Associating models

Summary

In this lesson, we introduce associations in Sails.js, which allow models to relate to one another. Unlike simple attributes like strings and numbers, associations create relationships between models.

Since an article can have many comments, we define a one-to-many association between the Article and Comment models:

1. In the Comment model: We add an article attribute with model: 'article', establishing a foreign key reference.

2. In the Article model: We define a comments collection and use the via property to link it to the article field in the Comment model.

This setup ensures that each comment belongs to one article, while an article can have multiple comments. In the next lesson, we’ll set up the route for adding comments.

Transcript

In the last lesson, I mentioned that we’d be adding a special attribute. Now, let's see what makes it special.

So far, we've only used attributes like strings, numbers, and booleans—basic types. But in Sails, we have something called associations, which allow us to define relationships between models.

For example, we can pass the foreign key of one model into another, creating a link—what we call an association in Sails or a relationship in relational databases.

Types of associations

Before implementing one, we need to determine the type of relationship we want. Sails supports:

• One-to-one associations

• One-to-many associations

• Many-to-many associations

In our case, an article can have many comments, meaning we need a one-to-many association. To set this up properly, we must edit both the Comment and Article models so they recognize each other.

Updating the comment model

Inside the Comment model, Sails provides some helpful defaults, but we don’t need them. Instead, we define a new attribute:

article: {
  model: 'article'
}

Here’s what’s happening:

• The model property links this field to another model—in this case, article.

• The value 'article' is the model identity, which is simply the lowercase version of the model name.

Updating the Article Model

Right now, the Article model doesn’t know about this relationship. To fix that, we add:

comments: {
  collection: 'comment',
  via: 'article'
}

This tells Sails that:

• comments is a collection of Comment models.

• The via property establishes the link using the article field in the Comment model.

With this, we’ve successfully set up a one-to-many relationship:

• Each comment belongs to a single article (foreign key in the Comment model).

• Each article can have multiple comments (collection in the Article model).

In the next lesson, we'll set up the route for adding comments.