Convert SQL UNIQUE Constraints to Sequelize unique Options

Unique Constraints in Sequelize

SQL offers three ways to define unique constraints, and the converter handles all of them: column-level UNIQUE, table-level UNIQUE constraints, and CREATE UNIQUE INDEX statements.

Column-Level UNIQUE

email VARCHAR(255) NOT NULL UNIQUE
-- becomes -->
email: { type: DataTypes.STRING(255), allowNull: false, unique: true }

Table-Level UNIQUE Constraint

CREATE TABLE team_members (
  team_id INTEGER NOT NULL,
  user_id INTEGER NOT NULL,
  role VARCHAR(50),
  UNIQUE (team_id, user_id)
);

Composite unique constraints become entries in the indexes array:

TeamMember.init({ ... }, {
  sequelize,
  indexes: [
    { fields: ['team_id', 'user_id'], unique: true },
  ],
});

CREATE UNIQUE INDEX

External unique index statements are also converted:

CREATE UNIQUE INDEX idx_email_org ON users(email, organization_id);
-- becomes -->
indexes: [
  { fields: ['email', 'organization_id'], unique: true },
]

Single vs Composite

The converter distinguishes between single-column and composite unique constraints:

• Single-column: Sets unique: true on the field definition
• Multi-column: Adds an entry to the model's indexes array with unique: true

Validation Behavior

When unique: true is set, Sequelize performs:

1. A pre-insert query to check for duplicates (in some configurations)
2. Relies on the database constraint for authoritative enforcement
3. Throws a SequelizeUniqueConstraintError if the constraint is violated

This two-layer approach means your application gets a clean JavaScript error rather than a raw database error.