POST with array of objects in payload

[JyotiRani]

I have a requirement to set an autogenerated field to the incoming payload of POST request. I have defined 'before save' operation hook in my loopback application which does this. However for payload with single object, it works as expected, but if i have array of objects in payload, then the autogenerated field is set same for all objects in the array while i want different value to be saved for all objects. So i am wondering what is the best place/hook to modify each object in array uniquely.

Note: the autogenerated field is fetched from db, and is incremented after every fetch, so next object in array should use the incremented value and so on.

[dhmlau]

@JyotiRani, to help accelerating the triaging, do you have a sample app? thanks.

[b-admike]

@JyotiRani You are correct in using the before save hook to do your manipulation. You can use a tool like lodash to iterate through the array and use the .extend() function on the objects to add your autogenerated field before saving. Here is an example app I created (I just used variable instead of the autogenerated field). The main file is under server/boot/script.js. I am going to close this ticket, but feel free to re-open if you are still experiencing issues.

[b-admike]

Example POST request and result:

{
  "contacts": [
    {"name": "Bob"},
    {"name": "Sarah"}
  ]
}

is saved as:

{
  "contacts": [
    {
      "name": "Bob",
      "counter": 1
    },
    {
      "name": "Sarah",
      "counter": 2
    }
  ],
  "id": 1
}

[JyotiRani]

@b-admike Your example work as expected, however i realized that the issue is with async call, my autogenerated number is result of db aync call response, so there, looks like aync call is initiated parallely for all object instances in array, so before the values gets updated to a new one in db, next object also requests for it and gets the old value. Can you try this at your end?

[b-admike]

Thank you @JyotiRani. Can you show me the SQL you use for the autogenerated field and which connector you are using? Also, which async call/method are you using?

[JyotiRani]

Its the dash db connector. Here is the snippet of the method:
var query = {where: {and:[{companyId:data.1},{itemType:'TASK'}]}};
Tasks.app.models.numgenerator.findOne(query, function(err, res){
if (err) return next(err);

	nextGenNum = res.itemPrefix + leftPad(res.nextSeqNumber, res.sizeRequired - res.itemPrefix.length, '0');
	console.log(nextGenNum);
	if(iType == 'TASK') {
		data.taskCode = nextGenNum;
		console.log('setting task code as:' + data.taskCode);							
	}
	});

Schema for number generator table is:
CREATE TABLE TASK_NUMGENERATOR
(
"NUMBER_ID" INTEGER NOT NULL GENERATED BY DEFAULT AS IDENTITY (START WITH 1, INCREMENT BY 1, CACHE 20),
"ITEMTYPE" VARCHAR(50) ,
"ITEM_PREFIX" VARCHAR(10) ,
"COMPANYID" INTEGER ,
"NEXT_SEQ_NUMBER" INTEGER ,
"SIZE_REQUIRED" INTEGER ,
"CREATEDDATE" TIMESTAMP ,
"MODIFIEDDATE" TIMESTAMP,
CONSTRAINT PK_NUMGEN_ID PRIMARY KEY (NUMBER_ID)
);

[JyotiRani]

Here is complete function which fetches and then updates the field in db:

function fetchGenNumberAndProceed(data, next, iType) {
var query = {};
if(data.companyId)
query = {where: {and:[{companyId:data.companyId},{itemType:iType}]}};
else
query = {where: {and:[{companyId:null},{itemType:iType}]}};

var nextGenNum;
Tasks.app.models.numgenerator.findOne(query, function(err, res){
	if (err) return next(err);
	
	nextGenNum = res.itemPrefix + leftPad(res.nextSeqNumber, res.sizeRequired - res.itemPrefix.length, '0');
	console.log(nextGenNum);
	if(iType == 'TASK') {
		data.taskCode = nextGenNum;
		console.log('setting task code as:' + data.taskCode);							
	} else {
		data.workItemId = nextGenNum;
		console.log('setting workitemId as:' + data.workItemId + nextGenNum);	
	}
	if(data.companyId)
		query = {"companyId":data.companyId, "itemType":iType};
	else
		query = {"companyId":null, "itemType":iType};

	Tasks.app.models.numgenerator.updateAll(query, {"nextSeqNumber": res.nextSeqNumber + 1}, function(err, updated) {
		if (err) return next(err);
		else {
			console.log("updated sequence number:" + updated.count);													
		}
	});
});	

}