# Resolver
<a name="sam-property-graphqlapi-resolver"></a>

Configure resolvers for the fields of your GraphQL API. AWS Serverless Application Model (AWS SAM) supports [JavaScript pipeline resolvers](https://docs.aws.amazon.com/appsync/latest/devguide/resolver-reference-overview-js.html).

## Syntax
<a name="sam-property-graphqlapi-resolver-syntax"></a>

To declare this entity in your AWS Serverless Application Model (AWS SAM) template, use the following syntax.

### YAML
<a name="sam-property-graphqlapi-resolver-syntax-yaml"></a>

```
OperationType:
  LogicalId:
    Caching: [CachingConfig](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-appsync-resolver-cachingconfig.html)
    CodeUri: String
    FieldName: String
    InlineCode: String 
    MaxBatchSize: Integer
    Pipeline: List
    Runtime: Runtime
    Sync: [SyncConfig](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-appsync-resolver-syncconfig.html)
```

## Properties
<a name="sam-property-graphqlapi-resolver-properties"></a>

`Caching`  <a name="sam-graphqlapi-resolver-caching"></a>
The caching configuration for the resolver that has caching activated.  
*Type*: [CachingConfig](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-appsync-resolver-cachingconfig.html)  
*Required*: No  
*CloudFormation compatibility*: This property is passed directly to the `[CachingConfig](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-resolver.html#cfn-appsync-resolver-cachingconfig)` property of an `AWS::AppSync::Resolver` resource.

`CodeUri`  <a name="sam-graphqlapi-resolver-codeuri"></a>
The resolver function code’s Amazon Simple Storage Service (Amazon S3) URI or path to a local folder.  
If you specify a path to a local folder, CloudFormation requires that the file is first uploaded to Amazon S3 before deployment. You can use the AWS SAM CLI to facilitate this process. For more information, see [How AWS SAM uploads local files at deployment](deploy-upload-local-files.md).  
If neither `CodeUri` or `InlineCode` are provided, AWS SAM will generate `InlineCode` that redirects the request to the first pipeline function and receives the response from the last pipeline function.  
*Type*: String  
*Required*: No  
*CloudFormation compatibility*: This property is passed directly to the `[CodeS3Location](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-resolver.html#cfn-appsync-resolver-codes3location)` property of an `AWS::AppSync::Resolver` resource.

`FieldName`  <a name="sam-graphqlapi-resolver-fieldname"></a>
The name of your resolver. Specify this property to override the `LogicalId` value.  
*Type*: String  
*Required*: No  
*CloudFormation compatibility*: This property is passed directly to the `[FieldName](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-resolver.html#cfn-appsync-resolver-fieldname)` property of an `AWS::AppSync::Resolver` resource.

`InlineCode`  <a name="sam-graphqlapi-resolver-inlinecode"></a>
The resolver code that contains the request and response functions.  
If neither `CodeUri` or `InlineCode` are provided, AWS SAM will generate `InlineCode` that redirects the request to the first pipeline function and receives the response from the last pipeline function.  
*Type*: String  
*Required*: No  
*CloudFormation compatibility*: This property is passed directly to the `[Code](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-resolver.html#cfn-appsync-resolver-code)` property of an `AWS::AppSync::Resolver` resource.

`LogicalId`  <a name="sam-graphqlapi-resolver-logicalid"></a>
The unique name for your resolver. In a GraphQL schema, your resolver name should match the field name that its used for. Use that same field name for `LogicalId`.  
*Type*: String  
*Required*: Yes  
*CloudFormation compatibility*: This property is unique to AWS SAM and doesn’t have an CloudFormation equivalent.

`MaxBatchSize`  <a name="sam-graphqlapi-resolver-maxbatchsize"></a>
The maximum number of resolver request inputs that will be sent to a single AWS Lambda function in a `BatchInvoke` operation.  
*Type*: Integer  
*Required*: No  
*CloudFormation compatibility*: This property is passed directly to the `[MaxBatchSize](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-resolver.html#cfn-appsync-resolver-maxbatchsize)` property of an `AWS::AppSync::Resolver` resource.

`OperationType`  <a name="sam-graphqlapi-resolver-operationtype"></a>
The GraphQL operation type that is associated with your resolver. For example, `Query`, `Mutation`, or `Subscription`. You can nest multiple resolvers by `LogicalId` within a single `OperationType`.  
*Type*: String  
*Required*: Yes  
*CloudFormation compatibility*: This property is passed directly to the `[TypeName](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-resolver.html#cfn-appsync-resolver-typename)` property of an `AWS::AppSync::Resolver` resource.

