Creating a GraphQL api with Apollo, Node, Express, Sequelize, and Postgres.

The models and data

If you follow the readme you should end up with a data set with 3 categories and 3 locations (this is generated via the migrations and seeds, you can find out more about this here).

There is a many-to-many relationship between tables. For example, a location can have many categories and vice versa. You can see how this is achieved with Sequelize in the models directory.

"use strict";
module.exports = (sequelize, DataTypes) => {
  var Categories = sequelize.define("Categories", {
    name: DataTypes.STRING,
    updatedAt: DataTypes.INTEGER,
    createdAt: DataTypes.INTEGER,
    id: {
      type: DataTypes.INTEGER,
      primaryKey: true,
      allowNull: false,
      autoIncrement: true
    }
  });
  Categories.associate = function(models) {
    Categories.belongsToMany(models.Locations, {
      through: "CategoriesLocations",
      foreignKey: "categoryId"
    });
  };
  return Categories;
};

Here’s the example categories model. As well as the basics of setting the property data types you can also see that we set the association using the name of the join table and foreign key. As this is a many-to-many relationship so we have a similar association in the locations model. Sequelize has various different features so I suggest looking at their documentation if you have a different use case.

Resolvers

Creating an Apollo server requires you to pass in resolvers. Resolvers essentially hold the logic of how your queries/mutations map to the appropriate data.

In the case of this project we have a categories resolver which uses Sequelize to query the database and return all of the categories.

categories: (parent, args, { db }, info) => {
  return db.Categories.findAll();
}

The rest of the resolvers can be found in the resolvers directory. There is a more complicated example for locations which shows how you can pass arguments from your query.

Queries/Mutations

After running your server you should be able to access the GraphQL playground on http://localhost:4000/graphql.

The api exposes a few simple queries. You can list all the categories and the locations. You can also pass in an argument to the locations query and only show locations based on their ID.

To find them all just take out the argument `(categoryId:1)`

query {
  locations(categoryId:1){
    name,
    id
  }
}

To find all categories:

query {
  categories{
    name,
    id
  }
}

There is also a mutation which allows you to add a category.

mutation {
  addCategory(categoryName: "Night life") {
    name
  }
}

The schema directory contains all the code for this. I followed a great article which showed a nice way modularise your types, queries and mutations.