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A practical functional library to use some of the key features that MongoDB provides.

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# Mongofn

A practical functional programming library to use [mongodb](https://www.npmjs.com/package/mongodb) 
in declarative way.

Focus of the library is definitely not to provide all features that `mongodb` provides.
Instead, Mongofn will provide you the most common functions wrapped with curried functions, 
so that you can skip initial setup for `client` and retrieval of `db` and `collection` objects,
and make them extremely reusable across your entire project.

Note: Mongofn is completely **dependent** on [ramda](https://github.com/ramda/ramda) library to
provide functional programming style for mongodb.

## Why Mongofn?

It is simple and extensible with the power of functional programming paradigm.
Since the most of the functions provided are curried functions, 
you can benefit from it by recomposing your implementations with different combinations of
arguments of functions as much as you need.

See [this](https://fr.umio.us/favoring-curry/) for more info about currying.

## What is the difference?

Performing simple read operation using original `mongodb` connector:

```js
// simple usage from official MongoDb Docs

// Connection URL
const url = 'mongodb://localhost:27017';

// Database Name
const dbName = 'myproject';

// Create a new MongoClient
const client = new MongoClient(url);

// Use connect method to connect to the Server
client.connect(function(err) {
  assert.equal(null, err);
  console.log("Connected successfully to server");

const db = client.db(dbName);

client.close();
});
```

To be able to reuse this code snippet you may be storing the client instance
somewhere and reach it from other place in your project, but it is still done
imperatively. Plus, you might have to implement your own reusable functions.

Mongofn provides this re-usability out of the box. Here is a collection usage in Mongofn:

```js
const { useCollection } = require('mongofn');

// Connection URL
const connectionString = 'mongodb://localhost:27017';

const useMainDb = useCollection(connectionString, 'mainDb');

const categoriesCol = useMainDb('collections')
    .then(collection => collection.find({}).toArray());
const articlesCol = useMainDb('articles')
    .then(collection => collection.find({}).toArray());

// or you can go little further
const connectionString = 'mongodb://localhost:27017';

const findInMaindDbBy = findBy(connectionString, 'mainDb');
const findInCategoriesBy = findInMaindDbBy('categories');
findInCategoriesBy({ name: 'some Categery' }).then(console.log);
findInCategoriesBy({ description: 'some Categery description' }).then(console.log);
```

It is simpler and reusable. When you pass url as first argument to `useCollection` or any other functions,
and if you don't provide all parameters, it keeps the given connection options in its scope,
once you provided all parameters, then it finally sends your request by first connecting to 
the MongoDB instance and finalize your actual operation on that MongoDB instance.

This particular approach applies to all other curried functions within Mongofn.

## TODO

- Implement findAndModify
- Implement insertOne
- Implement updateOne
- Tests
- Eventually, remove `ramda` dependency from the package

## Installation

```sh
# Using npm
npm install --save mongofn

# Using yarn
yarn add mongofn
```

## Usage

Mongofn essentially provides you some useful functions to connect a MongoDB client,
and perform most used operations on a MongoDB instance including CRUD operations.

Also, Mongofn provides `useDb` and `useCollection` functions
that simply give you original `Db` and `Collection` objects from `mongodb`,
then you can freely perform all `mongodb` operations.

All functions are curried functions. So, you can reap the benefit of it and construct
your own CRUD operations functions by partially implementing Mongofn functions and re-use
them in the entire app.

Here is an example of writing a set of baseRepository functions which you can the re-use them
in other parts of your app, for example in a categoriesRepository as it's shown below:

```js
// baseRepository.js
import {
  useDb,
  useCollection,
  findBy,
  findAll,
  findById,
  findByObjectId,
  upsert,
} from 'mongofn';
import {
  pipe, reduce, split, tail, toUpper, toLower, head, replace,
} from 'ramda';

const connectionString = process.env.MONGO_URI;
const databaseName = process.env.MAIN_DB;

export const useDbInMainDb = () => useDb(connectionString, databaseName);
export const useCollectionInMainDb = useCollection(connectionString, databaseName);
export const findInMainDbBy = findBy(connectionString, databaseName);
export const findAllInMainDb = findAll(connectionString, databaseName);
export const findInMainDbById = findById(connectionString, databaseName);
export const findInMainDbByObjectId = findByObjectId(connectionString, databaseName);
export const upsertInMainDb = upsert(connectionString, databaseName);

// categoriesRepository.js
import { toDoc, toModel } from 'mongofn';

import processPredicate from './helpers/processPredicate';

const collectionName = 'categories';

export const allCategories = () => findAllInMainDb(collectionName).then(toModel);
export const categoriesBy = (predicate) => {
  const processedPredicate = processPredicate(predicate);
  return findInMainDbBy(collectionName, processedPredicate).then(toModel)
};
export const categoriesById = (id) => findInMainDbById(collectionName, id).then(toModel);
export const saveCategory = (contentType) => upsertInMainDb(collectionName, toDoc(contentType)).then(toModel);
```

With this approach, you now are able to require and use only the features/functions
you need in your particular repository implementations.

## API

### createClient

Before you can perform operations on a MongoDB instance, first we need to connect to it.
To connect a MongoDB instance you can use `createClient` function.

```js
const { createClient } = require('mongofn');

const connectionString = 'mongodb://root:rootpassword@localhost:27017';
const options = {
  useNewUrlParser: true,
  useUnifiedTopology: true,
};

// Connect to given MongoDB instance and return a Promise<MongoClient>
// which you can do any configuration mongodb provides
createClient(connectionString, options).then(client => {
  const db = client.db('dbName');
  const collection = db.collection('collectionName');

return collection.find({}).toArray();
}).then(console.log);

```

#### Memoization
There is another function that you can connect to a MongoDB instance: `useMemoziedClient`.
This function is a memoized, so it will return the same instance if you call it with 
the same arguments.

