@loopback/sequelize

This is a loopback4 extension that provides Sequelize’s query builder at repository level in any loopback 4 application. It has zero learning curve as it follows similar interface as DefaultCrudRepository. For relational databases, Sequelize is a popular ORM of choice.

For pending features, refer to the Limitations section below.

Stability: ⚠️Experimental⚠️

Experimental packages provide early access to advanced or experimental functionality to get community feedback. Such modules are published to npm using 0.x.y versions. Their APIs and functionality may be subject to breaking changes in future releases.

Installation

To install this extension in your Loopback 4 project, run the following command:

npm install @loopback/sequelize

You’ll also need to install the driver for your preferred database:

# One of the following:
npm install --save pg pg-hstore # Postgres
npm install --save mysql2
npm install --save mariadb
npm install --save sqlite3
npm install --save tedious # Microsoft SQL Server
npm install --save oracledb # Oracle Database

Usage

You can watch a video overview of this extension by clicking here.

Both newly developed and existing projects can benefit from the extension by simply changing the parent classes in the target Data Source and Repositories.

Step 1: Configure DataSource

Change the parent class from juggler.DataSource to SequelizeDataSource like below.

// ...
import {SequelizeDataSource} from '@loopback/sequelize';

// ...
export class PgDataSource
  extends SequelizeDataSource
  implements LifeCycleObserver {
  // ...
}

SequelizeDataSource accepts commonly used config in the same way as LoopBack did. So in most cases you won’t need to change your existing configuration. But if you want to use sequelize specific options pass them in sequelizeOptions like below:

let config = {
  name: 'db',
  connector: 'postgresql',
  sequelizeOptions: {
    username: 'postgres',
    password: 'secret',
    dialectOptions: {
      ssl: {
        rejectUnauthorized: false,
        ca: fs.readFileSync('/path/to/root.crt').toString(),
      },
    },
  },
};

Note: Options provided in sequelizeOptions will take priority over others, For example, if you have password specified in both config.password and config.password.sequelizeOptions the latter one will be used.

Step 2: Configure Repository

Change the parent class from DefaultCrudRepository to SequelizeCrudRepository like below.

// ...
import {SequelizeCrudRepository} from '@loopback/sequelize';

export class YourRepository extends SequelizeCrudRepository<
  YourModel,
  typeof YourModel.prototype.id,
  YourModelRelations
> {
  // ...
}

Relations

Supported Loopback Relations

With SequelizeCrudRepository, you can utilize following relations without any additional configuration:

1. HasMany Relation
2. BelongsTo Relation
3. HasOne Relation
4. HasManyThrough Relation
5. ReferencesMany Relation

The default relation configuration, generated using the lb4 relation command (i.e. inclusion resolvers in the repository and property decorators in the model), remain unchanged.

INNER JOIN

Check the demo video of using inner joins here: https://youtu.be/ZrUxIk63oRc?t=76

When using SequelizeCrudRepository, the find(), findOne(), and findById() methods accept a new option called required in the include filter. Setting this option to true will result in an inner join query that explicitly requires the specified condition for the child model. If the row does not meet this condition, it will not be fetched and returned.

An example of the filter object might look like this to fetch the books who contains “Art” in their title, which belongs to category “Programming”:

{
  "where": {"title": {"like": "%Art%"}},
  "include": [
    {
      "relation": "category",
      "scope": {
        "where": {
          "name": "Programming"
        }
      },
      "required": true // 👈
    }
  ]
}

SQL Transactions

A Sequelize repository can perform operations in a transaction using the beginTransaction() method.

Isolation levels

When you call beginTransaction(), you can optionally specify a transaction isolation level. It support the following isolation levels:

• Transaction.ISOLATION_LEVELS.READ_UNCOMMITTED (default)
• Transaction.ISOLATION_LEVELS.READ_COMMITTED
• Transaction.ISOLATION_LEVELS.REPEATABLE_READ
• Transaction.ISOLATION_LEVELS.SERIALIZABLE

Options

Following are the supported options:

{
  autocommit?: boolean;
  isolationLevel?: Transaction.ISOLATION_LEVELS;
  type?: Transaction.TYPES;
  deferrable?: string | Deferrable;
  /**
   * Parent transaction.
   */
  transaction?: Transaction | null;
}

Example

// Get repository instances. In a typical application, instances are injected
// via dependency injection using `@repository` decorator.
const userRepo = await app.getRepository(UserRepository);

// Begin a new transaction.
// It's also possible to call `userRepo.dataSource.beginTransaction` instead.
const tx = await userRepo.beginTransaction({
  isolationLevel: Transaction.ISOLATION_LEVELS.SERIALIZABLE,
});

try {
  // Then, we do some calls passing this transaction as an option:
  const user = await userRepo.create(
    {
      firstName: 'Jon',
      lastName: 'Doe',
    },
    {transaction: tx},
  );

  await userRepo.updateById(
    user.id,
    {
      firstName: 'John',
    },
    {transaction: tx},
  );

  // If the execution reaches this line, no errors were thrown.
  // We commit the transaction.
  await tx.commit();
} catch (error) {
  // If the execution reaches this line, an error was thrown.
  // We rollback the transaction.
  await tx.rollback();
}

Switching from loopback defaults to sequelize transaction is as simple as this commit in loopback4-sequelize-transaction-example.

Debug strings reference

There are three built-in debug strings available in this extension to aid in debugging. To learn more about how to use them, see this page.

Limitations

Please note, the current implementation does not support the following:

1. Loopback Migrations (via default migrate.ts). Though you’re good if using external packages like db-migrate.

Community contribution is welcome.

Contributions

• Guidelines
• Join the team

Tests

Run npm test from the root folder.

Contributors

See all contributors.

License

MIT