android - 更新数据库。 Sqlite-asset-helper 库

标签 android sqlite

我使用图书馆android-sqlite-asset-helper

需要更新，但是让用户保存了数据。表、列的名称保持不变。只有表中的条目数增加了。

我增加了 DATABASE_VERSION。将数据库放入存档中。如说明中所述，创建文件 - brodsky.db_upgrade_1-2.sql 

ALTER TABLE "poems_table" RENAME TO 'poems_table_TMP'; CREATE TABLE
        "poems_table" ( "id" long NOT NULL, "title" text, "poem" text,
        "subject" text, "years" text, "favorite" text, PRIMARY KEY ("id") );
        INSERT INTO "poems_table"  ("id", "title", "poem", "subject",
        "years", "favorite") SELECT "id", "title", "poem", "subject",
        "years", "favorite" FROM "poems_table_TMP"; DROP TABLE
        "poems_table_TMP";

数据库助手

public class PoemsDbHelper extends SQLiteAssetHelper {

    private static String DB_NAME = "brodsky.db";
    private static final int DB_VERSION = 2;

    public PoemsDbHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }
}

没有任何改变。显示旧数据

最佳答案

根据您的代码，假设代码在 onUpgrade 方法中并且版本从 1 更改为 2，则代码没有任何用处。就是这样:-

  1. 重命名旧数据库的 poems_table
  2. 创建一个新的 poems_table
  3. 将重命名表的内容复制到新创建的表中
  4. 删除重命名的 poems_table。

它无处访问较新版本的 brodsky.db

您需要(我相信)做的是打开较新的 brodsky.db 并从该数据库复制数据。

工作示例

以下是此类工作示例的代码。

这将在数据库版本增加时(为简单起见任何升级):-

  1. 将新更新的数据库复制为一个单独的/附加的数据库，并
  2. 尝试将更新数据库中的行复制到现有数据库中
    1. 仅当它们不是现有行时(基于除 id 列之外的所有列，因为最终用户可能添加了诗歌并因此使用了 id)。

核心代码在 PoemsDbHelper.java 中并且是:-

public class PoemsDbHelper extends SQLiteAssetHelper {

    public static final String DBNAME = "brodsky.db";
    public static final int DBVERSION = 1;

    public static final String TBLNAME = "poems_table";

    public static final String COL_ID = "id";
    public static final String COL_TITLE = "title";
    public static final String COl_POEM = "poem";
    public static final String COL_SUBJECT = "subject";
    public static final String COL_YEARS = "years";
    public static final String COL_FAVOURITE = "favorite";

    Context mContext;

    public PoemsDbHelper(Context context) {
        super(context, DBNAME, null, DBVERSION);
        mContext = context;
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        getNewPoems(mContext, db); //<<<<<<<<<< get the new poems when upgraded
    }


    private void getNewPoems(Context context, SQLiteDatabase db) {

        Log.d("GETNEWPOEMS","Initiating getting new poems due to Database version increased.");

        // Prepare to copy the updated database from the assets folder
        InputStream is;
        OutputStream os;
        final String tempnewdbname = "tempbrodsky.db";
        int buffersize = 4096;
        byte[] buffer = new byte[buffersize];
        String newDBPath = mContext.getDatabasePath(tempnewdbname).getPath();

        // If a copied version of the updated database exists then delete it
        // This should not be required but better safe than sorry
        File newDBFile = new File(newDBPath);
        if (newDBFile.exists()) {
            newDBFile.delete();
        }

        // Just in case create the databases directory (it should exist)
        File newDBFileDirectory = newDBFile.getParentFile();
        if (!newDBFileDirectory.exists()) {
            newDBFileDirectory.mkdirs();
        }

        // Preapre to copy update database from the assets folder
        try {
            is = context.getAssets().open("databases/" + DBNAME);
            os = new FileOutputStream(newDBFile);
            int bytes_read;
            while ((bytes_read = is.read(buffer,0,buffersize)) > 0) {
                os.write(buffer);
            }
            os.flush();
            os.close();
            is.close();

        }catch (IOException e) {
            e.printStackTrace();
            throw new RuntimeException("Ouch updated database not copied - processing stopped - see stack-trace above.");
        }

        long id = maxid(db) + 1; // Get the next available id
        SQLiteDatabase newdb = SQLiteDatabase.openDatabase(newDBFile.getPath(),null,SQLiteDatabase.OPEN_READONLY);
        Cursor csr = newdb.query(TBLNAME,null,null,null,null,null,null);
        long insert_result;
        db.beginTransaction();
        while (csr.moveToNext()) {
            insert_result = insertCorePoem(
                    db,
                    id,
                    csr.getString(csr.getColumnIndex(COL_TITLE)),
                    csr.getString(csr.getColumnIndex(COl_POEM)),
                    csr.getString(csr.getColumnIndex(COL_SUBJECT)),
                    csr.getString(csr.getColumnIndex(COL_YEARS)),
                    csr.getString(csr.getColumnIndex(COL_FAVOURITE))
            );
            // If the row was inserted then increment the if ready for the next insert
            // If not inserted (result = -2) then leave id as it is as it was unused
            if (insert_result > 0) {
                id++;
            }

