What is the tecnology behind "The Graph"?

As we all know "The Graph" is an indexing protocol for querying networks like Ethereum and IPFS.

To create this, "The Graph" uses GraphQL Api.

GraphQL is a query language that provides clients with exactly the data requested by the user. It was created by Facebook in 2012 but went open and free in 2015, it is now supported by the GraphQL Foundation.

Making a request is easy, we just need to create a JSON (JavaScript Object Notation) with the necessary data.

How to create a basic graphql service?

Yes, we need a little bit of experience but is easy to create one. We just need Node.js and an editor like VS Code.

To test node is installed, open a powerShell or a propt and type:

npm --version

The installed version will appear, on the contrary you will need to install node.js from their site.

Then we need to create a folder where create our simple application.

mkdir GraphQlAPIcd .\GraphQlAPI\

After that we must initialize node and install graphql whith his server:

npm initnpm install express express-graphql graphql --save

In your project, now we have this situation

Now we can create our structure folder:

- src

   - data

   - schema

   - services

We need this structure to separate the concepts of our app.

Now let's create schema.js in src/schema:

var { buildSchema } = require('graphql');var schema = buildSchema(`    type Query {        token(id: Int!): Token        tokens(name: String): [Token]    },    type Token {        id: Int        name: String        price: Float        marketCap: Float    }`);module.exports = { schema };

The string in method buildSchema contains the IDL (GraphQL Interface Definition Language) code wich is used to describe the schema. This schema is validate each time the client makes an API call.

Now we create the service that will have to return the requested data. We will create 2 methods one for returning a point element by passing it an id (unique identifying value) and one for having all the elements. Let's create token-service.js in src/services:

var data = require('../data/tokens')var getToken = function(args) {     var id = args.id;    return data.tokens.filter(token => {        return token.id == id;    })[0];}var getTokens = function(args) {    if (args.name) {        var name = args.name;        return data.tokens.filter(token => token.name === name);    } else {        return data.tokens;    }}module.exports = { getToken, getTokens }

Now we need dataset, let's create tokens.js in src/data:

var tokens = [    {        id: 1,        name: 'Bitcoin',        price: 31750,        marketCap: 589066915097    },    {        id: 2,        name: 'Ethereum',        price: 1050,        marketCap: 118884401541    },    {        id: 3,        name: 'The Graph',        price: 0.3019,        marketCap: 376101076    }];module.exports = { tokens };

Now we have to create the core of our API. Then we create the server from which to start the application, let's create server.js in the main folder:

var express = require('express');var { graphqlHTTP } = require('express-graphql');var schemas = require('./src/schema/schema');var tokenService = require('./src/services/token-service');var root = {    token: tokenService.getToken,    tokens: tokenService.getTokens};var app = express();app.use('/graphql', graphqlHTTP({    schema: schemas.schema,    rootValue: root,    graphiql: true}));app.listen(8080, () => console.log('Express GraphQL Server Now Running On localhost:8080/graphql'));

Finally the Express server is created with a GraphQL endpoint:

http://localhost:8080/graphql

The result of our application is that:

Go in our powershell, and digit:

node server.js

After a few second we have this result in powershell:

Express GraphQL Server Now Running On localhost:8080/graphql

Now we can open browser and digit in url http://localhost:8080/graphql, this is the result:

In left side, we just insert our query, after that we must click button run and we have the result in right

This is the tecnology that "The Graph" cryptocurrency use.