Question

我正在尝试为测验建立数据库。我想将[quizName]存储在第一列中，并将[quizQuestions]存储在第二列中。

问题在于，即使创建了数据库并且存在列，我也会收到错误“没有这样的列： COLUMN-NAME ”

同时，如果我查询表中的所有数据，则实际上是从每一列中获取所有值。我真的找不到错误，我在做什么错了？

    class DatabaseHelper {
      static final _databaseName = "MyDatabase.db";
      static final _databaseVersion = 7;

      static final table = 'my_table';
      static final quizID = 'quizID';
      static final quizQuestions = 'quizQuestions';

      // make this a singleton class
      DatabaseHelper._privateConstructor();
      static final DatabaseHelper instance = DatabaseHelper._privateConstructor();

      // only have a single app-wide reference to the database
      static Database _database;
      Future<Database> get database async {
        if (_database != null) return _database;
        // lazily instantiate the db the first time it is accessed
        _database = await _initDatabase();
        return _database;
      }

      // this opens the database (and creates it if it doesn't exist)
      _initDatabase() async {
        Directory documentsDirectory = await getApplicationDocumentsDirectory();
        String path = join(documentsDirectory.path, _databaseName);
        return await openDatabase(path,
            version: _databaseVersion, onCreate: _onCreate);
      }

      // SQL code to create the database table
      Future _onCreate(Database db, int version) async {
        await db.execute('CREATE TABLE $table ($quizID TEXT, $quizQuestions TEXT)');
      }

      // Helper methods

      // Inserts a row in the database where each key in the Map is a column name
      // and the value is the column value. The return value is the id of the
      // inserted row.
      Future<int> insert(Map<String, dynamic> row) async {
        Database db = await instance.database;
        return await db.insert(table, row);
      }

      // All of the rows are returned as a list of maps, where each map is
      // a key-value list of columns.
      Future<List<Map<String, dynamic>>> queryAllRows() async {
        Database db = await instance.database;
        return await db.query(table);
      }

      // All of the methods (insert, query, update, delete) can also be done using
      // raw SQL commands. This method uses a raw query to give the row count.
      Future<int> queryRowCount() async {
        Database db = await instance.database;
        return Sqflite.firstIntValue(
            await db.rawQuery('SELECT COUNT(*) FROM $table'));
      }

// Below method is not finding column
      Future<List<Map<String, dynamic>>> queryQuestions(String quizName) async {
        Database db = await instance.database;
        return await db
            .rawQuery('SELECT * FROM $table WHERE $quizID = $quizName');
      }

      // We are assuming here that the id column in the map is set. The other
      // column values will be used to update the row.
      Future<int> update(Map<String, dynamic> row) async {
        Database db = await instance.database;
        int id = row[quizID];
        return await db.update(table, row, where: '$quizID = ?', whereArgs: [id]);
      }

      // Deletes the row specified by the id. The number of affected rows is
      // returned. This should be 1 as long as the row exists.
      Future<int> delete(int id) async {
        Database db = await instance.database;
        return await db.delete(table, where: '$quizID = ?', whereArgs: [id]);
      }
    }

最好的问候，鲁斯本

Answer 1

更改您的

return await db
            .rawQuery('SELECT * FROM $table WHERE $quizID = $quizName');

为此

return await db
            .rawQuery('SELECT * FROM $table WHERE $quizID = ?', [quizName]);

在$ quizName之前和之后，您基本上都缺少引号，但是最好使用？参数。

查询所有列，其中列包含特定单词不起作用？

1 个答案: