在 AWS Lambda 中将 DynamoDB 数据格式化为普通 JSON

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I think it's just a custom transformation exercise for each app. A simple conversion from DynamoDB's item format to you application format might look like this:

var response = {...} // your response from DynamoDB
var formattedObjects = response.videos.map(function(video) {
return {
"file": video.file.S,
"id": video.id.S,
"canvas": video.canvas.S
};
});

If you want to build a generic system for this, you would have to handle DynamoDB's various AttributeValue types. A function like the one below would do the job, but I've left out the hard work of handling most of DynamoDB's more complex attribute value types:

function dynamoItemToPlainObj(dynamoItem) {
var plainObj = {};
for (var attributeName in dynamoItem) {
var attribute = dynamoItem[attributeName];
var attributeValue;
for (var itemType in attribute) {
switch (itemType) {
case "S":
attributeValue = attribute.S.toString();
break;
case "N":
attributeValue = Number(attribute.N);
break;
// more attribute types...
default:
attributeValue = attribute[itemType].toString();
break;
}
}
plainObj[attributeName] = attributeValue;
}
return plainObj;
}
var formattedObjects = response.videos.map(dynamoItemToPlainObj);

小开

最佳答案

AWS JavaScript SDK was recently updated with Document Client which does exactly what you need. Check the announce and usage examples here: http://blogs.aws.amazon.com/javascript/post/Tx1OVH5LUZAFC6T/Announcing-the-Amazon-DynamoDB-Document-Client-in-the-AWS-SDK-for-JavaScript

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Here you can find gist which does that:

function mapper(data) {


let S = "S";
let SS = "SS";
let NN = "NN";
let NS = "NS";
let BS = "BS";
let BB = "BB";
let N = "N";
let BOOL = "BOOL";
let NULL = "NULL";
let M = "M";
let L = "L";


if (isObject(data)) {
let keys = Object.keys(data);
while (keys.length) {
let key = keys.shift();
let types = data[key];


if (isObject(types) && types.hasOwnProperty(S)) {
data[key] = types[S];
} else if (isObject(types) && types.hasOwnProperty(N)) {
data[key] = parseFloat(types[N]);
} else if (isObject(types) && types.hasOwnProperty(BOOL)) {
data[key] = types[BOOL];
} else if (isObject(types) && types.hasOwnProperty(NULL)) {
data[key] = null;
} else if (isObject(types) && types.hasOwnProperty(M)) {
data[key] = mapper(types[M]);
} else if (isObject(types) && types.hasOwnProperty(L)) {
data[key] = mapper(types[L]);
} else if (isObject(types) && types.hasOwnProperty(SS)) {
data[key] = types[SS];
} else if (isObject(types) && types.hasOwnProperty(NN)) {
data[key] = types[NN];
} else if (isObject(types) && types.hasOwnProperty(BB)) {
data[key] = types[BB];
} else if (isObject(types) && types.hasOwnProperty(NS)) {
data[key] = types[NS];
} else if (isObject(types) && types.hasOwnProperty(BS)) {
data[key] = types[BS];
}
}
}




return data;


function isObject(value) {
return typeof value === "object" && value !== null;
}

}

https://gist.github.com/igorzg/c80c0de4ad5c4028cb26cfec415cc600

小开

I know is a bit old but I had the same problem processing stream data from dynamoDB in node js lambda function. I used the proposed by @churro

import sdk and output converter

var AWS = require("aws-sdk");
var parse = AWS.DynamoDB.Converter.output;

use the parse function with a small hack

exports.handler = function( event, context, callback ) {
var docClient = new AWS.DynamoDB.DocumentClient();
event.Records.forEach((record) => {
console.log(record.eventID);
console.log(record.eventName);
console.log('DynamoDB Record:', parse({ "M": record.dynamodb.NewImage }));
});
callback(null, `Successfully processed ${event.Records.length} records.`);
}

