UpdateGoal.js

const AWS = require('aws-sdk');

const dynamoDb = new AWS.DynamoDB.DocumentClient();

exports.handler = (event, context, callback) => {
  // Request body is passed in as a JSON encoded string in 'event.body'
  const data = JSON.parse(event.body);

  const params = {
    TableName: process.env.TABLE_NAME, //[ProjectName]-Goals,
    // 'Key' defines the partition key and sort key of the item to be updated
    // - 'userId': user identities are federated through the Cognito Identity 
    //             Pool, we will use the identity id as the user id of the 
    //             authenticated user
    // - 'goalId': a unique identifier for the goal (uuid)
    Key: {
      userId: event.requestContext.identity.cognitoIdentityId,
      goalId: event.pathParameters.id
    },
    // 'UpdateExpression' defines the attributes to be updated
    // 'ExpressionAttributeValues' defines the value in the update expression
    // - ':title': defines 'title' to be the title parsed from the request body
    // - ':title': defines 'content' to be the content parsed from the request body
    UpdateExpression: "SET title = :title, content = :content",
    ExpressionAttributeValues: {
      ":title": data.title ? data.title : null,
      ":content": data.content ? data.content : null
    },
    ReturnValues: "ALL_NEW"
  };

  dynamoDb.update(params, (error, data) => {
    // Set response headers to enable CORS (Cross-Origin Resource Sharing)
    const headers = {
      "Access-Control-Allow-Origin": "*",
      "Access-Control-Allow-Credentials" : true
    };

    // Return status code 500 on error
    if (error) {
      console.log(error);
      const response = {
        statusCode: 500,
        headers: headers,
        body: error
      };
      callback(null, response);
      return;
    }

    // Return status code 200 on success
    const response = {
      statusCode: 200,
      headers: headers
    };
    callback(null, response);
  });
};