Flutter 数据库ORM框架floor使用详解

选型

数据库ORM框架可以提高开发效率，不用写一大堆的sql

网上搜了下，资料不多，官方也没有提供，第三方框架有但是在GitHub上的star数量都不高，以下是几个star数量比较靠前的：

对比了下，最后㐊选择了floor，因为它的API调用看起来比较舒服，和Android官方的Room框架比较类似。

使用方法

使用方法比较简单，直接看floor或者GitHub上的的文档写得很清晰，如果之前有用过Android的其他ORM框架的话，入手很快，直接看官方文档里的示例代码基本知道怎么用了。

这里直接copy官网上的文档，方便自己也方便大家查阅，基于版本0.9.0，如果有最新版本，可以到pub.dev或者GitHub查看

Table of contents #

How to use this library #

Add the runtime dependency floor as well as the generator floor_generator to your pubspec.yaml. The third dependency is build_runner which has to be included as a dev dependency just like the generator.
- floor holds all the code you are going to use in your application.
- floor_generator includes the code for generating the database classes.
- build_runner enables a concrete way of generating source code files.
```
 dependencies:
   flutter:
     sdk: flutter
   floor: ^0.9.0

 dev_dependencies:
   floor_generator: ^0.9.0
   build_runner: ^1.7.1
```
Creating an Entity

It will represent a database table as well as the scaffold of your business object. @entity marks the class as a persistent class. It's required to add a primary key to your table. You can do so by adding the @primaryKey annotation to an int property. There is no restriction on where you put the file containing the entity.
```
 // entity/person.dart

 import 'package:floor/floor.dart';

 @entity
 class Person {
   @primaryKey
   final int id;

   final String name;

   Person(this.id, this.name);
 }
```
Creating a DAO

This component is responsible for managing access to the underlying SQLite database. The abstract class contains the method signatures for querying the database which have to return a Future.
- You can define queries by adding the @Query annotation to a method. The SQL statement has to get added in parenthesis. The method must return a Future of the Entity you're querying for.
- @insert marks a method as an insertion method.
```
 // dao/person_dao.dart   

 import 'package:floor/floor.dart';

 @dao
 abstract class PersonDao {
   @Query('SELECT * FROM Person')
   Future<List<Person>> findAllPersons();

   @Query('SELECT * FROM Person WHERE id = :id')
   Future<Person> findPersonById(int id);

   @insert
   Future<void> insertPerson(Person person);
 }
```

Creating the Database

It has to be an abstract class which extends FloorDatabase. Furthermore, it's required to add @Database() to the signature of the class. Make sure to add the created entity to the entities attribute of the @Database annotation.

In order to make the generated code work, it's required to also add the listed imports.

 // database.dart

 // required package imports
 import 'dart:async';
 import 'package:floor/floor.dart';
 import 'package:path/path.dart';
 import 'package:sqflite/sqflite.dart' as sqflite;   

 import 'dao/person_dao.dart';
 import 'model/person.dart';   

 part 'database.g.dart'; // the generated code will be there

 @Database(version: 1, entities: [Person])
 abstract class AppDatabase extends FloorDatabase {
   PersonDao get personDao;
 }

Make sure to add part 'database.g.dart'; beneath the imports of this file. It's important to note, that 'database' has to get exchanged with the name of the file the entity and database is defined in. In this case, the file is named database.dart.
Run the generator with flutter packages pub run build_runner build. To automatically run it, whenever a file changes, use flutter packages pub run build_runner watch.
Use the generated code. For obtaining an instance of the database, use the generated $FloorAppDatabase class, which allows access to a database builder. The name is composited from $Floor and the database class name. The string passed to databaseBuilder() will be the database file name. For initializing the database, call build().
```
 final database = await $FloorAppDatabase.databaseBuilder('app_database.db').build();

 final person = await database.findPersonById(1);
 await database.insertPerson(person);
```

For further examples take a look at the example and floor_test directories.

Architecture #

The components for storing and accessing data are Entity, Data Access Object (DAO) and Database.

