Designing your GraphQL schema

The GraphQL schema is the foundation of any GraphQL server implementation. Each GraphQL API is defined by a single schema that contains types and fields describing how the data from requests will be populated. The data flowing through your API and the operations performed must be validated against the schema.

In general, the GraphQL type system describes the capabilities of a GraphQL server and is used to determine if a query is valid. A server’s type system is often referred to as that server’s schema and can consist of different object types, scalar types, input types, and more. GraphQL is both declarative and strongly typed, meaning the types will be well-defined at runtime and will only return what was specified.

AWS AppSync allows you to define and configure GraphQL schemas. The following section describes how to create GraphQL schemas from scratch using AWS AppSync's services.

Structuring a GraphQL Schema

GraphQL is a powerful tool for implementing API services. According to GraphQL's website, GraphQL is the following:

"GraphQL is a query language for APIs and a runtime for fulfilling those queries with your existing data. GraphQL provides a complete and understandable description of the data in your API, gives clients the power to ask for exactly what they need and nothing more, makes it easier to evolve APIs over time, and enables powerful developer tools."

This section covers the very first part of your GraphQL implementation, the schema. Using the quote above, a schema plays the role of "providing a complete and understandable description of the data in your API". In other words, a GraphQL schema is a textual representation of your service's data, operations, and the relations between them. The schema is considered the main entry point for your GraphQL service implementation. Unsurprisingly, it's often one of the first things you make in your project. We recommend reviewing the Schemas section before continuing.

To quote the Schemas section, GraphQL schemas are written in the Schema Definition Language (SDL). SDL is composed of types and fields with an established structure:

The simplest schemas will contain three different data categories:

To put this into perspective, imagine you're creating a service that stores authors and the books they've written. Each author has a name and an array of books they've authored. Each book has a name and a list of associated authors. We also want the ability to add or retrieve books and authors. A simple UML representation of this relationship may look like this:

In GraphQL, the entities Author and Book represent two different object types in your schema:

type Author {
}

type Book {
}

Author contains authorName and Books, while Book contains bookName and Authors. These can be represented as the fields within the scope of your types:

type Author {
  authorName: String
  Books: [Book]
}

type Book {
  bookName: String
  Authors: [Author]
}

As you can see, the type representations are very close to the diagram. However, the methods are where it gets a bit trickier. These will be placed in one of a few special object types as a field. Their special object categorization depends on their behavior. GraphQL contains three fundamental special object types: queries, mutations, and subscriptions. For more information, see Special objects.

Because getAuthor and getBook are both requesting data, they will be placed in a Query special object type:

type Author {
  authorName: String
  Books: [Book]
}

type Book {
  bookName: String
  Authors: [Author]
}

type Query {
  getAuthor(authorName: String): Author
  getBook(bookName: String): Book
}

The operations are linked to the query, which itself is linked to the schema. Adding a schema root will define the special object type (Query in this case) as one of your entry points. This can be done using the schema keyword:

schema {
  query: Query
}

type Author {
  authorName: String
  Books: [Book]
}

type Book {
  bookName: String
  Authors: [Author]
}

type Query {
  getAuthor(authorName: String): Author
  getBook(bookName: String): Book
}

Looking at the final two methods, addAuthor and addBook are adding data to your database, so they will be defined in a Mutation special object type. However, from the Types page, we also know that inputs directly referencing Objects aren't allowed because they're strictly output types. In this case, we can't use Author or Book, so we need to make an input type with the same fields. In this example, we added AuthorInput and BookInput, both of which accept the same fields of their respective types. Then, we create our mutation using the inputs as our parameters:

schema {
  query: Query
  mutation: Mutation
}

type Author {
  authorName: String
  Books: [Book]
}

input AuthorInput {
  authorName: String
  Books: [BookInput]
}

type Book {
  bookName: String
  Authors: [Author]
}

input BookInput {
  bookName: String
  Authors: [AuthorInput]
}

type Query {
  getAuthor(authorName: String): Author
  getBook(bookName: String): Book
}

type Mutation {
  addAuthor(input: [BookInput]): Author
  addBook(input: [AuthorInput]): Book
}

Let's review what we just did:

As you can see, the process of creating a schema takes a lot of concepts from data modeling (especially database modeling) in general. You can think of the schema as fitting the shape of the data from the source. It also serves as the model that the resolver will implement. In the following, sections, you'll learn how to make a schema using various AWS-backed tools and services.

Creating schemas

Your schema will be in a file called schema.graphql. AWS AppSync allows users to create new schemas for their GraphQL APIs using various methods. In this example, we'll be creating a blank API along with a blank schema.

Console

1. Sign in to the AWS Management Console and open the AppSync console.

   1. In the Dashboard, choose Create API.

   2. Under API options, choose GraphQL APIs, Design from scratch, then Next.

      1. For API name, change the prepopulated name to what your application needs.

      2. For contact details, you can enter a point of contact to identify a manager for the API. This is an optional field.

      3. Under Private API configuration, you can enable private API features. A private API can only be accessed from a configured VPC endpoint (VPCE). For more information, see Private APIs.

         We don't recommend enabling this feature for this example. Choose Next after reviewing your inputs.

   3. Under Create a GraphQL type, you can choose to create a DynamoDB table to use as a data source or skip this and do it later.

      For this example, choose Create GraphQL resources later. We will be creating a resource in a separate section.

   4. Review your inputs, then choose Create API.

2. You will be in the dashboard of your specific API. You can tell because the API's name will be at the top of the dashboard. If this isn't the case, you can select APIs in the Sidebar, then choose your API in the APIs dashboard.

   1. In the Sidebar underneath your API's name, choose Schema.

3. In the Schema editor, you can configure your schema.graphql file. It may be empty or filled with types generated from a model. On the right, you have the Resolvers section for attaching resolvers to your schema fields. We won't be looking at resolvers in this section.

CLI

Note

When using the CLI, make sure you have the correct permissions to access and create resources in the service. You may want to set least-privilege policies for non-admin users who need to access the service. For more information about AWS AppSync policies, see Identity and access management for AWS AppSync.

Additionally, we recommend reading the console version first if you haven't done so already.

1. If you haven't already done so, install the AWS CLI, then add your configuration.

2. Create a GraphQL API object by running the create-graphql-api command.

   You'll need to type in two parameters for this particular command:

   1. The name of your API.

   2. The authentication-type, or the type of credentials used to access the API (IAM, OIDC, etc.).

   Note

   Other parameters such as Region must be configured but will usually default to your CLI configuration values.

   An example command may look like this:

   aws appsync create-graphql-api --name testAPI123 --authentication-type API_KEY

   An output will be returned in the CLI. Here's an example:

   {
       "graphqlApi": {
           "xrayEnabled": false,
           "name": "testAPI123",
           "authenticationType": "API_KEY",
           "tags": {},
           "apiId": "abcdefghijklmnopqrstuvwxyz",
           "uris": {
               "GRAPHQL": "https://zyxwvutsrqponmlkjihgfedcba.appsync-api.us-west-2.amazonaws.com/graphql",
               "REALTIME": "wss://zyxwvutsrqponmlkjihgfedcba.appsync-realtime-api.us-west-2.amazonaws.com/graphql"
           },
           "arn": "arn:aws:appsync:us-west-2:107289374856:apis/abcdefghijklmnopqrstuvwxyz"
       }
   }

3. Note

   This is an optional command that takes an existing schema and uploads it to the AWS AppSync service using a base-64 blob. We will not be using this command for the sake of this example.

   Run the start-schema-creation command.

