This guide is an introduction to Leoric. After reading this guide, you will know:

Table of Contents

  1. What is Leoric
  2. Convention over Configuration
    1. Naming Conventions
    2. Schema Conventions
  3. Authoring Models
  4. Overriding the Naming Conventions
  5. Connecting Models to Database
  6. Reading and Writing Data
    1. Create
    2. Read
    3. Update
    4. Delete

What is Leoric

Leoric is a thin Object Relational Mapping layer between Node.js and database. It can be used as the M in MVC - which is the layer of the system responsible for representing business data and logic.

Object Relational Mapping, or ORM, is a way of connecting rich objects of an application to tables in a relational database management system. The idea of ORM is quite popular in a lot of the programming languages, such as Active Record for Ruby, SQLAlchemy for Python, or Hibernate for Java. Leoric is heavily influenced by Active Record which you probably can tell already by the similar documentation structure.

As one of the many ORM libraries for JavaScript, the most promising features of Leoric shall be the abilities to:

Convention over Configuration

Generally speaking, configuration is preferred over convention because of its explicitness. However, if you follow the conventions introduced by Leoric, you’ll need to write few configuration when authoring models.

Naming Conventions

By default, Leoric uses some naming conventions to find out how the mapping between models and database tables should be created. Here’re the rules:

Here’s a few transform examples.

Model/Class Table/Schema
Shop shops
TagMap tagMaps
Mouse mice
Person people

Under the hood, Leoric uses pluralize to transform table names from model names. If you find the transform rules counter intuitive (which is very common for non-native speakers), you can explicitly configure the table name or rename the attribute. We’ll cover that in the Overrding the Naming Conventions section.

Schema Conventions

Leoric provides three static methods for relationship authoring, .hasMany(), .hasOne(), and .belongsTo(). The conventional primary keys and foreign keys are as below,

There’re some optional column names that will add additional features to Leoric:

column attribute description
created_at createdAt updated when the record is first created.
updated_at updatedAt updated whenever the record is updated.
deleted_at deletedAt updated whenever the record is softly deleted

For TDDL users, the conventional gmt_create is mapped to createdAt, gmt_modified is mapped to updatedAt, and gmt_deleted (if present) is mapped to deletedAt.

When Bone.remove({...}) is called on a Model with deletedAt present, Leoric will perform a soft delete by updating the value of deletedAt column instead of delete it from the database permanently. Call Bone.remove({...}, true) to force delete.

Authoring Models

Suppose the shops table were created already:

  id int(11) NOT NULL auto_increment,
  name varchar(255),

Simply extend from the Bone class exported by Leoric, have it connected to database, and you’re all set:

const { Bone } = require('leoric');
class Shop extends Bone {}
await connect({ host: 'localhost', models: [ Shop ]});

It is possible to manage schema with Leoric as well. By defining attributes when authring models, Leoric learns what the model needs and will have the schema migrated when necessary:

const { Bone, Realm } = require('leoric');
const { BIGINT, STRING } = Bone.DataTypes;

// define Shop
class Shop extends Bone {
  static attributes = {
    id: { type: BIGINT, primaryKey: true },
    name: STRING,

// connecting Shop to shops table in database
const realm = new Realm({ host: 'localhost', models: [ Shop ] });
// synchronize model attributes to table
await realm.sync();

Now we have got the models connected to and synchronized with database, we can start querying:

const shop = new Shop({ name: 'Horadric Cube' })
// or simply
await Shop.create({ name: 'Horadric Cube' })

Overriding the Naming Conventions

Most of the conventional names and keys can be overridden by corresponding methods. You can specify static table to override the default table name:

class Shop extends Bone {
  static table = 'stores'

It’s also possible to override the the name of the primary key by specifying static primaryKey:

class Shop extends Bone {
  static primaryKey = 'shopId'

We can rename the attribute names too. By default, these names are transformed from column names by converting them into camel case. If the names don’t match, we can specify the column names manually in static attributes, such as:

class Shop extends Bone {
  static attributes = {
    deletedAt: { type: DATE, columnName: 'removed_at' },

We can also rename the attribute in the static initialize() method, which gets called after models are loaded.

class Shop extends Bone {
  static initialize() {
    this.renameAttribute('removedAt', 'deletedAt')

