drift_crdt 1.0.11

A Flutter-only implementation of a drift CRDT database, based on the `sqlite_crdt` package and `sqflite`.

drift_crdt

drift_crdt contains a CRDT drift database implementation based on the sqflite package. This package is a plugin for Drift by Simon Binder and is based on Simon Binder's drift_sqflite package.

For more information on drift, see its documentation.

Usage

The CrdtQueryExecutor class can be passed to the constructor of your drift database class to make it use sqflite.

@DriftDatabase(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 the documentation.
  @override
  int get schemaVersion => 1;
}

QueryExecutor _openConnection() {
  return CrdtQueryExecutor.inDatabaseFolder(path: 'db.sqlite');
}

Drift migrations

At the moment migrations are not supported. This is because the CRDT implementation hijacks the SQL queries and modifies them to manage the CRDT functions.

However, the migrations can be made to work.

1. Create the migrations as usual.

2. Create closures for generating the columns

Add CRDT related closures to the top of the schema_versions.dart file like this:

i1.GeneratedColumn<int> _column_is_deleted(String aliasedName) =>
    i1.GeneratedColumn<int>('is_deleted', aliasedName, false,
        type: i1.DriftSqlType.int, defaultValue: i1.Constant(0));
i1.GeneratedColumn<String> _column_hlc(String aliasedName) =>
    i1.GeneratedColumn<String>(
      'hlc',
      aliasedName,
      false,
      type: i1.DriftSqlType.string,
    );
i1.GeneratedColumn<String> _column_node_id(String aliasedName) =>
    i1.GeneratedColumn<String>('node_id', aliasedName, false,
        type: i1.DriftSqlType.string);
i1.GeneratedColumn<String> _column_modified(String aliasedName) =>
    i1.GeneratedColumn<String>('modified', aliasedName, false,
        type: i1.DriftSqlType.string);

3. Add the CRDT columns to the schema_versions

Assuming the columns field inside the VersionedTable object looks like this:

  late final Shape0 epochs = Shape0(
    source: i0.VersionedTable(
      entityName: 'epochs',
      withoutRowId: true,
      isStrict: false,
      tableConstraints: [
        'PRIMARY KEY(id)',
      ],
      columns: [
        _column_0,
        _column_1,
        _column_2,
        _column_3,
        _column_4,
        _column_5,
      ],
      attachedDatabase: database,
    ),
    alias: null);

Change it like this:

  late final Shape0 epochs = Shape0(
    source: i0.VersionedTable(
      entityName: 'epochs',
      withoutRowId: true,
      isStrict: false,
      tableConstraints: [
        'PRIMARY KEY(id)',
      ],
      columns: [
        _column_0,
        _column_1,
        _column_2,
        _column_3,
        _column_4,
        _column_5,
        _column_is_deleted,
        _column_hlc,
        _column_node_id,
        _column_modified,
      ],
      attachedDatabase: database,
    ),
    alias: null);

Then proceed to add the CRDT column references to every single shape class within the schema_versions file.

I would love to automate this process, but I don't have the tools to do it yet. If this plugin ever gets more popular, I am sure Simon will add a feature that will enable us to inject these shapes.

Until then, you will have to do it manually.

Querying in drift_crdt and you!

When performing queries by default deleted records are not returned.

The reason is that we want the CRDT implementation to be seamless and should not break your application by default.

However if you want to query for deleted records you can use the queryDeleted helper function.

Example, to get all users including deleted ones:

  final result = await queryDeleted(
    (db.executor) as CrdtQueryExecutor,
    () async => db.select(db.users).get()
  );

CRDT specific features

Use CrdtQueryExecutor.getLastModified to get the last modified timestamp of the database. See CrdtQueryExecutor.getLastModified for more information.

  final changeset = await (db.executor as CrdtQueryExecutor).getCLastModified();

Use CrdtQueryExecutor.getChangeset to get the changeset of the database. See CrdtQueryExecutor.getChangeset for more information.

  final changeset = await (db.executor as CrdtQueryExecutor).getChangeset();

Use 'CrdtQueryExecutor.merge' to merge a changeset into the database. See CrdtQueryExecutor.merge for more information.

  await (db.executor as CrdtQueryExecutor).merge(changeset);

Serialization into JSON

I am using the json_annotation package to serialize the changesets into and from JSON in my own project. You can see an example of such in the test suite of this package.

Note: The drift_crdt package is an alternative to the standard approach suggested in the drift documentation (which consists of a NativeDatabase instead of CrdtQueryExecutor).

Note: Hasn't been tested on iOS and Android yet.