How to update() DynamoDB - node.js

Question

I'm working with DynamoDB for the first time and so far, not too bad. Having some understanding of Node is making this easier, but having none of noSQL, well that hurts!. My application relies on quickly searching a GROUPS list and returning members from that group.
When I add the data using the console, I am able to create a JSON document like this:
"GROUP_ID":"GroupA", "MEMBER": ["MemberA", "MemberB", "MemberC"], "STATUS": ["OWNER", "MEMBER", "INVITED"], "ADD_DATE":[1234567, 2345671, 3456712]
I am using this to create the GROUP_ID as the primary key:
const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient({region:'us-east-1'});
exports.handler = (event, context, callback) => {
var tableName = "USER_GROUPS";
var checkParams = {
TableName: tableName,
Key:{"GROUP_NAME": event.group_id}
};
var createParams = {
TableName: tableName,
Key:{"GROUP_NAME": event.group_id},
Item:{"GROUP_NAME": event.group_id, "MEMBER_NAME":[event.device_id], "MEMBER_SATUS":["OWNER"], "MEMBER_DATE" : [event.date]}
};
var checkGroupExists = new Promise((resolve, reject) => {
docClient.get(checkParams, (err, data) => {
if(err){
reject(err);
}
if(data.Item){ // exists...
console.log("found Group ID");
reject();
}
else{
console.log("Group ID not found...");
resolve();
}
});
});
checkGroupExists.then((err, data) => {
console.log("adding Group: ");
console.log(data);
docClient.put(createParams, (err, data) =>{
if(err){
console.log(err);
callback(err, null);
}else{
console.log("added device: " + createParams.Key);
callback(null, {"created":createParams.Key.GROUP_NAME});
}
});
}).catch((err) => {
if(err){
callback(err, null);
}
else{
callback(err, {"used":createParams.Key.GROUP_NAME});
}
});
};
but when I use update() I am adding to the array and end up with a type name for the arrays
["S":"MemberA", "S":"MemberB", "S":"MemberC"]
kind of thing....
This is where I have left off, quite frustrated here!
const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient({region:'us-east-1'});
exports.handler = (event, context, callback) => {
var tableName = "USER_GROUPS";
var checkParams = {
TableName: tableName,
Key:{"GROUP_NAME": event.group_id},
Item:{"MEMBER_NAME": event.member_name}
};
var updateParams = {
TableName: tableName,
Key:{"GROUP_NAME": event.group_id},
//Item:{"MEMBER_NAME":[event.device_id], "MEMBER_STATUS":["OWNER"], "MEMBER_DATE" : [event.date]},
AttributeUpdates: {
"MEMBER_NAME": {
Action: 'ADD',
Value: event.device_id
},
"MEMBER_STATUS":{
Action : 'ADD',
Value: "ENVITED"
},
"MEMBER_DATE":{
Action: 'ADD',
Value: event.date
}
},
};
var checkGroupExists = new Promise((resolve, reject) => {
docClient.get(checkParams, (err, data) => {
console.log(data);
if(err){
reject(err);
}
if(data.Item.GROUP_NAME){ // exists...
console.log("found the group...");
resolve();
}
else{
reject();
}
});
});
checkGroupExists.then((err, data) => {
docClient.update(updateParams, (err, data) =>{
if(err){
console.log(err);
callback(err, null);
}else{
callback(null, {"updated" : updateParams.Key.GROUP_NAME});
}
});
}).catch((err) => {
if(err){
callback(err, null);
}
else{
callback(err, {"noGroup":createParams.Key.GROUP_NAME});
}
});
};
It seems I am lacking the understanding of how to process updates to include NEW item in the member array. Any assistance would be appreciated!

Answer 1

Use list_append() together in an UpdateExpression to append to a list column along with a ConditionExpression to prevent updates to a non-existent group:
const AWS = require('aws-sdk');
const DB = new AWS.DynamoDB.DocumentClient({region:'us-east-1'});
const UpdateExpression = 'SET ' + [
'#members = list_append(#members, :member)',
'#statuses = list_append(#statuses, :status)',
'#dates = list_append(#dates, :date)',
].join(', ')
const ConditionExpression = [
'attribute_type(#members, :L)',
'attribute_type(#statuses, :L)',
'attribute_type(#dates, :L)'
].join(' AND ')
const ExpressionAttributeNames = {
'#members': 'MEMBER_NAME',
'#statuses': 'MEMBER_STATUS',
'#dates': 'MEMBER_DATE'
}
exports.handler = (event, context, callback) => {
DB.update({
TableName: 'USER_GROUPS',
Key: { GROUP_NAME: e.group_id },
ReturnValues: 'ALL_NEW',
UpdateExpression: UpdateExpression,
ConditionExpression: ConditionExpression,
ExpressionAttributeNames: ExpressionAttributeNames,
ExpressionAttributeValues: {
':member': [e.member_name],
':status': ['ENVITED'],
':date': [e.date],
':L': 'L'
}
}, callback)
}