android - queryBuilder.appendWhere() 的意义何在？安卓

Question

这里使用 queryBuilder.appendWhere() 有什么意义？在Cursor cursor = queryBuilder.query()中设置where子句是不是简单多了？还是两种设置“where”子句的方式不同？

  public Cursor query(Uri uri, String[] projection, String selection,
      String[] selectionArgs, String sortOrder) {

    // Uisng SQLiteQueryBuilder instead of query() method
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();

    // Check if the caller has requested a column which does not exists
    checkColumns(projection);

    // Set the table
    queryBuilder.setTables(TodoTable.TABLE_TODO);

    int uriType = sURIMatcher.match(uri);
    switch (uriType) {
    case TODOS:
      break;
    case TODO_ID:
      // Adding the ID to the original query
      queryBuilder.appendWhere(TodoTable.COLUMN_ID + "="
          + uri.getLastPathSegment());
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }

    SQLiteDatabase db = database.getWritableDatabase();
    Cursor cursor = queryBuilder.query(db, projection, selection,
        selectionArgs, null, null, sortOrder);
    // Make sure that potential listeners are getting notified
    cursor.setNotificationUri(getContext().getContentResolver(), uri);

    return cursor;
  }

Answer 1

如果您要根据条件构建 WHERE 子句的各个部分，则可以使用 appendWhere()。