Thanks to Richard Threlkeld and Attila Hajdrik for their help writing this article.

How to implement a real-world & comprehensive data model covering over 17 different access patterns using GraphQL, AWS Amplify, and a NoSQL database (Amazon DynamoDB).

• Understanding the GraphQL directives
• 17 data access patterns
• Additional basic access patterns
• Running locally

At the core of most applications is one thing: the data. Easily being able to, and understanding how to, model and access data in your app allows you to focus on delivering core features and business value instead of architecting and re-architecting your back end.

This is usually not an easy task, and requires a lot of thought. Part of getting this right is understanding the relationships between different types of data and how to make them work together.

In this tutorial I cover, in depth, how to do this using GraphQL, AWS Amplify, a NoSQL database, and the GraphQL Transform library.

Understanding the GraphQL directives

In this tutorial we will be leveraging the @model, @connection, and @key directives to model relationships between our data. To better understand how this works, let's have a look at these three directives.

@model - Generates a NoSQL database, resolvers, and CRUD + List + subscription GraphQL operation definitions from a base GraphQL type

@connection - Enables relationships between GraphQL types

@key - Enables efficient queries with conditions by using underlying database index structures for optimization

Let's say that we have basic GraphQL types that look like this:

type Book {
  id: ID!
  title: String
  author: Author
}

type Author {
  id: ID!
  name: String!
}

To first expand this into a full API with database, resolvers, CRUD + List operations, and subscriptions, we can add the @model directive to each type:

type Book @model {
  id: ID!
  title: String
  author: Author
}

type Author @model {
  id: ID!
  name: String!
}

Next, we want to add a relationship between the book and the author. To do this, we can use the @connection directive:

type Book @model {
  id: ID!
  title: String
  author: Author @connection
}

type Author @model {
  id: ID!
  name: String!
}

Next, let's say we want a way to query the books by book title. How could we manage this? We could update the Book type with a @key directive:

type Book @model
  @key(name: "byTitle", fields: ["title"], queryField: "bookByTitle") {
  id: ID!
  title: String
  author: Author @connection
}

Now, we can use the following query to query by book title:

query byTitle {
  bookByTitle(title: "Grapes of Wrath") {
    items {
      id
      title
    }
  }
}

The @key directive in the above example takes the following arguments:

# name - name of the key
# fields - field(s) that we will be querying by
# queryField - name of the GraphQL query to be generated

@key(name: "byTitle", fields: ["title"], queryField: "bookByTitle")

Let's take this one step further. What if we want to create a Publisher type and assign books to a certain publisher? We want to use our existing Book type and associate it with our new Publisher type. We could do this with the following updates to the schema:

type Publisher @model {
  name: String!
  id: ID!
  books: [Book] @connection(keyName: "byPublisherId", fields: ["id"])
}

type Book @model
  @key(name: "byTitle", fields: ["title"], queryField: "bookByTitle")
  @key(name: "byPublisherId", fields: ["publisherId"], queryField: "booksByPublisherId")
{
  id: ID!
  publisherId: ID!
  title: String
  author: Author @connection
}

Here, we've added a new @key directive named byPublisherId and associated it with the resolved books field of the Publisher type. Now, we can query publishers and also get the associated books and authors:

query listPublishers {
  listPublishers {
    items {
      id
        books {
        items {
          id
          title
          author {
            id
            name
          }
        }
      }       
    }
  }
}

Furthermore, with the new booksByPublisherId query, we can also directly query all books by publisher ID:

query booksByPublisherId($publisherId: ID!) {
  booksByPublisherId(publisherId: $publisherId) {
    items {
      id
      title
    }
  }
}

Understanding how to use these directives opens the door to a wide array of access patterns on your database. In the next section, we will dive even deeper into this.

17 Access patterns

In the DynamoDB documentation for modeling relational data in a NoSQL database, there is an in depth example of 17 access patterns from the 'First Steps for Modeling Relational Data in DynamoDB' page. In this tutorial, I will show how to support these data access patterns using GraphQL, AWS Amplify, and the GraphQL Transform library.