   You'll need to type in two parameters for this particular command:

   1. Your api-id from the previous step.

   2. The schema definition is a base-64 encoded binary blob.

   An example command may look like this:

    aws appsync start-schema-creation --api-id abcdefghijklmnopqrstuvwxyz --definition "aa1111aa-123b-2bb2-c321-12hgg76cc33v"

   An output will be returned:

   {
       "status": "PROCESSING"
   }

   This command will not return the final output after processing. You must use a separate command, get-schema-creation-status, to see the result. Note that these two commands are asynchronous, so you can check the output status even while the schema is still being created.

CDK

Tip

Before you use the CDK, we recommend reviewing the CDK's official documentation along with AWS AppSync's CDK reference.

The steps listed below will only show a general example of the snippet used to add a particular resource. This is not meant to be a working solution in your production code. We also assume you already have a working app.

1. The starting point for the CDK is a bit different. Ideally, your schema.graphql file should already be created. You just need to create a new file with the .graphql file extension. This can be an empty file.

2. In general, you may have to add the import directive to the service you're using. For example, it may follow the forms:

   import * as x from 'x'; # import wildcard as the 'x' keyword from 'x-service'
   import {a, b, ...} from 'c'; # import {specific constructs} from 'c-service'

   To add a GraphQL API, your stack file needs to import the AWS AppSync service:

   import * as appsync from 'aws-cdk-lib/aws-appsync';

   Note

   This means we're importing the entire service under the appsync keyword. To use this in your app, your AWS AppSync constructs will use the format appsync.construct_name. For instance, if we wanted to make a GraphQL API, we would say new appsync.GraphqlApi(args_go_here). The following step depicts this.

3. The most basic GraphQL API will include a name for the API and the schema path.

   const add_api = new appsync.GraphqlApi(this, 'API_ID', {
     name: 'name_of_API_in_console',
     schema: appsync.SchemaFile.fromAsset(path.join(__dirname, 'schema_name.graphql')),
   });

   Note

   Let's review what this snippet does. Inside the scope of api, we're creating a new GraphQL API by calling appsync.GraphqlApi(scope: Construct, id: string, props: GraphqlApiProps). The scope is this, which refers to the current object. The id is API_ID, which will be your GraphQL API's resource name in AWS CloudFormation when it's created. The GraphqlApiProps contains the name of your GraphQL API and the schema. The schema will generate a schema (SchemaFile.fromAsset) by searching the absolute path (__dirname) for the .graphql file (schema_name.graphql). In a real scenario, your schema file will probably be inside the CDK app.

   To use changes made to your GraphQL API, you'll have to redeploy the app.

Adding types to schemas

Now that you've added your schema, you can start adding both your input and output types. Note that the types here shouldn't be used in real code; they're just examples to help you understand the process.

First, we'll create an object type. In real code, you don't have to start with these types. You can make any type you want at any time so long as you follow GraphQL's rules and syntax.

Console

• You can create an object type using the type keyword along with the type's name:

  type Type_Name_Goes_Here {}

  Inside the type's scope, you can add fields that represent the object's characteristics:

  type Type_Name_Goes_Here {
    # Add fields here
  }

  Here's an example:

  type Obj_Type_1 {
    id: ID!
    title: String
    date: AWSDateTime
  }

  Note

  In this step, we added a generic object type with a required id field stored as ID, a title field stored as a String, and a date field stored as an AWSDateTime. To see a list of types and fields and what they do, see Schemas. To see a list of scalars and what they do, see the Type reference.

CLI

Note

We recommend reading the console version first if you haven't done so already.

• You can create an object type by running the create-type command.

  You'll need to enter a few parameters for this particular command:

  1. The api-id of your API.

  2. The definition, or the content of your type. In the console example, this was:

     type Obj_Type_1 {
       id: ID!
       title: String
       date: AWSDateTime
     }

  3. The format of your input. In this example, we're using SDL.

  An example command may look like this:

  aws appsync create-type --api-id abcdefghijklmnopqrstuvwxyz --definition "type Obj_Type_1{id: ID! title: String date: AWSDateTime}" --format SDL

  An output will be returned in the CLI. Here's an example:

  {
      "type": {
          "definition": "type Obj_Type_1{id: ID! title: String date: AWSDateTime}",
          "name": "Obj_Type_1",
          "arn": "arn:aws:appsync:us-west-2:107289374856:apis/abcdefghijklmnopqrstuvwxyz/types/Obj_Type_1",
          "format": "SDL"
      }
  }

  Note

  In this step, we added a generic object type with a required id field stored as ID, a title field stored as a String, and a date field stored as an AWSDateTime. To see a list of types and fields and what they do, see Schemas. To see a list of scalars and what they do, see Type reference.

