Flutter数据库封装

SQLite

如果您正在编写一个需要持久化且查询大量本地设备数据的 app，可考虑采用数据库，而不是本地文件夹或关键值库。总的来说，相比于其他本地持久化方案来说，数据库能够提供更为迅速的插入、更新、查询功能。

Flutter应用程序中可以通过 sqflite package 来使用 SQLite 数据库。本文将通过使用 sqflite 来演示插入，读取，更新，删除各种数据。

如果你对于 SQLite 和 SQL 的各种语句还不熟悉，请查看 SQLite 官方的教程 SQLite 教程，在查看本文之前需要掌握基本的SQL语句。

添加sqflite依赖

dependencies:
  flutter:
    sdk: flutter
  sqflite:
  path:

封装

MessageDB

MessageDB以单例实现，提供以下功能。

数据库初始化
表初始化
数据库打开关闭
是持有表对象【SessionListTable、SessionChatTable、】

class MessageDB {
  // 单例公开访问点
  factory MessageDB() => _sharedInstance();

  static MessageDB get instance => _sharedInstance();

  // 静态私有成员，没有初始化
  static MessageDB _instance;

  // 私有构造函数
  MessageDB._() {
    // 具体初始化代码
  }

  // 静态、同步、MessageDB
  static MessageDB _sharedInstance() {
    if (_instance == null) {
      _instance = MessageDB._();
    }
    return _instance;
  }

  /// init db
  Future database;
  final SessionListTable sessionListTable = SessionListTable();
  final SessionChatTable sessionChatTable = SessionChatTable();

  initDB() async {
    try {
      String uid = UserManager.instance.userInfo.uid;
      database = openDatabase(
        // Set the path to the database.
        // 需要升级可以直接修改数据库名称
        join(await getDatabasesPath(), 'message_database_v1_$uid.db'),
        // When the database is first created, create a table to store dogs.
        onCreate: (db, version) {
          // Run the CREATE TABLE statement on the database.
          try {
            Batch batch = db.batch();
            _createTable().forEach((element) {
              batch.execute(element);
            });
            batch.commit();
          } catch (err) {
            throw (err);
          }
        },
        onUpgrade: (Database db, int oldVersion, int newVersion) {
          try {
            Batch batch = db.batch();
            _createTable().forEach((element) {
              batch.execute(element);
            });
            batch.commit();
          } catch (err) {
            throw (err);
          }
        },
        // Set the version. This executes the onCreate function and provides a
        // path to perform database upgrades and downgrades.
        version: 1,
      );
      sessionListTable.database = database;
      sessionChatTable.database = database;
    } catch (err) {
      throw (err);
    }
  }

  /// close db
  closeDB() async {
    await database
      ..close();
  }

  /// create table
  List _createTable() {
    return [sessionListTable.createTable(), sessionChatTable.createTable()];
  }
}

SessionTableListener

SessionTableListener作为抽象类，提供以下接口。

abstract class SessionTableListener {
  Future database;

  createTable();

  insertList(List values);

  queryListMaxVersionId({num id});

  queryList({num id});

  deleteItem(num id);
}

SessionListTable和SessionChatTable继承SessionTableListener实现对表数据的增删查改操作。

SessionListTable实现如下。

class SessionListTable implements SessionTableListener {

  @override
  Future database;

  final String sessionListTable = 'session_list';

  @override
  createTable() {
    return "CREATE TABLE IF NOT EXISTS $sessionListTable ("
        "peer_id INTEGER PRIMARY KEY,"
        " last_msg_id INTEGER,"
        " unread_count INTEGER,"
        " version_id INTEGER,"
        " update_time INTEGER,"
        " last_msg TEXT,"
        " contact_type INTEGER,"
        " contact_user TEXT,"
        " unread_gift_count INTEGER,"
        " del_status INTEGER,"
        " top_weight INTEGER,"
        " sort_key INTEGER,"
        " stick INTEGER)";
  }

  ///插入会话列表
  @override
  insertList(List values) async {
    // Get a reference to the database.
    final Database db = await database;

    // Insert the Dog into the correct table. You might also specify the
    // `conflictAlgorithm` to use in case the same maps is inserted twice.
    //
    // In this case, replace any previous data.
    try {
      Batch batch = db.batch();
      values.forEach((element) {
        Map values = Map();
        values['peer_id'] = element['peer_id'];
        values['last_msg_id'] = element['last_msg_id'];
        values['unread_count'] = element['unread_count'];
        values['version_id'] = element['version_id'];
        values['update_time'] = element['update_time'];
        values['last_msg'] = element['last_msg'];
        values['contact_type'] = element['contact_type'];
        values['contact_user'] = element['contact_user'];
        values['unread_gift_count'] = element['unread_gift_count'];
        values['del_status'] = element['del_status'];
        values['top_weight'] = element['top_weight'];
        values['sort_key'] = element['sort_key'];
        values['stick'] = element['stick'];

        batch.insert(
          sessionListTable,
          values,
          conflictAlgorithm: ConflictAlgorithm.replace,
        );
      });
      await batch.commit();
    } catch (err) {
      throw err;
    }
  }

