If I have 3 different database schemas, is it possible for a user to upgrade to version 2? In other words, do I need to check for every possible combination of oldVersion and newVersion in the onUpgrade() method of my SQLiteOpenHelper subclass?
Clarification:
After I release an update with a 3rd database schema is it possible that onUpgrade() will be called with a newVersion of 2 (where the original database schema is 1 and the newest one is 3)?
It is possible for them to skip a version, but this doesn't mean you have to check for every possible combination. What I usually do is put the upgrades in their unique methods and call those methods from a switch:
private void updateTo1(){
//Code to update schema to version 1.
}
private void updateTo2(){
//Code to update schema to version 2.
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){
switch(oldVersion){
case 0:
updateTo1();
case 1:
updateTo2();
}
}
This will ensure that even if they upgrade from version 0 straight to version 2, the schema will first go through version 1 making sure that it's compatible with and ready for the version 2 update.
Related
So I have an app with a database with one table. I am wanting to put out a big update that includes a new table in the database.
I successfully used the onUpgrade method to create the new table in the old database by doing "db.execSQL(SQL_CREATE_STRING" in the onUpgrade method.
My question might not be a great one... but it's a question I can't find the answer for.
What happens next time I upgrade the database? Before I added the table the database's version was 2, after the new table the database version is 3. What happens if later down the road I want to add yet another table? Do I leave the current "db.execSQL(SQL_CREATE_STRING" in the onUpgrade or would I have to first remove it?
The SQL_CREATE_STRING starts with "CREATE TABLE IF NOT EXISTS", so I'm assuming I could just leave it in the onUpgrade method, correct? Since if it sees the table already it already exists, it wont try to make another one.
I'm just trying to confirm this thinking.
Thanks!
The SQL_CREATE_STRING starts with "CREATE TABLE IF NOT EXISTS", so I'm assuming I could just leave it in the onUpgrade method, correct? Since if it sees the table already it already exists, it wont try to make another one.
That sounds right. However, when you start having a few more versions it might be hard to keep track of which updates are okay to run regardless and which aren't.
What I recommend doing is having each of the upgrade steps in their own methods, and executing all the ones that need to for the given upgrade call in sequence. So for example:
public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion) {
for(int i = oldVersion + 1; i < newVersion; i++) {
switch(i) {
case 2: upgradeFromv1Tov2(); break;
case 3: upgradeFromv2Tov3(); break;
...
}
}
That way if someone is updating from e.g. v1 to v3, the upgrade will run the v1->v2 then v2->v3 logic. Doing it this way means when you create each upgrade step you know exactly what state the database schema will be in (ie the version before), so you don't have to worry about interactions between all the upgrade steps at the same time.
OK, so my app is ready for full release. I want to prepare my SQLite db correctly for release. My initial development program utilized the following code for onUpgrade (SQLite db helper class).
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
Then, as I needed to update my database, I followed this tutorial to increase the revision numbers, add columns, and all worked very well. For example, my onUpgrade changed to this.
private static final String DATABASE_ALTER_ADD_VELOCITY = "ALTER TABLE walk_run_table ADD COLUMN VELOCITY_CALC REAL";
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (oldVersion < 2) db.execSQL(DATABASE_ALTER_ADD_VELOCITY);
if (oldVersion < 3) db.execSQL(DATABASE_ALTER_ADD_ELEVATION);
}
Now, I'm preparing for release and want to bring my version back down to 1 (since all users will be getting a fresh install of course). Should my onUpgrade revert to "DROP TABLE IF EXISTS".... ? And then proceed with revisions as shown in the tutorial mentioned earlier? This worked well for me in development and I suspect will work well for release, but want to make sure for uploading my program to google play. Is there a better practice to prepare the SQLite db for future revisions?
It does not matter which actual version number you are using; it can go up to four billion.
And future app versions will have to increase the database version anyway; there's nothing gained by setting it to one now.
Your released app will never encounter an old database, so you can remove the code to update from older development versions.
If you do encounter a smaller version number, you have accidentally run it on a development machine, or the database file got corrupted, or someone copied a fake database into your application's storage. In all cases, the correct response is to error out.
I am making one android app where I am using SQLite database. I have already released one version of it and now for second and third version suppose I require to change in the database table like adding/removing fields.
So How can I handle this upgrade in Android. Here I don't want to drop the complete table like stuff, Here it should use Alter to update the tables.
Suppose user has installed my first version of my application then after few days I released next version 1.1 with changes in database table - added one field and here user did not upgrade it and meanwhile I again released the 1.2 again added one more field
So here How I could handle this situation when this user upgrade my application from Version 1 to Version 1.2, where Version 1.1 is missed and attribute which I added is also missed that can create problems.
Any solution to handle this ??
Assuming you're using SQLiteOpenHelper, just increment the database version number for any to-be-released version with database schema changes. In case there's an older database file around, your onUpgrade() will be called so you can migrate the database from any old version.
