android - 带有 NULLABLE 外键的 SQLite

Question

我遇到了导致 SQLiteConstraintException 异常的 NULLABLE 外键问题。通过使用启用外键:

PRAGMA foreign_keys = ON

这些表是使用以下语句创建的:

CREATE TABLE conversation (_id INTEGER PRIMARY KEY);
CREATE TABLE message (_id INTEGER PRIMARY KEY, conversation_id INTEGER, FOREIGN KEY(conversation_id) REFERENCES conversation (_id) ON DELETE CASCADE);

语句被简化以提高阅读能力。

如您所见，外键“conversation_id”被声明为 NULLABLE，这样我就不必将每条消息都链接到对话(例如，当创建的草稿消息没有对应的对话时)。

当我尝试插入一 strip 有 conversation_id 的新消息时，一切正常。当我在没有的情况下尝试时，出现以下错误:

11-07 16:44:55.190  20582-20582/com.miawe.miabe E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.miawe.miabe, PID: 20582
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.miawe.miabe/com.miawe.miabe.gui.MainActivity}: android.database.sqlite.SQLiteConstraintException: foreign key constraint failed (code 19)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
        at android.app.ActivityThread.access$800(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5017)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: android.database.sqlite.SQLiteConstraintException: foreign key constraint failed (code 19)
        at android.database.sqlite.SQLiteConnection.nativeExecuteForLastInsertedRowId(Native Method)
        at android.database.sqlite.SQLiteConnection.executeForLastInsertedRowId(SQLiteConnection.java:782)
        at android.database.sqlite.SQLiteSession.executeForLastInsertedRowId(SQLiteSession.java:788)
        at android.database.sqlite.SQLiteStatement.executeInsert(SQLiteStatement.java:86)
        at android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1469)
        at android.database.sqlite.SQLiteDatabase.insertOrThrow(SQLiteDatabase.java:1365)
        at com.miawe.miabe.database.DatabaseDataSource.insert(DatabaseDataSource.java:244)
        at com.miawe.miabe.database.DatabaseDataSource.createDummyData(DatabaseDataSource.java:307)
        at com.miawe.miabe.gui.MainActivity.onCreate(MainActivity.java:64)
        at android.app.Activity.performCreate(Activity.java:5231)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)

似乎 sqlite3 忽略了我的 NULL 约束并强制每条消息都有一个外键。我该怎么做才能使列 conversation_id 接受 NULL 值？

Answer 1

您需要显式地将 NULL 传递给插入。