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How to read in this MongoDb field that contains dynamic children fields, in JavaScript?

Given the following MongoDB document structure (which I cannot change), I'm not sure how to read this in JavaScript?
so loginHistory is the main field name. It contains an Object type (okay???)
it can then contain multiple children fields (this above example has only ONE child), which are arrays. These field names are dynamic, but unique.
the 'array' content is a C# DateTimeOffset , I've been told.
So in the example above, Jane is the field and the value is an Array, but really it's a DateTime.Offset.
Here's another document I've found:
4x fields
So i don't know how to read this with node/JavaScript. Oh - and the field loginHistory might not exist on some documents, also :(
So given that existing document schema/structure, I need to somehow read in each loginHistory value and then create a new document (which i'll do other stuff with later).
This is some JavaScript code I tried, but doesn't work:
users.loginHistory.forEach(loginHistory => {
// do stuff, like create a new { id = users._id, name = "Jane", createdOn = "that date/time offset" }
}

Assuming we have an input set of docs like the screen shots e.g.:
var r = [
{
loginHistory: {
"Jane": [ 1648835363929, 0 ],
"Bob": [ 1648835363929, 0 ]
}
},
{
noLoginHistory: "nope"
},
{
loginHistory: {
"Dan": [ 1648835363929, 0 ],
"Dave": [ 1648835363929, 0 ],
"Jane": [ 1648835363929, 0 ]
}
}
];
then the following pipeline will create new, "converted" docs in a collection named foo2.
db.foo.aggregate([
// OK if loginHistory does not exist. X will be set to null
// and the $unwind will not produce anything:
{$project: {X: {$objectToArray: "$$ROOT.loginHistory"} }},
{$unwind: "$X"},
// Now we have individual docs of
// X: {k: name, v: the array}
// The OP wanted to make a new doc for each one. I don't know
// what function to apply to turn X.v[0] into a MongoDB datetime
// because I don't know what that big int (637807576034080256) is
// supposed to be so I used regular ms since epoch for the example
// instead. The OP will have to get more creative with division
// and such to turn 637807576034080256 into something "toDate-able"
// in MongoDB. You *could* store the big int as is but it is always
// good to try to turn a datetime into a real datetime in mongodb.
{$project: {
_id: false,
name: '$X.k',
createdOn: {$toDate: {$arrayElemAt:['$X.v',0]}}
}}
// Now we have docs like :
// {name: "Jane", createdOn: ISODate(...) }
// By calling $out to a new collection, a new _id will be assigned
// to each:
,{$out: "foo2"}
]);

Embedded Objects to Arrays

I was given an existing project where the data structure is below:
[
{
"key": "username",
"value": ""
},
{
"key": "password",
"value": ""
},
{
"key": "cars",
"value": [
{"ABC-1234-1234": "s4LmoNzee9Xr6f7uu/"},
{"ABC-5678-5678": "s5LmoNzee9Xr5f9uu/"}
]
}
]
Cars' value is an array of objects.
To create the initial object in the cars' array, I do the following:
var encryptedStuff = json.data;
var carkey = carid;
var entry = {};
entry[carkey] = encryptedStuff;
var carArray = [];
key="cars";
carArray.push(entry);
I need to push the array into another function that turns it into a string in a stored variable.
My problem...and I'm really rusty on embedded objects...is to do the following:
1.) Get the string
2.) JSON.parse back into an object (I got this far as I'm using a jQuery grep but I'd prefer to use JavaScript).
Here's my problem...
3.) locate the cars key in the object and get its value.
4.) Turn the value into an array to either delete an item or to add one (as per the code above where I'm writing the object into the array.
In the case of adding, I would have to copy the cars' value into the carArray[] and then push the new item into it.
In the case of deleting, I would have to remove the item and push back everything back into the carArray[].
I would do things differently but I can't change the structure of the data as this is approved company-wide.
Any help would be appreciated.
Thanks

You don't need to make a copy of the car's value array to add new entries nor make a copy then "push back" to remove an entry - you can reference it directly in the parsed object.
You can use
JSON.parse
array.find
array.push
array.splice
JSON.stringify
Giving:
var source = `[
{
"key": "username",
"value": ""
},
{
"key": "password",
"value": ""
},
{
"key": "cars",
"value": [
{"ABC-1234-1234": "s4LmoNzee9Xr6f7uu/"},
{"ABC-5678-5678": "s5LmoNzee9Xr5f9uu/"}
]
}
]`
// convert json to an object
var data = JSON.parse(source);
console.log(data, data.find(e=>e.key=="cars").value)
// add an item to the cars.value
data.find(e=>e.key=="cars").value.push({"ABC-": "s6..." });
// remove an item from the cars.value
data.find(e=>e.key=="cars").value.splice(1,1);
// confirm items added/removed
console.log(data, data.find(e=>e.key=="cars").value)
// convert back to a strng to send back to the service
var result = JSON.stringify(data);
console.log(result);