`Pipeline`  <a name="sam-graphqlapi-resolver-pipeline"></a>
Functions linked with the pipeline resolver. Specify functions by logical ID in a list.  
*Type*: List  
*Required*: Yes  
*CloudFormation compatibility*: This property is unique to AWS SAM and doesn't have an CloudFormation equivalent. It is similar to the `[PipelineConfig](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-resolver.html#cfn-appsync-resolver-pipelineconfig)` property of an `AWS::AppSync::Resolver` resource.

`Runtime`  <a name="sam-graphqlapi-resolver-runtime"></a>
The runtime of your pipeline resolver or function. Specifies the name and version to use.  
*Type*: [Runtime](sam-property-graphqlapi-resolver-runtime.md)  
*Required*: Yes  
*CloudFormation compatibility*: This property is unique to AWS SAM and doesn't have an CloudFormation equivalent. It is similar to the `[Runtime](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-resolver.html#cfn-appsync-resolver-runtime)` property of an `AWS::AppSync::Resolver` resource.

`Sync`  <a name="sam-graphqlapi-resolver-sync"></a>
Describes a Sync configuration for a resolver.  
Specifies which Conflict Detection strategy and Resolution strategy to use when the resolver is invoked.  
*Type*: [SyncConfig](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-appsync-resolver-syncconfig.html)  
*Required*: No  
*CloudFormation compatibility*: This property is passed directly to the `[SyncConfig](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-resolver.html#cfn-appsync-resolver-syncconfig)` property of an `AWS::AppSync::Resolver` resource.

## Examples
<a name="sam-property-graphqlapi-resolver-examples"></a>

### Use the AWS SAM generated resolver function code and save fields as variables
<a name="sam-property-graphqlapi-resolver-examples-example1"></a>

Here is the GraphQL schema for our example:

```
schema {
  query: Query
  mutation: Mutation
}

type Query {
  getPost(id: ID!): Post
}

type Mutation {
  addPost(author: String!, title: String!, content: String!): Post!
}

type Post {
  id: ID!
  author: String
  title: String
  content: String
}
```

Here is a snippet of our AWS SAM template:

```
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
...
Resources:
  MyGraphQLApi:
    Type: AWS::Serverless::GraphQLApi
    Properties:
      ...
      Functions:
        preprocessPostItem:
          ...
        createPostItem:
          ...
      Resolvers:
        Mutation:
          addPost:
            Runtime:
              Name: APPSYNC_JS
              Version: 1.0.0
            Pipeline:
            - preprocessPostItem
            - createPostItem
```

In our AWS SAM template, we don’t specify `CodeUri` or `InlineCode`. At deployment, AWS SAM automatically generates the following inline code for our resolver:

```
export function request(ctx) {
  return {};
}

export function response(ctx) {
  return ctx.prev.result;
}
```

This default resolver code redirects the request to the first pipeline function and receives the response from the last pipeline function.

In our first pipeline function, we can use the provided `args` field to parse the request object and create our variables. We can then use these variables within our function. Here is an example of our `preprocessPostItem` function:

```
import { util } from "@aws-appsync/utils";

export function request(ctx) {
  const author = ctx.args.author;
  const title = ctx.args.title;
  const content = ctx.args.content;
  
  // Use variables to process data
  
}

export function response(ctx) {
  return ctx.result;
}
```

# Runtime
<a name="sam-property-graphqlapi-resolver-runtime"></a>

The runtime of your pipeline resolver or function. Specifies the name and version to use.

## Syntax
<a name="sam-property-graphqlapi-resolver-runtime-syntax"></a>

To declare this entity in your AWS Serverless Application Model (AWS SAM) template, use the following syntax.

### YAML
<a name="sam-property-graphqlapi-resolver-runtime-syntax-yaml"></a>

```
Name: String
Version: String
```

## Properties
<a name="sam-property-graphqlapi-resolver-runtime-properties"></a>

`Name`  <a name="sam-graphqlapi-resolver-runtime-name"></a>
The name of the runtime to use. Currently, the only allowed value is `APPSYNC_JS`.  
*Type*: String  
*Required*: Yes  
*CloudFormation compatibility*: This property is passed directly to the `[Name](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-appsync-resolver-appsyncruntime.html#cfn-appsync-resolver-appsyncruntime-name)` property of an `AWS::AppSync::Resolver AppSyncRuntime` object.

`Version`  <a name="sam-graphqlapi-resolver-runtime-version"></a>
The version of the runtime to use. Currently, the only allowed version is `1.0.0`.  
*Type*: String  
*Required*: Yes  
*CloudFormation compatibility*: This property is passed directly to the `[RuntimeVersion](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-appsync-resolver-appsyncruntime.html#cfn-appsync-resolver-appsyncruntime-runtimeversion)` property of an `AWS::AppSync::Resolver AppSyncRuntime` object.