[英]PostgreSQL check constraint for foreign key condition
我有一個用戶表,例如:
create table "user" (
id serial primary key,
name text not null,
superuser boolean not null default false
);
和一張有工作的桌子:
create table job (
id serial primary key,
description text
);
可以將作業分配給用戶,但只能分配給超級用戶。 其他用戶無法分配作業。
因此,我有一個表格,可以查看將哪個作業分配給了哪個用戶:
create table user_has_job (
user_id integer references "user"(id),
job_id integer references job(id),
constraint user_has_job_pk PRIMARY KEY (user_id, job_id)
);
但是我想創建一個檢查約束,以使user_id
引用具有user.superuser = True
的用戶。
那可能嗎? 還是有其他解決方案?
這將適用於INSERTS:
create or replace function is_superuser(int) returns boolean as $$
select exists (
select 1
from "user"
where id = $1
and superuser = true
);
$$ language sql;
然后在user_has_job表上檢查約束:
create table user_has_job (
user_id integer references "user"(id),
job_id integer references job(id),
constraint user_has_job_pk PRIMARY KEY (user_id, job_id),
constraint chk_is_superuser check (is_superuser(user_id))
);
適用於插入物:
postgres=# insert into "user" (name,superuser) values ('name1',false);
INSERT 0 1
postgres=# insert into "user" (name,superuser) values ('name2',true);
INSERT 0 1
postgres=# insert into job (description) values ('test');
INSERT 0 1
postgres=# insert into user_has_job (user_id,job_id) values (1,1);
ERROR: new row for relation "user_has_job" violates check constraint "chk_is_superuser"
DETAIL: Failing row contains (1, 1).
postgres=# insert into user_has_job (user_id,job_id) values (2,1);
INSERT 0 1
但是,這是可能的:
postgres=# update "user" set superuser=false;
UPDATE 2
因此,如果允許更新用戶,則需要在users表上創建一個更新觸發器,以防止該用戶有工作。
我能想到的唯一方法是在(id, superuser)
上向users
表添加唯一約束(id, superuser)
並通過“復制” superuser
標志從user_has_job
表中引用該user_has_job
:
create table users (
id serial primary key,
name text not null,
superuser boolean not null default false
);
-- as id is already unique there is no harm adding this additional
-- unique constraint (from a business perspective)
alter table users add constraint uc_users unique (id, superuser);
create table job (
id serial primary key,
description text
);
create table user_has_job (
user_id integer references users (id),
-- we need a column in order to be able to reference the unique constraint in users
-- the check constraint ensures we only reference superuser
superuser boolean not null default true check (superuser),
job_id integer references job(id),
constraint user_has_job_pk PRIMARY KEY (user_id, job_id),
foreign key (user_id, superuser) references users (id, superuser)
);
insert into users
(id, name, superuser)
values
(1, 'arthur', false),
(2, 'ford', true);
insert into job
(id, description)
values
(1, 'foo'),
(2, 'bar');
由於使用default
值,因此在插入到user_has_job
表中時不必指定superuser
列。 因此,以下插入有效:
insert into user_has_job
(user_id, job_id)
values
(2, 1);
但是嘗試將亞瑟插入表中失敗:
insert into user_has_job
(user_id, job_id)
values
(1, 1);
這也可以防止將福特變成非超級用戶。 以下更新:
update users
set superuser = false
where id = 2;
失敗並顯示錯誤
錯誤:表“ users”上的更新或刪除違反了表“ user_has_job”上的外鍵約束“ user_has_job_user_id_fkey1”
詳細信息:仍從表“ user_has_job”中引用鍵(id,superuser)=(2,t)。
創建一個從user
表繼承的單獨的superuser
user
表:
CREATE TABLE "user" (
id serial PRIMARY KEY,
name text NOT NULL,
);
CREATE TABLE superuser () INHERITS ("user");
然后, user_has_job
表可以引用superuser
表:
CREATE TABLE user_has_job (
user_id integer REFERENCES superuser (id),
job_id integer REFERENCES job(id),
PRIMARY KEY (user_id, job_id)
);
通過插入和刪除,根據需要在表之間移動用戶:
WITH promoted_user AS (
DELETE FROM "user" WHERE id = 1 RETURNING *
) INSERT INTO superuser (id, name) SELECT id, name FROM promoted_user;
我不知道這是否是一個好方法,但似乎可行
INSERT INTO user_has_job (user_id, job_id) VALUES (you_user_id, your_job_id)
WHERE EXIST (
SELECT * FROM user WHERE id=your_user_id AND superuser=true
);
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