  On a further note, you may have realized that entering the definition directly works for smaller types but is infeasible for adding larger or multiple types. You can opt to add everything in a .graphql file and then pass it as the input.

CDK

Tip

Before you use the CDK, we recommend reviewing the CDK's official documentation along with AWS AppSync's CDK reference.

The steps listed below will only show a general example of the snippet used to add a particular resource. This is not meant to be a working solution in your production code. We also assume you already have a working app.

To add a type, you need to add it to your .graphql file. For instance, the console example was:

type Obj_Type_1 {
  id: ID!
  title: String
  date: AWSDateTime
}

You can add your types directly to the schema like any other file.

Note

To use changes made to your GraphQL API, you'll have to redeploy the app.

The object type has fields that are scalar types such as strings and integers. AWS AppSync also allows you to use enhanced scalar types like AWSDateTime in addition to the base GraphQL scalars. Also, any field that ends in an exclamation point is required.

The ID scalar type in particular is a unique identifier that can be either String or Int. You can control these in your resolver code for automatic assignment.

There are similarities between special object types like Query and "regular" object types like the example above in that they both use the type keyword and are considered objects. However, for the special object types (Query, Mutation, and Subscription), their behavior is vastly different because they are exposed as the entry points for your API. They're also more about shaping operations rather than data. For more information, see The query and mutation types.

On the topic of special object types, the next step could be to add one or more of them to perform operations on the shaped data. In a real scenario, every GraphQL schema must at least have a root query type for requesting data. You can think of the query as one of the entry points (or endpoints) for your GraphQL server. Let's add a query as an example.

Console

• To create a query, you can simply add it to the schema file like any other type. A query would require a Query type and an entry in the root like this:

  schema {
    query: Name_of_Query
  }
  
  type Name_of_Query {
    # Add field operation here
  }

  Note that Name_of_Query in a production environment will simply be called Query in most cases. We recommend keeping it at this value. Inside the query type, you can add fields. Each field will perform an operation in the request. As a result, most, if not all, of these fields will be attached to a resolver. However, we're not concerned with that in this section. Regarding the format of the field operation, it might look like this:

  Name_of_Query(params): Return_Type # version with params
  Name_of_Query: Return_Type # version without params

  Here's an example:

  schema {
    query: Query
  }
  
  type Query {
    getObj: [Obj_Type_1]
  }
  
  type Obj_Type_1 {
    id: ID!
    title: String
    date: AWSDateTime
  }

  Note

  In this step, we added a Query type and defined it in our schema root. Our Query type defined a getObj field that returns a list of Obj_Type_1 objects. Note that Obj_Type_1 is the object of the previous step. In production code, your field operations will normally be working with data shaped by objects like Obj_Type_1. In addition, fields like getObj will normally have a resolver to perform the business logic. That will be covered in a different section.

  As an additional note, AWS AppSync automatically adds a schema root during exports, so technically you don't have to add it directly to the schema. Our service will automatically process duplicate schemas. We're adding it here as a best practice.

CLI

Note

We recommend reading the console version first if you haven't done so already.