A lot of schema settings can be done within the static initialize() method. We’ll get to that later. For TypeScript projects this static method is unnecessary, most of the settings can be tweaked with the equivalent decorators. The example above can be refactored with decorator like below:

class Shop extends Bone {
  @Column({ name: 'removed_at' })
  deltedAt: Date;

Connecting Models to Database

Models need to be connected to database before use, which can be connected in the following way:

const Realm = require('leoric');
const realm = new Realm({
  dialect: 'mysql',
  host: 'localhost',
  models: '/path/to/models',
await realm.sync();

realm.sync() not only connects models to database, but also tries to synchronize Model.attributes in each model back to database structure automatically to make sure consistency between each other. If your application data changes a lot, this practice is not recommended.

In that case, please use the migrations to change database structure instead.

const Realm = require('leoric');
const realm = new Realm(...);
await realm.connect();

For those who started using Leoric since v0.x, we can still connect() to database directly.

const { connect } = require('leoric');

await connect({
  host: '',
  port: 3306,
  user: 'john',
  password: 'inputYourCodeHere',
  db: 'tmall',
  models: [Shop]

// or
await connect({ ...opts, path: '/path/to/models' });

If developing web applications with Egg framework, it’s highly recommended using the egg-orm plugin.

Reading and Writing Data

With the models defined and connected, developers can,

async function() {
  // create shop
  await Shop.create({ name: 'Barracks' })

  // find one and update it
  const shop = await Shop.findOne({ name: 'Barracks' }) = 'Horadric Cube'

  // remove the shop
  await Shop.remove({ name: 'Horadric Cube' })


There are two ways in Leoric to INSERT records into database. We can do this either by calling Model.create() with one blow:

const shop = await Shop.create({ name: 'Barracks', credit: 10000 })

or by instantiating a model from scratch, settings the attributes, the it at last:

const shop = new Shop({ name: 'Barracks' }) = 10000

The SQL equivalent of both is:

INSERT INTO shops (name, credit, type) VALUES ('Barracks', 10000);


Although Leoric provides a rich API for starting a query, Model.find() and Model.findOne() are the most used methods.

// find all of the shops
// => SELECT * FROM shops;

// find the first one
// => SELECT * FROM shops LIMIT 1;

// find the shop of Deckard Cain
Shop.findOne({ name: 'Deckard Cain' })
// => SELECT * FROM shops WHERE name = 'Deckard Cain' LIMIT 1;

// find a collection of shops with their credit above 1000
Shop.where('credit > 1000')
// => SELECT * FROM shops WHERE credit > 1000;

For detailed introductions about reading data from the database, please read Query Interface


Like the way records are created, records can be updated in two manners too. If the objects are already at hand, we can fiddle their attributes and persist the updates by calling

const shop = await Shop.findOne({ name: 'Barracks' })
// => Shop { id: 1, name: 'Barracks' } = 10000

The SQL equivalent of the above is:

UPDATE shops SET credit = 10000 WHERE id = 1;

If the back and forth traffic needs to be skipped, we can also update the records with one blow using Model.update():

await Shop.update({ name: 'Barracks' }, { credit: 10000 })

The SQL equivalent of the above is:

UPDATE shops SET credit = 10000 WHERE name = 'Barracks';


Likewise, both model.remove() and Model.remove() are available to delete records from database. For example:

const shop = await Shop.find({ name: 'Barracks' })
// => Shop { id: 1, name: 'Barracks' }
await shop.remove(true)
// DELETE FROM shops WHERE id = 1

await Shop.remove({ name: 'Barracks' }, true)
// DELETE FROM shops WHERE name = 'Barracks'

What’s with the parameter true you might ask. That is because by default Leoric performs a soft delete instead of truly DELETE FROM the database. To make soft delete possible, the model must have a attribute called deletedAt to be used as a mark of deletion.

Therefore, if deletedAt were present in Shop model:

const shop = await Shop.find({ name: 'Barracks' })
// => Shop { id: 1, name: 'Barracks' }
await shop.remove()
// UPDATE shops SET deleted_at = NOW() WHERE id = 1

await Shop.remove({ name: 'Barracks' })
// UPDATE shops SET deleted_at = NOW() WHERE name = 'Barracks'

If deletedAt were absent in Shop model, calling either model.remove() or Model.remove() without passing true throws an Error.