I'm working with Sequelize v6, and facing a circular dependency between two models: User and Profile. To solve this, I am setting constraints: false in one association and then manually adding the Foreign Key constraint using queryInterface after synchronization.

User Model:

class User extends Model {
    static associate(models) {
        User.belongsTo(models.Profile, {
            foreignKey: {
                name: 'profile_id',
                allowNull: true,
            },
            constraints: false  // Disable FK constraint
        });
    }
}

Profile Model:

class Profile extends Model {
    static associate(models) {
        Profile.belongsTo(models.User, {
            foreignKey: {
                name: 'created_by_user_id',
                allowNull: false,
            },
            constraints: true  // Keep FK constraint here
        });
    }
}

Sync Script:

const { QueryInterface } = require('sequelize');

async function syncDatabase() {
    await db.sequelize.sync({ alter: true });
    
    // Manually add FK constraint for User -> Profile
    const qi = db.sequelize.getQueryInterface();
    await qi.addConstraint('users', {
        fields: ['profile_id'],
        type: 'foreign key',
        name: 'user_profile_id_fkey',
        references: { 
            table: 'profiles', 
            field: 'id' 
        }
    });
}

syncDatabase();

I am trying to understand the differences between using the default constraints: true and my current approach of setting constraints: false and creating the Foreign Key manually.

Does it affect Sequelize's ORM behavior or any hidden side effects when Sequelize manages the relationship in memory ?

Does it affect Sequelize's built-in methods (like user.getProfile(), user.setProfile() ) or Eager Loading performance (User.findOne({ include: Profile })).