1. Create a schema root with a query definition by running the create-type command.

   You'll need to enter a few parameters for this particular command:

   1. The api-id of your API.

   2. The definition, or the content of your type. In the console example, this was:

      schema {
        query: Query
      }

   3. The format of your input. In this example, we're using SDL.

   An example command may look like this:

   aws appsync create-type --api-id abcdefghijklmnopqrstuvwxyz --definition "schema {query: Query}" --format SDL

   An output will be returned in the CLI. Here's an example:

   {
       "type": {
           "definition": "schema {query: Query}",
           "name": "schema",
           "arn": "arn:aws:appsync:us-west-2:107289374856:apis/abcdefghijklmnopqrstuvwxyz/types/schema",
           "format": "SDL"
       }
   }

   Note

   Note that if you didn't input something correctly in the create-type command, you can update your schema root (or any type in the schema) by running the update-type command. In this example, we'll be temporarily changing the schema root to contain a subscription definition.

   You'll need to enter a few parameters for this particular command:

   1. The api-id of your API.

   2. The type-name of your type. In the console example, this was schema.

   3. The definition, or the content of your type. In the console example, this was:

      schema {
        query: Query
      }

      The schema after adding a subscription will look like this:

      schema {
        query: Query
        subscription: Subscription
      }

   4. The format of your input. In this example, we're using SDL.

   An example command may look like this:

   aws appsync update-type --api-id abcdefghijklmnopqrstuvwxyz --type-name schema --definition "schema {query: Query subscription: Subscription}" --format SDL

   An output will be returned in the CLI. Here's an example:

   {
       "type": {
           "definition": "schema {query: Query subscription: Subscription}",
           "arn": "arn:aws:appsync:us-west-2:107289374856:apis/abcdefghijklmnopqrstuvwxyz/types/schema",
           "format": "SDL"
       }
   }

   Adding preformatted files will still work in this example.

2. Create a Query type by running the create-type command.

   You'll need to enter a few parameters for this particular command:

   1. The api-id of your API.

   2. The definition, or the content of your type. In the console example, this was:

      type Query {
        getObj: [Obj_Type_1]
      }

   3. The format of your input. In this example, we're using SDL.

   An example command may look like this:

   aws appsync create-type --api-id abcdefghijklmnopqrstuvwxyz --definition "type Query {getObj: [Obj_Type_1]}" --format SDL

   An output will be returned in the CLI. Here's an example:

   {
       "type": {
           "definition": "Query {getObj: [Obj_Type_1]}",
           "name": "Query",
           "arn": "arn:aws:appsync:us-west-2:107289374856:apis/abcdefghijklmnopqrstuvwxyz/types/Query",
           "format": "SDL"
       }
   }

   Note

   In this step, we added a Query type and defined it in your schema root. Our Query type defined a getObj field that returned a list of Obj_Type_1 objects.

   In the schema root code query: Query, the query: part indicates that a query was defined in your schema, while the Query part indicates the actual special object name.

CDK

Tip

Before you use the CDK, we recommend reviewing the CDK's official documentation along with AWS AppSync's CDK reference.

The steps listed below will only show a general example of the snippet used to add a particular resource. This is not meant to be a working solution in your production code. We also assume you already have a working app.

You'll need to add your query and the schema root to the .graphql file. Our example looked like the example below, but you'll want to replace it with your actual schema code:

schema {
  query: Query
}

type Query {
  getObj: [Obj_Type_1]
}

type Obj_Type_1 {
  id: ID!
  title: String
  date: AWSDateTime
}

You can add your types directly to the schema like any other file.

Note

Updating the schema root is optional. We added it to this example as a best practice.

To use changes made to your GraphQL API, you'll have to redeploy the app.

You've now seen an example of creating both objects and special objects (queries). You've also seen how these can be interconnected to describe data and operations. You can have schemas with only the data description and one or more queries. However, we'd like to add another operation to add data to the data source. We'll add another special object type called Mutation that modifies data.

