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android数据库升级的措辞
网友分享于:Jan 1, 1970 8:00:00 AM    来源: IT货架   

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在基类table增加upgrade操作:

public abstract class DbBaseTable {

	private static final String TAG = "DbBaseTable";

	/**
	 * @return the DB table name
	 */
	abstract String getName();

	/**
	 * Creates the DB table according to the DB scheme
	 * 
	 * @param db
	 */
	abstract void onCreate(SQLiteDatabase db);
	
	void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion, String tempName) {
        
        //Rename old table to temporary name
	<strong>DbUtils.renameTable(db, getName(), tempName);</strong>
		
        //Create clear table according to the new scheme
       <strong> onCreate(db);</strong>
        //Copy content of the matching columns from the old table to the new one
       <strong> joinColumns(db, tempName, getName());</strong>
        
        //Delete old table
       <strong> DbUtils.dropTable(db, tempName);</strong>
        
        //这个是更新一些表的内容
        initTableContent(db);
    }
    
    void initTableContent(SQLiteDatabase db) {
    }
   
    void joinColumns(SQLiteDatabase db, String tempName, String tableName) {
    	<strong>DbUtils.joinColumns(db, tempName, tableName);</strong>
    }

}

final class DbUtils {
    
    private static final String TAG = "DbUtils";
    private static final boolean DEBUG = false;
    
    private static final String SQLITE_STMT_LIST_TABLES =
        "SELECT name FROM sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%' AND name NOT LIKE 'android%'";
    private static final String SQLITE_TABLE_NAME_COLUMN = "name";
    private static final String SQLITE_STMT_TEMPLATE_LIST_COLUMNS = "SELECT * FROM %s LIMIT 1";
    private static final String SQLITE_STMT_TEMPLATE_DROP_TABLE = "DROP TABLE IF EXISTS %s";
    private static final String SQLITE_STMT_TEMPLATE_RENAME_TABLE = "ALTER TABLE %s RENAME TO %s";
    private static final String SQLITE_STMT_TEMPLATE_COPY_COLUMNS = "INSERT INTO %s (%s) SELECT %s FROM %s";

    
    /**
     * @param db
     * @return Collection object containing table names in the database 
     */
    static Collection<String> listTables(SQLiteDatabase db) {

        Cursor cursor = db.rawQuery(SQLITE_STMT_LIST_TABLES, null);
        if (cursor == null || !cursor.moveToFirst()) {

            if (cursor != null) {
                cursor.close();
            }
            return null;
        }
        
        int table_name_column = cursor.getColumnIndex(SQLITE_TABLE_NAME_COLUMN);
        HashSet<String> tables = new HashSet<String>(cursor.getCount());
        do {
            tables.add(cursor.getString(table_name_column));
        } while (cursor.moveToNext());
        cursor.close();

        
        return tables;
    }

    
    /**
     * @param db
     * @param table
     * @return List of column names in the DB table
     */
    public static List<String> listColumns(SQLiteDatabase db, String table) {
        
        Cursor cursor = db.rawQuery(String.format(SQLITE_STMT_TEMPLATE_LIST_COLUMNS, table), null);
        if (cursor == null) {
            return null;
        }
        
        List<String> columns = Arrays.asList(cursor.getColumnNames());
        cursor.close();

        return columns;
    }
    
    
    /**
     * @param db
     * @param table
     */
    static void dropTable(SQLiteDatabase db, String table) {

        db.execSQL(String.format(SQLITE_STMT_TEMPLATE_DROP_TABLE, table));
    }
    

    static void renameTable(SQLiteDatabase db, String oldName, String newName) {

        db.execSQL(String.format(SQLITE_STMT_TEMPLATE_RENAME_TABLE, oldName, newName));
    }
    
    
    static void joinColumns(SQLiteDatabase db, String oldTable, String newTable) {
        
        //Delete all records in the new table before copying from the old table
        db.delete(newTable, null, null);
        
        //Find columns which exist in both tables
        ArrayList<String> old_columns = new ArrayList<String>(listColumns(db, oldTable));
        List<String> new_columns = listColumns(db, newTable);
        old_columns.retainAll(new_columns);

        String common_columns = TextUtils.join(",", old_columns);
        
        //Copy records from old table to new table  example:<span style="font-family: 微软雅黑;"><strong><span style="font-size:10px;">INSERT INTO Mytest1 (_id,account_id,test1,test3) SELECT _id,account_id,test1,test3 FROM Mytest1_temp_</span></strong></span>
        db.execSQL(String.format(SQLITE_STMT_TEMPLATE_COPY_COLUMNS, newTable, common_columns, common_columns, oldTable));
    }

}

然后在DBHelper中重载onUpgrade方法:

 @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

        //Get table names in the old DB
        Collection<String> old_tables = DbUtils.listTables(db);
        if (old_tables == null || old_tables.size() == 0) {
            onCreate(db);
            return;
        }
        
        //Get table names in the new DB
        Set<String> new_tables = DataBaseClass.sRCMDbTables.keySet();
        
        try {
            db.beginTransaction();
            //Remove old tables which are not in the new DB scheme
            HashSet<String> obsolete_tables = new HashSet<String>();
            for (String table : old_tables) {
                if (!new_tables.contains(table)) {
                	System.out.println("====DBHelp onUpgrade droptable table="+table);
                    DbUtils.dropTable(db, table);
                    obsolete_tables.add(table);
                }
            }
            old_tables.removeAll(obsolete_tables);
    
            //Create and upgrade new tables 
            DbBaseTable table_descriptor; 
            for (String table : new_tables) {
                table_descriptor = DataBaseClass.sRCMDbTables.get(table);
                
                //Check if the new table exists in the old DB
                if (old_tables.contains(table)) {
                    String temp_name = getTempTableName(table, old_tables, new_tables);
                    System.out.println("====DBHelp onUpgrade temp_name ="+temp_name);
                    table_descriptor.onUpgrade(db, oldVersion, newVersion, temp_name);
                } else {
                    table_descriptor.onCreate(db);
                }
            }
            db.setTransactionSuccessful();
        } catch (Throwable e) {
            
            throw new RuntimeException("DB upgrade failed: " + e.getMessage());
        } finally {
            db.endTransaction();
        }
    }


中心思想是:

对照新旧的database结构,假设旧表中有table新的database里没有,则删除旧表里的

假设新database中有一个table更新。则须要更新这个表的结构。然后把旧表中数据拷贝过来

(把旧表rename一个名字。把命名后的表中的数据复制到新表中)

代码能够在http://download.csdn.net/detail/baidu_nod/7684479下载

版权声明:本文博客原创文章。博客,未经同意,不得转载。

android数据库升级的措辞

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