Develop Reference

Drop a column when the schema changes in ORMLite

I am working with Android and ORMLite. I am newbie and I upgrading the database to the Version 2. I have the class “Auto” and need to drop the column Alias.
#DatabaseTable(tableName = "Auto")
public class Auto {
public static final String ALIAS = "alias";
public static final String PLACA = "placa";
#DatabaseField(generatedId = true, columnName = "ID")
private int id;
#DatabaseField(canBeNull = false, columnName = ALIAS)
private String alias;
#DatabaseField(canBeNull = false, columnName = PLACA)
public Auto()
{
//ORMLite needs a no-arg constructor
}
public Auto(String alias, String placa) {
this.alias = alias;
this.placa = placa;
}
…..
…..
}
I change the class Auto to…
#DatabaseTable(tableName = "Auto")
public class Auto {
public static final String PLACA = "placa";
#DatabaseField(generatedId = true, columnName = "ID")
private int id;
#DatabaseField(canBeNull = false, columnName = PLACA)
public Auto()
{
//ORMLite needs a no-arg constructor
}
public Auto(String alias, String placa) { this.placa = placa;
}
…..
…..
}
I need to know if ORMLite automatically drops the column Alias when execute “onUpgradeMethod” or I have to do manually like this.
#Override
public void onUpgrade(SQLiteDatabase db, ConnectionSource connectionSource, int oldVersion, int newVersion) {
if(oldVersion == 1) {
try {
Dao dao;
dao = getAutoDao();
dao.executeRaw("ALTER TABLE `Auto` DROP COLUMN alias;");
} catch (SQLException e) {
Log.e(DatabaseHelper.class.getName(), "Error ", e);
}
}
}

This links help me to solve it.
Drop column in SQLite
FAQ SQLite 11
Delete column from SQL
save data before table upgrade
Drop table if it already exists and then re-create it?
SQLite has limited ALTER TABLE support that you can use to add a column to the end of a table or to change the name of a table. If you want to make more complex changes in the structure of a table, you will have to recreate the table. You can save existing data to a temporary table, drop the old table, create the new table, then copy the data back in from the temporary table.
For example, suppose you have a table named "t1" with columns names
"a", "b", and "c" and that you want to delete column "c" from this
table. The following steps illustrate how this could be done:
BEGIN TRANSACTION;
CREATE TEMPORARY TABLE t1_backup(a,b);
INSERT INTO t1_backup SELECT a,b FROM t1;
DROP TABLE t1; CREATE TABLE t1(a,b); INSERT INTO t1 SELECT a,b FROM t1_backup;
DROP TABLE t1_backup;
COMMIT;
The possible solution according to Phil's comments is this. 4
So your choices are:
leave things as they are,
add a new column, copying all the data from old to new as part of the upgrade, and just ignore the old column altogether, or
Use a drop/create strategy to upgrade: back up the data from table into a temporary table, drop the table, re-create it as you'd like it
to be, copy all the data back into it, and finally drop the temporary
table.
Database upgrades are always nervous affairs (need lots of error
handling, lots of testing), frankly if the name is the only thing that
concerns you, I'd leave it alone (option 1). If you really need to
change it then option 2 is low risk but leaves a 'dead' column and
data lying around. Option 3 may be your choice if, for example, the
data is a significant percentage of the overall database size.
I decided to delete the data from the column but don't drop the column, that is similar to solution 2.

Manage DB before uploading to playstore in android

I have uploaded an application to play store couple of weeks back. This application involves sqlite database that stores information on username, password, other details that given are by user while using the application locally.
Now I have couple of more tables and fields added to database and wanna upload the application to playstore as an update?
My worry is if the user updates the application from playstore - After update - all the data stored in database will be saved or will the user has to recreate everything from scratch?
Let me know!
Thanks!

You have to override the onUpgade method of SQLiteOpenHelper. In the OnUpgrade method you can either erase the data(drop sqlite command) or maintain the data with the additional columns(alter sqlite command) or create new table (create sqlite command).
Refer the following snippet.
I assume your version would be 1.(Plz check the constructor of your SqliteOpenHelper class)
Increment the version by 1.
class DatabaseHelper extends SqliteOplenHelper{
private static final int DATABASE_VERSION = 2; //new version of the database
private static final int Database_name = "MyDatabase";
private static final String alterUserName = "alter table users add name text";
private static final String table_users = "create table if not exists "
+ users + "(" + "_id integer primary key autoincrement,"
+ "email text" + ")";
public DatabaseHelper(Context context) {
super(context, Database_name, null, DATABASE_VERSION);
cntxt = context;
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL(table_users);
db.execSQL(alterUserName);
}
}
Now everytime when you roll the next update with database changes be sure to increment the database version by 1 else let it remain the same.