Console

• A mutation will be called Mutation. Like Query, the field operations inside Mutation will describe an operation and will be attached to a resolver. Also, note that we need to define it in the schema root because it's a special object type. Here's an example of a mutation:

  schema {
    mutation: Name_of_Mutation
  }
  
  type Name_of_Mutation {
    # Add field operation here
  }

  A typical mutation will be listed in the root like a query. The mutation is defined using the type keyword along with the name. Name_of_Mutation will usually be called Mutation, so we recommend keeping it that way. Each field will also perform an operation. Regarding the format of the field operation, it might look like this:

  Name_of_Mutation(params): Return_Type # version with params
  Name_of_Mutation: Return_Type # version without params

  Here's an example:

  schema {
    query: Query
    mutation: Mutation
  }
  
  type Obj_Type_1 {
    id: ID!
    title: String
    date: AWSDateTime
  }
  
  type Query {
    getObj: [Obj_Type_1]
  }
  
  type Mutation {
    addObj(id: ID!, title: String, date: AWSDateTime): Obj_Type_1
  }

  Note

  In this step, we added a Mutation type with an addObj field. Let's summarize what this field does:

  addObj(id: ID!, title: String, date: AWSDateTime): Obj_Type_1

  addObj is using the Obj_Type_1 object to perform an operation. This is apparent due to the fields, but the syntax proves this in the : Obj_Type_1 return type. Inside addObj, it's accepting the id, title, and date fields from the Obj_Type_1 object as parameters. As you may see, it looks a lot like a method declaration. However, we haven't described the behavior of our method yet. As stated earlier, the schema is only there to define what the data and operations will be and not how they operate. Implementing the actual business logic will come later when we create our first resolvers.

  Once you're done with your schema, there's an option to export it as a schema.graphql file. In the Schema editor, you can choose Export schema to download the file in a supported format.

  As an additional note, AWS AppSync automatically adds a schema root during exports, so technically you don't have to add it directly to the schema. Our service will automatically process duplicate schemas. We're adding it here as a best practice.

CLI

Note

We recommend reading the console version first if you haven't done so already.

1. Update your root schema by running the update-type command.

   You'll need to enter a few parameters for this particular command:

   1. The api-id of your API.

   2. The type-name of your type. In the console example, this was schema.

   3. The definition, or the content of your type. In the console example, this was:

      schema {
        query: Query
        mutation: Mutation
      }

   4. The format of your input. In this example, we're using SDL.

   An example command may look like this:

   aws appsync update-type --api-id abcdefghijklmnopqrstuvwxyz --type-name schema --definition "schema {query: Query mutation: Mutation}" --format SDL

   An output will be returned in the CLI. Here's an example:

   {
       "type": {
           "definition": "schema {query: Query mutation: Mutation}",
           "arn": "arn:aws:appsync:us-west-2:107289374856:apis/abcdefghijklmnopqrstuvwxyz/types/schema",
           "format": "SDL"
       }
   }

2. Create a Mutation type by running the create-type command.

   You'll need to enter a few parameters for this particular command:

   1. The api-id of your API.

   2. The definition, or the content of your type. In the console example, this was

      type Mutation {
        addObj(id: ID!, title: String, date: AWSDateTime): Obj_Type_1
      }

   3. The format of your input. In this example, we're using SDL.

   An example command may look like this:

   aws appsync create-type --api-id abcdefghijklmnopqrstuvwxyz --definition "type Mutation {addObj(id: ID! title: String date: AWSDateTime): Obj_Type_1}" --format SDL

   An output will be returned in the CLI. Here's an example:

   {
       "type": {
           "definition": "type Mutation {addObj(id: ID! title: String date: AWSDateTime): Obj_Type_1}",
           "name": "Mutation",
           "arn": "arn:aws:appsync:us-west-2:107289374856:apis/abcdefghijklmnopqrstuvwxyz/types/Mutation",
           "format": "SDL"
       }
   }

CDK

Tip

Before you use the CDK, we recommend reviewing the CDK's official documentation along with AWS AppSync's CDK reference.

The steps listed below will only show a general example of the snippet used to add a particular resource. This is not meant to be a working solution in your production code. We also assume you already have a working app.

