npm package: @ryank1m/core
Description: TypeScript ORM for Node.js based on Data Mapper, Unit of Work and Identity Map patterns. Supports MongoDB, MySQL, PostgreSQL and SQLite databases as well as usage with vanilla JavaScript.
Author: Martin Adámek
Latest version: 4.0.0

<h1 align="center">
  <a href="https://mikro-orm.io"><img src="https://raw.githubusercontent.com/mikro-orm/mikro-orm/master/docs/static/img/logo-readme.svg?sanitize=true" alt="MikroORM" /></a>
</h1>

TypeScript ORM for Node.js based on Data Mapper, [Unit of Work](https://mikro-orm.io/docs/unit-of-work/) 
and [Identity Map](https://mikro-orm.io/docs/identity-map/) patterns. Supports MongoDB, MySQL, 
MariaDB, PostgreSQL and SQLite databases. 

> Heavily inspired by [Doctrine](https://www.doctrine-project.org/) and [Nextras Orm](https://nextras.org/orm/).

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## 🤔 Unit of What?

You might be asking: _What the hell is Unit of Work and why should I care about it?_

> Unit of Work maintains a list of objects (_entities_) affected by a business transaction 
> and coordinates the writing out of changes. [(Martin Fowler)](https://www.martinfowler.com/eaaCatalog/unitOfWork.html)

> Identity Map ensures that each object (_entity_) gets loaded only once by keeping every 
> loaded object in a map. Looks up objects using the map when referring to them. 
> [(Martin Fowler)](https://www.martinfowler.com/eaaCatalog/identityMap.html)

So what benefits does it bring to us?

### Implicit Transactions

First and most important implication of having Unit of Work is that it allows handling
transactions automatically. 

When you call `em.flush()`, all computed changes are queried inside a database
transaction (if supported by given driver). This means that you can control the boundaries 
of transactions simply by calling `em.persistLater()` and once all your changes 
are ready, calling `flush()` will run them inside a transaction. 

> You can also control the transaction boundaries manually via `em.transactional(cb)`.

```typescript
const user = await em.findOneOrFail(User, 1);
user.email = 'foo@bar.com';
const car = new Car();
user.cars.add(car);

// thanks to bi-directional cascading we only need to persist user entity
// flushing will create a transaction, insert new car and update user with new email
// as user entity is managed, calling flush() is enough
await em.flush();
```

### ChangeSet based persistence

MikroORM allows you to implement your domain/business logic directly in the entities. 
To maintain always valid entities, you can use constructors to mark required properties. 
Let's define the `User` entity used in previous example:

```typescript
@Entity()
export class User {

  @PrimaryKey()
  id!: number;

  @Property()
  name!: string;

  @OneToOne()
  address?: Address;

  @ManyToMany()
  cars = new Collection<Car>(this);

  constructor(name: string) {
    this.name = name;
  }

}
```

Now to create new instance of the `User` entity, we are forced to provide the `name`:

```typescript
const user = new User('John Doe'); // name is required to create new user instance
user.address = new Address('10 Downing Street'); // address is optional
```

Once your entities are loaded, make a number of synchronous actions on your entities,
then call `em.flush()`. This will trigger computing of change sets. Only entities 
(and properties) that were changed will generate database queries, if there are no changes, 
no transaction will be started.

```typescript
const user = await em.findOneOrFail(User, 1, ['cars', 'address']);
user.title = 'Mr.';
user.address.street = '10 Downing Street'; // address is 1:1 relation of Address entity
user.cars.getItems().forEach(car => car.forSale = true); // cars is 1:m collection of Car entities
const car = new Car('VW');
user.cars.add(car);

// now we can flush all changes done to managed entities
await em.flush();
```

`em.flush()` will then execute these queries from the example above:

```sql
begin;
update user set title = 'Mr.' where id = 1;
update user_address set street = '10 Downing Street' where id = 123;
update car set for_sale = true where id = 1;
update car set for_sale = true where id = 2;
update car set for_sale = true where id = 3;
insert into car (brand, owner) values ('VW', 1);
commit;
```

### Only One Instance of Entity

Thanks to Identity Map, you will always have only one instance of given entity in one context. 
This allows for some optimizations (skipping loading of already loaded entities), as well as 
comparison by identity (`ent1 === ent2`). 

## 📖 Documentation

MikroORM v4 documentation, included in this repo in the root directory, is built with 
[Jekyll](https://jekyllrb.com/) and publicly hosted on GitHub Pages at https://mikro-orm.io.

There is also auto-generated [CHANGELOG.md](CHANGELOG.md) file based on commit messages 
(via `semantic-release`). 

> You can browse MikroORM v3 docs at [https://mikro-orm.io/docs/3.6/installation](https://mikro-orm.io/docs/3.6/installation).

> To upgrade to v4, please see the [upgrading guide](https://mikro-orm.io/docs/upgrading-v3-to-v4).

