
    [Project2].[StudentID1] AS [StudentID1], 
    [Project2].[GradeID] AS [GradeID]
    FROM ( SELECT 
        [Limit1].[ID] AS [ID], 
        [Limit1].[EnrollmentDate] AS [EnrollmentDate], 
        [Limit1].[LastName] AS [LastName], 
        [Limit1].[FirstName] AS [FirstName], 
        [Limit1].[StudentID] AS [StudentID], 
        [Limit1].[Value] AS [Value], 
        [Extent3].[EnrollmentID] AS [EnrollmentID], 
        [Extent3].[CourseID] AS [CourseID], 
        [Extent3].[StudentID] AS [StudentID1], 
        [Extent3].[GradeID] AS [GradeID], 
        CASE WHEN ([Extent3].[EnrollmentID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
        FROM   (SELECT TOP (2) 
            [Extent1].[ID] AS [ID], 
            [Extent1].[EnrollmentDate] AS [EnrollmentDate], 
            [Extent1].[LastName] AS [LastName], 
            [Extent1].[FirstName] AS [FirstName], 
            [Extent2].[StudentID] AS [StudentID], 
            [Extent2].[Value] AS [Value]
            FROM  [dbo].[Student] AS [Extent1]
            LEFT OUTER JOIN [dbo].[GPA] AS [Extent2] ON [Extent1].[ID] = [Extent2].[StudentID]
            WHERE [Extent1].[ID] = @p__linq__0 ) AS [Limit1]
        LEFT OUTER JOIN [dbo].[Enrollment] AS [Extent3] ON [Limit1].[ID] = [Extent3].[StudentID]
    )  AS [Project2]
    ORDER BY [Project2].[StudentID] ASC, [Project2].[ID] ASC, [Project2].[C1] ASC: 
iisexpress.exe Information: 0 : Component:SQL Database;Method:SchoolInterceptor.NonQueryExecuted;Timespan:00:00:00.0012696;Properties:
Command: DELETE [dbo].[Enrollment]
WHERE ([EnrollmentID] = @0): 
iisexpress.exe Information: 0 : Component:SQL Database;Method:SchoolInterceptor.NonQueryExecuted;Timespan:00:00:00.0002634;Properties:
Command: DELETE [dbo].[Enrollment]
WHERE ([EnrollmentID] = @0): 
iisexpress.exe Information: 0 : Component:SQL Database;Method:SchoolInterceptor.NonQueryExecuted;Timespan:00:00:00.0002512;Properties:
Command: DELETE [dbo].[Enrollment]
WHERE ([EnrollmentID] = @0): 
iisexpress.exe Error: 0 : Error executing command: DELETE [dbo].[Student]
WHERE ([ID] = @0) Exception: System.Data.SqlClient.SqlException (0x80131904): The DELETE statement conflicted with the REFERENCE constraint "FK_dbo.GPA_dbo.Student_StudentID". The conflict occurred in database "<databasename>", table "dbo.GPA", column 'StudentID'.
The statement has been terminated.
sql-server  constraint 
— 嬉皮市区
source

Answers:

7

这是时间问题。考虑删除StudentID＃1：

  1. 该行从Student表中删除
  2. 级联删除从中删除相应的行 Enrollment
  3. 外键关系GPA-> Student已检查
  4. 触发器触发，呼叫 MergeGPA

此时，MergeGPA检查表中是否有学生＃1的条目GPA。没有（否则，步骤3中的FK检查将引发错误）。

所以，在WHEN NOT MATCHED条款中MergeGPA尝试INSERT一排GPA的StudentID＃1。该尝试失败（带有FK错误），因为已经从Student表中删除了StudentID＃1 （在步骤1）。

— 保罗·怀特9
source
1
我想你正在做某事。如果创建一个有注册的学生，但未分配成绩，则该学生在GPA表中没有任何条目。当数据库删除该学生时，它查看数据库，看到要删除的注册，但没有GPA条目。因此，它着手删除注册，这会导致触发触发器，从而创建GPA条目，然后导致违反约束？因此，解决方案是在我创建学生时创建GPA条目。然后，我的插入触发器将不需要条件，并且我的存储过程将不需要合并，只需更新即可。
— DowntownHippie
-1

无需阅读全部内容，仅从图中即可：您在“注册”中有一个条目，或在GPA中有一个条目指向您要删除的学生。

在删除学生条目之前，需要先删除具有外键的条目（或将键设置为null，但这是不正确的做法）。

还有一些数据库具有ON DELETE CASCADE，它将删除所有带有外键的条目，这些条目都指向您要删除的条目。

另一种方法是不将其声明为外键，而仅使用键值，但这也不是必需的。

— 用户名
source
如果失败，则在“注册”中有一个条目，但在GPA中没有一个。
— DowntownHippie
使用ON DELETE CASCADE有一些约束，而没有约束。尝试将该行添加到所有约束。之后，请尝试禁用所有触发器，然后在进行最小设置的测试之后。祝你好运
— user44286
我看到那些ON DELETE CASCADE陈述。这些表创建语句，删除语句都不是手写的，它们都是由entityframework生成的。级联是因为注册具有的外键不是主键，而是外键。GPA的外键约束是它的主键，因此它不需要级联。我已经对此进行了测试，如果您删除具有GPA表条目的学生，则该条目将被删除。唯一的问题是有入学率但没有gpa的学生。
— DowntownHippie
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