Sequelize: 'findAll' in instance method getParticipants()?

Question

Specification for my conference instance method:

getParticipants() : Promise -> Participant array

Conference model:

return sequelize.define('conference', {

    id: {
        type: Sequelize.UUID,
        defaultValue: Sequelize.UUIDV4,
        primaryKey: true
    },

    name: {
        type: Sequelize.STRING,
        allowNull: false,
        unique: true
    },

    maxParticipants: {
        type: Sequelize.INTEGER,
        allowNull: false
    },

    fileShareSession: {
        type: Sequelize.STRING,
        defaultValue: null,
        allowNull: true
    },

    startDate: {
        type: Sequelize.DATE,
        defaultValue: null,
        allowNull: true
    },

    endDate: {
        type: Sequelize.DATE,
        defaultValue: null,
        allowNull: true
    },

    state: {
        type: Sequelize.ENUM(
            ConferenceState.new,
            ConferenceState.starting,
            ..
        ),
        defaultValue: ConferenceState.new,
        required: true,
        allowNull: false
    }

Participant model:

return sequelize.define('participant', {

    id: {
        type: Sequelize.UUID,
        defaultValue: Sequelize.UUIDV4,
        primaryKey: true
    },

    displayName: {
        type: Sequelize.STRING,
        defaultValue: null,
        allowNull: true
    },

    mediaResourceId: {
        type: Sequelize.STRING,
        defaultValue: null,
        allowNull: true
    },

    screenSharingId: {
        type: Sequelize.STRING,
        defaultValue: null,
        allowNull: true
    },

    mediaType: {
        type: Sequelize.ENUM(
            MediaType.AUDIO_VIDEO),
        defaultValue: MediaType.AUDIO_VIDEO,
        allowNull: false
    },

    state: {
        type: Sequelize.ENUM(
            ParticipantState.new,
            ParticipantState.joining,
            ..
        ),
        defaultValue: ParticipantState.new,
        required: true,
        allowNull: false
    }

Question:

So can I do a participant.findAll in my conferencing instance model or not? When yes, do I get an Array back with a findAll?

I would have done it like that:

// getParticipants() : Promise -> Participant array
      getParticipants() {
          return new Promise((resolve, reject) => {
              var Participant = sequelize.models.participant;
              Participant.findAll({
                  where: {
                      id: id
                  }
              }).then(function(participant) {
                  if (_.isObject(participant)) {
                      resolve(participant);
                  } else {
                      throw new ResourceNotFound(conference.name, {id: id});
                  }
              }).catch(function(err) {
                  reject(err);
              });
          });
      },

Answer 1

LAZY loading is implemented by sequelize when you make relationships between tables. You could make a relationship as follows:

var Conference = sequelize.define('conference', { ... });

var Participant = sequelize.define('participant', { ... });

Conference.belongsToMany(Participant, { through: 'ConferenceParticipants'});

Participant.belongsToMany(Conference, { through: 'ConferenceParticipants'});

Then you can implement EAGER loading when you query your database like:

// Obtain the participant list included in the original object (EAGER)
var conference = 
 Conference.findOne({ 
    attributes: ['field1', 'field2', ...],
    where: {title: 'Conference A'},
    includes: [{
      attributes: ['field1', 'field2', ...],
      model: Participant,
      through: { model: 'ConferenceParticipants'} // You have to name the join table
    }]
  })
  .then(function(conference) {
      // Here you will have the conference with the list of participants

  });

If you want to use LAZY loading, sequelize implement it for you, you just need to call below methods:

// Obtain the participant LAZY
conference.getParticipants().then(function(participants) {
  // participants is an array of participant
})

// You can also pass filters to the getter method.
// They are equal to the options you can pass to a usual finder method.
conference.getParticipants({ where: 'id > 10' }).then(function(participants) {
  // participants with an id greater than 10 :)
})

// You can also only retrieve certain fields of a associated object.
conference.getParticipants({attributes: ['title']}).then(function(participants) {
    // retrieve participants with the attributes "title" and "id"
})

You can get a reference to sequelize relationship implementation in next document.