This example has the following types:

• Warehouse
• Product
• Inventory
• Employee
• AccountRepresentative
• Customer
• Product

Let's have a look at the access patterns that we'll be implementing in this tutorial:

1. Look up employee details by employee ID
2. Query employee details by employee name
3. Find an employee's phone number(s)
4. Fine a customer's phone number(s)
5. Get orders for a given customer within a given date range
6. Show all open orders within a given date range across all customers
7. See all employees recently hired
8. Find all employees working in a given warehouse
9. Get all items on order for a given product
10. Get current inventories for a given product at all warehouses
11. Get customers by account representative
12. Get orders by account representative and date
13. Get all items on order for a given product
14. Get all employees with a given job title
15. Get inventory by product and warehouse
16. Get total product inventory
17. Get account representatives ranked by order total and sales period

The following schema introduces the required keys and connections so that we can support 17 access patterns.

type Order @model
  @key(name: "byCustomerByStatusByDate", fields: ["customerID", "status", "date"])
  @key(name: "byCustomerByDate", fields: ["customerID", "date"])
  @key(name: "byRepresentativebyDate", fields: ["accountRepresentativeID", "date"])
  @key(name: "byProduct", fields: ["productID", "id"])
{
  id: ID!
  customerID: ID!
  accountRepresentativeID: ID!
  productID: ID!
  status: String!
  amount: Int!
  date: String!
}

type Customer @model
  @key(name: "byRepresentative", fields: ["accountRepresentativeID", "id"])
{
  id: ID!
  name: String!
  phoneNumber: String
  accountRepresentativeID: ID!
  ordersByDate: [Order] @connection(keyName: "byCustomerByDate", fields: ["id"])
  ordersByStatusDate: [Order] @connection(keyName: "byCustomerByStatusByDate", fields: ["id"])
}

type Employee @model
  @key(name: "newHire", fields: ["newHire", "id"], queryField: "employeesNewHire")
  @key(name: "newHireByStartDate", fields: ["newHire", "startDate"], queryField: "employeesNewHireByStartDate")
  @key(name: "byName", fields: ["name", "id"], queryField: "employeeByName")
  @key(name: "byTitle", fields: ["jobTitle", "id"], queryField: "employeesByJobTitle")
  @key(name: "byWarehouse", fields: ["warehouseID", "id"])
{
  id: ID!
  name: String!
  startDate: String!
  phoneNumber: String!
  warehouseID: ID!
  jobTitle: String!
  newHire: String! # We have to use String type, because Boolean types cannot be sort keys
}

type Warehouse @model {
  id: ID!
  employees: [Employee] @connection(keyName: "byWarehouse", fields: ["id"])
}

type AccountRepresentative @model
  @key(name: "bySalesPeriodByOrderTotal", fields: ["salesPeriod", "orderTotal"], queryField: "repsByPeriodAndTotal")
{
  id: ID!
  customers: [Customer] @connection(keyName: "byRepresentative", fields: ["id"])
  orders: [Order] @connection(keyName: "byRepresentativebyDate", fields: ["id"])
  orderTotal: Int
  salesPeriod: String
}

type Inventory @model
  @key(name: "byWarehouseID", fields: ["warehouseID"], queryField: "itemsByWarehouseID")
  @key(fields: ["productID", "warehouseID"])
{
  productID: ID!
  warehouseID: ID!
  inventoryAmount: Int!
}

type Product @model {
  id: ID!
  name: String!
  orders: [Order] @connection(keyName: "byProduct", fields: ["id"])
  inventories: [Inventory] @connection(fields: ["id"])
}

Now that we have the schema created, let's create the items in the database that we will be operating against:

# first
mutation createWarehouse {
  createWarehouse(input: {id: "1"}) {
    id
  }
}

# second
mutation createEmployee {
  createEmployee(input: {
    id: "amanda"
    name: "Amanda",
    startDate: "2018-05-22",
    phoneNumber: "6015555555",
    warehouseID: "1",
    jobTitle: "Manager",
    newHire: "true"}
  ) {
    id
    jobTitle
    name
    newHire
    phoneNumber
    startDate
    warehouseID
  }
}

# third
mutation createAccountRepresentative {
  createAccountRepresentative(input: {
    id: "dabit"
    orderTotal: 400000
    salesPeriod: "January 2019"
  }) {
    id
    orderTotal
    salesPeriod
  }
}

# fourth
mutation createCustomer {
  createCustomer(input: {
    id: "jennifer_thomas"
    accountRepresentativeID: "dabit"
    name: "Jennifer Thomas"
    phoneNumber: "+16015555555"
  }) {
    id
    name
    accountRepresentativeID
    phoneNumber
  }
}