        }
        db.setTransactionSuccessful();
        db.endTransaction();
        csr.close();
        newDBFile.delete(); // Delete the copied database as no longer required
    }

    public long insertCorePoem(SQLiteDatabase db, long id, String title, String poem, String subject, String years, String favourite) {

        String whereclause = COL_TITLE + "=? AND " + COl_POEM + "=? AND " + COL_SUBJECT + "=? AND " + COL_YEARS + "=?";
        String[] whereargs = new String[]{
                title,
                poem,
                subject,
                years
        };

        Cursor csr = db.query(TBLNAME,null,whereclause,whereargs,null,null,null);
        boolean rowexists = (csr.getCount() > 0);
        csr.close();
        if (rowexists) {
            Log.d("INSERTCOREPOEM","Skipping insert of row");
            return -2; // Don't insert if the poem already exists
        }

        ContentValues cv = new ContentValues();
        cv.put(COL_ID,id);
        cv.put(COL_TITLE,title);
        cv.put(COl_POEM,poem);
        cv.put(COL_SUBJECT,subject);
        cv.put(COL_YEARS,years);
        cv.put(COL_FAVOURITE,favourite);
        Log.d("INSERTCOREPOEM","Inserting new column with id " + String.valueOf(id));
        return db.insert(TBLNAME, null, cv);
    }

    private long maxid(SQLiteDatabase db) {
        long rv = 0;
        String extractcolumn = "maxid";
        String[] col = new String[]{"max(" + COL_ID + ") AS " + extractcolumn};
        Cursor csr = db.query(TBLNAME,col,null,null,null,null,null);
        if (csr.moveToFirst()) {
            rv = csr.getLong(csr.getColumnIndex(extractcolumn));
        }
        csr.close();
        return rv;
    }

    public Cursor getAllPoems() {
        SQLiteDatabase db = this.getWritableDatabase();
        return db.query(TBLNAME,null,null,null,null,null,null);
    }
}
  • getNewPoems 是执行上述操作的主要方法(请注意它是如何从 onUpgrade 方法中调用的)。这从 assets 文件夹复制更新的数据库，然后提取所有诗歌(应用程序 () 提供的核心诗歌)。
  • 准备插入列使用 ma​​xid 方法从现有数据库获取当前最高 ID 并加 1，以便新的第一个 ID 是唯一的。
  • 尝试插入每一行，但是如果要插入的行已经存在，那么它将被跳过。这是在 insertCorePoem 方法中确定的。
  • getAllPoems 方法返回一个游标(由调用 Activity 使用)。
  • 注意您可能有其他应包含的现有方法。

测试

使用外部工具创建了一个名为 brodsky.db 的数据库，其中包含 3 首诗。这被复制到 Assets 文件夹的数据库文件夹中。

调用 Activity 中使用了以下内容:-

public class MainActivity extends AppCompatActivity {
    PoemsDbHelper mDBHlpr;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mDBHlpr = new PoemsDbHelper(this);
        Log.d("DBVERSION", "Database version = " + String.valueOf(PoemsDbHelper.DBVERSION));
        Cursor csr = mDBHlpr.getAllPoems();
        DatabaseUtils.dumpCursor(csr);
        csr.close();
    }
}

