PureSrc: A functional programming approach to the repository pattern

The repository pattern revisited in terms of functional programming.

PureSrc let you define a set of methods for exchanging data with a remote source.

Each repository instantiated by PureSrc is composed by a delivery method with its options and a set of protocols requests.

createPureSrc() is the function used to initialize a repository. It creates a stream of data from an address using a delivery method. The results are mapped into the application using the mapFromSource function parameter or dispatched immediately after a mapToSource execution. It returns another function which defines requests using a delivery request with a defined set of options. This other function returns a last function that executes requests with custom parameters.

In this implementation the repositories are a typical RESTful client with specific tools for connecting to an API server and a lightweight json database.

The provided delivery method for the first repository is src/deliveryMethods/fetch/fetchDeliveryMethod.js which uses the global method fetch to access to remote resource. The repository requests manage the data mapping, but the command to retrieve the data is entirely executed in the fetch delivery method function.

The intended scope for the latter repository is to provide a lightweight support for testing a frontend app in isolation. The delivery method is src/deliveryMethods/ForeRunnerDB/foreRunnerDBDeliveryMethod.js which wraps the database collection object.

You can add your own delivery method or your repository requests files according to your own protocol.

For a complete example open the file test/e2e/fetchRepository/index.js or test/e2e/foreRunnerDBRepository/index.js.

Prerequisites

What things you need to install the software

docker 17+
docker-compose 1.19.0+

Installing

# Get the latest snapshot
git clone https://github.com/claclacla/PureSrc-A-functional-programming-approach-to-the-repository-pattern

# Go to the docker dev folder
cd docker/dev

# Create a .env file with your docker/dev folder
# with the path to PureSrc folders
echo "PURE_SRC_FOLDER=/your-path-to/PureSrc-A-functional-programming-approach-to-the-repository-pattern
API_SERVER_FOLDER=/your-path-to/PureSrc-A-functional-programming-approach-to-the-repository-pattern/docker/dev/api-server
WEB_SERVER_FOLDER=/your-path-to/PureSrc-A-functional-programming-approach-to-the-repository-pattern/public" > .env

Development

# Go to the docker dev folder
cd docker/dev

# Compose the docker containers
sudo docker-compose up -d

# Change directory
cd PureSrc-A-functional-programming-approach-to-the-repository-pattern

# Test if the api server is up and running 
sudo docker exec -e apiaddress=pure-src-api-server:3000 -it PureSrc /usr/src/app/node_modules/.bin/mocha --ui tdd /usr/src/app/docker/dev/api-server/test/e2e

# Launch webpack in watch mode
sudo docker exec -it PureSrc npm start --prefix /usr/src/app 

# Open your browser and type the following address
http://localhost:8080

Build

# Go to the docker dev folder
cd docker/dev

# Compose the docker containers
sudo docker-compose up -d

# Build the new PureSrc version
sudo docker exec -it PureSrc npm run build --prefix /usr/src/app 

Publish to NPM

# Go to the docker dev folder
cd docker/dev

# Compose the docker containers
sudo docker-compose up -d

# Modify the npm package version on webpack/build/package.json

# Build the new npm version using the Build section command

# Connect to the PureSrc container
sudo docker exec -it PureSrc bash

# Login to the npm repository
npm login

# Move to the dist folder
cd /usr/src/app/dist

# Publish the new version to the npm repository
npm publish

Usage

createPureSrc() receives four arguments:

• the source address {string}
• the delivery method {function}: this function contains the method used to access the repository data
• the mapper from source data {function}: this function is used to map the source object data to the application entity
• the mapper to source data {function}: this function is used to map the application entity data to the source object

Returns another function to actually create the repository methods

Usage example:

let resourceRepository = createPureSrc(`${API_ADDRESS}/sources`, fetchDeliveryMethod, mapFromSource, mapToSource);

A delivery method receives two arguments:

• the source address {string}
• the method options {object}

Delivery method example:

# Create a delivery method for json data type using the fetch() method

export default async function fetchDeliveryMethod(address, options) {
  let body = null;
  let fetchResponse = null;

  try {
    fetchResponse = await fetch(address, options);
  } catch (error) {
    throw new PureSrcError(`Failed to connect to ${address}`);
  }

  if (!fetchResponse.ok) {
    throw new DeliveryError({
      status: fetchResponse.status,
      message: fetchResponse.statusText
    });
  }

  let fetchResponseBody = await fetchResponse.text();

  if (fetchResponseBody) {
    try {
      body = stringToJson(fetchResponseBody);
    } catch (error) {
      throw new Error("Error parsing response data");
    }
  }
  else {
    body = fetchResponseBody;
  }

  let response = new FetchDeliveryResponse({ status: fetchResponse.status, body });

  return response;
}

resourceRepository() receives two arguments:

• the delivery request {function}: Each kind of repository has a corresponding preset of request methods used to define how to access the repository resource. These methods are injected into the final requests creation and define how they will act.
• the delivery options {object}: These options will be passed to the devivery method.

Returns a function to access the repository resource

Usage example:

let resourceGetRequest = resourceRepository(restGetRequest, fetchDeliveryGetOptions());

A delivery request receives five required arguments:

• the delivery method {function}
• the source address {string}
• the method options {object}
• mapFromSource {function}
• mapToSource {function}

Furthermore it receives other optional parameters from the function returned by the resourceRepository() function. These parameters are helpful to add custom options to the request or to extend the resource address.

Delivery request example:

export default async function restGetRequest(deliveryMethod, source, options, mapFromSource, mapToSource, query) {
  if (query) {
    source += "?" + query;
  }

  let restResponse = await restDelivery(deliveryMethod, source, options);

  let srcObjects = restResponse.body.data;
  let object = {};
  let responseObjects = [];

  srcObjects.forEach(srcObject => {
    object = mapFromSource(srcObject);
    responseObjects.push(object);
  });

  return responseObjects;
}

Authors

• Simone Adelchino - claclacla

License

This project is licensed under the MIT License

Acknowledgments

• Currying in javascript
• Javascript functional programming
• ForeRunnerDB