# fifth
mutation createProduct {
  createProduct(input: {
    id: "yeezyboost"
    name: "Yeezy Boost"
  }) {
    id
    name
  }
}

# sixth
mutation createInventory {
  createInventory(input: {
    productID: "yeezyboost"
    warehouseID: "1"
    inventoryAmount: 300
  }) {
    id
    productID
    inventoryAmount
    warehouseID
  }
}

# seventh
mutation createOrder {
  createOrder(input: {
    amount: 300
    date: "2018-07-12"
    status: "pending"
    accountRepresentativeID: "dabit"
    customerID: "jennifer_thomas"
    productID: "yeezyboost"
  }) {
    id
    customerID
    accountRepresentativeID
    amount
    date
    customerID
    productID
  }
}

1. Look up employee details by employee ID:
This can simply be done by querying the employee model with an employee ID, no @key or @connection is needed to make this work.

query getEmployee($id: ID!) {
  getEmployee(id: $id) {
    id
    name
    phoneNumber
    startDate
    jobTitle
  }
}

2. Query employee details by employee name:
The @key byName on the Employee type makes this access-pattern feasible because under the covers an index is created and a query is used to match against the name field. We can use this query:

query employeeByName($name: String!) {
  employeeByName(name: $name) {
    items {
      id
      name
      phoneNumber
      startDate
      jobTitle
    }
  }
}

3. Find an Employee’s phone number:
Either one of the previous queries would work to find an employee’s phone number as long as one has their ID or name.

4. Find a customer’s phone number:
A similar query to those given above but on the Customer model would give you a customer’s phone number.

query getCustomer($customerID: ID!) {
  getCustomer(id: $customerID) {
    phoneNumber
  }
}

5. Get orders for a given customer within a given date range:
There is a one-to-many relation that lets all the orders of a customer be queried.

This relationship is created by having the @key name byCustomerByDate on the Order model that is queried by the connection on the orders field of the Customer model.

A sort key with the date is used. What this means is that the GraphQL resolver can use predicates like Between to efficiently search the date range rather than scanning all records in the database and then filtering them out.

The query one would need to get the orders to a customer within a date range would be:

query getCustomerWithOrdersByDate($customerID: ID!) {
  getCustomer(id: $customerID) {
    ordersByDate(date: {
      between: [ "2018-01-22", "2020-10-11" ]
    }) {
      items {
        id
        amount
        productID
      }
    }
  }
}

6. Show all open orders within a given date range across all customers:
The @key byCustomerByStatusByDate enables you to run a query that would work for this access pattern.

In this example, a composite sort key (combination of two or more keys) with the status and date is used. What this means is that the unique identifier of a record in the database is created by concatenating these two fields (status and date) together, and then the GraphQL resolver can use predicates like Between or Contains to efficiently search the unique identifier for matches rather than scanning all records in the database and then filtering them out.

query getCustomerWithOrdersByStatusDate($customerID: ID!) {
  getCustomer(id: $customerID) {
    ordersByStatusDate (statusDate: {
      between: [
        { status: "pending" date:  "2018-01-22" },
        { status: "pending", date: "2020-10-11"}
      ]}) {
        items {
            id
            amount
            date
        }
    }
  }
}

7. See all employees hired recently:
Having ‘@key(name: "newHire", fields: ["newHire", "id"])’ on the Employee model allows one to query by whether an employee has been hired recently.

query employeesNewHire {
  employeesNewHire(newHire: "true") {
    items {
      id
      name
      phoneNumber
      startDate
      jobTitle
    }
  }
}

We can also query and have the results returned by start date by using the employeesNewHireByStartDate query:

query employeesNewHireByDate {
  employeesNewHireByStartDate(newHire: "true") {
    items {
      id
      name
      phoneNumber
      startDate
      jobTitle
    }
  }
}

8. Find all employees working in a given warehouse:
This needs a one to many relationship from warehouses to employees. As can be seen from the @connection in the Warehouse model, this connection uses the byWarehouse key on the Employee model. The relevant query would look like this:

query getWarehouse($warehouseID: ID!) {
  getWarehouse(id: $warehouseID) {
    id
    employees{
      items {
        id
        name
        startDate
        phoneNumber
        jobTitle
      }
    }
  }
}

9. Get all items on order for a given product:
This access-pattern would use a one-to-many relation from products to orders. With this query we can get all orders of a given product:

query getProductOrders($productID: ID!) {
  getProduct(id: $productID) {
    id
    orders {
      items {
        id
        status
        amount
        date
      }
    }
  }
}

10. Get current inventories for a product at all warehouses:

The query needed to get the inventories of a product in all warehouses would be:

query getProductInventoryInfo($productID: ID!) {
  getProduct(id: $productID) {
    id
    inventories {
      items {
        warehouseID
        inventoryAmount
      }
    }
  }
}

11. Get customers by account representative:
This uses a one-to-many connection between account representatives and customers:

The query needed would look like this:

query getCustomersForAccountRepresentative($representativeId: ID!) {
  getAccountRepresentative(id: $representativeId) {
    customers {
      items {
        id
        name
        phoneNumber
      }
    }
  }
}

12. Get orders by account representative and date:

As can be seen in the AccountRepresentative model this connection uses the byRepresentativebyDate field on the Order model to create the connection needed. The query needed would look like this:

query getOrdersForAccountRepresentative($representativeId: ID!) {
  getAccountRepresentative(id: $representativeId) {
    id
    orders(date: {
      between: [
         "2010-01-22", "2020-10-11"
      ]
    }) {
        items {
          id
          status
          amount
          date
        }
    }
  }
}

13. Get all items on order for a given product:
This is the same as number 9.

14. Get all employees with a given job title:
Using the byTitle @key makes this access pattern quite easy.

query employeesByJobTitle {
  employeesByJobTitle(jobTitle: "Manager") {
    items {
      id
      name
      phoneNumber
      jobTitle
    }
  }
}

15. Get inventory by product by warehouse:
Here having the inventories be held in a separate model is particularly useful since this model can have its own partition key and sort key such that the inventories themselves can be queried as is needed for this access-pattern.

A query on this model would look like this:

query inventoryByProductAndWarehouse($productID: ID!, $warehouseID: ID!) {
  getInventory(productID: $productID, warehouseID: $warehouseID) {
    productID
    warehouseID
    inventoryAmount
  }
}

We can also get all inventory from an individual warehouse by using the itemsByWarehouseID query created by the byWarehouseID key:

query byWarehouseId($warehouseID: ID!) {
  itemsByWarehouseID(warehouseID: $warehouseID) {
    items {
      inventoryAmount
      productID
    }
  }
}

16. Get total product inventory:
How this would be done depends on the use case. If one just wants a list of all inventories in all warehouses, one could just run a list inventories on the Inventory model:

query listInventorys {
  listInventorys {
    items {
      productID
      warehouseID
      inventoryAmount
    }
  }
}

17. Get sales representatives ranked by order total and sales period:
It's uncertain exactly what this means. My take is that the sales period is either a date range or maybe even a month or week. Therefore we can set the sales period as a string and query using the combination of salesPeriod and orderTotal. We can also set the sortDirection in order to get the return values from largest to smallest:

query repsByPeriodAndTotal {
  repsByPeriodAndTotal(
    sortDirection: DESC,
    salesPeriod: "January 2019",
    orderTotal: {
      ge: 1000
    }) {
    items {
      id
      orderTotal
    }
  }
}

Additional basic access patterns

Since we are using the GraphQL Transform library, we will be getting all of the basic read & list operations on each type as well. So for each type, we will have a get and list operation.

So for Order, Customer, Employee, Warehouse, AccountRepresentative, Inventory, and Product we can also perform basic get by ID and list operations:

query getOrder($id: ID!) {
  getOrder(id: $id) {
    id
    customerID
    accountRepresentativeID
    productID
    status
    amount
    date
  }
}

query listOrders {
  listOrders {
    items {
      id
      customerID
      accountRepresentativeID
      productID
      status
      amount
      date
    }
  }
}

Running locally

To try or test these out locally, you can get up and running in just a couple of minutes using the Amplify CLI.

1. Download the latest version of the Amplify CLI:

$ npm install -g @aws-amplify/cli

2. Configure the CLI

$ amplify configure

For a video guide on how to configure the CLI, check out the documentation here

3. Create a new Amplify project

$ amplify init

4. Add a GraphQL API

$ amplify add API

# Choose GraphQL
# Choose API key as the authorization type
# Use the schema in this tutorial

5. Mock the API locally

$ amplify mock