Getting started with sql

Learn how to get started with the SQL version of moor, or how to migrate an existing project to moor.

The regular getting started guide explains how to get started with moor by declaring both tables and queries in Dart. This version will focus on how to use moor with SQL instead.

Adding the dependency

First, lets add moor to your project’s pubspec.yaml. At the moment, the current version of moor_flutter is Flutter version and the current version of moor_generator is Generator version

dependencies:
  moor_flutter: # use the latest version

dev_dependencies:
  moor_generator: # use the latest version
  build_runner: 

The moor_flutter package will execute sql at runtime, while the moor_generator will generate typesafe Dart based on your SQL queries.

Declaring tables and queries

To declare tables and queries in sql, create a file called tables.moor next to your Dart files (for instance in lib/database/tables.moor).

You can put the CREATE TABLE statements for your queries in there. The following example creates two tables to model a todo-app. If you’re migrating an existing project to moor, you would put the CREATE TABLE for your tables in there.

-- this is the tables.moor file
CREATE TABLE todos (
    id INT NOT NULL PRIMARY KEY AUTOINCREMENT,
    title TEXT,
    body TEXT,
    category INT REFERENCES categories (id)
);

CREATE TABLE categories (
    id INT NOT NULL PRIMARY KEY AUTOINCREMENT,
    description TEXT,
) AS Category; -- see the explanation on "AS Category" below

/* after declaring your tables, you can put queries in here. Just
   write the name of the query, a colon (:) and the SQL: */
todosInCategory: SELECT * FROM todos WHERE category = ?;

/* Here's a more complex query: It counts the amount of entries per 
category, including those entries which aren't in any category at all. */
countEntries:     
  SELECT
    c.desc,
    (SELECT COUNT(*) FROM todos WHERE category = c.id) AS amount
  FROM categories c
  UNION ALL
  SELECT null, (SELECT COUNT(*) FROM todos WHERE category IS NULL)

Generating matching code

After you declared the tables, lets generate some Dart code to actually run them. Moor needs to know which tables are used in a database, so we have to write a small Dart class that moor will then read. Lets create a file called database.dart next to the tables.moor file you wrote in the previous step.

import 'package:moor_flutter/moor_flutter.dart';

part 'database.g.dart';

@UseMoor(
  include: {'tables.moor'},
)
class AppDb extends _$AppDb {
  AppDb() : super(FlutterQueryExecutor.inDatabaseFolder('app.db'));

  @override
  int get schemaVersion => 1;
}

To generate the database.g.dart file which contains the _$AppDb superclass, run flutter pub run build_runner build on the command line.

What moor generates

Let’s take a look at what moor generated during the build:

  • Generated data classes (Todo and Category) - these hold a single row from the respective table.
  • Companion versions of these classes. Those are only relevant when using the Dart apis of moor, you can learn more here.
  • A CountEntriesResult class, it holds the result rows when running the countEntries query.
  • A _$AppDb superclass. It takes care of creating the tables when the database file is first opened. It also contains typesafe methods for the queries declared in the tables.moor file:
    • a Selectable<Todo> todosInCategory(int) method, which runs the todosInCategory query declared above. Moor has determined that the type of the variable in that query is int, because that’s the type of the category column we’re comparing it to.
      The method returns a Selectable to indicate that it can both be used as a regular query (Selectable.get returns a Future<List<Todo>>) or as an auto-updating stream (by using .watch instead of .get()).
    • a Selectable<CountEntriesResult> countEntries() method, which runs the other query when used.

By the way, you can also put insert, update and delete statements in a .moor file - moor will generate matching code for them as well.

Learning more

Know that you know how to use moor together with sql, here are some further guides to help you learn more:

Last modified October 1, 2019: More guides for moor 2.0 (742cec4)