Sequelize: 'findAll' in instance method getParticipants()? - node.js

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.