This isn't done for you automatically. In your SQLiteOpenHelper, you need to increment the Schema integer. This will trigger the on upgrade method for your existing users.
Adding a table is not a problem, just do this in onUpgrade, nothing breaks.
However to add fields, you should use the 'ALTER TABLE' SQL command
If you add new columns you can use ALTER TABLE to insert them into a live table. If you rename or remove columns you can use ALTER TABLE to rename the old table, then create the new table and then populate the new table with the contents of the old tab
See the official reference here

Storing application database schema

In example apps database is in most cases single table, so db schema is stored in static variable.
Storing large schema in seperate file is more friendly for me.
How can I do that? I thought about using resources (R.strings.db_schema) but probably there is a better way.
Could somebody give me any advice?

You could put the schema data in a raw file under res/raw. Then you can just load and parse that file the first time.

The way I do is to have a class per table, named after the table with "Table" suffix (e.g. PlayerTable or EventTable).
These classes contain all the static variable for the table name and all the field names, and they also contain two static methods:
public static void onCreate(SQLiteDatabase database)
public static void onUpgrade(SQLiteDatabase database, int oldVersion, int newVersion)
So that my SQLiteOpenHelper can just call all of them, without having hundreds of static variables with all the fields and create queries. E.g:
#Override
public void onCreate(SQLiteDatabase database) {
PlayerTable.onCreate(database);
EventTables.onCreate(database);
..... any other table you have .....
}
This class is then injected into all my data access objects (select / update / insert queries). For them I have dedicated classes that contain all my methods, by functionality (e.g. EventHandlingDAO for all the queries that deal with event handling).
And finally, theses DAO are injected into the activities that need them, when needed.
EDIT: A few more details about my code:
My main objects are the DAO (data access objects), in which I have methods like:
// in EventHandlingDAO:
public void addEvent(Event event) {
SQLiteDatabase database = databaseHelper.getWritableDatabase();
try {
database.execSQL("INSERT INTO " + EventTable.EVENT_TABLE_NAME + " (...."); // list of fields and values
} finally {
database.close();
}
}
public List<Event> getAllEvents() {
final List<Event> result = new ArrayList<Event>();
SQLiteDatabase database = databaseHelper.getReadableDatabase();
try {
final Cursor cursor = database.rawQuery("SELECT " + EventTable.KEY_NAME + ", " + EventTable.KEY_DATE_AS_STRING + " FROM " + EventTable.TABLE_NAME, null);
cursor.moveToFirst();
// ... rest of the logic, that iterates over the cursor, creates Event objects from the cursor columns and add them to the result list
return result;
} finally {
database.close();
}
}
So in that DAO, I have my databaseHelper object, which instanciates my class that extends SQLiteOpenHelper with the methods I talked about above.
And of course, I have interfaces to all my DAO, so that I can inject a Stub or mocked implementation in my tests (or experiment with different implementations if I want to try another solution based on SharedPreference for example)
And the code for my PlayerTable table:
public static void onCreate(SQLiteDatabase database) {
database.execSQL(TABLE_CREATE); // TABLE_CREATE is my "CREATE TABLE..." query
}
public static void onUpgrade(SQLiteDatabase database, int oldVersion, int newVersion) {
// A bit blunt, that destroys the data unfortunately, I'll think about doing something more clever later ;)
database.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(database);
}

Android: duplicate values are being inserted in to database

Each time i run the project same values are also being inserted in the android database. Even i have given the drop if exists query.What i need is that the data in the database gets updated only if there are some changes in the response from the server side instead of cresting database every time but what is happening with me is that same values got insertes again in the tables. How do I solve this? Following is my code:
public void onCreate(SQLiteDatabase database) {
try{
// onUpgrade(database, oldVersion, newVersion)
database.execSQL(DATABASE_CREATE);
}
catch (Exception e) {
System.out.println("in on create db"+e);
}}
public void onUpgrade(SQLiteDatabase database, int oldVersion,
int newVersion) {
database.execSQL("DROP TABLE IF EXISTS" +DATABASE_CREATE);
onCreate(database);
}
private static final String INSERT = "insert into "
+ DATABASE_TABLE + "(KEY_TYPE,KEY_ENCODING,KEY_WIDTH,KEY_HEIGHT,KEY_DATA,KeyIId)"+" values (?,?,?,?,?,?)";
public WineDatabaseAdapter(Context context) {
try{
this.context = context;
openHelper = new WineDatabaseHelper(context);
this.db=openHelper.getWritableDatabase();
this.insertStmt=this.db.compileStatement(INSERT);
}
catch(Exception e)
{
System.out.println(e);
}
}
Can anyone help me how to solve this problem.
Thanks

