Sequelize.js: How to Save an Array in a Column

Overview

Sequelize.js is a popular ORM (Object-Relational Mapping) library for Node.js that allows developers to manage relational databases using JavaScript objects instead of SQL queries. One common requirement is storing arrays in a single database column. This tutorial will cover how to efficiently save and retrieve arrays in a column using Sequelize.js.

Before diving into the specifics, it’s important to know that relational databases typically don’t support array data types natively, except for PostgreSQL. Keeping this limitation in mind, we will explore multiple approaches, including serializing arrays into strings, using join tables, and leveraging JSON or array data types in databases that support them, like PostgreSQL.

Let’s go step by step. We’ll start with basic examples and gradually move to more advanced scenarios, while covering best practices for each.

Prerequisites

To follow along, you need:

• Basic knowledge of Node.js and Sequelize.js
• A Node.js environment setup
• Sequelize.js and a database (like PostgreSQL) installed

Basic Example: Serializing Arrays with JSON.stringify

The simplest way to save an array to a database column is by serializing it into a string. We can achieve this using JSON.stringify to convert the array into a JSON string before saving the model and JSON.parse for retrieving it.

const { DataTypes } = require('sequelize');
const sequelize = new Sequelize('database', 'username', 'password', {
  dialect: 'postgres'
});

const User = sequelize.define('user', {
  hobbies: {
    type: DataTypes.STRING,
    get() {
      const value = this.getDataValue('hobbies');
      return value ? JSON.parse(value) : null;
    },
    set(value) {
      this.setDataValue('hobbies', JSON.stringify(value));
    }
  }
});

Although this approach is simple, it may not be the most efficient or elegant solution, especially for complex arrays or when database search operations are needed.

Using PostgreSQL Array Data Type

PostgreSQL supports an array data type, which Sequelize.js can leverage. This allows you to directly store arrays without serializing them into strings.

const User = sequelize.define('user', {
  hobbies: {
    type: DataTypes.ARRAY(DataTypes.TEXT)
  }
});

With this definition, Sequelize will handle the serialization and deserialization of the array behind the scenes. When querying, you can directly use array functions provided by PostgreSQL.

Storing Arrays in a Separate Join Table

For relational databases that do not support array types, a common workaround is to create a separate join table. This involves rethinking the relational model to accommodate a one-to-many relationship.

const User = sequelize.define('user', { /* ... */ });
const Hobby = sequelize.define('hobby', {
  name: DataTypes.STRING
});

User.hasMany(Hobby, { as: 'hobbies' });
Hobby.belongsTo(User);

This setup creates a ‘Hobbies’ table that stores individual hobbies and links them to users. This approach allows for greater flexibility, normalization and better querying capabilities.

Advanced Use Case: Storing Arrays with JSON Data Types

In databases that support JSON data types, such as MySQL (from version 5.7.8) and PostgreSQL, you can use Sequelize’s DataTypes.JSON or DataTypes.JSONB to store complex arrays and even objects.

const User = sequelize.define('user', {
  meta: {
    type: DataTypes.JSONB,
    get() {
      const value = this.getDataValue('meta');
      return value ? value : {};
    },
    set(value) {
      this.setDataValue('meta', value);
    }
  }
});

This allows you to store an array as part of a larger JSON object and query it using JSON-specific operations provided by the database.

Handling Array Operations

We’ve looked at storing arrays, but what about modifying them? Using array data types or JSON, we can leverage database functions to perform operations like adding or removing items from an array directly within a query.

// Example: PostgreSQL array function
await User.update(
  { hobbies: sequelize.fn('array_append', sequelize.col('hobbies'), 'new_hobby') },
  { where: { id: userId } }
);

Beyond these operations, it’s crucial to understand transactions and proper error handling when working with relational databases to maintain data integrity, especially when dealing with related tables or complex operations.

Final Words

In this tutorial, we have explored various methods to save an array in a column using Sequelize.js. From simple JSON serialization to advanced database-specific features, we’ve covered the essentials you need to work with arrays in Sequelize effectively. As always, carefully consider which method best fits your application’s needs based on the database you are using and the operations you need to perform. Remember to utilize Sequelize’s features to maintain clean and maintainable codebase while harnessing the power of your relational database.