The first, Entity, represents a persistent class and thus a database table. DAOs manage the access to Entities and take care of the mapping between in-memory objects and table rows. Lastly, Database, is the central access point to the underlying SQLite database. It holds the DAOs and, beyond that, takes care of initializing the database and its schema. Room serves as the source of inspiration for this composition, because it allows creating a clean separation of the component's responsibilities.

The figure shows the relationship between Entity, DAO and Database.

Floor Architecture

Querying #

Method signatures turn into query methods by adding the @Query() annotation with the query in parenthesis to them. Be patient about the correctness of your SQL statements. They are only partly validated while generating the code. These queries have to return either a Future or a Stream of an entity or void. Returning Future<void> comes in handy whenever you want to delete the full content of a table, for instance. Some query method examples can be seen in the following.

@Query('SELECT * FROM Person WHERE id = :id')
Future<Person> findPersonById(int id);

@Query('SELECT * FROM Person WHERE id = :id AND name = :name')
Future<Person> findPersonByIdAndName(int id, String name);

@Query('SELECT * FROM Person')
Future<List<Person>> findAllPersons(); // select multiple items

@Query('SELECT * FROM Person')
Stream<List<Person>> findAllPersonsAsStream(); // stream return

@Query('DELETE FROM Person')
Future<void> deleteAllPersons(); // query without returning an entity

@Query('SELECT * FROM Person WHERE id IN (:ids)')
Future<List<Person>> findPersonsWithIds(List<int> ids); // query with IN clause

Query arguments, when using SQLite's LIKE operator, have to be supplied by the input of a method. It's not possible to define a pattern matching argument like %foo% in the query itself.

// dao
@Query('SELECT * FROM Person WHERE name LIKE :name')
Future<List<City>> findPersonsWithNamesLike(String name);

// usage
final name = '%foo%';
await dao.findPersonsWithNamesLike(name);

Persisting Data Changes #

Use the @insert, @update and @delete annotations for inserting and changing persistent data. All these methods accept single or multiple entity instances.

Insert

@insert marks a method as an insertion method. When using the capitalized @Insert you can specify a conflict strategy. Else it just defaults to aborting the insert. These methods can return a Future of either void, int or List<int>.
- void return nothing
- int return primary key of inserted item
- List<int> return primary keys of inserted items
Update

@update marks a method as an update method. When using the capitalized @Update you can specify a conflict strategy. Else it just defaults to aborting the update. These methods can return a Future of either void or int.
- void return nothing
- int return number of changed rows
Delete

@delete marks a method as a deletion method. These methods can return a Future of either void or int.
- void return nothing
- int return number of deleted rows

// examples of changing multiple items with return 

@insert
Future<List<int>> insertPersons(List<Person> person);

@update
Future<int> updatePersons(List<Person> person);

@delete
Future<int> deletePersons(List<Person> person);

Streams #

As already mentioned, queries can not only return a value once when called but also a continuous stream of query results. The returned stream keeps you in sync with the changes happening to the database table. This feature plays really well with the StreamBuilder widget.

These methods return a broadcast stream. Thus, it can have multiple listeners.

// definition
@Query('SELECT * FROM Person')
Stream<List<Person>> findAllPersonsAsStream();

// usage
StreamBuilder<List<Person>>(
  stream: dao.findAllPersonsAsStream(),
  builder: (BuildContext context, AsyncSnapshot<List<Person>> snapshot) {
    // do something with the values here
  },
);

Transactions #

Whenever you want to perform some operations in a transaction you have to add the @transaction annotation to the method. It's also required to add the async modifier. These methods can only return Future<void>.

@transaction
Future<void> replacePersons(List<Person> persons) async {
  await deleteAllPersons();
  await insertPersons(persons);
}

Entities #

An entity is a persistent class. Floor automatically creates the mappings between the in-memory objects and database table rows. It's possible to supply custom metadata to Floor by adding optional values to the Entity annotation. It has the additional attribute of tableName which opens up the possibility to use a custom name for that specific entity instead of using the class name. foreignKeys allows adding foreign keys to the entity. More information on how to use these can be found in the Foreign Keys section. Indices are supported as well. They can be used by adding an Index to the indices value of the entity. For further information of these, please refer to the Indices section.

