正确使用 FOREIGN KEY 函数

Question

在我的数据库中，我有两个 table 名为艺术家和曲目。在创建曲目 table 时，我将 FOREIGN KEY 设置为艺术家。但是当我运行这个显示的代码时，插入一个不存在的艺术家的曲目行是没有问题的。

那绝对不是目的...

在 http://homepages.ecs.vuw.ac.nz/~adam/scie201/lec_R_SQLite.html 上，我发现我必须使用 PRAGMA foreign_keys=ON 之类的东西打开此功能 - 但我不知道我应该如何编写此代码...

这是我的问题：如何正确实现 FOREIGN KEY 功能？

非常感谢您的帮助！

现在我的代码：

   # needed packages for this script
   # install.packages("sqldf")  # install this package if necessary
   library(sqldf)

    # connection to the database TestDB.sqlite
    db=dbConnect(SQLite(), dbname="TestDB.sqlite")

    # create the first table of the database
    dbSendQuery(conn = db,
        "CREATE TABLE IF NOT EXISTS artists
        (ID INTEGER,
        name TEXT,
        PRIMARY KEY (ID))")

    # create the second table
    dbSendQuery(conn = db,
        "CREATE TABLE IF NOT EXISTS tracks
        (track_ID INTEGER,
        title TEXT,
        artist INTEGER,
        FOREIGN KEY(artist) REFERENCES artists(ID),
        PRIMARY KEY (track_ID))")

    # filling the artist table with two rows
    dbSendQuery(conn = db,
        paste0("INSERT INTO artists
        VALUES (1,'Tom Chapin')"))
    dbSendQuery(conn = db,
        paste0("INSERT INTO artists
        VALUES (2,'Harry Chapin')"))

    # filling the tracks table
    dbSendQuery(conn = db,
        paste0("INSERT INTO tracks
        VALUES (1,'Cats in the Cradle',1)"))
    # with the following tracks filling order there must occur an error
    ### but how to switch on the 'FOREIGN KEY'
    dbSendQuery(conn = db,
        paste0("INSERT INTO tracks
        VALUES (2,'Cats in the Cradle',3)"))

    # list the tables of the database
    print(dbListTables(db))

    # list the columns of a specific table
    print(dbListFields(db,"artists"))  # of artists
    print(dbListFields(db,"tracks"))   # of tracks

    # show the data ...
    print(dbReadTable(db,"artists"))  # of artists
    print(dbReadTable(db,"tracks"))   # of tracks

    # close the connection
    dbDisconnect(db)

Answer 1

打开连接后需要向数据库发送PRAGMA语句：

dbExecute(conn = db, "PRAGMA foreign_keys=ON")

请注意，文档指出：

Foreign key constraints are disabled by default (for backwards compatibility), so must be enabled separately for each database connection.

因此每次连接到数据库时都必须这样做。

正确使用 FOREIGN KEY 函数

correct usage of the FOREIGN KEY function

sqlite

r

foreign-keys

rsqlite