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    6.3.2 • Public • Published


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    Sequelize model based service, exposes basic CRUD methods, pub/sub mechanisms, computed properties through decorations.


    • node >= 7.10
    • typescript >= 2.4
    • inversify >= 4.13


    npm i inversify reflect-metadata @bluejay/sequelize-service


    Creating a SequelizeService

    The only required dependency is a Sequelize model.

    • TUserWriteProperties is an interface describing a user's properties used during write and update operations. It is recommended to require properties that are required to create the object and leaving the others as optional.
    • TUserReadProperties is an interface describing a user's properties used during read operations. It is recommend to define as readonly.
    • TUserComputedProperties is an interface describing the possible computed properties for a user object.
    • UserModel is the User Sequelize model.


    const userService = new SequelizeService<TUserWriteProperties, TUserReadProperties, TUserComputedProperties>(UserModel);

    Using inversify

    // TUserReadProperties is the most inclusive interface, describing all the fields from the User schema
    export class UserService extends SequelizeService<TUserWriteProperties, TUserReadProperties, TUserComputedProperties> {
      @inject(ID.UserModel) protected model: Sequelize.Model<TUserReadProperties, TUserReadProperties>;
    // ---
    // Make sure to declare the service as a singleton to ensure events are caught by all subscribers
    container.bind<ISequelizeService<TUserWriteProperties, TUserReadProperties, TUserComputedProperties>>(ID.UserService).to(UserService).inSingletonScope();


    All hooks and many methods receive a Session object which provides various handful methods to deal with a set of data, in a particular context.

    A Session inherits from Collection, so you can manipulate/iterate data asynchronous without the need of external libraries.

    Sessions also expose various methods related to the type of query you're currently dealing with. For example during an update:

    class UserService extends SequelizeService<TUserWriteProperties, TUserReadProperties, TUserComputedProperties> {
      // ...
      protected async beforeUpdate(session: UpdateSession<TUserWriteProperties, TUserReadProperties, TUserComputedProperties>) {
        session.getOption('transaction'); // Get the transaction under which this update is being performed
        session.hasFilter('email'); // Whether os not this update is filtered by email
        session.getValue('email'); // Get the update value of `email`, if present
        await session.fetch(); // Performs a select
        await session.ensureIdentified(); // Make sure all objects corresponding to the filters have their primary key set
        await session.ensureProperties({ select: ['email', 'age'] }); // Only performs a SELECT if not all objects have their age and email set
        // Run a callback for each user, in parallel
        await session.forEachParallel(async user => {
        // Run a callback for each user, in series
        await session.forEachSeries(async user => {
        // Get all the users IDs
        const ids = session.mapByProperty('id');

    You might notice that this documentation never refers to particular instances, this is because this entire module is based on sessions, which in turn encourage you to think all queries as bulk operations, and therefore optimize for multiple objects.


    All methods returning multiple objects return a Collection. Methods returning a single return an unwrapped object.

    Creating objects

    Creating a single object
    const user = await userService.create({ email: '', password: 'abcdefg' });
    console.log(; //
    Creating multiple objects
    const users = await userService.createMany([{ email: '', password: 'abcdefg' } /*, ...*/ ]);
    users.forEach(user => console.log(;

    Finding objects

    // Find multiple users
    const users = await userService.find({ email: { in: ['', ''] } });
    // Find a single user by its primary key
    const user = await userService.findByPrimaryKey(1);
    // Find multiple users by their primary key
    const users = await userService.findByPrimaryKeys([1, 2]);

    Updating objects

    // Change the user email to another value
    await userService.update({ email: 'foo@example.comn' }, { email: '' });
    // Target a user by primary key
    await userService.updateByPrimaryKey(1, {  email: '' });

    Upserting an obejct

    Caution: This methods will lock the "candidate" row, and perform either a create or an update depending on if a candidate was found.

    Note: For consistency, the created/updated row is always returned, meaning that we perform a SELECT after the update, if necessary.

    This method uses a more MongoDB like syntax, allowing you to pass complex filters as part of the matching criteria.

    // Make sure a user older than 21 exists
    await userService.replaceOne({ email: '', age: { gte: 21 } }, { email: '', age: 21 });

    Deleting objects

    // Remove all users younger than 21 
    await userService.delete({ age: { lt: 21 } });

    Counting objects

    const count = await userService.count({ age: { lt: 30 } });

    Working with transactions

    Note: All writing methods automatically create a transaction, which encapsulates both the hooks and the model call itself, meaning that if an afterCreate hooks fails, for example, the entire creation will be rolled back,.

    Creating a transaction

    Within your service, the protected transaction() method allows you to create a new transaction.

    return await this.transaction({}, async transaction => {
      // Your code here

    Ensuring a transaction

    There are times when you want to make sure you're running under a transaction, but not necessarily create a new one, if, for example, your current method's caller already created one.

    The transaction() method takes an options parameter, which may contain a transaction property, in which the transaction will be reused.

    return await this.transaction({}, async transaction => {
      return await this.transaction({ transaction }, newTransaction => {
        console.log(newTransaction === transaction); // true

    Passing transactions to methods

    All query methods accept an optional transaction.

    await userService.find({}, { transaction });
    await userService.create({ email: '', password: 'abcdefg' }, { transaction });

    Working with hooks

    Hooks are a convenient way to validate and transform you data.

    Hooks are ran for all write queries, before and after the query.

    class UserService extends SequelizeService<TUserWriteProperties, TUserReadProperties, TUserComputedProperties> {
      /// ...
      protected async beforeCreate(session: CreateSession<TUserWriteProperties, TUserReadProperties, TUserComputedProperties>) {
        await session.forEachParallel(async user => {
          // Your code here

    Working with events

    Computed properties

    Computed properties allow you to decorate objects with properties that are not stored in your DB.

    Computed properties are instances of the abstract ComputedProperty class and must implement their transform method, which takes a Session as an argument.

    class UserAge extends ComputedProperty<TUserWriteProperties, TUserReadProperties, TUserComputedProperties, number> { // "age" is a number
      public async transform(session: Session<TUserWriteProperties, TUserReadProperties, TUserComputedProperties>) { // "transform" is abstract and must be implemented
        session.forEach(user => {
          user.age = moment.duration(moment().diff(user.date_of_birth)).get('years'); // We set "age" on each object of the session, based on the date of birth
    class UserIsAdult extends ComputedProperty<TUserWriteProperties, TUserReadProperties, TUserComputedProperties, boolean> {
      public async transform(session: Session<TUserWriteProperties, TUserReadProperties, TUserComputedProperties>) {
        await session.ensureProperties({ compute: ['age'] }); // We make sure the age is set
        session.forEach(user => {
          user.isAdult = user.age >= 21

    To make your service aware of the computed properties, you need to create a manager:

    class UserComputedPropertiesManager extends UserComputedPropertiesManager<TUserWriteProperties, TUserReadProperties, TUserComputedProperties> {
      protected map() {
        return {
          age: new UserAge(),
          isAdult: { property: new UserIsAdult(), dependencies: ['age'] } // We make sure that the age is fetched before

    And finally you can set the manager on your service:

    class UserService extends SequelizeService<TUserWriteProperties, TUserReadProperties, TUserComputedProperties> {
      protected computedPropertiesManager = new UserComputedPropertiesManager();
      // ...

    You can now request age and isAdult to be computed using the compute option:

    const myUser = await userService.findByPrimaryKey(1, { compute: ['age', 'isAdult'] });


    See Github Pages.




    npm i @bluejay/sequelize-service

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