Question

我打算建立一个通知系统，向用户发送不同类型的消息（用户之间的私人消息，发布帖子的消息等）我正在寻找的是某种有条件的外键。 this_id表格中的notification列，以便它可以从表comments或pm中找到特定的行，我发现此 thread < / strong>这正是我想要的。所以我创建了一个“supertable”表，只有一列（SERIAL PRIMARY KEY）由comments和PM引用。并且为了确保在任何新行插入comments和PM之前首先在supertable中插入新行以生成密钥，我设置了两个BEFORE INSERT INTO触发器

CREATE TRIGGER `before_insert_comments` BEFORE INSERT ON `comments` FOR EACH ROW BEGIN INSERT INTO supertable (this_id) VALUES ('') END; CREATE TRIGGER `before_insert_pm` BEFORE INSERT ON `PM` FOR EACH ROW BEGIN INSERT INTO supertable (this_id) VALUES ('') END;

但是当将记录插入表comments或PM时，我仍然会收到错误消息 Cannot add or update a child row: a foreign key constraint fails ( CONSTRAINT comments FOREIGN KEY (this_id) REFERENCES supertable (this_id) ON DELETE CASCADE ON UPDATE CASCADE)。任何人都知道触发器的问题是什么？

表架构

CREATE TABLE notification ( id INT NOT NULL AUTO_INCREMENT, this_id SERIAL PRIMARY KEY, user_id INT, is_read TINYINT, FOREIGN KEY (this_id) REFERENCES supertable(this_id) ON UPDATE CASCADE ON DELETE CASCADE ); CREATE TABLE supertable ( this_id SERIAL PRIMARY KEY ); CREATE TABLE comments ( this_id SERIAL PRIMARY KEY, user_id INT , post TEXT, is_approved TINYINT, ... FOREIGN KEY (this_id) REFERENCES supertable(this_id) ON UPDATE CASCADE ON DELETE CASCADE ); CREATE TABLE PM ( this_id SERIAL PRIMARY KEY, sender_id INT, recipient_id INT , msg TEXT, ... FOREIGN KEY (this_id) REFERENCES supertable(this_id) ON UPDATE CASCADE ON DELETE CASCADE );

Answer 1

再次检查列映射。这里很少有关键点。

您的通知表主键应设置为id而不是this_foreign_id（我将其重命名以避免混淆）。
this_foreign_id的数据类型应该是BIGINT UNSIGNED以映射到SERIAL，因为1个表只能有1个自动增量列，它应该是主键。
，插入null而不是＆＃39;＆＃39;原因SERIAL列适用于BIGINT UNSIGNED

让我知道它是否有效。

CREATE TABLE supertable (
  this_id SERIAL PRIMARY KEY
);

CREATE TABLE notification (
  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
  this_foreign_id BIGINT UNSIGNED,
  user_id INT,
  is_read TINYINT,
  FOREIGN KEY (this_foreign_id) REFERENCES supertable(this_id)
  ON UPDATE CASCADE
  ON DELETE CASCADE
);

CREATE TABLE comments (
  this_id SERIAL PRIMARY KEY,
  user_id INT ,
  post    TEXT,
  is_approved TINYINT,
  FOREIGN KEY (this_id) REFERENCES supertable(this_id)
  ON UPDATE CASCADE
  ON DELETE CASCADE
);

CREATE TABLE PM (
  this_id SERIAL PRIMARY KEY,
  sender_id INT,
  recipient_id INT ,
  msg TEXT,
  FOREIGN KEY (this_id) REFERENCES supertable(this_id)
  ON UPDATE CASCADE
  ON DELETE CASCADE
);

CREATE TRIGGER before_insert_comments
BEGIN
    BEFORE INSERT ON comments
    FOR EACH ROW BEGIN
    INSERT INTO supertable (this_id) VALUES (NULL);
END;



CREATE TRIGGER before_insert_pm
BEGIN
    BEFORE INSERT ON PM
    FOR EACH ROW BEGIN
    INSERT INTO supertable (this_id) VALUES (NULL);
END;

无法触发BEFORE INSERT INTO只有一个自动增量列的表

1 个答案: