Moor files

Learn everything about the new .moor files which can contain tables and queries

Moor files are a new feature that lets you write all your database code in SQL - moor will generate typesafe APIs for them.

Getting started

To use this feature, lets create two files: database.dart and tables.moor. The Dart file only contains the minimum code to setup the database:

import 'package:moor_flutter/moor_flutter.dart';

part 'database.g.dart';

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

  @override
  int get schemaVersion => 1;
}

We can now declare tables and queries in the moor file:

CREATE TABLE todos (
    id INT NOT NULL PRIMARY KEY AUTOINCREMENT,
    title TEXT NOT NULL,
    content TEXT NOT NULL,
    category INTEGER REFERENCES categories(id)
);

CREATE TABLE categories (
    id INT NOT NULL PRIMARY KEY AUTOINCREMENT,
    description TEXT NOT NULL
) AS Category; -- the AS xyz after the table defines the data class name

-- we can put named sql queries in here as well:
createEntry: INSERT INTO todos (title, content) VALUES (:title, :content);
deleteById: DELETE FROM todos WHERE id = :id;
watchAllTodos: SELECT * FROM todos;

After running the build runner with flutter pub run build_runner build, moor will write the database.g.dart file which contains the _$MoorDb superclass. Let’s take a look at what we got:

  • Generated data classes (Todo and Category), and companion versions for inserts (see Dart Interop for info). By default, moor strips a trailing “s” from the table name for the class. That’s why we used AS Category on the second table - it would have been called Categorie otherwise.
  • Methods to run the queries:
    • a Future<int> createEntry(String title, String content) method. It creates a new todo entry with the provided data and returns the id of the entry created.
    • Future<int> deleteById(int id): Deletes a todo entry by its id, and returns the amount of rows affected.
    • Selectable<AllTodosResult> allTodos(). It can be used to get, or watch, all todo entries. It can be used with allTodos().get() and allTodos().watch().
  • Classes for select statements that don’t match a table. In the example above, thats the AllTodosResult class, which contains all fields from todos and the description of the associated category.

Variables

We support regular variables (?), explictly indexed variables (?123) and colon-named variables (:id). We don’t support variables declared with @ or $. The compiler will attempt to infer the variable’s type by looking at its context. This lets moor generate typesafe apis for your queries, the variables will be written as parameters to your method.

Arrays

If you want to check whether a value is in an array of values, you can use IN ?. That’s not valid sql, but moor will desugar that at runtime. So, for this query:

entriesWithId: SELECT * FROM todos WHERE id IN ?;

Moor will generate a Selectable<Todo> entriesWithId(List<int> ids) method (entriesWithId([1,2]) would run SELECT * ... id IN (?1, ?2) and bind the arguments accordingly). To support this, we only have two restrictions:

  1. No explicit variables: Running WHERE id IN ?2 will be rejected at build time. As the variable is expanded, giving it a single index is invalid.
  2. No higher explicit index after a variable: Running WHERE id IN ? OR title = ?2 will also be rejected. Expanding the variable can clash with the explicit index, which is why moor forbids it. Of course, id IN ? OR title = ? will work as expected.

Supported column types

We use this algorithm to determine the column type based on the declared type name.

Additionally, columns that have the type name BOOLEAN or DATETIME will have bool or DateTime as their Dart counterpart. Both will be written as an INTEGER column when the table gets created.

Imports

You can put import statements at the top of a moor file:

import 'other.moor'; -- single quotes are required for imports

All tables reachable from the other file will then also be visible in the current file and to the database that includes it. Importing Dart files into a moor file will also work - then, all the tables declared via Dart tables can be used inside queries. We support both relative imports and the package: imports you know from Dart.

Dart interop

Moor files work perfectly together with moor’s existing Dart API:

  • you can write Dart queries for tables declared in a moor file: dart Future<void> insert(TodosCompanion companion) async { await into(todos).insert(companion); }
  • by importing Dart files into a moor file, you can write sql queries for tables declared in Dart.
  • generated methods for queries can be used in transactions, they work together with auto-updating queries, etc.

Dart components in SQL

You can make most of both SQL and Dart with “Dart Templates”, which is a Dart expression that gets inlined to a query at runtime. To use them, declare a $-variable in a query:

_filterTodos: SELECT * FROM todos WHERE $predicate;

Moor will generate a Selectable<Todo> _filterTodos(Expression<bool, BoolType> predicate) method which can be used to construct dynamic filters at runtime:

Stream<List<Todo>> watchInCategory(int category) {
    return _filterTodos(todos.category.equals(category)).watch();
}

This lets you write a single SQL query and dynamically apply a predicate at runtime! This feature also works for

  • expressions
  • single ordering terms: SELECT * FROM todos ORDER BY $term, id ASC will generate a method taking an OrderingTerm.
  • whole order-by clauses: SELECT * FROM todos ORDER BY $order
  • limit clauses: SELECT * FROM todos LIMIT $limit

Supported statements

At the moment, the following statements can appear in a .moor file.

  • import 'other.moor': Import all tables and queries declared in the other file into the current file.
  • DDL statements (CREATE TABLE): Declares a table. We don’t currently support indices and views, #162 tracks support for that.
  • Query statements: We support INSERT, SELECT, UPDATE and DELETE statements.

All imports must come before DDL statements, and those must come before the named queries.

If you need support for another statement, or if moor rejects a query you think is valid, please create an issue!