## ✨ Core Features

- [Clean and Simple Entity Definition](https://mikro-orm.io/docs/defining-entities/)
- [Identity Map](https://mikro-orm.io/docs/identity-map/)
- [Entity References](https://mikro-orm.io/docs/entity-references/)
- [Using Entity Constructors](https://mikro-orm.io/docs/using-entity-constructors/)
- [Modelling Relationships](https://mikro-orm.io/docs/relationships/)
- [Collections](https://mikro-orm.io/docs/collections/)
- [Unit of Work](https://mikro-orm.io/docs/unit-of-work/)
- [Transactions](https://mikro-orm.io/docs/transactions/)
- [Cascading persist and remove](https://mikro-orm.io/docs/cascading/)
- [Composite and Foreign Keys as Primary Key](https://mikro-orm.io/docs/composite-keys/)
- [Filters](https://mikro-orm.io/docs/filters/)
- [Using `QueryBuilder`](https://mikro-orm.io/docs/query-builder/)
- [Preloading Deeply Nested Structures via populate](https://mikro-orm.io/docs/nested-populate/)
- [Property Validation](https://mikro-orm.io/docs/property-validation/)
- [Lifecycle Hooks](https://mikro-orm.io/docs/lifecycle-hooks/)
- [Vanilla JS Support](https://mikro-orm.io/docs/usage-with-js/)
- [Schema Generator](https://mikro-orm.io/docs/schema-generator/)
- [Entity Generator](https://mikro-orm.io/docs/entity-generator/)

## 📦 Example Integrations

You can find example integrations for some popular frameworks in the [`mikro-orm-examples` repository](https://github.com/mikro-orm/mikro-orm-examples): 

### TypeScript Examples

- [Express + MongoDB](https://github.com/mikro-orm/express-ts-example-app)
- [Nest + MySQL](https://github.com/mikro-orm/nestjs-example-app)
- [RealWorld example app (Nest + MySQL)](https://github.com/mikro-orm/nestjs-realworld-example-app)
- [Koa + SQLite](https://github.com/mikro-orm/koa-ts-example-app)
- [GraphQL + PostgreSQL](https://github.com/driescroons/mikro-orm-graphql-example)
- [Inversify + PostgreSQL](https://github.com/PodaruDragos/inversify-example-app)
- [NextJS + MySQL](https://github.com/jonahallibone/mikro-orm-nextjs)

### JavaScript Examples 
- [Express + MongoDB](https://github.com/mikro-orm/express-js-example-app)

## Articles

- Introducing MikroORM, TypeScript data-mapper ORM with Identity Map
  - on [medium.com](https://medium.com/dailyjs/introducing-mikro-orm-typescript-data-mapper-orm-with-identity-map-9ba58d049e02)
  - on [dev.to](https://dev.to/b4nan/introducing-mikroorm-typescript-data-mapper-orm-with-identity-map-pc8)
- Handling transactions and concurrency in MikroORM
  - on [medium.com](https://medium.com/dailyjs/handling-transactions-and-concurrency-in-mikro-orm-ba80d0a65805)
  - on [dev.to](https://dev.to/b4nan/handling-transactions-and-concurrency-in-mikroorm-2cfj)
- MikroORM 3: Knex.js, CLI, Schema Updates, Entity Generator and more…
  - on [medium.com](https://medium.com/dailyjs/mikro-orm-3-knex-js-cli-schema-updates-entity-generator-and-more-e51ecbbc508c)
  - on [dev.to](https://dev.to/b4nan/mikroorm-3-knex-js-cli-schema-updates-entity-generator-and-more-3g56)

## 🚀 Quick Start

First install the module via `yarn` or `npm` and do not forget to install the database driver as well:

> Since v4, you should install the driver package, but not the db connector itself,
> e.g. install `@mikro-orm/sqlite`, but not `sqlite3` as that is already included
> in the driver package.

```sh
yarn add @mikro-orm/core @mikro-orm/mongodb     # for mongo
yarn add @mikro-orm/core @mikro-orm/mysql       # for mysql/mariadb
yarn add @mikro-orm/core @mikro-orm/mariadb     # for mysql/mariadb
yarn add @mikro-orm/core @mikro-orm/postgresql  # for postgresql
yarn add @mikro-orm/core @mikro-orm/sqlite      # for sqlite
```

or

```sh
npm i -s @mikro-orm/core @mikro-orm/mongodb     # for mongo
npm i -s @mikro-orm/core @mikro-orm/mysql       # for mysql/mariadb
npm i -s @mikro-orm/core @mikro-orm/mariadb     # for mysql/mariadb
npm i -s @mikro-orm/core @mikro-orm/postgresql  # for postgresql
npm i -s @mikro-orm/core @mikro-orm/sqlite      # for sqlite
```

Next you will need to enable support for [decorators](https://www.typescriptlang.org/docs/handbook/decorators.html)
as well as `esModuleInterop` in `tsconfig.json` via:

```json
"experimentalDecorators": true,
"emitDecoratorMetadata": true,
"esModuleInterop": true,
```

Then call `MikroORM.init` as part of bootstrapping your app:

```typescript
const orm = await MikroORM.init({
  entities: ['./dist/entities'], // path to your JS entities (dist), relative to `baseDir`
  dbName: 'my-db-name',
  type: 'mongo',
  clientUrl: '...', // defaults to 'mongodb://localhost:27017' for mongodb driver
});
console.log(orm.em); // access EntityManager via `em` property
```

There are more ways to configure your entities, take a look at 
[installation page](https://mikro-orm.io/docs/installation/).

