Floor

A supportive SQLite abstraction for your Flutter applications.

The Floor library provides a lightweight SQLite abstraction with automatic mapping between in-memory objects and database rows while still offering full control of the database with the use of SQL.

It's important to note that this library is not a full featured ORM like Hibernate and will never be. Thus not supporting automatic relationship mapping is intentional.

This package is still in an early phase and the API will likely change.

Build Status

Table of contents

  1. How to use this library
  2. Architecture
  3. Querying
  4. Persisting Data Changes
  5. Streams
  6. Transactions
  7. Entities
  8. Foreign Keys
  9. Indices
  10. Migrations
  11. Examples
  12. Naming
  13. Bugs and Feedback
  14. License

How to use this library

  1. 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: ^0.2.0
    
     dev_dependencies:
       floor_generator: ^0.2.0
       build_runner: ^1.2.8
    
  2. 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.

     import 'package:floor/floor.dart';
    
     @entity
     class Person {
       @primaryKey
       final int id;
    
       final String name;
    
       Person(this.id, this.name);
     }
    
  3. Creating a DAO

    This component is responsible for managing the 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.

     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);
     }
    
  4. 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.

    The class holds functionality for opening the database. _$open() is a function that will get implemented by running the code generator. The warning, of it not being implemented, will go away then.

     import 'package:floor/floor.dart';
     import 'package:path/path.dart';
     import 'package:sqflite/sqflite.dart' as sqflite;
    
     part 'database.g.dart'; // the generated code will be there
    
     @Database(version: 1, entities: [Person])
     abstract class AppDatabase extends FloorDatabase {
       static Future<AppDatabase> openDatabase() async => _$open();   
    
       PersonDao get personDao;
     }
    
  5. 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.

  6. 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.

  7. Use the generated code.

     final database = await AppDatabase.openDatabase();
    
     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 to create 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.

@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

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.

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

// usage
StreamBuilder<List<Person>>(
  stream: database.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. Another attribute foreignKeys allows to add 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 a 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.

@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);
}

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. Increase the database version and change the openDatabase method to take in a list of Migrations. This parameter has to get passed to the _$open() method. Define a Migration which specifies a startVersion, an endVersion and a function that executes SQL to migrate the data. Lastly, call openDatabase with your newly created Migration. 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 {
  static Future<AppDatabase> openDatabase(List<Migration> migrations) async =>
      _$open(migrations);
}

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

final database = await AppDatabase.openDatabase([migration1to2]);

Examples

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

Naming

Floor - the bottom layer of a Room.

Bugs and Feedback

For bugs, questions and discussions please use the Github Issues.

License

Copyright 2019 Vitus Ortner

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

Libraries

floor