DROP TABLE seems a pretty extreme way of trying to stop duplicate values. It's a bit hard to follow the code you've posted, but the normal way of stopping duplicates is to add a unique index on the appropriate column(s). Have you tried that yet ? E.g. something like
CREATE UNIQUE INDEX idx_keytype ON tableName (key_type)

What does your schema look like? If you don't want duplicate rows and you know a certain column will be unique use the "UNIQUE" specifier on it. If what you really want is for the row to be replaced you have to use the databaseHelper command "replace" ie. dbHelper.replace(...);

onCreate not being called after getWritableDatabase/getReadableDatabase

My app's got a database with three tables in it: one to store the names of the people it tracks, one to track an ongoing event, and one - for lack of a better term - for settings.
I load the first table when the app starts. I ask for a readable database to load in members to display, and later I write to the database when the list changes. I've had no problems here.
The other two tables, however, I can't get to work. The code in the helper classes is identical with the exception of class names and column names, and (at least until the point where I try to access the table) the code to use the table is nearly identical as well.
Here's the code for my helper class (I've got a separate helper for each table, and as I said, it's identical except for class names and columns):
public class db_MembersOpenHelper extends SQLiteOpenHelper
{
public static final String TABLE_NAME = "members_table";
public static final String[] COLUMN_NAMES = new String[] {
Constants.KEY_ID,
"name",
"score"
};
private static final String TABLE_CREATE = "CREATE TABLE " + TABLE_NAME + " ("
+ COLUMN_NAMES[0] + " INTEGER PRIMARY KEY autoincrement, "
+ COLUMN_NAMES[1] + " TEXT, "
+ COLUMN_NAMES[2] + " INTEGER);";
public db_MembersOpenHelper(Context context)
{
super(context, Constants.DATABASE_NAME, null, Constants.DATABASE_VERSION);
}
#Override
public void onCreate(SQLiteDatabase db) { db.execSQL(TABLE_CREATE); }
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
Log.w("TaskDBAdapter", "Upgrading from version " + oldVersion + " to " + newVersion + ".");
// Do nothing. We do not have any updated DB version
}
}
Here's how I use it successfully:
db_MembersOpenHelper membersDbHelper = new db_MembersOpenHelper(this);
SQLiteDatabase membersDb = membersDbHelper.getReadableDatabase();
Cursor membersResult = membersDb.query(TABLE_NAME, null, null, null, null, null, null);
members = new HashMap<String, Integer>();
membersResult.moveToFirst();
for(int r = 0; r < membersResult.getCount(); r++)
{
members.put(membersResult.getString(1), membersResult.getInt(2));
membersResult.moveToNext();
}
membersDb.close();
And here's where it fails:
db_PlayersOpenHelper playersDbHelper = new db_PlayersOpenHelper(this);
final SQLiteDatabase playersDb = playersDbHelper.getWritableDatabase();
if(newGame)
{
for(String name : players)
{
ContentValues row = new ContentValues();
row.put(COLUMN_NAMES[1], name);
row.put(COLUMN_NAMES[2], (Integer)null);
playersDb.insert(TABLE_NAME, null, row);
}
}
The first one works like a charm. The second results in ERROR/Database(6739): Error inserting achievement_id=null name=c
android.database.sqlite.SQLiteException: no such table: players_table: , while compiling: INSERT INTO players_table(achievement_id, name) VALUES(?, ?);
...
I did do some testing, and the onCreate method is not being called at all for the tables that aren't working. Which would explain why my phone thinks the table doesn't exist, but I don't know why the method isn't getting called.
I can't figure this out; what am I doing so wrong with the one table that I accidentally did right with the other?

I think the problem is that you are managing three tables with with three helpers, but only using one database. SQLiteOpenHelper manages on database, not one table. For example, it checks to see whether the database, not table, exists when it starts. It already does, so onCreate() does not fire.
I would manage all tables with one helper.

Let me see if I get this right. You are trying to create one database with three tables. But when you create the database, you create just one table; you are somehow instantiating the same database at a different place and wonder why its onCreate method doesn't get called. Is this a correct interpretation?
My strategy would be to try and create all three tables in the single onCreate() method.

If you are working with multiple tables, then you have to create all of the tables at once. If you have run your application first and later you update your database, then it will not upgrade your DB.
Now delete your application, then run it again.

There is one more solution but it is not proper. You can declare onOpen method in which you can call onCreate. And add IF NOT EXISTS before table name in your create table string. – Sourabh just now edit