For example, if your 1.0 database version is 1, 1.1 is 2 and 1.2 is 3 and the user is updating version 1.0 to 1.2. onUpgrade() is called with oldVersion set to 1 and newVersion set to 3. From these version numbers your code can figure out what needs to be done, like:
#Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
switch (oldVersion) {
case 1:
updateFrom1To2(db);
case 2: // fall-through
updateFrom2To3(db);
break;
default:
Assert.fail("You forgot to write code for oldVersion " + oldVersion);
}
}
You can do anything you want in onUpgrade in sqldb
. You can use ALTER to add new columns to your table.
Worst case, if your schema is completely and entirely different, you'll have to create the new table, populate it using data from the old table, and then delete the old table.
In any case, onUpgrade was designed to allow for a smooth upgrade without any loss of data. It's just up to you to implement it properly.
You should put all changes in your onUpgrade method you can use this code:
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
String sql = "ALTER TABLE " + TABLE_SECRET + " ADD COLUMN " +
"name_of_column_to_be_added" + " INTEGER";
db.execSQL(sql);
}
for more look this
EDIT
This is a nice thought and i found one solution(not tested), you need
to check the update ,example - Check for the ALTER you have done in 1.1 in the
version 1.2 by reading the db rows or some thing , if it
is not there, you want to Alter this too with the 1.2 alter .
I usually follow a different kind of implementation to onUpgrade method to support backward compatibility in databases.
Note: Here I only show implementation to add more columns in the latest database versions.
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// 1. Copy the database file to temproary file.
// 2. Drop all the old tables from db
// db.execSQL("DROP TABLE IF EXISTS " + <TABLE NAME> );
// 3. Create tables using new Schema
// this.onCreate(db);
// 4. Copy the data from temproary file to new db
// 5. Remove the temprorary file
}
It is more convenient for me to use this kind of implementation than using ALTER commands.
As the title says, I have a production Android app with about 1000 installs. I had to make a DB change in SQLite, up to this point the version of the SQLite DB has been set to version "1".
Hopefully I explain the code below sufficiently in the comments, this code resides in my SQLiteOpenHelper Class so the onUpgrade method is part of the Class:
// Provides an upgrade path for the DB when the apps version is updated.
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// First version of the DB was 1. Logic: each if statement will
// alter the DB cumulatively based on the version code. So, if the
// newVersion was version 3, there would be two if statements, one
// for oldVersion 1 and one for oldVersion 2. oldVersion 2 will
// contain the logic for upgrading from version 2 to 3, while
// oldVersion 1 will contain a combination of alter statements
// allowing the database to upgrade from version 1 directly to
// version 3.
if (oldVersion == 1) {
db.execSQL("ALTER TABLE plans ADD COLUMN " + App.CURRENCYCODE
+ " TEXT");
Locale locale = Locale.getDefault();
ContentValues content_values = new ContentValues();
content_values.put(App.CURRENCYCODE, locale.toString());
db.update(App.DBPLANS, content_values, App.ID + " > ?", new String[] {
"0"
});
}
if (oldVersion == 2) {
// Placeholder for next database upgrade instructions.
}
}
Please let me know if there are any pitfalls here. So far, it's tested fine, though I'm very concerned about messing up my first DB upgrade. I have a 1,000 users or so, I'd hate to lose them all.
Thanks again!
When I need to update a database like this, I typically do it with a switch statement where cases fall through to one another, such as:
switch (oldVersion) {
case 1:
// update to version 2
// do _not_ break; -- fall through!
case 2:
// update to version 3
// again, do not break;
case 3:
// you're already up to date
The benefits to this is you do not end up repeating your update statements in multiple if-statements as you continue to change the database, and adding a database update requires only adding a new case statement, not updating multiple blocks of code.
There are sometimes exceptions to this, such as a column added in one version but then deleted in a future one, so you need to pay attention as you go.
I have updated the application's database. But users who have updated the application from market will see a crash everytime app is started because new database structure is not compatible with old database. Its not good to ask them to uninstall and install the app, I need to perform an operation just for single time at the time of installation i.e. clear the old database and create new one. This should not be called everytime the app starts, only at the time of installation..or when the app starts for the first time.
I think I have clearly defined my situation, now where do I go from here? Should I bug users to uninstall and install app or its possible to do what I have asked?
Just change the version of your database and by overriding onUpgrade on your DatabaseHelper class.
private static final int DATABASE_VERSION = 2;
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion
+ ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS " + TABLE_CREATION);
onCreate(db);
}
Why don't you implement the onUpgrade() method of SQLiteOpenHelper?
This class provides useful onCreate() and onUpgrade() methods.
See here : Is the onUpgrade method ever called?
Or here : How to update table schema after an app upgrade on Android?
First of all it is really a bad idea to clear the old database and create a new one (Users will be really pissed seeing there data lost).
You should always try to upgrade the previous data with new columns and stuff. Instead of clearing the whole data, you should always try to alter the structure of tables without clearing the data.
One more thing is that you can upgrade to new database in onUpgrade() method of the DBHelper class.