  ///查询会话列表最大的version id
  @override
  queryListMaxVersionId({num id}) async {
    final Database db = await database;
    List maps = await db.query(sessionListTable, orderBy: 'version_id DESC', limit: 1);
    if (maps.length>0) {
      return maps[0]['version_id'];
    }
    else {
      return 0;
    }
  }

  ///查询所有的会话列表
  @override
  queryList({num id}) async {
    // Get a reference to the database.
    final Database db = await database;

    //联系人类型 0 普通 1 打招呼 100 系统
    // Query the table for all The maps.
    final List> maps = await db.query(sessionListTable,
        where: 'del_status = ? AND contact_type != ?',
        whereArgs: [0, 100],
        orderBy: 'sort_key DESC');

    return maps;
  }

  ///会话删除
  @override
  deleteItem(num id) async {
    // Get a reference to the database.
    final Database db = await database;

    await db.delete(sessionListTable, where: 'peer_id = ?', whereArgs: [id]);
  }

  ///所有会话未读数
  querySessionAllUnRead() async {
    // Get a reference to the database.
    final Database db = await database;

    //联系人类型 0 普通 1 打招呼 100 系统
    final List> maps = await db.query(sessionListTable,
        columns: ['unread_count'],
        where: 'unread_count > ? AND contact_type != ?',
        whereArgs: [0, 100]);
    int count = maps.fold(0, (previousValue, element) => previousValue+element['unread_count']);
    return count;
  }

  ///所有会话标记已读
  updateSessionMarkAllRead() async {
    // Get a reference to the database.
    final Database db = await database;

    await db.update(sessionListTable, {'unread_count':0});
  }

  ///会话标记已读
  updateSessionMarkRead(num id) async {
    // Get a reference to the database.
    final Database db = await database;

    await db.update(sessionListTable, {'unread_count':0}, where: 'peer_id = ?', whereArgs: [id]);
  }

}

问题

异步初始化数据库

//初始化数据库
MessageDB.instance.initDB();

登录成功之后，初始化数据库为异步操作。同时会拉取会话列表，这时可能数据库还未初始化完成。解决办法，延迟2s后再拉取会话列表。

Future.delayed(Duration(seconds: 2), () {
      MessageDB.instance.sessionChatTable.queryList(id: _peerUser.id)
});

数据库升级

升级表或字段，修改version，会调用onUpgrade方法，可以在此处升级。

// Set the version. This executes the onCreate function and provides a
// path to perform database upgrades and downgrades.
version: 1,

如果业务比较简单，本地数据不是很重要，服务端会同步数据。不如简单粗暴，直接更改数据库名称，重新创建数据库。

  database = openDatabase(
    // Set the path to the database.
    // 需要升级可以直接修改数据库名称
    join(await getDatabasesPath(), 'message_database_v1_$uid.db'),

v1改为v2

添加新的字段

  insertList(List values) async {
    // Get a reference to the database.
    final Database db = await database;

    // Insert the Dog into the correct table. You might also specify the
    // `conflictAlgorithm` to use in case the same maps is inserted twice.
    //
    // In this case, replace any previous data.
    try {
      Batch batch = db.batch();
      values.forEach((element) {
        Map values = Map();
        values['peer_id'] = element['peer_id'];
        values['last_msg_id'] = element['last_msg_id'];
        values['unread_count'] = element['unread_count'];
        values['version_id'] = element['version_id'];
        values['update_time'] = element['update_time'];
        values['last_msg'] = element['last_msg'];
        values['contact_type'] = element['contact_type'];
        values['contact_user'] = element['contact_user'];
        values['unread_gift_count'] = element['unread_gift_count'];
        values['del_status'] = element['del_status'];
        values['top_weight'] = element['top_weight'];
        values['sort_key'] = element['sort_key'];
        values['stick'] = element['stick'];

        batch.insert(
          sessionListTable,
          values,
          conflictAlgorithm: ConflictAlgorithm.replace,
        );
      });
      await batch.commit();
    } catch (err) {
      throw err;
    }
  }

不要把List values直接传入table，如果map包含table不存在的数据，就会插入失败。为了保证传入的map包含的key都存在table的字段，对values的map需要的字段做一次解析，再传入sql。