Android Database Upgrade

Database Upgrade: v1.0-v2.1
Upgrade from v1.0 to v2.01, do not go oncreate, go onupdategrade
Install v2.0 directly, go oncreate;

v1.0-v3.0: Three kinds of cases
1.v1.0 upgrade to v3.0: Don't go oncreate, go onupgrade
2.v2.0 upgrade to v3.0: Don't go oncreate, go onupgrade
3. Direct installation v3.0: Walk OnCreate, not go onupgrade
Public classDBHelperextendsSqliteopenhelper {//private static final int database_version = +;    Private Static Final intDatabase_version = 1001; //private static final int database_version = 1002;    Private Static FinalString database_name = "Mall.db"; Private StaticDBHelper instance =NULL; /*The Operational database has two very important classes: Sqlitedatabase and Sqliteopenhelper * 1.SQLiteDatabase examples represent the SQLite database, through some common methods of sqlitedatabase, Can execute SQL statements, * Add, delete, update, find and modify database operations

* 2.SQLiteOpenHelper is an auxiliary class that is primarily responsible for creating and opening databases and managing the version of the database. * Sqliteopenhelper is an abstract class that needs to inherit it and implement several of its callback functions **/   /*1. Write internal class inheritance Sqliteopenhelper 2. Build Implementation Method (1) Create public void OnCreate (Sqlitedatabase db) {(2) upgrade public voi D Onupgrade (sqlitedatabase db, int oldversion, int newversion) {3. Builder calls the constructor method of the parent class public DBHelper (String name, int v Ersion) {4. Click event Call construction method DBHelper Create connection Database*/    //internal class inheritance requires you to generate the constructor yourself     PublicDBHelper (Context context) {Super(Context, database_name,NULL, database_version); }    //Create an object (singleton mode)     Public synchronizedDBHelper getinstance (context context) {if(Instance = =NULL) {instance=NewDBHelper (context); }        returninstance; }    //Build Table@Override Public voidonCreate (sqlitedatabase sqlitedatabase) {sqlitedatabase.execsql (SQL.        Create_table_favorate); //perform a database upgrade directly if the first version is not installed//do not modify the value of First_database_version, which is the first database version size        Final intfirst_database_version = 1000;    Onupgrade (Sqlitedatabase, first_database_version, database_version); } @Override Public voidOnupgrade (Sqlitedatabase sqlitedatabase,intOldversion,intnewversion) {        //upgrading databases across versions using for         for(inti = oldversion; i < newversion; i++) {            Switch(i) { Case1000:                    //upgrade from v1.0 to v1.1upgradeToVersion1001 (sqlitedatabase);  Break;  Case1001:                    //upgrade from v1.1 to v1.2upgradeToVersion1002 (sqlitedatabase);  Break; default:                     Break; }        }    }    Private voidupgradeToVersion1001 (Sqlitedatabase db) {//Favorite Table 1 new fieldsString SQL1 = "ALTER TABLE" + SQL. T_favorite + "ADD COLUMN deleted VARCHAR";    Db.execsql (SQL1); }    Private voidupgradeToVersion1002 (Sqlitedatabase db) {//Favorite Table added 2 fields, add new field can only one field one field Plus, SQLite has a limit not allowed a statement plus multiple fieldsString SQL1 = "ALTER TABLE" + SQL. T_favorite + "ADD COLUMN message VARCHAR"; String SQL2= "ALTER TABLE" + SQL. T_favorite + "ADD COLUMN type VARCHAR";        Db.execsql (SQL1);    Db.execsql (SQL2); }}

Create a database (build a table)

 Public class SQL {    publicstaticfinal String t_favorite = "favorite";      Public Static Final String create_table_favorate= "CREATE TABLE t_favorite if not exists" +            "(_id Integer primary key autoincrement," +
    "title Varchar,url varchar," +            "creatadate varchar)";}

Android Database Upgrade