Sequelize - many to many relationship - node.js

Question

I have multiple tables relating to each other, what i want to do now is create a many to many relationship between Document and Tag.
A single document can have many tags and a single Tag can have many Documents, How can i do this many to many relationship in sequelize?
In models/index.js i have:
Tab.sync().then(() => {
Group.sync().then(() => {
User.sync().then(() => {
Document.sync().then(() => {
Reference.sync().then(() => {
Tag.sync().then(() => {
User.hasMany(Group, {foreignKey: 'userAssigned', as: 'groups'})
Group.belongsTo(User, {foreignKey: 'userAssigned', as: 'user'})
Document.belongsTo(Group, {foreignKey: 'groupId', as: 'group'})
Group.hasMany(Document, {foreignKey: 'groupId', as: 'documents'})
Tab.hasMany(Group, {foreignKey: 'tabId', as: 'groups'})
Group.belongsTo(Tab, {foreignKey: 'tabId', as: 'tab'})
Document.hasMany(Reference, {foreignKey: 'docId', as: 'references'})
Reference.belongsTo(Document, {foreignKey: 'docId', as: 'docs'})
//trying to create many to many relationship here//
Document.hasMany(Tag)
Tag.hasMany(Document)
//---------------------//
})
})
})
})
})
})
ps: i've already read about through parameter, but i cannot understand how it would work

Answer 1

Many-to-many relations are described using belongsToMany in Sequelize:
// Do you already have the DocumentTag model and a table?
// I'm assuming here DocumentTag has docId and tagId fields
Document.belongsToMany(Tag, { through: DocumentTag, foreignKey: 'docId', otherKey: 'tagId' })
Tag.belongsToMany(Document, { through: DocumentTag, foreignKey: 'tagId', otherKey: 'docId' })
To get documents along with linked tags you can query like this:
const docs = await database.Document.findAll({
where: {
// here are your search conditions
},
include: [database.Tag]
})
To add tags to a certain document you can call the addTags model instance method:
const tags = await database.Tag.findAll({
where: {
// here are your search conditions
},
// to link tags to documents we don't need all attributes but `id`
attributes: ['id']
})
const doc = await database.Document.findById(documentId)
await doc.addTags(tags)