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Asp.net mvc 当我尝试在表中添加两个外键时，我面临很多问题

[英]Asp.net mvc when i am trying to add two foreign key in a table i face many problem

原文 2022-08-16 17:40:47 5 1 asp.net/ entity-framework/ model-view-controller/ migration

when i am added migration then update database then face this error:当我添加迁移然后更新数据库然后遇到这个错误：

foreign key constraint 'fk_ students countries_countriesid' on table 'students' may cause cycles or multiple cascade paths.表 'students' 上的外键约束 'fk_student countries_countriesid' 可能会导致循环或多个级联路径。 specify on delete no action or on update no action, or modify other foreign key constraints.指定删除不操作或更新不操作，或修改其他外键约束。 could not create constraint or index.无法创建约束或索引。

i have face this type of error.我面临这种类型的错误。 plzz help me to find error请帮我找出错误

1 个解决方案

Imagine a situation when you have table1 and table2, each having a foreign key to each-other with on delete cascade specification.想象一下当您有 table1 和 table2 的情况，每个都有一个foreign key ，并且具有on delete cascade规范。

In this situation, if you try to delete a record from table1 that is referenced by a record from table2, then the RDBMS will try to remove the record from table2.在这种情况下，如果您尝试从 table1 中删除被 table2 中的记录引用的记录，则 RDBMS 将尝试从 table2 中删除该记录。 Yet, if the record in table2 is referenced by a record in table1 (especially if it is the initial record), then this triggers a removal from table1.然而，如果 table2 中的记录被 table1 中的记录引用（特别是如果它是初始记录），那么这会触发从 table1 中删除。 So, r1 triggers the removal of r2 which triggers the removal of r3.因此，r1 触发了 r2 的删除，从而触发了 r3 的删除。 Yet, if the pattern of records to be removed gets repeated (infinitely) many times, then you get into an infinite cycle.但是，如果要删除的记录模式重复（无限）多次，那么您将进入无限循环。

The above is the simplest way of an infinite cascading loop of record removal, in more general terms以上是记录删除的无限级联循环的最简单方法，更笼统地说

you have table1, <0 or more tables>, table1 where each table cascades removal on the next table, resulting in an infinite cascading loop of record removal.您有 table1, <0 or more tables>, table1 其中每个表在下一个表上级联删除，导致记录删除的无限级联循环。

This is the type of issue the error is warning you about and it suggests that you should change the on delete behavior to no action .这是错误警告您的问题类型，它建议您将on delete行为更改为no action 。 That would technically prevent this error from occurring, yet, understandably, you may want to trigger removals.从技术上讲，这将防止此错误发生，但是可以理解的是，您可能希望触发删除。

A neat way of doing it might be to have an一个巧妙的方法可能是拥有一个

on delete set null

and add after update triggers to the tables you change this way so if the given foreign key becomes null , then it is removed.并将after update触发器添加到您以这种方式更改的表中，因此如果给定的foreign key变为null ，则将其删除。 I did not test this approach and it's unclear what RDBMS you use, but it's worth trying.我没有测试这种方法，也不清楚您使用的是什么 RDBMS，但值得一试。

If all else fails, then you can implement a stored procedure that does the cleanup and call that stored procedure.如果一切都失败了，那么您可以实现一个存储过程来进行清理并调用该存储过程。