源码 - 附加数据库 [英] sqlite - attach database

问题描述

我跟一些我发现在网上如何安装SQLite数据库从一个sqlite的数据库表复制到其他目的的信息，但我似乎无法得到它的工作。我尝试用这个code附加数据库：

I followed some of the information I found on web about attaching a sqlite database for the purpose of copying a table from one sqlite db to another but I can't seem to get it working. I try to attach the database with this code:

DB_PATH = context.getDatabasePath("WineDB.sqlite").toString();
SQLiteDatabase backupDatabase = backupDBHandler.getWritableDatabase();
backupDatabase.execSQL("ATTACH '" + DB_PATH + "' AS 'tempDb'");

到现在为止，它在运行时出现错误。 然后，我尝试从tempdb中复制它来创建备份数据库中的新表：

Up until now it runs without an error. Then I try to create a new table in the backup database by copying it from the tempDb:

sqlDB.execSQL("CREATE TABLE my_Producent AS SELECT * FROM tempDb.my_Producent");

和它有一个错误崩溃没有这样的表tempDb.my_Producent不过我相信该表存在于数据库WineDB.sqlite我在onCreate方法创建它被称为前，我的数据库附加到backupDatabase

And it crashes with an error "no such table "tempDb.my_Producent" However I am sure the table exists in the database "WineDB.sqlite". I create it in onCreate method which is called before I attach the database to backupDatabase.

感谢您的帮助 干杯 user2302510

Thanks for any help Cheers user2302510

推荐答案

@Phil。是的，我已经得到了它的工作。不过，我真的不记得什么是真正的问题是任何更多，所以我就写的步骤，我发现在我的关于从复制code简化程序的 firstDB 为 secondDB 。我在执行以下操作的 SQLiteOpenHelper 的 firstDB

@Phil. Yes I've got it working. However I don't really remember what the real issue was any more, so I'll just write a simplified sequence of steps I found in my code regarding copying from firstDB to secondDB. I execute the following operations in a SQLiteOpenHelper for the firstDB.

public class firstDBHandler extends SQLiteOpenHelper {

    SQLiteDatabase firstDB;
    //FIRST_DB_NAME is something like 'xxx1.sqlite'
    private static String FIRST_DB_PATH = context.getDatabasePath(FIRST_DB_NAME).toString();

    public void copyFromFirstToSecond(String secondDBName, int secondDBVersion) {
        //use the same context as for the firstDBHandler
        secondDBHandler = new SecondDBHandler(myContext, secondDBName, secondDBVersion);
        //here you create the secondDB if it does not exist yet
        try {
            secondDBHandler.createDataBase();
        } catch (IOException e) {
            e.printStackTrace();
        }
        SQLiteDatabase secondDB = secondDBHandler.getWritableDatabase();

        //note there are single quotation marks around FIRST_DB_PATH but none around tempDb
        secondDB.execSQL("ATTACH DATABASE '" + FIRST_DB_PATH + "' AS tempDb");

        //here you start to copy the tables from firstDB first by checking if the table exists in secondDB (secondDB is now the 'main' one, tempDB is the attached firstDB
        secondDB.execSQL("DROP TABLE IF EXISTS main." + SECOND_DB_TABLE_NAME);

        //here you create a table as a copy of
        secondDB.execSQL("CREATE TABLE main." + SECOND_DB_TABLE_NAME + " AS SELECT * FROM tempDb." + FIRST_DB_TABLE_NAME);

        //you can run the last two lines of code as many times as you need to copy all of the tables

        //after you have copied all of them, you need to detach the tempDB
        secondDB.execSQL("DETACH tempDb"); 
    }

}

public class SecondDBHandler extends SQLiteOpenHelper {

     //SECOND_DB_NAME is something like 'xxx2.sqlite'
    private static String SECOND_DB_PATH = context.getDatabasePath(SECOND_DB_NAME).toString();
     public void createDataBase() throws IOException {

          boolean dbExist = checkDataBase();
          if (dbExist) {
              // do nothing - database already exist
          } else {
              //This calls onCreate method of this SecondDBHandler, where you 
              //create tables that you need initially (but not those which you
              //intent to copy from firstDB)
              this.getReadableDatabase();
              this.close();
          }
    }

    public boolean checkDataBase() {
        File file = new File(SECOND_DB_PATH);
        return file.exists();
    }    
}

那么你只需要调用：

then you just call:

FirstDBHandler firstDBHandler = new FirstDBHandler(getBaseContext(), FIRST_DB_NAME, FIRST_DB_VERSION);
firstDBHandler.getReadableDatabase();
firstDBHandler.copyFromFirstToSecond(SECOND_DB_NAME, SECOND_DB_VERSION);

当然还有的onCreate方法缺失对于 SQLiteOpenHandler 的，但它是由一个应用程序所做的事情在那里。

Of course there are onCreate methods missing for both SQLiteOpenHandler's but it is up to an application what is done there.

希望的答案没有任何错误。我没有测试它自己，只是提取的简化版本，从我的更复杂的code。如果它有几个upvotes，我将其标记为一个答案。

Hopefully the answer contains no errors. I have not tested it myself, just extracted a simplified version from my more complex code. If it has a few upvotes I will mark it as an answer.

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