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Cover image for Creating business logic on Amplify
Yasunori Tanaka
Yasunori Tanaka

Posted on

Creating business logic on Amplify

As described in this document, GraphQL on AppSync can connect many data sources as business logic. For example, API Gateway, another AppSync, and Fargate via HTTP and lambda function.

I think, for a small project, the lambda function as a data source is useful for writing business logic.

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We have two approaches to get data. A lambda function gets data from DynamoDB and GraphQL.

Create a lambda function

See also, https://docs.amplify.aws/guides/functions/dynamodb-from-js-lambda/q/platform/js.

$ amplify add function
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Amplify function needs permission to read/write to DynamoDB and GraphQL

$ amplify update function

? Do you want to update the Lambda function permissions to access other resources in this project? Yes
? Select the category api, storage
Api category has a resource called amplifynuxt
? Select the operations you want to permit for amplifynuxt create, read, update, delete
Storage category has a resource called <Your DynamoDB table>:@model(appsync)
? Select the operations you want to permit for <Your DynamoDB table>:@model(appsync) create, read, update, delete
...

You can access the following resource attributes as environment variables from your Lambda function
        API_<Your API name>_GRAPHQLAPIENDPOINTOUTPUT
        API_<Your API name>_GRAPHQLAPIIDOUTPUT
        API_<Your API name>_GRAPHQLAPIKEYOUTPUT
        API_<Your API name>_PROPERTYTABLE_ARN
        API_<Your API name>_PROPERTYTABLE_NAME
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Add a query in schema.graphql

schema.graphql

type Query {
  getData(msg: String): String @function(name: "<your lambda function name>-${env}")
}
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Gets data from DynamoDB

In your index.js in amplify/backend/function/<your lambda function name>/src, change code like blow.

const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient();

const params = {
  TableName : 'your-table-name',
  Item: {
     id: '12345',
  }
}

async function getItem(){
  try {
    await docClient.put(params).promise();
  } catch (err) {
    return err;
  }
}

exports.handler = async (event) => {
  try {
    await getItem()
    return { body: 'Successfully created item!' }
  } catch (err) {
    return { error: err }
  }
};
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Push code.

$ amplify push
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Test the function.

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gets data from GraphQL

$ npm install axios, graphql-tag, graphql
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Update the index.js

/* Amplify Params - DO NOT EDIT
    API_<Your API name>_GRAPHQLAPIENDPOINTOUTPUT
    API_<Your API name>_GRAPHQLAPIIDOUTPUT
    API_<Your API name>_GRAPHQLAPIKEYOUTPUT
    API_<Your API name>_PROPERTYTABLE_ARN
    API_<Your API name>_PROPERTYTABLE_NAME
    ENV
    REGION
Amplify Params - DO NOT EDIT */
const axios = require('axios');
const gql = require('graphql-tag');
const graphql = require('graphql');
const { print } = graphql;

const listPropertys = gql`
  query listPropertys {
    listPropertys {
      items {
        id
        name
      }
    }
  }
`

exports.handler = async (event) => {
  try {
    const graphqlData = await axios({
      url: process.env.API_<Your API name>_GRAPHQLAPIENDPOINTOUTPUT,
      method: 'post',
      headers: {
        'x-api-key': process.env.API_<Your API name>_GRAPHQLAPIKEYOUTPUT
      },
      data: {
        query: print(listPropertys),
      }
    });
    const body = {
        graphqlData: graphqlData.data.data.listPropertys
    }
    return {
        statusCode: 200,
        body: JSON.stringify(body),
        headers: {
            "Access-Control-Allow-Origin": "*",
        }
    }
  } catch (err) {
    console.log('error posting to appsync: ', err);
  } 
}
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Push code.

$ amplify push
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Test the function.

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