When is SQLiteOpenHelper onCreate() / onUpgrade()

Question

I have created my tables in my SQLiteOpenHelper onCreate() but receive

SQLiteException: no such table

or

SQLiteException: no such column

errors. Why?

NOTE:

(This is the amalgamated summary of tens of similar questions every week. Attempting to provide a "canonical" community wiki question/answer here so that all those questions can be directed to a good reference.)

Answer 1

To further add missing points here, as per the request by Jaskey

Database version is stored within the SQLite database file.

catch is the constructor

SQLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version)

So when the database helper constructor is called with a name (2nd param), platform checks if the database exists or not and if the database exists, it gets the version information from the database file header and triggers the right call back

As already explained in the older answer, if the database with the name doesn't exists, it triggers onCreate.

Below explanation explains onUpgrade case with an example.

Say, your first version of application had the DatabaseHelper (extending SQLiteOpenHelper) with constructor passing version as 1 and then you provided an upgraded application with the new source code having version passed as 2, then automatically when the DatabaseHelper is constructed, platform triggers onUpgrade by seeing the file already exists, but the version is lower than the current version which you have passed.

Now say you are planing to give a third version of application with db version as 3 (db version is increased only when database schema is to be modified). In such incremental upgrades, you have to write the upgrade logic from each version incrementally for a better maintainable code

Example pseudo code below:

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
  switch(oldVersion) {
    case 1:
       //upgrade logic from version 1 to 2
    case 2:
       //upgrade logic from version 2 to 3
    case 3:
       //upgrade logic from version 3 to 4
       break;
    default:
       throw new IllegalStateException(
                "onUpgrade() with unknown oldVersion " + oldVersion);
  }
}

Notice the missing break statement in case 1 and 2. This is what I mean by incremental upgrade.

Say if the old version is 2 and new version is 4, then the logic will upgrade the database from 2 to 3 and then to 4

If old version is 3 and new version is 4, it will just run the upgrade logic for 3 to 4

Answer 2

SQLiteOpenHelper onCreate() and onUpgrade() callbacks are invoked when the database is actually opened, for example by a call to getWritableDatabase(). The database is not opened when the database helper object itself is created.

SQLiteOpenHelper versions the database files. The version number is the int argument passed to the constructor. In the database file, the version number is stored in PRAGMA user_version.

onCreate() is only run when the database file did not exist and was just created. If onCreate() returns successfully (doesn't throw an exception), the database is assumed to be created with the requested version number. As an implication, you should not catch SQLExceptions in onCreate() yourself.

onUpgrade() is only called when the database file exists but the stored version number is lower than requested in constructor. The onUpgrade() should update the table schema to the requested version.

When changing the table schema in code (onCreate()), you should make sure the database is updated. Two main approaches:

1. Delete the old database file so that onCreate() is run again. This is often preferred at development time where you have control over the installed versions and data loss is not an issue. Some ways to to delete the database file:

   • Uninstall the application. Use the application manager or adb uninstall your.package.name from shell.

   • Clear application data. Use the application manager.

2. Increment the database version so that onUpgrade() is invoked. This is slightly more complicated as more code is needed.

   • For development time schema upgrades where data loss is not an issue, you can just use execSQL("DROP TABLE IF EXISTS <tablename>") in to remove your existing tables and call onCreate() to recreate the database.

   • For released versions, you should implement data migration in onUpgrade() so your users don't lose their data.

Answer 3

onCreate is called for the first time when creation of tables are needed. We need to override this method where we write the script for table creation which is executed by SQLiteDatabase. execSQL method. After executing in first time deployment, this method will not be called onwards.

onUpgrade This method is called when database version is upgraded. Suppose for the first time deployment , database version was 1 and in second deployment there was change in database structure like adding extra column in table. Suppose database version is 2 now.

Answer 4

If you forget to provide a "name" string as the second argument to the constructor, it creates an "in-memory" database which gets erased when you close the app.

Answer 5

Uninstall your application from the emulator or device. Run the app again. (OnCreate() is not executed when the database already exists)

Answer 6

Recheck your query in ur DatabaseHandler/DatabaseManager class(which ever you have took)