flutter数据库-moor

官方文档：https://moor.simonbinder.eu/docs/

配置：

dependencies:
  flutter:
    sdk: flutter


  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^1.0.2

  moor: ^4.3.2
  sqlite3_flutter_libs: ^0.5.0
  path_provider: ^2.0.2
#  path: ^1.8.0

dev_dependencies:
  flutter_test:
    sdk: flutter

  moor_generator: ^4.3.1
  build_runner: ^2.0.5

创建：

import 'dart:io';

import 'package:moor/ffi.dart';
import 'package:moor/moor.dart';
import 'package:path/path.dart' as p;
import 'package:path_provider/path_provider.dart';

// assuming that your file is called filename.dart. This will give an error at first,
// but it's needed for moor to know about the generated code
part 'moor_database.g.dart';

// this will generate a table called "todos" for us. The rows of that table will
// be represented by a class called "Todo".
class Todos extends Table {
  IntColumn get id => integer().autoIncrement()();
  TextColumn get title => text().withLength(min: 6, max: 32)();
  TextColumn get content => text().named('body')();
  IntColumn get category => integer().nullable()();
}

// This will make moor generate a class called "Category" to represent a row in this table.
// By default, "Categorie" would have been used because it only strips away the trailing "s"
// in the table name.
@DataClassName("Category")
class Categories extends Table {
  IntColumn get id => integer().autoIncrement()();
  TextColumn get description => text()();
}

LazyDatabase _openConnection() {
  // the LazyDatabase util lets us find the right location for the file async.
  return LazyDatabase(() async {
    // put the database file, called db.sqlite here, into the documents folder
    // for your app.
    final dbFolder = await getApplicationDocumentsDirectory();
    final file = File(p.join(dbFolder.path, 'db.sqlite'));
    return VmDatabase(file);
  });
}

@UseMoor(tables: [Todos, Categories])
class MyDatabase extends _$MyDatabase {
  // we tell the database where to store the data with this constructor
  MyDatabase() : super(_openConnection());

  // you should bump this number whenever you change or add a table definition. Migrations
  // are covered later in this readme.
  @override
  int get schemaVersion => 1;

  //增

// returns the generated id
  Future addTodo(TodosCompanion entry) {
    return into(todos).insert(entry);
  }

  //删

  Future feelingLazy() {
    // delete the oldest nine tasks
    return (delete(todos)..where((t) => t.id.isSmallerThanValue(10))).go();
  }

  //改

  Future moveImportantTasksIntoCategory(Category target) {
    // for updates, we use the "companion" version of a generated class. This wraps the
    // fields in a "Value" type which can be set to be absent using "Value.absent()". This
    // allows us to separate between "SET category = NULL" (`category: Value(null)`) and not
    // updating the category at all: `category: Value.absent()`.
    return (update(todos)..where((t) => t.title.like('%Important%'))).write(
      TodosCompanion(
        category: Value(target.id),
      ),
    );
  }

  // Future update(Todo entry) {
  //   // using replace will update all fields from the entry that are not marked as a primary key.
  //   // it will also make sure that only the entry with the same primary key will be updated.
  //   // Here, this means that the row that has the same id as entry will be updated to reflect
  //   // the entry's title, content and category. As its where clause is set automatically, it
  //   // cannot be used together with where.
  //   return update(todos).replace(entry);
  // }

  //查

  // loads all todo entries
  Future> get allTodoEntries => select(todos).get();

  // watches all todo entries in a given category. The stream will automatically
  // emit new items whenever the underlying data changes.
  Stream> watchEntriesInCategory(Category c) {
    return (select(todos)..where((t) => t.category.equals(c.id))).watch();
  }
}

注意：

• part 'moor_database.g.dart';中moor_database是自己创建的文件名

  
  
  图片.png
• 使用命令行创建moor_database.g.dart文件
  只创建一次使用：

flutter packages pub run build_runner build

一直在动态创建：

flutter packages pub run build_runner watch

图片.png

图片.png

出现的问题：

1. Tables can't override primaryKey and use autoIncrement()
   主键和自增不能同时设置，设置自增就默认是主键了

2.生成的文件变量都是final，在空安全状况下使用的时候会出现问题
解决方法：

图片.png

targets:
  $default:
    builders:
      moor_generator:
        options:
          mutable_classes: true

配置地址