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Finding random (auto) id assigned to our document by Firestore

I know its a bit weird question but how can I access the unique (auto) id google firebase generates for my document whenever I create new document. For example this is my code
val postCollections = db.collection("posts")
val newPost = Post(text, user, currentTime)
postCollections.document().set(newPost)
How can I know that what is the id generated for this document of "newPost" because i want to use that id in my code and at the same time i dont want to send custom id because it won't be unique

val postCollections = db.collection("posts")
val newPost = Post(text, user, currentTime)
postCollections.document().set(newPost)
As you've likely discovered, .set() returns a Promise <void> .
But what you've ignored is .set() only operates on a DocumentReference - which is what you get from postCollections.document(). A DocumentReference has properties id and path - it is the .document() that creates a new, unique, documentId.
So:
val postCollections = db.collection("posts")
val newPost = Post(text, user, currentTime)
val newRef = postCollections.document()
newRef.set(newPost)
And now you have the document id (and path) available as properties of newRef.
https://firebase.google.com/docs/reference/js/firebase.firestore.DocumentReference

How to get RTC work item attribute data using java API?

I am using below code and it returns some information about "Filed Against"
attribute. But there I am not able to find attribute data. Please help
IAttribute someAttribute= workItemClient.findAttribute(projectAreaHandle, workItem.CATEGORY_PROPERTY, monitor);
Using below code to find out the work item by Id :
workItemClient = (IWorkItemClient) repo.getClientLibrary(IWorkItemClient.class);
int id = new Integer("339406").intValue();
IWorkItem workItem = workItemClient.findWorkItemById(id, IWorkItem.FULL_PROFILE, monitor);
using this work item I want to fetch parent and children like Epic and story work items related to the work item. And then there attributes like story status, story planned for etc.

From this thread:
You can't just put a string in there, I think.
You have to find the category object from the string and then put in the ICategory object.
That means:
private static String CATEGORY_NAME = "UI1";
List<ICategory> findCategories = workItemCommon.findCategories(projectArea, ICategory.FULL_PROFILE, monitor);
for(ICategory category : findCategories) {
if(category.getName().contains(CATEGORY_NAME)){
filedAgainstAttribute = QueryableAttributes.getFactory(IWorkItem.ITEM_TYPE).findAttribute(projectArea, IWorkItem.CATEGORY_PROPERTY, auditableClient, monitor);
filedAgainstExpression = new AttributeExpression(filedAgainstAttribute, AttributeOperation.EQUALS, category);
}
}

Changefeed on one column RethinkDB

I want to have a changefeed on one attribute of my object in rethinkdb in the java language.
I tried this:
Cursor curs = r.db("mytestdb").
table("tennis").
get(Constants.WORKING_PROJECT_ID).
getField("time").
changes().
run(conn);
for (Object doc : curs) {
System.out.println(doc);
}
but I get this com.rethinkdb.gen.exc.ReqlQueryLogicError: Cannot convert STRING to SEQUENCE as an Exception.
Im really new to rethinkDB. Can someone help me ?

getField("time") gets particular field value, you can't subscribe on value.
That's what this com.rethinkdb.gen.exc.ReqlQueryLogicError: Cannot convert STRING to SEQUENCE says.
You can filter changes you want to get:
Cursor curs = r.db("mytestdb").
table("tennis").get(Constants.WORKING_PROJECT_ID)
.filter(row -> row.g("new_val").g("time").ne(row.g("old_val").g("time")))
.changes().run(conn);
for (Object doc : curs) {
}

Cannot find sub-field

I have this data on my mongodb database:
{
"_id" : BinData(3, "bU0bX4VEAMnW7AJ28wXcoA=="),
"online" : false,
"money" : 0,
"rank" : "USER",
"ban" : {
"end" : NumberLong("3027259780628"),
"reason" : "hello"
}
}
and I use this code to access to the ban.end sub-field saved in it:
final Document doc = collcetion.find(new Document("_id", myId)).
projection(Projections.include("ban.end"));
System.out.println(doc); // here is all ok.
// It print out the _id with the
// ban and the end values.
final long a = doc.getLong("ban.end"); // nullptr exception because
// I tryied to do this:
long a = (Long) null;
Is there any way to fix the null pointer reported above? I think I failed something with mongodb, I'm not sure in using ban.end as field name.
I already tried to get, for example, the money value and it works.

getLong returns a Long, not a long. See http://api.mongodb.org/java/current/org/bson/Document.html#getLong-java.lang.Object-.
In other words, you're getting the nullpointer because you're implicitly unboxing it. Just use
final long a = doc.getLong("ban.end");
instead, the handle the null case separately.

I'm not sure in using "ban.end" as field name.
Sadly, you are. You need to get the ban objcect first, before you could access its end attribute.
The logic remains the same for whatever versions.
code in 3.0.4 version of the java driver,
DBCursor docs = collection.find(new BasicDBObject("_id", myId),
new BasicDBObject("ban.end", 1));
while (docs.hasNext())
{
BasicDBObject banObj = (BasicDBObject) docs.next().get("ban");
long end = banObj.getLong("end");
System.out.println(end);
}

Java MongoDB getting value for sub document

I am trying to get the value of a key from a sub-document and I can't seem to figure out how to use the BasicDBObject.get() function since the key is embedded two levels deep. Here is the structure of the document
File {
name: file_1
report: {
name: report_1,
group: RnD
}
}
Basically a file has multiple reports and I need to retrieve the names of all reports in a given file. I am able to do BasicDBObject.get("name") and I can get the value "file_1", but how do I do something like this BasicDBObject.get("report.name")? I tried that but it did not work.

You should first get the "report" object and then access its contents.You can see the sample code in the below.
DBCursor cur = coll.find();
for (DBObject doc : cur) {
String fileName = (String) doc.get("name");
System.out.println(fileName);
DBObject report = (BasicDBObject) doc.get("report");
String reportName = (String) report.get("name");
System.out.println(reportName);
}

I found a second way of doing it, on another post (didnt save the link otherwise I would have included that).
(BasicDBObject)(query.get("report")).getString("name")
where query = (BasicDBObject) cursor.next()

You can also use queries, as in the case of MongoTemplate and so on...
Query query = new Query(Criteria.where("report.name").is("some value"));

You can try this, this worked for me
BasicDBObject query = new BasicDBObject("report.name", "some value");