Parse server javascript pointer data extraction

I have parse server which I have this query on
const empList = Parse.Object.extend("EmpList");
const query = new Parse.Query(empList);
query.equalTo("relation", Parse.User.current());
query.find({
success: (results) => {
// results.map((each)=>this.data = each.id)
this.data = results
},
Parse server has 2 classes ( users and EmpList), there is a pointer in EmpList which points correctly to the current user submitted the employee.The returned data also includes the pointer ( which has a name "relation" ) and I can see the username exists as an object in this fashion
Array [
Object {
"createdAt" "2018-07-05T20 17 45.173Z",
"name" "1the latter",
"objectId" "D2kThKcg9z",
"phone" "111",
"relation" Object {
"ACL" Object {
"*" Object {
"read" true,
},
"H2rQJxNyTD" Object {
"read" true,
"write" true,
},
},
"__type" "Object",
"className" "_User",
"createdAt" "2018-07-05T18 43 40.536Z",
"objectId" "H2rQJxNyTD",
"password" undefined,
"sessionToken" "r c45063a034dd81d646bef51ae2055c85",
"updatedAt" "2018-07-05T20 17 35.976Z",
"username" "1",
},
"shift" "tue",
"updatedAt" "2018-07-05T20 22 11.158Z",
},
]
Yet I am unable to extract the username in relation object.
please help me do so by data[0].relation.username or data[0].relation().username

There are two things you can do. The simplest is to eagerly fetch the related object as part of the query using include() ...
const query = new Parse.Query(empList);
query.equalTo("relation", Parse.User.current());
query.include("relation");
(Incidentally, "relation" isn't a great name for that column. A better choice would be something relating to it's meaning, like submittedByUser. Calling it relation is like naming your poodle "Poodle").
The drawback of using include is that it will eagerly fetch all of the related objects on the query, making the query take longer and potentially produce data that you don't need. If you only want the related object on one or a handful of the query results, skip the include() and query the relations individually...
const query = new Parse.Query(empList);
query.equalTo("relation", Parse.User.current());
query.find({
success: results => {
// for one or some of the results...
let submittedByUserRelation = user.relation("relation");
submittedByUserRelation.query().find({
success: user => {
// user.username will be the username
}
});

Check the query() function on the relation that you can use to get all the object in the relation .

Update object with given ID embed in array without restructuring Mongo database

I've got the following document named "clients" which includes id, name and list of projects (array of objects):
{
"_id": {
"$oid": "572225d997bb651819f379f7"
},
"name": "ppg",
"projects": [
{
"name": "aaa",
"job_description": "",
"projectID": 20
},
{
"name": "bbbb",
"job_description": "",
"projectID": 21
}
]
}
I would like to update "job_description" of project with given "projectID" like this:
module.exports.saveJobDesc = function(client, idOfProject, textProvided) {
db.clients.update({ name: client},
{ $set: {'projects.0.job_description': textProvided }});
};
But instead of hardcoded index "0" of array I want to find specific project using "projectID". Is there a way to achieve this without changing the structure of collection and/or document?

If you want to update the "job_description" where name="ppg" and project_id=20 then you can use below mongo query:-
db.clients.update({ "name":"ppg","projects.projectID":20 },{$set: {"projects.$.job_description": "abcd"}})
Please let me know if any thing else is required

You cannot update multiple array elements in single update operation, instead you can update one by one which takes time depends upon number of elements in array and number of such documents in collection. see New operator to update all matching items in an array
db.test2.find().forEach( function(doc) {
var projects = doc.projects;
for(var i=0;i<projects.length;i++){
var project = projects[i];
if(project.projectID == 20){
var field = "projects."+i+".job_description";
var query = {};
query[field] = "textasdsd";
db.test2.update({ _id: doc._id},{ $set:query});
}
}
})

Create a text index on MongoDB schema which references another schema

I am trying to add an index to a certain Schema with mongoose for text searches. If I add a text index to individual fields it works fine, also with compound indexes it is okay. For example the answer provided here is great:
Full text search with weight in mongoose
However, I am trying to add an index to fields which are references to other Schemas. For example my model looks like the following:
var Book = new Schema({
"title": String,
"createdAt": Date,
"publisher": {
"type": Schema.ObjectId,
"ref": "Publisher"
},
"author": {
"type": Schema.ObjectId,
"ref": "Author"
},
"isbn": String
});
So something like the following indexing doesn't work when you perform a search query as described below:
Indexing:
Book.index({"title": "text", "publisher.name": "text", "author.firstName": "text"});
Search query:
function searchBooks(req, res) {
var query = req.query.searchQuery;
Book.find({ $text: { $search: query } })
.populate('author publisher')
.limit(25)
.exec(function(err, books) {
if (err) {
res.json(err);
} else {
res.json(books);
}
}
);
}
Does anyone have any suggestions of how to add a text index in for the "publisher" and "author" fields, I am using the "populate" mongodb method to pull in the data for these schemas.

I think, what you are looking for is the ability to join tables of data and perform a query against the sum of that data. That is something you need a relational database for, which MongoDB isn't.
So I recommend you change your approach in how you would like to preform your search, e.g. search for your keyword within both author and title instead of attempting to search the whole dataset at the same time.