One-to-One Relationships

Or as Sequelize calls it, associations.

Say that now our users each can have one story, so we want a relationship between a user and their story.

A new model definition is necessary, in Stories.js:

const Stories = db.define(
    'Stories',
    {
        story_id: {
            type: DataTypes.INTEGER.UNSIGNED,
            primaryKey: true,
            autoIncrement: true
        },
        created_by: {
            type: DataTypes.INTEGER.UNSIGNED,
            allowNull: false,
            references: {
                model: Users, // or "Users"
                key: 'user_id'
            }
        },
        title: {
            type: DataTypes.STRING(255),
            allowNull: false
        },
        content: {
            type: DataTypes.TEXT,
            allowNull: false
        }
    },
    {
        tableName: 'stories',
        timestamps: true,
        createdAt: 'created_at',
        updatedAt: 'updated_at'
    }
);

The created_by column is a foreign key column, which references the user model, either the model itself or the model alias.

Relationship

The relationship between the two would be:

Users.hasOne(Stories, {
    // the user can have only one story
    foreignKey: 'created_by', // the key that references Users in Stories
    as: 'story' // relationship alias
});

Stories.belongsTo(Users, {
    // the story has an author (who is the user)
    foreignKey: 'created_by', // the key that references Users in Stories
    as: 'author' // relationship alias
});

When a relationship has an alias, it must be queried with the alias.

The model that references the another is where the foreign key is stored. In this case, it is in the Stories model, because that is where the created_by foreign key column is.

Querying this Relationship

Largely similar to our queries in the previous chapter.

Create

While creating a new user, you can also create a story as well.

await Users.create({
    username: "boris",
    email: "boris@example.com",
    password: "kvass123",
    story: {
        title: "cheeki breeki cheburek",
        content: "how to make cheburek at your cousin's place"
    }
}, { include: "story" });

Note that created_by (the foreign key column) is not necessary to fill.

But you can also create them separately, then associate them. It is now however necessary to fill the created_by column.

await Stories.create({
    created_by: 1, // user id
    title: "cheeki breeki cheburek",
    content: "how to make cheburek at your cousin's place"
});

Read

Include the user’s story:

await Users.findAll({
    include: "story"
});

Or the opposite - include the story’s author:

await Stories.findAll({
    include: "author"
});

However, if you need to have query options on the include, it is a bit longer.

In stories.js:

await Stories.findAll({
    include: {
        // model: Users,
        // as: 'author',
        // or the shortcut for the 2 lines above
        association: 'author',
        attributes: { exclude: ['password'] }
    }
});