For most of the cases defining a fixed schema when the application starts, by adding Query and Mutation types solely using schema language is good enough. But sometimes we might need to define a dynamic schema and we can achieve this by creating a new JS objects.

Construct dynamic schema for ‘User Greeting’ example.

Let’s get again to the ‘Greetings user’ example, because of it’s simplicity and define a Query with field named greetingUser which will accept userName and bornMonth parameters, first of type string and the second of type int and return userType.

And the userType will return greetingOne  which will simply say “Hello [userName]” and greetingTwo  that will let the user know how many months left till their next birthday. Both of type string.

./src/server.js

var express = require('express');
var graphqlHTTP = require('express-graphql');
var { buildSchema } = require('graphql');
var dogs = require('./src/models/mock_data/dogs.js');
const graphql = require('graphql');

// Define the User type
var userType = new graphql.GraphQLObjectType({
  name: 'UserType',
  fields: {
    greetingOne: { type: graphql.GraphQLString },
    greetingTwo: { type: graphql.GraphQLString },
  }
});

// Define the Query type
var queryType = new graphql.GraphQLObjectType({
  name: 'Query',
  fields: {
    greetingUser: {
      type: userType,
      args: {
        userName: { type: graphql.GraphQLString },
        bornMonth: { type: graphql.GraphQLInt }
      },
      resolve: function (_, {userName, bornMonth}) {
        var date = new Date();
        var daysLeft = bornMonth - (date.getMonth() + 1);
        daysLeft = daysLeft < 0 ? daysLeft + 12 : daysLeft;
        return {
          greetingOne: `Hello ${userName}`,
          greetingTwo: `Your birthday is comming in ${daysLeft} month(s)`
        };
      }
    }
  }
});

var schema = new graphql.GraphQLSchema({query: queryType});


// Logger middleware
var logger = function(req, res, next) {
  console.log("GOT REQUEST >", req.ip);
  next(); // Passing the request to the next handler in the stack.
}

var app = express();
app.use(logger);
app.use('/graphql', graphqlHTTP({
  schema: schema,
  graphiql: true,
}));
app.listen(4000);
console.log('Running a GraphQL API server at localhost:4000/graphql');

what we just did:
– we defined the user type which is pretty self explanatory (Lines 8-14)
– then we created the query type, that has these parameters:
– type which is the return type, in this case userType
– args is the input parameter types.
– resolve is the resolver function.

Transform Dogs catalog to use dynamic schema.

Creating the dog type

var dogType = new graphql.GraphQLObjectType({
  name: 'dogType',
  fields: {
    id: { type: graphql.GraphQLString },
    breed: { type: graphql.GraphQLString },
    displayImage: { type: graphql.GraphQLString },
  }
});

Creating the query type

// Define the Query type
var queryType = new graphql.GraphQLObjectType({
  name: 'Query',
  fields: {
    getDogByBreed: {
      type: dogType,
      args: {
        breed: { type: graphql.GraphQLString }
      },
      resolve: function (_, {breed}) {

        var result = dogs.find(function(dog){
          return breed == dog.breed;
        });
        return result;
      }
    }
  }
});

Creating a mutation type

...
    addDogBreed: {
      type: graphql.GraphQLString,
      args: {
        id: { type: graphql.GraphQLString },
        breed: { type: graphql.GraphQLString },
        displayImage: { type: graphql.GraphQLString }
      },
      resolve: function (_, {id, breed, displayImage}) {
        dogs.push({
          id: id,
          breed: breed,
          displayImage: displayImage
        });
        return "OK!";
      }
    } 
...

Adding the query schema

...
var schema = new graphql.GraphQLSchema({query: queryType});

...
app.use('/graphql', graphqlHTTP({
  schema: schema,
  graphiql: true,
}));
...

Putting it all together

var express = require('express');
var graphqlHTTP = require('express-graphql');
var { buildSchema } = require('graphql');
var dogs = require('./src/models/mock_data/dogs.js');
const graphql = require('graphql');

// Define the dogs type
var dogType = new graphql.GraphQLObjectType({
  name: 'dogType',
  fields: {
    id: { type: graphql.GraphQLString },
    breed: { type: graphql.GraphQLString },
    displayImage: { type: graphql.GraphQLString },
  }
});

// Define the Query type
var queryType = new graphql.GraphQLObjectType({
  name: 'Query',
  fields: {
    getDogByBreed: {
      type: dogType,
      args: {
        breed: { type: graphql.GraphQLString }
      },
      resolve: function (_, {breed}) {

        var result = dogs.find(function(dog){
          return breed == dog.breed;
        });
        return result;
      }
    },
    addDogBreed: {
      type: graphql.GraphQLString,
      args: {
        id: { type: graphql.GraphQLString },
        breed: { type: graphql.GraphQLString },
        displayImage: { type: graphql.GraphQLString }
      },
      resolve: function (_, {id, breed, displayImage}) {
        dogs.push({
          id: id,
          breed: breed,
          displayImage: displayImage
        });
        return "OK!";
      }
    }    
  }
});


var schema = new graphql.GraphQLSchema({query: queryType});


// Logger middleware
var logger = function(req, res, next) {
  console.log("GOT REQUEST >", req.ip);
  next(); // Passing the request to the next handler in the stack.
}

var app = express();
app.use(logger);
app.use('/graphql', graphqlHTTP({
  schema: schema,
  graphiql: true,
}));
app.listen(4000);
console.log('Running a GraphQL API server at localhost:4000/graphql');