When does SQLiteOpenHelper onCreate() / onUpgrade() run?

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.)

Solution 1

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 the 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 delete the database file:

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

Solution 2

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

Solution 3

onCreate()

1. When we create DataBase at a first time (i.e Database is not exists) onCreate() create database with version which is passed in SQLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version)

2. onCreate() method is creating the tables you’ve defined and executing any other code you’ve written. However, this method will only be called if the SQLite file is missing in your app’s data directory (/data/data/your.apps.classpath/databases).

3. This method will not be called if you’ve changed your code and relaunched in the emulator. If you want onCreate() to run you need to use adb to delete the SQLite database file.

onUpgrade()

1. SQLiteOpenHelper should call the super constructor.
2. The onUpgrade() method will only be called when the version integer is larger than the current version running in the app.
3. If you want the onUpgrade() method to be called, you need to increment the version number in your code.

Solution 4

May be I am too late but I would like to share my short and sweet answer. Please check Answer for a same problem. It will definitely help you. No more deep specifications.

If you are confident about syntax for creating table, than it may happen when you add new column in your same table, for that...

1) Uninstall from your device and run it again.

OR

2) Setting -> app -> ClearData

OR

3) Change DATABASE_VERSION in your "DatabaseHandler" class (If you have added new column than it will upgrade automatically)

public DatabaseHandler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

OR

4) Change DATABASE_NAME in your "DatabaseHandler" class (I faced same problem. But I succeed by changing DATABASE_NAME.)

Solution 5

Points to remember when extending SQLiteOpenHelper

1. super(context, DBName, null, DBversion); - This should be invoked first line of constructor
2. override onCreate and onUpgrade (if needed)
3. onCreate will be invoked only when getWritableDatabase() or getReadableDatabase() is executed. And this will only invoked once when a DBName specified in the first step is not available. You can add create table query on onCreate method
4. Whenever you want to add new table just change DBversion and do the queries in onUpgrade table or simply uninstall then install the app.

View more solutions

Comments

[laalto]

@Ndupza This isn't an actual problem of mine, just fed up writing the same answer/comment for the Nth time.

[bCliks]

@Laalto //data migration in onUpgrade()// Can you please explain about this.

[laalto]

@bala Not in the scope of this question/answer. If you have a question, feel free to post it as a question.

[JaskeyLam]

"onUpgrade() is only called when the database file exists but the stored version number is lower than requested in constructor. " Would you please explain for this a little bit more? Do you mean the when the client create a DBHelper, it should know the db version? How can the client pass a right db version without knowing the db ?

[laalto]

@Jaskey The version number is for your code i.e. what schema version the code expects to run against. If the file is older (from a previous version of your app), it needs to be upgraded.

[JaskeyLam]

So, I need to hard code the DB VERSION in the SQLiteHelper each time I modify the schema, so that when the old app runs and get the db connection and find it is old, and then onUpgrade will be trgiigered instead of onCreate, is this right?

[laalto]

When you update your database schema to an incompatible version then yes, you need to update the version number to distinguish incompatible database files. onCreate() is never triggered if the database already exists.

[JaskeyLam]

Thank you ! This make sense to me. Please verify if I understand well.So we need to do 1. every time we update the schema, modify the DB_VERSION variable(hard code). 2. In onUpdate(), check every old version and do proper data migration . And then when a user update their app(they have old db files), onUpgrade will be Triggered, and if the user is newly install, onCreate() is triggered.

[joe p]

I think you want your switch(newVersion) to be switch(oldVersion) instead. You may also want to verify that newVersion is 4 (and not 5, or 3; because your logic is assuming the new version should be 4).As it is, if the old version is 2 and new version is 5, you'll hit the case 4: and upgrade from 3 to 4 (which should probably not be expected behavior).

[Aun]

right - typo.. but if new version is 5 -> then it will always throw IllegalStateException and developer will be fixing it by adding case 5..

[Paramvir Singh]

What if the user upgrades his app from version 2 to 3 only? In that case also, all the cases upto case 4 will run.

[Mohammed H]

@param user cannot do that. He can upgrade 2 to latest (here 4) only.

[abarisone]

Could you please elaborate more your answer adding a little more description about the solution you provide?

[Roger Huang]

onUpgrade method is called when the database version increases, not when the number of column is changed. Ref: developer.android.com/reference/android/database/sqlite/…, int, int)

[Behzad]

I have my own DB and using SQLiteAssetHelper class. So, I did create the DB by sql script before and the db was created. By using the SQLiteAssetHelper it couldn't copy the DB until uninstalling the app form the emulator or device, because it was a db with the same version.

[LordWabbit]

On a side note, when onUpgrade is called (actually it looks like before) the PRAGMA user_version is set to the newVersion, so even if nothing is done in onUpgrade it will only fire ONCE. Afterwards it will consider the database upgraded because the version number in code will match the user_version in the database.