You'll need to add your query and the schema root to the .graphql file. Our example looked like the example below, but you'll want to replace it with your actual schema code:

schema {
  query: Query
  mutation: Mutation
}

type Obj_Type_1 {
  id: ID!
  title: String
  date: AWSDateTime
}

type Query {
  getObj: [Obj_Type_1]
}

type Mutation {
  addObj(id: ID!, title: String, date: AWSDateTime): Obj_Type_1
}

Note

Updating the schema root is optional. We added it to this example as a best practice.

To use changes made to your GraphQL API, you'll have to redeploy the app.

Optional considerations - Using enums as statuses

At this point, you know how to make a basic schema. However, there are many things you could add to increase the schema's functionality. One common thing found in applications is the use of enums as statuses. You can use an enum to force a specific value from a set of values to be chosen when called. This is good for things that you know will not change drastically over long periods of time. Hypothetically speaking, we could add an enum that returns the status code or String in the response.

As an example, let's assume we're making a social media app that's storing a user's post data in the backend. Our schema contains a Post type that represents an individual post's data:

type Post {
  id: ID!
  title: String
  date: AWSDateTime
  poststatus: PostStatus
}

Our Post will contain a unique id, post title, date of posting, and an enum called PostStatus that represents the post's state as it's processed by the app. For our operations, we'll have a query that returns all post data:

type Query {
  getPosts: [Post]
}

We'll also have a mutation that adds posts to the data source:

type Mutation {
  addPost(id: ID!, title: String, date: AWSDateTime, poststatus: PostStatus): Post
}

Looking at our schema, the PostStatus enum could have several statuses. We might want the three basic states called success (post successfully processed), pending (post being processed), and error (post unable to be processed). To add the enum, we could do this:

enum PostStatus {
  success
  pending
  error
}

The full schema might look like this:

schema {
  query: Query
  mutation: Mutation
}

type Post {
  id: ID!
  title: String
  date: AWSDateTime
  poststatus: PostStatus
}

type Mutation {
  addPost(id: ID!, title: String, date: AWSDateTime, poststatus: PostStatus): Post
}

type Query {
  getPosts: [Post]
}

enum PostStatus {  
  success
  pending
  error
}

If a user adds a Post in the application, the addPost operation will be called to process that data. As the resolver attached to addPost processes the data, it will continually update the poststatus with the status of the operation. When queried, the Post will contain the final status of the data. Keep in mind, we're only describing how we want the data to work in the schema. We're assuming a lot about the implementation of our resolver(s), which will implement the actual business logic for handling the data to fulfill the request.

Optional considerations - Subscriptions

Subscriptions in AWS AppSync are invoked as a response to a mutation. You configure this with a Subscription type and @aws_subscribe() directive in the schema to denote which mutations invoke one or more subscriptions. For more information about configuring subscriptions, see Real-time data.

Optional considerations - Relations and pagination

Suppose you had a million Posts stored in a DynamoDB table, and you wanted to return some of that data. However, the example query given above only returns all posts. You wouldn’t want to fetch all of these every time you made a request. Instead, you would want to paginate through them. Make the following changes to your schema:

schema {
  query: Query
  mutation: Mutation
}

type Post {
  id: ID!
  title: String
  date: AWSDateTime
  poststatus: PostStatus
}

type Mutation {
  addPost(id: ID!, title: String, date: AWSDateTime, poststatus: PostStatus): Post
}

type Query {
  getPosts(limit: Int, nextToken: String): PostIterator
}

enum PostStatus {
  success
  pending
  error
}

type PostIterator {
  posts: [Post]
  nextToken: String
}

The PostIterator type allows you to return a portion of the list of Post objects and a nextToken for getting the next portion. Inside PostIterator, there is a list of Post items ([Post]) that is returned with a pagination token (nextToken). In AWS AppSync, this would be connected to Amazon DynamoDB through a resolver and automatically generated as an encrypted token. This converts the value of the limit argument to the maxResults parameter and the nextToken argument to the exclusiveStartKey parameter. For examples and the built-in template samples in the AWS AppSync console, see Resolver reference (JavaScript).