相关疑难解决方法(0)

我有这个已经运行并向上游发送的原始迁移:

create table(:videos) do
  add :url, :string
  add :title, :string
  add :description, :text
  add :user_id, references(:users, on_delete: :nothing)

  timestamps
end
create index(:videos, [:user_id])

现在我希望将外键user_id改为级联删除,这样当用户被删除时,他的所有相关视频也将被删除.

我尝试过以下迁移:

alter table(:videos) do
  modify :user_id, references(:users, on_delete: :delete_all)
end

但这会引发错误:

(Postgrex.Error) ERROR (duplicate_object): constraint "videos_user_id_fkey" for relation "videos" already exists

如何根据我的要求制定将更改此外键的迁移脚本？

UPDATE

我最终得到了以下解决方案:

def up do
  execute "ALTER TABLE videos DROP CONSTRAINT videos_user_id_fkey"
  alter table(:videos) do
    modify :user_id, references(:users, on_delete: :delete_all)
  end
end

def down do
  execute "ALTER TABLE videos DROP CONSTRAINT videos_user_id_fkey" …

当表名更改后,如何更改PostgreSQL中对表的引用？

说我有:

CREATE TABLE example1 (
   id serial NOT NULL PRIMARY KEY,
   name varchar(100)
);

CREATE TABLE example2 (
   id serial NOT NULL PRIMARY KEY,
   example1fk integer REFERENCES example1 (id) DEFERRABLE INITIALLY DEFERRED
);

后来我做了:

ALTER TABLE example1 RENAME TO example3; 

如何更改外键约束的定义？

example1fk integer REFERENCES example1 (id) DEFERRABLE INITIALLY DEFERRED,