Retrieve Records From Multiple Tables in Sequelize

In Sequelize, the data of associated models can essentially be fetched in two ways, through eager loading and lazy loading.

Eager loading refers to querying all the data of a model and its associated model at once, which in SQL translates to a LEFT OUTER JOIN query.

Lazy loading, on the other hand, refers to querying the data of a model, and later on, querying the data of its associated model only when you really need it.

Eager loading

In Sequelize, eager loading is done by querying a model using query methods, such as findOne() and findAll(), and specifying the associated model through the include property of the configuration object:

await ModelA.findOne|findAll({  include: {    model: ModelB  }});

Where:

• ModelA is a model instance associated with another model through the hasOne() or hasMany() method.
• ModelB is a model instance associated with another model through the belongsTo() method.

This will cause the query method to return an object containing the fields of the main model, as well as the fields of the associated models.

Note: By default, Sequelize uses the name of the associated model as the name of the property under which the fields of the associated model are stored. However, in case of a one-to-many relationship, the property's name will be automatically pluralized.