Introduction to Objection ORM

Objection.js is a powerful ORM (Object-Relational Mapper) for Node.js, built on top of the SQL query builder Knex. It provides a straightforward solution for interacting with relational databases using JavaScript/TypeScript.

Key Features

• Support for numerous SQL databases through Knex.js.
• Document-based querying with JSON schemas.
• Powerful and customizable querying capabilities.
• Easy-to-use migration and seeding functionality.

Setting Up Objection.js

  
    const { Model } = require('objection');
    const Knex = require('knex');

    // Initialize knex.
    const knex = Knex({
      client: 'sqlite3',
      connection: {
        filename: './mydb.sqlite'
      }
    });

    // Bind all models to the knex instance.
    Model.knex(knex);
  

Example: Defining Models and Queries

Defining a Model

  
    const { Model } = require('objection');

    class Person extends Model {
      static get tableName() {
        return 'persons';
      }

      static get idColumn() {
        return 'id';
      }

      static get jsonSchema() {
        return {
          type: 'object',
          required: ['firstName', 'lastName'],

          properties: {
            id: { type: 'integer' },
            firstName: { type: 'string', minLength: 1, maxLength: 255 },
            lastName: { type: 'string', minLength: 1, maxLength: 255 },
          }
        };
      }
    }
  

Basic Queries

  
    // Insert a new person.
    await Person.query().insert({ firstName: 'John', lastName: 'Doe' });

    // Fetch a person by ID.
    const person = await Person.query().findById(1);

    // Fetch all persons.
    const persons = await Person.query().select('*');
  

Advanced Queries

  
    // Fetch persons with certain criteria.
    const persons = await Person.query().where('firstName', 'John').orWhere('lastName', 'Smith');

    // Update a person.
    await Person.query().patchAndFetchById(1, { lastName: 'Doe-Smith' });

    // Delete a person.
    await Person.query().deleteById(1);
  

Relationship Mapping

  
    class Animal extends Model {
      static get tableName() {
        return 'animals';
      }

      static get relationMappings() {
        return {
          owner: {
            relation: Model.BelongsToOneRelation,
            modelClass: Person,
            join: {
              from: 'animals.ownerId',
              to: 'persons.id'
            }
          }
        };
      }
    }
  

Fetching Related Data

  
    // Fetch animal with its owner.
    const animals = await Animal.query().withGraphFetched('owner');
  

Building a Simple App with Objection.js

Let’s build a simple Node.js application that connects to an SQLite database using Objection.js.

App Setup

  
    const express = require('express');
    const { Model } = require('objection');
    const Knex = require('knex');
    const app = express();

    // Initialize knex.
    const knex = Knex({
      client: 'sqlite3',
      connection: {
        filename: './mydb.sqlite'
      }
    });

    // Bind all models to the knex instance.
    Model.knex(knex);

    // Define models.
    class Person extends Model {
      static get tableName() {
        return 'persons';
      }
    }

    // Route to fetch all persons.
    app.get('/persons', async (req, res) => {
      const persons = await Person.query();
      res.json(persons);
    });

    // Start the server.
    app.listen(3000, () => {
      console.log('App listening on port 3000');
    });
  

With this simple setup, you can interact with an SQLite database using Objection.js, performing CRUD operations and more.

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