阶段 1 - 验证/检查现有数据库

当第一次运行时，数据库(包含 3 首诗)从 assets 文件夹中复制并且日志包含(就像在这个阶段运行应用程序时一样):-

12-18 06:19:58.505 3574-3574/? D/DBVERSION: Database version = 1
12-18 06:19:58.505 3574-3574/? W/SQLiteAssetHelper: copying database from assets...
12-18 06:19:58.505 3574-3574/? W/SQLiteAssetHelper: database copy complete
12-18 06:19:58.521 3574-3574/? I/SQLiteAssetHelper: successfully opened database brodsky.db
12-18 06:19:58.521 3574-3574/? I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@534758c8
12-18 06:19:58.521 3574-3574/? I/System.out: 0 {
12-18 06:19:58.521 3574-3574/? I/System.out:    id=1
12-18 06:19:58.521 3574-3574/? I/System.out:    title=A Poem
12-18 06:19:58.521 3574-3574/? I/System.out:    poem=This is a poem
12-18 06:19:58.521 3574-3574/? I/System.out:    subject=poem
12-18 06:19:58.521 3574-3574/? I/System.out:    years=2018
12-18 06:19:58.521 3574-3574/? I/System.out:    favorite=NO
12-18 06:19:58.521 3574-3574/? I/System.out: }
12-18 06:19:58.521 3574-3574/? I/System.out: 1 {
12-18 06:19:58.521 3574-3574/? I/System.out:    id=2
12-18 06:19:58.521 3574-3574/? I/System.out:    title=Another Poem
12-18 06:19:58.521 3574-3574/? I/System.out:    poem=This is another poem
12-18 06:19:58.521 3574-3574/? I/System.out:    subject=another poem
12-18 06:19:58.521 3574-3574/? I/System.out:    years=2017
12-18 06:19:58.521 3574-3574/? I/System.out:    favorite=NO
12-18 06:19:58.521 3574-3574/? I/System.out: }
12-18 06:19:58.521 3574-3574/? I/System.out: 2 {
12-18 06:19:58.521 3574-3574/? I/System.out:    id=3
12-18 06:19:58.521 3574-3574/? I/System.out:    title=the Third Poem
12-18 06:19:58.521 3574-3574/? I/System.out:    poem=This is the third poem
12-18 06:19:58.521 3574-3574/? I/System.out:    subject=third poem
12-18 06:19:58.521 3574-3574/? I/System.out:    years=2018
12-18 06:19:58.521 3574-3574/? I/System.out:    favorite=NO
12-18 06:19:58.521 3574-3574/? I/System.out: }
12-18 06:19:58.521 3574-3574/? I/System.out: <<<<<

第 2 阶段 - 使用更新的数据库(但版本号未更改)。

  1. 使用 SQlite 工具将另外 3 行添加到数据库
  2. Assets 文件夹中的现有数据库已重命名(易于恢复以进行测试调试)。
  3. 更新的数据库已复制到 Assets 文件夹中的数据库文件夹中。