> Read more about all the possible configuration options in [Advanced Configuration](https://mikro-orm.io/docs/configuration) section.

Then you will need to fork entity manager for each request so their 
[identity maps](https://mikro-orm.io/docs/identity-map/) will not collide. 
To do so, use the `RequestContext` helper:

```typescript
const app = express();

app.use((req, res, next) => {
  RequestContext.create(orm.em, next);
});
```

> You should register this middleware as the last one just before request handlers and before
> any of your custom middleware that is using the ORM. There might be issues when you register 
> it before request processing middleware like `queryParser` or `bodyParser`, so definitely 
> register the context after them. 

More info about `RequestContext` is described [here](https://mikro-orm.io/docs/identity-map/#request-context).

Now you can start defining your entities (in one of the `entities` folders). This is how
simple entity can look like in mongo driver:

**`./entities/MongoBook.ts`**

```typescript
@Entity()
export class MongoBook {

  @PrimaryKey()
  _id: ObjectID;

  @SerializedPrimaryKey()
  id: string;

  @Property()
  title: string;

  @ManyToOne()
  author: Author;

  @ManyToMany()
  tags = new Collection<BookTag>(this);

  constructor(title: string, author: Author) {
    this.title = title;
    this.author = author;
  }

}
```

For SQL drivers, you can use `id: number` PK:

**`./entities/SqlBook.ts`**

```typescript
@Entity()
export class SqlBook {

  @PrimaryKey()
  id: number;

}
```

Or if you want to use UUID primary keys:

**`./entities/UuidBook.ts`**

```typescript
import { v4 } from 'uuid';

@Entity()
export class UuidBook {

  @PrimaryKey()
  uuid = v4();

}
```

More information can be found in
[defining entities section](https://mikro-orm.io/docs/defining-entities/) in docs.

When you have your entities defined, you can start using ORM either via `EntityManager`
or via `EntityRepository`s.

To save entity state to database, you need to persist it. Persist takes care or deciding 
whether to use `insert` or `update` and computes appropriate change-set. Entity references
that are not persisted yet (does not have identifier) will be cascade persisted automatically. 

```typescript
// use constructors in your entities for required parameters
const author = new Author('Jon Snow', 'snow@wall.st');
author.born = new Date();

const publisher = new Publisher('7K publisher');

const book1 = new Book('My Life on The Wall, part 1', author);
book1.publisher = publisher;
const book2 = new Book('My Life on The Wall, part 2', author);
book2.publisher = publisher;
const book3 = new Book('My Life on The Wall, part 3', author);
book3.publisher = publisher;

// just persist books, author and publisher will be automatically cascade persisted
await orm.em.persistAndFlush([book1, book2, book3]);
```

To fetch entities from database you can use `find()` and `findOne()` of `EntityManager`: 

```typescript
const authors = orm.em.find(Author, {});

for (const author of authors) {
  console.log(author); // instance of Author entity
  console.log(author.name); // Jon Snow

  for (const book of author.books) { // iterating books collection
    console.log(book); // instance of Book entity
    console.log(book.title); // My Life on The Wall, part 1/2/3
  }
}
```

More convenient way of fetching entities from database is by using `EntityRepository`, that
carries the entity name so you do not have to pass it to every `find` and `findOne` calls:

```typescript
const booksRepository = orm.em.getRepository(Book);

// with sorting, limit and offset parameters, populating author references
const books = await booksRepository.find({ author: '...' }, ['author'], { title: QueryOrder.DESC }, 2, 1);

// or with options object
const books = await booksRepository.find({ author: '...' }, { 
  populate: ['author'],
  limit: 1,
  offset: 2,
  orderBy: { title: QueryOrder.DESC },
});

console.log(books); // Book[]
```

Take a look at docs about [working with `EntityManager`](https://mikro-orm.io/docs/entity-manager/)
or [using `EntityRepository` instead](https://mikro-orm.io/docs/repositories/).

## 🤝 Contributing

Contributions, issues and feature requests are welcome. Please read 
[CONTRIBUTING.md](CONTRIBUTING.md) 
for details on the process for submitting pull requests to us.

## Authors

👤 **Martin Adámek**

- Twitter: [@B4nan](https://twitter.com/B4nan)
- Github: [@b4nan](https://github.com/b4nan)

See also the list of contributors who [participated](https://github.com/mikro-orm/mikro-orm/contributors) in this project.

## Show Your Support

Please ⭐️ this repository if this project helped you!

## 📝 License

Copyright © 2018 [Martin Adámek](https://github.com/b4nan).

This project is licensed under the MIT License - see the [LICENSE file](LICENSE) for details.