android:使用ContentResolver时的sqlite事务

我已经看到在谷歌I/O应用程序的源代码中,它们重写了 ContentProvider 的 applyBatch() 方法并使用其中的事务。因此,您可以创建一批 ContentProviderOperation 然后调用 getContentResolver().applyBatch(uri_authority, batch) .

我打算用这种方法来看看它是如何工作的。我很好奇是否还有人尝试过。

正如Kaciula所提到的,由于android 2.1使用ContentProviderOperation,因此可以非常干净地执行基于事务的多表插入。

当您构建ContentProviderOperation对象时,可以调用.WithValueBackReference(FieldName,Refnr)。当使用applybatch应用该操作时,结果是随insert()调用提供的contentValues对象将注入一个整数。该整数将使用字段名字符串进行键控,其值将从以前应用的ContentProvider属性的ContentProviderResult中检索,该属性由refnr索引。

请参阅下面的代码示例。在示例中,在表1中插入一行,然后在表2中插入行时,将生成的ID(在本例中为“1”)用作值。为了简洁起见,ContentProvider未连接到数据库。在ContentProvider中,有一些打印输出适合添加事务处理。

public class BatchTestActivity extends Activity {
    /** Called when the activity is first created. */
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ArrayList<ContentProviderOperation> list = new
            ArrayList<ContentProviderOperation>();

        list.add(ContentProviderOperation.
            newInsert(BatchContentProvider.FIRST_URI).build());
        ContentValues cv = new ContentValues();
        cv.put("name", "second_name");
        cv.put("refId", 23);

        // In this example, "refId" in the contentValues will be overwritten by
        // the result from the first insert operation, indexed by 0
        list.add(ContentProviderOperation.
            newInsert(BatchContentProvider.SECOND_URI).
            withValues(cv).withValueBackReference("refId", 0).build());

        try {
            getContentResolver().applyBatch(
                BatchContentProvider.AUTHORITY, list);
        } catch (RemoteException e) {
            e.printStackTrace();
        } catch (OperationApplicationException e) {
            e.printStackTrace();
        }
    }
}

public class BatchContentProvider extends ContentProvider {

    private static final String SCHEME = "content://";
    public static final String AUTHORITY = "com.test.batch";

    public static final Uri FIRST_URI =
        Uri.parse(SCHEME + AUTHORITY + "/" + "table1");
    public static final Uri SECOND_URI =
        Uri.parse(SCHEME + AUTHORITY + "/" + "table2");


    public ContentProviderResult[] applyBatch(
        ArrayList<ContentProviderOperation> operations)
            throws OperationApplicationException {
        System.out.println("starting transaction");
        ContentProviderResult[] result;
        try {
            result = super.applyBatch(operations);
        } catch (OperationApplicationException e) {
            System.out.println("aborting transaction");
            throw e;
        }
        System.out.println("ending transaction");
        return result;
    }

    public Uri insert(Uri uri, ContentValues values) {
        // this printout will have a proper value when
        // the second operation is applied
        System.out.println("" + values);

        return ContentUris.withAppendedId(uri, 1);
    }

    // other overrides omitted for brevity
}

好吧-所以这并不是漫无目的的:我唯一能想到的方法是将startTransaction和endTransaction编码为基于URL的查询请求。有点像 ContentResolver.query(START_TRANSACTION, null, null, null, null) .然后在 ContentProvider#query 基于注册的URL调用开始或结束事务

您可以获取内容提供者对象本身的实现(如果在同一进程中,提示:您可以使用multiprocess=“true”或process=“”控制提供者的进程) http://developer.android.com/guide/topics/manifest/provider-element.html )使用ContentProviderClient.GetLocalContentProvider(),它可以强制转换到提供程序实现中,提供额外的功能,如关闭和删除数据库的reset(),还可以使用save()和close()方法返回自定义事务类实例。

public class Transaction {
    protected Transaction (SQLiteDatabase database) {
        this.database = database;
        database.beginTransaction ();
    }

    public void save () {
        this.database.setTransactionSuccessful ();
    }

    public void close () {
        this.database.endTransaction ();
    }

    private SQLiteDatabase database;
}

public Transaction createTransaction () {
    return new Transaction (this.dbHelper.getWritableDatabase ());
}

然后:

ContentProviderClient client = getContentResolver ().acquireContentProviderClient (Contract.authorityLocal);
Transaction tx = ((LocalContentProvider) client.getLocalContentProvider ()).createTransaction ();