SQLite扑朔迷离，数据库资产如何工作 [英] Sqlite in flutter, how database assets work

问题描述

我正在查看此( https://github.com/tekartik/sqflite/blob/master/doc/opening_asset_db.md )用于填充已格式化且需要应用程序的数据，仅用于读取功能.

I am looking at this (https://github.com/tekartik/sqflite/blob/master/doc/opening_asset_db.md) for populating data that is already formatted and need for the app, for read functionality only.

因此，当我已经在外部csv文件中拥有所有信息时，我对创建sqlite数据库的理解是，在我的应用程序的.dart文件中创建类模型，例如

So my understanding of creating a sqlite database when we already have all the information in an outside csv file is to, create the class models in a .dart file in my app, such as

class User {

  int id;
  String _firstName;
  String _lastName;
  String _dob;

  User(this._firstName, this._lastName, this._dob);

  User.map(dynamic obj) {
    this._firstName = obj["firstname"];
    this._lastName = obj["lastname"];
    this._dob = obj["dob"];
  }

  String get firstName => _firstName;

  String get lastName => _lastName;

  String get dob => _dob;

  Map<String, dynamic> toMap() {
    var map = new Map<String, dynamic>();
    map["firstname"] = _firstName;
    map["lastname"] = _lastName;
    map["dob"] = _dob;
    return map;
  }
  void setUserId(int id) {
    this.id = id;
  }
}

然后，如果我有一个包含所有用户信息的csv文件(其值与用户类相对应)，是否可以使用数据库资产填写该信息，然后在其中调用扑扑的应用程序?我意识到可能有很多方法可以解决此问题，但是.db文件到底存储了什么，以及它的格式如何?我可以在此.db文件中实现.csv文件吗?

then if i have a csv file with all the user information inside of it (with values that correspond to the user class), could i be using the database asset to have that fill out the information and then call to it inside of the flutter app? I realize there are probably many ways to go about this, but What exactly is the .db file storing, and how is it formatted? Can i implement a .csv file into this .db file?

推荐答案

首先，您需要从csv构建一个sqlite数据库.这可以通过以下方式完成:

First off, you will need to construct a sqlite database from your csv. This can be done in the following way:

1. 创建必要的表(users.sql)

1. Create the necessary table (users.sql)

CREATE TABLE users(
   firstname TEXT NOT NULL,
   lastname TEXT NOT NULL,
   dob TEXT NOT NULL
);

创建sqlite数据库

Create the sqlite database

sqlite3 database.db < users.sql

插入csv数据

Insert the csv data

sqlite3 database.db
.mode csv
.import data.csv users

将database.db放入您的资产中，并将其添加到pubspec.yaml中.

Put database.db into your assets and add that in pubspec.yaml.

flutter:
  # ...
  assets:
    - assets/database.db

在您的应用中，您必须将资产文件复制到文档"中.这有点复杂.

In your app, you'll have to copy the asset file into "documents". This is slightly complicated.

// Construct a file path to copy database to
Directory documentsDirectory = await getApplicationDocumentsDirectory();
String path = join(documentsDirectory.path, "asset_database.db");

// Only copy if the database doesn't exist
if (FileSystemEntity.typeSync(path) == FileSystemEntityType.notFound){
  // Load database from asset and copy
  ByteData data = await rootBundle.load(join('assets', 'database.db'));
  List<int> bytes = data.buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);

  // Save copied asset to documents
  await new File(path).writeAsBytes(bytes);
}

最后，您可以像这样访问数据库.

Lastly, you can access the database like so.

Directory appDocDir = await getApplicationDocumentsDirectory();
String databasePath = join(appDocDir.path, 'asset_database.db');
this.db = await openDatabase(databasePath);
initialized = true;

示例查询(this._initialize()是步骤6)

Example query (this._initialize() is step 6)

Future<List<Page>> search(String word, int parentId) async {
    if (!initialized) await this._initialize();
    String query = '''
      SELECT * FROM users
      LIMIT 25''';
    return await this.db.rawQuery(query);
}

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