For more info: see [memoizeWith](https://ramdajs.com/docs/#memoizeWith) 
and [Memoization (1D, 2D and 3D)](https://www.geeksforgeeks.org/memoization-1d-2d-and-3d/)

### useDb and useCollection

In `mongodb`, we start with connection client and pass a callback function to perform
operations over connected `mongodb` instance. It is repeated and very imperative way of
using mongodb. In Mongofn, you can use `useDb` and `useCollection` functions which
accepts `client` as first argument to use with, to perform all kinds of `Db` and `Collection` 
in declarative way.

```js
// useMainDb.js
const { useDb } = require('mongofn');

const connectionString = 'mongodb://localhost:27017';

export const useMainDb = () => useDb(connectionString, 'mainDb');

// someOther.js
const { useMainDb } = require('./useMainDb');

useMainDb().then(console.log); // Original Db object of mongodb

```

Here is an example of fetching all data that a collection contains.

```js
const { useCollection } = require('mongofn');

const connectionString = 'mongodb://localhost:27017';

useCollection(connectionString, 'mainDb', 'someCollection')
    .then(collection => {
            return collection.find({}).toArray(); // retrieve all
        }
    )
    .then(console.log);
```

Since it uses original `Collection` object of `mongodb`, you can simply
do anything you want that `mongodb` provides.

If we want to make it reusable across our entire app we can benefit from
currying.

As we noted before, most of the functions are curried in Mongofn.

Let's make an example and compose a function which will help you use collections
in a db without repeating code for the setup.

```js
const { useCollection } = require('mongofn');

const connectionString = 'mongodb://localhost:27017';

// Here we do not pass the last argument so that it will return another
// function which accepts only collectionName argument
const useCollectionInMainDb = useCollection(connectionString, 'mainDb');

useCollectionInMainDb('categories').then(console.log);
useCollectionInMainDb('articles').then(console.log);
useCollectionInMainDb('users').then(console.log);
```

### __ object

Before we give you more info about CRUD operations in Mongofn, we need to understand
one crucial object `__`. It is a special placeholder which you can use in curried functions
to be able to recompose your function allowing partial application of any combination
 of arguments, regardless of their positions.
 
```js
const { useCollection } = require('mongofn');

const connectionString = 'mongodb://localhost:27017';

const useCategoriesIn = useCollection(connectionString, __, 'categories');

useCategoriesIn('mainDb').then(console.log);
useCategoriesIn('otherDb').then(console.log);
```

As you may have noticed, after passing `__` object to useCollection as `dbName` argument,
`useCollection` returns another function which you can pass any `dbName` you need, so you
reuse the rest of the setup of the function. This is useful in mostly CRUD operations since
they await more parameters from you to perform certain operations.

### Using findBy, findAll, findById, and findByObjectId

`useDb` and `useCollection` functions provide full capability of
using original `Db` and `Collection` objects in `mongodb` in functional way.
However, we tend to use `mongodb` for mostly CRUD operations.

Mongofn provide following functions for finding operations:
- `findBy(client, dbName, collectionName, predicate) : Promise<Array>`
    - Accepts predicate object as it is documented at 
    [here](http://mongodb.github.io/node-mongodb-native/3.5/reference/ecmascriptnext/crud/#read-methods)
    and returns a `Promise<Array>`.
- `findAll(client, dbName, collectionName) : Promise<Array>`
    - Does not need any additional specific argument. 
    It simply returns all data in given collection as: `Promise<Array>`
- `findById(client, dbName, collectionName, id) : Promise<object>`
    - Accepts `id` value to look for the `Document` with given `id` in given
    collection, and return `Promise<object>`.
- `findByObjectId(client, dbName, collectionName, id) : Promise<object>`
    - It's a wrapper function of `findById` to rescue you from repeatedly pass
    your id value in an instance of `ObjectId`.

Note: `find` operations also accept `Array` as the last argument in which
the first element is the `predicate`, and the second element is the
`options` to be passed to the corresponding `mongodb` operation.
  
All the CRUD operations functions are curried, so you can freely use them as we
used `useDb` and `useCollection` functions.

Here are some examples of usage.

```js
// findBy example
const { createClient, findBy, __ } = require('mongofn');

const connectionString = 'mongodb://localhost:27017';

const findInMaindDbBy = findBy(connectionString, 'mainDb');

findInMaindDbBy('categories', { name: 'some Categery' }).then(console.log);
// You can pass options as well if you prefer passing an array
findInMaindDbBy(
  'articles', [
    { name: 'some Article' },
    { projection: { _id: 0, name: 1 }}
  ]).then(console.log); // projected result

const findInCategoriesBy = findInMaindDbBy('categories');
findInCategoriesBy({ name: 'some Categery' }).then(console.log);
findInCategoriesBy({ description: 'some Categery description' }).then(console.log);

// Say we have multiple replica client
const client1 = createClient(connectionString, options);
const client2 = createClient(connectionString, options);

const findInMainDbUsing = findBy(__, 'mainDb');
const findInCategoriesUsing = (__, 'categories');

findInCategoriesUsing(client1, { name: 'some Categery' }).then(console.log);
findInCategoriesUsing(client2, { name: 'some Categery' }).then(console.log);

findInMainDbUsing(client1, 'users', { name: 'some User name' }).then(console.log);
findInMainDbUsing(client2, 'users', { name: 'some User name' }).then(console.log);

// You can think of all combinations you need. 
```

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