node.js - How can I query DynamoDB and return all child values for a specific key in an array -

i have table in dynamodb each row has following structure:

{      "id": 1,      "data": [          {              "key": "a",              "value": "a"          },          {              "key": "b",              "value": "b"          }      ]  },  ... 

i create query returns single row of data "value" keys have been filtered out of results. essentially, looking way produce output:

{      "id": 1,      "data": [          {              "key": "a"          },          {              "key": "b"          }      ] } 

the trick "data" list contains unknown number of elements. using following code projection expressions, can close need in nodejs:

var aws = require('aws-sdk');  var docclient = new aws.dynamodb.documentclient();  var params = {      tablename: "mytable",     key: {         "id": 1     },     projectionexpression:"id, data[0].key" };  docclient.get(params, function(err, data) {     if (err)         console.log(json.stringify(err, null, 2));     else         console.log(json.stringify(data, null, 2)); }); 

the code above returns following data:

{      "id": 1,      "data": [          {              "key": "a"          }      ] } 

how can dynamodb return keys inside data , not one?

this isn't supported.

as see it, have 2 options:

• if there's upper cap on number of entries in data, e.g., 100, can modify projectionexpression like: "id, data[0].key, data[1].key, data[2].key, data[3].key, ..., data[100].key". should work, because per dynamodb documentation, there 1 constraint on list indexes:

the index in list dereference must non-negative integer

• if there no such upper cap, filter out on client-side.