How to Set Default Values in Sequelize.js (3 Ways)

Learn some different ways to set default values in Sequelize.js and Node.js.

Solution 1: Model Definition Defaults

Define default values directly within the model’s attributes during its definition. This is the most straightforward method to set default values for a given column.

• Step 1: Install Sequelize and set up your model.
• Step 2: Define the model attributes, specifying the default value using the ‘defaultValue’ key.
• Step 3: Sync or migrate your model to create the database schema.

const User = sequelize.define('User', {
  username: {
    type: Sequelize.STRING,
    defaultValue: 'Anonymous'
  }
});

Pros: Easy to implement; directly integrated into Sequelize’s model definitions.

Cons: Limited to static values or Sequelize-provided functions; not suitable for dynamic calculations based on other fields.

Solution 2: Virtual Fields with Hooks

Use virtual fields in combination with model hooks to compute default values dynamically based on other fields or logic.

• Step 1: Define a virtual field in the model which will not be persisted in the database.
• Step 2: Use the ‘beforeCreate’ hook to set the actual default value by applying logic to the virtual field’s value.
• Step 3: Create instances of the model without specifying the value for the actual field to see the default being applied.

const User = sequelize.define('User', {
  username: Sequelize.STRING,
  defaultUsername: {
    type: Sequelize.VIRTUAL,
    defaultValue: 'Anonymous'
  }
});

User.addHook('beforeCreate', (user) => {
  if (!user.username) {
    user.username = user.defaultUsername;
  }
});

Pros: Allows for dynamic default values; can implement complex logic.

Cons: More complex to implement; virtual fields do not get persisted.

Solution 3: Database Level Defaults

Set default values directly on the database schema, using Sequelize to define the model with database-specific functions or expressions as default values.

• Step 1: Define the model with database function or expression in defaultValue option.
• Step 2: Sync or migrate your model to apply the defaults on the database level.
• Step 3: Insert records into the database and observe the database applying default values.

const User = sequelize.define('User', {
  createdAt: {
    type: Sequelize.DATE,
    defaultValue: Sequelize.literal('CURRENT_TIMESTAMP')
  }
});

Pros: Offloads logic to the database; generally more performant.

Cons: Less flexibility in a Sequelize context; limited by database functions.

Final Words

In conclusion, setting default values in Sequelize can be achieved through model definitions, virtual fields with hooks, or database level defaults. The choice of solution depends on whether the defaults are static, dynamic, or if they would benefit from being database-centric. Developers should choose a method that suits their application’s needs while considering the trade-offs in terms of simplicity, flexibility, and performance.