导致:-

enter image description here

然后重新运行该应用程序，但作为中间检查，版本号没有更改。结果高于预期，即由于版本号未更改，因此未运行 onUpgrade 方法。

第 3 阶段 - 更改版本号。

版本号从1增加到2，App运行。

导致按照 :- 添加 3 行

12-18 06:24:46.973 3689-3689/? D/DBVERSION: Database version = 2
12-18 06:24:46.981 3689-3689/? I/SQLiteAssetHelper: successfully opened database brodsky.db
12-18 06:24:46.981 3689-3689/? D/GETNEWPOEMS: Initiating getting new poems due to Database version increased.
12-18 06:24:46.981 3689-3689/? D/INSERTCOREPOEM: Skipping insert of row
12-18 06:24:46.985 3689-3689/? D/INSERTCOREPOEM: Skipping insert of row
12-18 06:24:46.985 3689-3689/? D/INSERTCOREPOEM: Skipping insert of row
12-18 06:24:46.985 3689-3689/? D/INSERTCOREPOEM: Inserting new column with id 4
12-18 06:24:46.985 3689-3689/? D/INSERTCOREPOEM: Inserting new column with id 5
12-18 06:24:46.985 3689-3689/? D/INSERTCOREPOEM: Inserting new column with id 6
12-18 06:24:46.993 3689-3689/? I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@53462060
12-18 06:24:46.993 3689-3689/? I/System.out: 0 {
12-18 06:24:46.993 3689-3689/? I/System.out:    id=1
12-18 06:24:46.993 3689-3689/? I/System.out:    title=A Poem
12-18 06:24:46.993 3689-3689/? I/System.out:    poem=This is a poem
12-18 06:24:46.993 3689-3689/? I/System.out:    subject=poem
12-18 06:24:46.993 3689-3689/? I/System.out:    years=2018
12-18 06:24:46.993 3689-3689/? I/System.out:    favorite=NO
12-18 06:24:46.993 3689-3689/? I/System.out: }
12-18 06:24:46.993 3689-3689/? I/System.out: 1 {
12-18 06:24:46.993 3689-3689/? I/System.out:    id=2
12-18 06:24:46.993 3689-3689/? I/System.out:    title=Another Poem
12-18 06:24:46.993 3689-3689/? I/System.out:    poem=This is another poem
12-18 06:24:46.993 3689-3689/? I/System.out:    subject=another poem
12-18 06:24:46.993 3689-3689/? I/System.out:    years=2017
12-18 06:24:46.993 3689-3689/? I/System.out:    favorite=NO
12-18 06:24:46.993 3689-3689/? I/System.out: }
12-18 06:24:46.993 3689-3689/? I/System.out: 2 {
12-18 06:24:46.993 3689-3689/? I/System.out:    id=3
12-18 06:24:46.993 3689-3689/? I/System.out:    title=the Third Poem
12-18 06:24:46.993 3689-3689/? I/System.out:    poem=This is the third poem
12-18 06:24:46.993 3689-3689/? I/System.out:    subject=third poem
12-18 06:24:46.993 3689-3689/? I/System.out:    years=2018
12-18 06:24:46.993 3689-3689/? I/System.out:    favorite=NO
12-18 06:24:46.993 3689-3689/? I/System.out: }
12-18 06:24:46.993 3689-3689/? I/System.out: 3 {
12-18 06:24:46.993 3689-3689/? I/System.out:    id=4
12-18 06:24:46.993 3689-3689/? I/System.out:    title=The Update Poem
12-18 06:24:46.993 3689-3689/? I/System.out:    poem=This is a new poem
12-18 06:24:46.993 3689-3689/? I/System.out:    subject=4th Core Poem
12-18 06:24:46.993 3689-3689/? I/System.out:    years=2019
12-18 06:24:46.993 3689-3689/? I/System.out:    favorite=NO
12-18 06:24:46.993 3689-3689/? I/System.out: }
12-18 06:24:46.993 3689-3689/? I/System.out: 4 {
12-18 06:24:46.993 3689-3689/? I/System.out:    id=5
12-18 06:24:46.993 3689-3689/? I/System.out:    title=Another Updated Poem
12-18 06:24:46.993 3689-3689/? I/System.out:    poem=This is another updated poem
12-18 06:24:46.997 3689-3689/? I/System.out:    subject=5th Core Poem
12-18 06:24:46.997 3689-3689/? I/System.out:    years=2019
12-18 06:24:46.997 3689-3689/? I/System.out:    favorite=NO
12-18 06:24:46.997 3689-3689/? I/System.out: }
12-18 06:24:46.997 3689-3689/? I/System.out: 5 {
12-18 06:24:46.997 3689-3689/? I/System.out:    id=6
12-18 06:24:46.997 3689-3689/? I/System.out:    title=The 3rd Updated Poem
12-18 06:24:46.997 3689-3689/? I/System.out:    poem=This is the 3rd updated poem
12-18 06:24:46.997 3689-3689/? I/System.out:    subject=6th Core Poem
12-18 06:24:46.997 3689-3689/? I/System.out:    years=2019
12-18 06:24:46.997 3689-3689/? I/System.out:    favorite=NO
12-18 06:24:46.997 3689-3689/? I/System.out: }
12-18 06:24:46.997 3689-3689/? I/System.out: <<<<<

再次运行应用程序，没有任何改变。

将版本增加到 3 会产生相同的 6 行。但是，onUpgrade 运行并尝试添加行但它们都被跳过，按照:-

12-18 06:27:08.933 3789-3789/so53801149.so53801149poemupdatefromassets D/DBVERSION: Database version = 3
12-18 06:27:08.937 3789-3789/so53801149.so53801149poemupdatefromassets I/SQLiteAssetHelper: successfully opened database brodsky.db
12-18 06:27:08.937 3789-3789/so53801149.so53801149poemupdatefromassets D/GETNEWPOEMS: Initiating getting new poems due to Database version increased.
12-18 06:27:08.937 3789-3789/so53801149.so53801149poemupdatefromassets D/INSERTCOREPOEM: Skipping insert of row
12-18 06:27:08.945 3789-3789/so53801149.so53801149poemupdatefromassets D/INSERTCOREPOEM: Skipping insert of row
12-18 06:27:08.945 3789-3789/so53801149.so53801149poemupdatefromassets D/INSERTCOREPOEM: Skipping insert of row
12-18 06:27:08.945 3789-3789/so53801149.so53801149poemupdatefromassets D/INSERTCOREPOEM: Skipping insert of row
12-18 06:27:08.945 3789-3789/so53801149.so53801149poemupdatefromassets D/INSERTCOREPOEM: Skipping insert of row
12-18 06:27:08.945 3789-3789/so53801149.so53801149poemupdatefromassets D/INSERTCOREPOEM: Skipping insert of row
12-18 06:27:08.949 3789-3789/so53801149.so53801149poemupdatefromassets I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@5347529c
..... results same as above (6 rows)
  • 注意您可能需要在 insertCorePoem 方法中定制查询以满足您的需要。

关于android - 更新数据库。 Sqlite-asset-helper 库，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53801149/

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