如何在Sequelize中消除相同模型之间的多个关联之间的歧义

Question

I have three models — Book , User and Institution — which are associated to one another as follows:

• Books are associated to Institutions via a Book_Institution join table (many to many relationship)

   Book.belongsToMany(models.Institution, { through: 'Book_Institution' }) 

  and

   Institution.belongsToMany(models.Book, { through: 'Book_Institution' }) 

• Users can be associated to Institutions in two ways: as reader or author. This is done via two join tables: Author_Institution and Reader_Institution :

   Institution.belongsToMany(models.User, { through: 'Author_Institution' }) Institution.belongsToMany(models.User, { through: 'Reader_Institution' }) 

  and

   User.belongsToMany(models.Institution, { through: 'Author_Institution' }) User.belongsToMany(models.Institution, { through: 'Reader_Institution' }) 

  (Each time leaving out foreignKey for brevity.)

I want to query the Book model to find all books that belong to an author. Sequelize provides the include option to easily join two associated tables. The problem I'm stuggling with is that using include as shown below defaults to the Reader_Institution association. How can I specify which association should be used?

getBooks: (obj, args, context) => {
  const { user } = context

  return Book.findAll({
    attributes: ['id', 'path'],
    include: [{
      include: [{
        attributes: ['id'],
        model: User,
        where: { id: user }
      }],
      model: Institution,
      required: true // inner join
    }]
  })
}

Thanks in advance for your help.

Answer 1

I use as which allows you to reference the relationship through that alias.

Institution.belongsToMany(models.User, { 
    through: 'Author_Institution', // many-to-many relationship table name
    as: 'AuthorInstitution' // alias
})

With your models set up this way, you can use as to to specify which relationship you want to include when querying.

getBooks: (obj, args, context) => {
  const { user } = context

  return Book.findAll({
    attributes: ['id', 'path'],
    include: [{
      include: [{
        attributes: ['id'],
        model: User,
        where: { id: user },
        as: 'AuthorInstitution'
      }],
      model: Institution,
      required: true // inner join
    }]
  })
}

Also, with this methodology, it allows you you to reference the relationship data via the as , so you can do book.AuthorInstitution and it will be the value of that object.