android - ContentResolver.bulkInsert(..) 有什么意义？

Question

我的目标

我想批量(事务性)将多条记录插入到 sqlite 中。

我的问题

我找到了 android.content.ContentResolver 方法。 bulkInsert (..) 有趣但 javadoc 指出:

This function make no guarantees about the atomicity of the insertions.

为什么 android 会提供一个残废的方法？你能说出非原子插入的用例吗？我显然要覆盖 ContentProvider.bulkInsert(..) 以确保我自己的原子性，所以我不确定为什么它是这样的短语。

Answer 1

我们需要重写批量插入方法，如下所示...

public class Provider extends ContentProvider {
    public static final Uri URI = Uri.parse("content://com.example.android.hoge/");
    @Override
    public String getType(Uri uri) {
        return null;
    }
    @Override
    public boolean onCreate() {
        return false;
    }
    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        Helper helper = Helper.getInstance(getContext(), null);
        SQLiteDatabase sdb = helper.getReadableDatabase();
        Cursor cursor = sdb.query(
                Table.TABLENAME,
                new String[]{Table.ID, Table.DATA, Table.CREATED},
                selection,
                selectionArgs,
                null,
                null,
                sortOrder,
                null
        );
        return cursor;
    }
    @Override
    public Uri insert(Uri uri, ContentValues values) {
        Helper helper = Helper.getInstance(getContext(), null);
        SQLiteDatabase sdb = helper.getWritableDatabase();
        sdb.insert(Table.TABLENAME, null, values);
        getContext().getContentResolver().notifyChange(uri, null);
        return uri;
    }

    /**
     * super.bulkInsert is implemented the loop of insert without transaction
     * So we need to override it and implement transaction.
     */
    @Override
    public int bulkInsert(Uri uri, ContentValues[] values) {
        Helper helper = Helper.getInstance(getContext(), null);
        SQLiteDatabase sdb = helper.getWritableDatabase();

        sdb.beginTransaction();
        SQLiteStatement stmt = sdb.compileStatement(
            "INSERT INTO `" + Table.TABLENAME + "`(`" + Table.DATA + "`, `" + Table.CREATED + "`) VALUES (?, ?);"
        );
        int length = values.length;
        for(int i = 0; i < length; i++){
            stmt.bindString(1, values[i].getAsString(Table.DATA));
            stmt.bindLong(2, values[i].getAsLong(Table.CREATED));
            stmt.executeInsert();
        }
        sdb.setTransactionSuccessful();
        sdb.endTransaction();
        return length;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        Helper helper = Helper.getInstance(getContext(), null);
        SQLiteDatabase sdb = helper.getWritableDatabase();
        int rows = sdb.update(Table.TABLENAME, values, selection, selectionArgs);
        getContext().getContentResolver().notifyChange(uri, null);
        return rows;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        Helper helper = Helper.getInstance(getContext(), null);
        SQLiteDatabase sdb = helper.getWritableDatabase();
        int rows = sdb.delete(Table.TABLENAME, selection, selectionArgs);
        getContext().getContentResolver().notifyChange(uri, null);
        return rows;
    }

    private static class Helper extends SQLiteOpenHelper {
        static Helper INSTANCE = null;
        private Helper(Context context, CursorFactory factory) {
            super(context, Table.FILENAME, factory, Table.VERSION);
        }
        public static Helper getInstance(Context context, CursorFactory factory) {
            if (INSTANCE == null) {
                INSTANCE = new Helper(context, factory);
            }
            return INSTANCE;
        }
        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(
                "CREATE TABLE `" + Table.TABLENAME + "`(" +
                " `" + Table.ID      + "` INTEGER PRIMARY KEY AUTOINCREMENT," +
                " `" + Table.CREATED + "` INTEGER," +
                " `" + Table.DATA    + "` TEXT" +
                ");"
            );
        }
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        }
    }
}