Hope it helps

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If you need online editor try this

https://2json.net/dynamo

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Node.js Use the unmarshall function from AWSJavaScriptSDK:

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

exports.handler = function( event, context, callback ) {
const newImages = event.Records.map(
(record) => AWS.DynamoDB.Converter.unmarshall(record.dynamodb.NewImage)
);
console.log('Converted records', newImages);
callback(null, `Success`);
}

Python Use TypeDeserializer.deserialize from boto3.dynamodb.types:

import json
from boto3.dynamodb.types import TypeDeserializer


def ddb_deserialize(r, type_deserializer = TypeDeserializer()):
return type_deserializer.deserialize({"M": r})


def lambda_handler(event, context):
new_images = [ ddb_deserialize(r["dynamodb"]["NewImage"]) for r in event['Records'] ]
print('Converted records', json.dumps(new_images, indent=2))

小开

Javascript: AWS SDK provides the unmarshall function
Python: use TypeDeserializer from boto3.dynamodb.types:

from boto3.dynamodb.types import TypeDeserializer, TypeSerializer


def from_dynamodb_to_json(item):
d = TypeDeserializer()
return {k: d.deserialize(value=v) for k, v in item.items()}


## Usage:
from_dynamodb_to_json({
"Day": {"S": "Monday"},
"mylist": {"L": [{"S": "Cookies"}, {"S": "Coffee"}, {"N": "3.14159"}]}
})
# {'Day': 'Monday', 'mylist': ['Cookies', 'Coffee', Decimal('3.14159')]}

小开

If you are using python in the lambda you can utilise the dynamodb-json library.

Install library

pip install dynamodb-json

and use the below snippet

from dynamodb_json import json_util as util


def marshall(regular_json):
dynamodb_json = util.dumps(reular_json)


def unmarshall(dynamodb_json):
regular_json = util.loads(dynamodb_json)

Reference https://pypi.org/project/dynamodb-json/

小开

I tried several solutions here but none worked with multi-level data, such as if it includes a list of maps e.g.

{
"item1": {
"M": {
"sub-item1": {
"L": [
{
"M": {
"sub-item1-list-map": {
"S": "value"

Below, adapted from @igorzg's answer (which also has that drawback), fixes that.

Example usage:

dynamodb.getItem({...}, function(err, data) {
if (!err && data && data.Item) {
var converted = ddb_to_json(data.Item);

Here's the conversion function:

function ddb_to_json(data) {
  

function isObject(value) {
return typeof value === "object" && value !== null;
}


if(isObject(data))
return convert_ddb({M:data});


function convert_ddb(ddbData) {
if (isObject(ddbData) && ddbData.hasOwnProperty('S'))
return ddbData.S;
if (isObject(ddbData) && ddbData.hasOwnProperty('N'))
return parseFloat(ddbData.N);
if (isObject(ddbData) && ddbData.hasOwnProperty('BOOL'))
return ddbData.BOOL;
if (isObject(ddbData) && ddbData.hasOwnProperty('NULL'))
return null;
if (isObject(ddbData) && ddbData.hasOwnProperty('M')) {
var x = {};
for(var k in ddbData.M)
x[k] = convert_ddb(ddbData.M[k])
return x;
}
if (isObject(ddbData) && ddbData.hasOwnProperty('L'))
return ddbData.L.map(x => convert_ddb(x));
if (isObject(ddbData) && ddbData.hasOwnProperty('SS'))
return ddbData.SS;
if (isObject(ddbData) && ddbData.hasOwnProperty('NN'))
return ddbData.NN;
if (isObject(ddbData) && ddbData.hasOwnProperty('BB'))
return ddbData.BB;
if (isObject(ddbData) && ddbData.hasOwnProperty('NS'))
return ddbData.NS;
if (isObject(ddbData) && ddbData.hasOwnProperty('BS'))
return ddbData.BS;


return data;
}


return data;
}