SQL Server：两个外键指向一个表。错误：引入 FOREIGN KEY 约束可能会导致循环或多个级联路径

Question

我收到了错误：

消息 1785，第 16 级，状态 0，第 238 行
在表“Studios”上引入 FOREIGN KEY 约束“FK_Studios_Members_HeadId”可能会导致循环或多个级联路径。指定 ON DELETE NO ACTION 或 ON UPDATE NO ACTION，或修改其他 FOREIGN KEY 约束。

下面是我遇到问题的两个表格的简化版本：

CREATE TABLE [Members] 
(
    [MemberId] int NOT NULL IDENTITY
)

CREATE TABLE [Studios] 
(
    [StudioId] int NOT NULL IDENTITY,
    [HeadId] int,
    [OwnerId] int,

    CONSTRAINT [PK_Studios] PRIMARY KEY ([StudioId]),

    CONSTRAINT [FK_Studios_Members_OwnerId] 
         FOREIGN KEY ([OwnerId]) REFERENCES [Members] ([MemberId]) 
            ON DELETE SET NULL,
    CONSTRAINT [FK_Studios_Members_HeadId] 
         FOREIGN KEY ([HeadId]) REFERENCES [Members] ([MemberId]) 
            ON DELETE SET NULL
)

我发现如果我切换两个FK的顺序，第二个总是会出错。我不明白为什么这会导致级联问题，因为两者都有“ON DELETE SET NULL”。

这是由 EF Core 代码优先生成的，所以我需要这些关系并且不能只在后端触发。

我错过了什么？

Answer 1

我不确定答案是否适用于您所拥有的东西，我不确定您的设计有多牢固......但作为一种替代设计，我认为不会有相同的问题你考虑过单独的中间关系表吗？

这种方法的一个好处是它允许您在每个位置拥有多个成员。

CREATE TABLE [Members] 
(
    [MemberId] int NOT NULL IDENTITY
)

CREATE TABLE [Studios] 
(
    [StudioId] int NOT NULL IDENTITY,

    CONSTRAINT [PK_Studios] PRIMARY KEY ([StudioId]),

)

--Contains Owner, Head, etc.
CREATE TABLE [Relationships] 
(
    [RelationshipId] int NOT NULL IDENTITY,
    [RelationshipId] nvarchar(20) NOT NULL
)

CREATE TABLE [StudioMemberRelationships]
(
    [StudioMemberRelationshipId] int NOT NULL IDENTITY,
    [StudioId] int NOT NULL,
    [MemberId] int NOT NULL,
    [RelationshipTypeId] int NOT NULL,

    CONSTRAINT [FK_StudioMemberRelationships_StudioId] 
         FOREIGN KEY ([StudioId]) REFERENCES [Studios] ([StudioId]) 
            ON DELETE SET NULL,
    CONSTRAINT [FK_StudioMemberRelationships_MemberId] 
         FOREIGN KEY ([MemberId]) REFERENCES [Members] ([MemberId]) 
            ON DELETE SET NULL,
    CONSTRAINT [FK_StudioMemberRelationships_RelationshipId] 
         FOREIGN KEY ([RelationshipId]) REFERENCES [Relationships] ([RelationshipId]) 
            ON DELETE SET NULL
)