@PrimaryKey marks property of a class as the primary key column. This property has to be of type int. The value can be automatically generated by SQLite when autoGenerate is enabled. For more information about primary keys and especially compound primary keys, refer to the Primary Keys section.

@ColumnInfo enables custom mapping of single table columns. With the annotation, it's possible to give columns a custom name and define if the column is able to store null.

@Entity(tableName: 'person')
class Person {
  @PrimaryKey(autoGenerate: true)
  final int id;

  @ColumnInfo(name: 'custom_name', nullable: false)
  final String name;

  Person(this.id, this.name);
}

Primary Keys #

Whenever a compound primary key is required (e.g. n-m relationships), the syntax for setting the keys differs from the previously mentioned way of setting primary keys. Instead of annotating a field with @PrimaryKey, the @Entity annotation's primaryKey attribute is used. It accepts a list of column names that make up the compound primary key.

@Entity(primaryKeys: ['id', 'name'])
class Person {
  final int id;

  final String name;

  Person(this.id, this.name);
}

Foreign Keys #

Add a list of ForeignKeys to the Entity annotation of the referencing entity. childColumns define the columns of the current entity, whereas parentColumns define the columns of the parent entity. Foreign key actions can get triggered after defining them for the onUpdate and onDelete properties.

@Entity(
  tableName: 'dog',
  foreignKeys: [
    ForeignKey(
      childColumns: ['owner_id'],
      parentColumns: ['id'],
      entity: Person,
    )
  ],
)
class Dog {
  @PrimaryKey()
  final int id;

  final String name;

  @ColumnInfo(name: 'owner_id')
  final int ownerId;

  Dog(this.id, this.name, this.ownerId);
}

Indices #

Indices help speeding up query, join and grouping operations. For more information on SQLite indices please refer to the official documentation. To create an index with floor, add a list of indices to the @Entity annotation. The example below shows how to create an index on the custom_name column of the entity.

The index, moreover, can be named by using its name attribute. To set an index to be unique, use the unique attribute.

@Entity(tableName: 'person', indices: [Index(value: ['custom_name'])])
class Person {
  @primaryKey
  final int id;

  @ColumnInfo(name: 'custom_name', nullable: false)
  final String name;

  Person(this.id, this.name);
}

Migrations #

Whenever are doing changes to your entities, you're required to also migrate the old data.

First, update your entity. Next, Increase the database version. Define a Migration which specifies a startVersion, an endVersion and a function that executes SQL to migrate the data. At last, use addMigrations() on the obtained database builder to add migrations. Don't forget to trigger the code generator again, to create the code for handling the new entity.

// update entity with new 'nickname' field
@Entity(tableName: 'person')
class Person {
  @PrimaryKey(autoGenerate: true)
  final int id;

  @ColumnInfo(name: 'custom_name', nullable: false)
  final String name;
  
  final String nickname;

  Person(this.id, this.name, this.nickname);
}

// bump up database version
@Database(version: 2)
abstract class AppDatabase extends FloorDatabase {
  PersonDao get personDao;
}

// create migration
final migration1to2 = Migration(1, 2, (database) {
  database.execute('ALTER TABLE person ADD COLUMN nickname TEXT');
});

final database = await $FloorAppDatabase
    .databaseBuilder('app_database.db')
    .addMigrations([migration1to2])
    .build();

In-Memory Database #

To instantiate an in-memory database, use the static inMemoryDatabaseBuilder() method of the generated $FloorAppDatabase class instead of databaseBuilder().

final database = await $FloorAppDatabase.inMemoryDatabaseBuilder('app_database.db').build();

Callback #

In order to hook into Floor's database initialization process, Callback should be used. It allows the invocation of three separate callbacks which are triggered when the database has been

initialized for the first time (onCreate).
opened (onOpen).
upgraded (onUpgrade).

Each callback is optional.

Their usage can be seen in the following snippet.

final callback = Callback(
   onCreate: (database, version) { /* database has been created */ },
   onOpen: (database) { /* database has been opened */},
   onUpgrade: (database, startVersion, endVersion) { /* database has been upgraded */ },
);

final database = await $FloorAppDatabase
    .databaseBuilder('app_database.db')
    .addCallback(callback)
    .build();

Examples #