Question

基于SQLite foreign key documentation，它应该是创建两个数据库的方式，如果父字段得到更新，引用父字段的字段也会更新。

问题：一旦我按照下面的步骤操作，一切正常，直到最后一个命令 SELECT * FROM track;因为结果仍然保持不变，如下所示，它应该更改为最后显示的结果。

  trackid  trackname          trackartist
    -------  -----------------  -----------
    11       That's Amore       1
    12       Christmas Blues    1
    13       My Way             2

编码：

-- Database schema
CREATE TABLE artist(
  artistid    INTEGER PRIMARY KEY, 
  artistname  TEXT
);
CREATE TABLE track(
  trackid     INTEGER,
  trackname   TEXT, 
  trackartist INTEGER REFERENCES artist(artistid) ON UPDATE CASCADE
);

sqlite> SELECT * FROM artist;
artistid  artistname       
--------  -----------------
1         Dean Martin      
2         Frank Sinatra    

sqlite> SELECT * FROM track;
trackid  trackname          trackartist
-------  -----------------  -----------
11       That's Amore       1
12       Christmas Blues    1
13       My Way             2  

sqlite> -- Update the artistid column of the artist record for "Dean Martin".
sqlite> -- Normally, this would raise a constraint, as it would orphan the two
sqlite> -- dependent records in the track table. However, the ON UPDATE CASCADE clause
sqlite> -- attached to the foreign key definition causes the update to "cascade"
sqlite> -- to the child table, preventing the foreign key constraint violation.
sqlite> UPDATE artist SET artistid = 100 WHERE artistname = 'Dean Martin';

sqlite> SELECT * FROM artist;
artistid  artistname       
--------  -----------------
2         Frank Sinatra    
100       Dean Martin      

sqlite> SELECT * FROM track;
trackid  trackname          trackartist
-------  -----------------  -----------
11       That's Amore       100
12       Christmas Blues    100  
13       My Way             2

为什么会这样？

Answer 1

您应该更加小心地阅读fine manual：

<强> 2。启用外键支持
  [...]
  假设在使用外键约束的情况下编译库，应用程序必须在运行时使用PRAGMA foreign_keys命令启用它。例如：
sqlite> PRAGMA foreign_keys = ON;
默认情况下禁用外键约束（为了向后兼容），因此必须分别为每个数据库连接单独启用。

所以，如果你这样说：

sqlite> PRAGMA foreign_keys = ON;
sqlite> UPDATE artist SET artistid = 100 WHERE artistname = 'Dean Martin';

然后你会在track看到你所期待的100。当然，假设您的SQLite是使用FK支持编译的。

SQLITE ON UPDATE操作

1 个答案: