Develop Reference

Firestore query StartAt(DocumentReference) not giving proper result

In my firestore database,there are 12+ documents.I am getting the first 3 documents correctly by calling the below function on button click. But on the secondclick, though the documentReference is passed correctly, its not retrieving any data.The querySnapshot size is coming 0. What could be the problem.
Given below is the declaration
private val db: FirebaseFirestore = FirebaseFirestore.getInstance()
private val colRef: CollectionReference = db.collection("Notebook")
private var lastResult: DocumentReference? = null
private lateinit var query: Query
and below is the onButtonClick code :
private fun loadNoteNew() {
#Suppress("SENSELESS_COMPARISON", "LiftReturnOrAssignment")
if (lastResult == null) {
query = colRef.orderBy("priority")
.limit(3)
} else {
Log.i(TAG, "Start ${lastResult!!.id}")
query = colRef.orderBy("priority")
.startAfter(lastResult)
.limit(3)
}
Log.i(TAG, "before get")
query.get()
.addOnSuccessListener { querySnapshot ->
var data = ""
Log.i(TAG, "querySnapshot Size : ${querySnapshot.size()}")
if (lastResult != null) {
Log.i(TAG, "querySnapshot ID : ${lastResult!!.id}")
}
for (snapshot in querySnapshot) {
val note = snapshot.toObject(Note::class.java)
note.id = snapshot.id
val title = note.title
val desc = note.description
val priority = note.priority
data += "${note.id} \nTitle =$title \nDescription = $desc\nPriority : $priority\n\n"
}
if (querySnapshot.size() > 0) {
data += "---------------\n\n"
textView_loadData.append(data)
lastResult = querySnapshot.documents[querySnapshot.size() - 1].reference
Log.i(TAG, lastResult!!.id)
}
}
}
Given below is the logcat for first click
I/FireStoreExample: before get
I/FireStoreExample: querySnapshot Size : 3
I/FireStoreExample: P9hIw4Ai7w4IHP6H3ew3
and given below is the logcat of second click
I/FireStoreExample: Start P9hIw4Ai7w4IHP6H3ew3
I/FireStoreExample: before get
I/FireStoreExample: querySnapshot Size : 0
I/FireStoreExample: querySnapshot ID : P9hIw4Ai7w4IHP6H3ew3
Please help me find out,where i am getting it wrong.
Thanks

The second query result is empty because of a misunderstanding on the semantics of query pagination using startAt and startAfter methods.
Let's say the Notebook collection contains N documents. When you make the first query you're asking for the first 3 documents ordered by the priority field so the query is returning documents 1..3. Then upon the second click you're expecting the query to return the next 3 results so indeed you're expecting documents 4..6. The keypoint here is that both startAt and startAfter paginate based on the value of the ordered field rather than with the last document retrieved. Overall the semantics of startAt and startAfter are roughly as follows.
orderby(X).startAt(Y) => Return documents whose X field is greater than or equal Y
orderby(X).startAfter(Y) => Return documents whose X field is strictly greater than Y
With that in mind, let's examine what the code is actually doing when you make the second query:
// At the end of the first query...
lastResult = querySnapshot.documents[querySnapshot.size() - 1].reference
// Second query
query = colRef.orderBy("priority")
.startAfter(lastResult)
.limit(3)
In the code above you're asking for the documents whose "priority" field is greater than document reference "P9hIw4Ai7w4IHP6H3ew3" and indeed there are no documents greater than that, therefore the result set is empty. Here is api reference for both.
There is yet another thing to note. Because these methods filter upon the fields value the position of the cursor could be ambiguous. For instance, if you have 4 documents with priority 3 and already retrieved the leading three if you set startAfter(3) you'll be missing a document. Similarly, if startAt(3) were to be made you'll get back the same three documents. This is also pointed out in the documentation. All in all you have a couple of options to make this work as intended:
Add another orderby in another field so that documents are uniquely identified by the combination so to prevent any cursor ambiguity and be able to use startAfter with guarantees. Next snippet build upon the doc samples and your code.
// first query
query = colRef.orderBy("priority")
.orderBy("AnotherField")
.limit(3)
// Save last document
lastResult = querySnapshot.documents[querySnapshot.size() - 1]
// Second and next queries
query = colRef.orderBy("priority")
.orderBy("AnotherField")
.startAfter(lastResult)
.limit(3)
Lastly remember that it might be simpler to just query all the documents if they're not many and delay optimizations until they become a performance issue.

How to remove duplicate entries in Android Contacts App which gets added when adding new contacts programatically?

I have an app which inserts/updates a contact in the phone book using below code, the code works but the problem I am facing is if there is similar contact with the same phone number eg. a WhatsApp, dou, Viber etc. contact then those app contact takes over my contacts DisplayName and merges together but due to this, we are having multiple duplicate entries in some versions of android like (Samsung, LG, MI A5 stock android) etc.
But works on some phones like MI Max and a few others, does anyone have a solution to this problem or is there I am missing some fields that need to be present to avoid duplicate contacts.
private fun insertContact(contact: Contact): Boolean {
try {
val operations = ArrayList<ContentProviderOperation>()
ContentProviderOperation.newInsert(RawContacts.CONTENT_URI).apply {
withValue(RawContacts.ACCOUNT_NAME, "abcd#gmail.com")
withValue(RawContacts.ACCOUNT_TYPE, "google.com")
operations.add(build())
}
ContentProviderOperation.newInsert(Data.CONTENT_URI).apply {
withValueBackReference(Data.RAW_CONTACT_ID, 0)
withValue(Data.MIMETYPE, StructuredName.CONTENT_ITEM_TYPE)
withValue(StructuredName.GIVEN_NAME, contact.firstName)
withValue(StructuredName.FAMILY_NAME, contact.lastName)
withValue(StructuredName.SUFFIX, "AppName")
operations.add(build())
}
addUpdatePhone(operations, contact.phoneNumbers)
//similar function for other fields email, address, birthday, profilePic etc
val results = context.contentResolver.applyBatch(ContactsContract.AUTHORITY, operations)
return true
} catch (e: Exception) {
LOG.e( "Error inserting contact")
return false
}
}
private fun updateContact(contact: contact, rawContactId: String): Boolean {
try {
val operations = ArrayList<ContentProviderOperation>()
ContentProviderOperation.newUpdate(Data.CONTENT_URI).apply {
val selection = "${Data.RAW_CONTACT_ID} = ? AND ${Data.MIMETYPE} = ?"
val selectionArgs = arrayOf(rawContactId, StructuredName.CONTENT_ITEM_TYPE)
withSelection(selection, selectionArgs)
withValue(StructuredName.GIVEN_NAME, contact.firstName)
withValue(StructuredName.FAMILY_NAME, contact.lastName)
withValue(StructuredName.SUFFIX, "AppName")
operations.add(build())
}
addUpdatePhone(operations, contact.phoneNumbers, true, rawContactId)
//similar function for other fields email, address, birthday, profilePic etc
context.contentResolver.applyBatch(ContactsContract.AUTHORITY, operations)
return true
} catch (e: Exception) {
LOG.e("Error updating contact")
return false
}
}
private fun addUpdatePhone(operations: ArrayList<ContentProviderOperation>, phoneNumbers: List<PhoneNumber>, isUpdate: Boolean = false, rawContactId: String = "") {
if(isUpdate) {
//delete old data with the given raw_contact_id
ContentProviderOperation.newDelete(Data.CONTENT_URI).apply {
val selection = "${Data.RAW_CONTACT_ID} = ? AND ${Data.MIMETYPE} = ? "
val selectionArgs = arrayOf(rawContactId, Phone.CONTENT_ITEM_TYPE)
withSelection(selection, selectionArgs)
operations.add(build())
}
}
phoneNumbers.forEach {
//add new rows of phone number for the given raw_contact_id
ContentProviderOperation.newInsert(Data.CONTENT_URI).apply {
if(isUpdate) {
withValue(Data.RAW_CONTACT_ID, rawContactId)
} else {
withValueBackReference(Data.RAW_CONTACT_ID, 0)
}
withValue(Data.MIMETYPE, Phone.CONTENT_ITEM_TYPE)
withValue(Phone.TYPE, it.type)
withValue(Phone.LABEL, it.label)
withValue(Phone.NUMBER, it.value)
withValue(Phone.NORMALIZED_NUMBER, it.value.normalizeNumber())
operations.add(build())
}
}
}
//similar functions as above for other fields
private fun otherUpdateFunAsAbove() {}

After adding a new RawContact, Android needs to make a decision if this is a brand new Contact or if there's already an existing contact that represents the same person.
Android has an algorithm, which changes and evolved with different OS versions, and might have been tweaked by makers like Samsung, but usually it looks for a very similar name with some other item (such as phone or email) that is either identical or very close.
In that case it'll merge the two contacts using RawContact Aggregation.
Apps can control this process via AggregationExceptions in which an app can state "Keep these two RawContacts separate" or "Keep these two RawContacts merged" regardless of that algorithm.
So what you're explaining would be normal behavior, your original name should still had been kept within the RawContacts.
In any way, I would not recommend trying to find a RawContact (i.e. in your selection clause) using an ID + Name, instead you should use just the RawContact ID.
If you can't find that RawContact ID, this still doesn't mean you should create a new one, instead use the RawContact's lookupUri that you need to store in your app, and get a possibly new ID from that, in a way similar to the approach suggested for Contacts.

Android Kotlin Executing SQLite query in MainActivity

I'm trying to figure out how to execute a SQL query from my MainActivity. I'm currently using a large portion of this example. Upon clicking my Acknowledge button, it finds the selected rows, gets the jsonID of said row, then I'm wanting to update a value in my SQLite table of those rows.
So my question is, how do I execute my "jsonQuery" string, to my SQLite database upon clicking my Acknowledge button?
Here's the code I have in my MainActivity:
acknowledge.setOnClickListener {
var jsonData_text: String = ""
for (i in 0 until JSONParser.MrAdapter.public_modelArrayList!!.size) {
if (JSONParser.MrAdapter.public_modelArrayList!!.get(i).getSelecteds()) {
jsonData_text = jsonData_text + JSONParser.MrAdapter.public_modelArrayList!!.get(i).getJSONID() + ","
}
}
val jsonSQLQuery = jsonData_text.dropLast(1)
val jsonQuery = "update Notes set acknowledged = 1 WHERE jsonID in ("+jsonSQLQuery+")"
Log.d("logged_json", jsonQuery)
}
Thanks for any help!

How to check if record exists or not using Anko?

I am learning to fetching data from sqlite using anko. I can print the data successfully (if the record exist) but my application always crash when the data doesn't exist.
the error says:
parseSingle accepts only cursors with a single entry
I know exactly the meaning of error, I just dont know how to solve it.
here is the code for query:
fun getUserByUid(uid: Int): UserModel
{
val data = context.database.use {
val db = context.database.readableDatabase
val columns = UserModel.COLUMN_ID + "," + UserModel.COLUMN_NAME + "," + UserModel.COLUMN_API_KEY
val query = db.select(UserModel.TABLE_NAME, columns)
.whereArgs("(uid = {userId})",
"userId" to uid)
query.exec {
val rowParser = classParser<UserModel>()
parseSingle(rowParser) // this line that trigger error exception
}
}
return data
}
I tried to find count function in query or rowParser variable to check if the record exist or not but could not find it.

From the wiki page.
https://github.com/Kotlin/anko/wiki/Anko-SQLite#parsing-query-results
Parsing query results
So we have some Cursor, and how can we parse it into regular classes? Anko provides functions parseSingle, parseOpt and parseList to do it much more easily.
Method Description
parseSingle(rowParser): T Parse exactly one row
parseOpt(rowParser): T? Parse zero or one row
parseList(rowParser): List Parse zero or more rows
Note that parseSingle() and parseOpt() will throw an exception if the received Cursor contains more than one row.

Xamarin.Mobile Contacts API takes up a lot of time while fetching contacts?

I'm using Xamarin.Mobile Component for Android to fetch contacts using the code:
var book = new AddressBook (Activity) {PreferContactAggregation = true};
var contData = data.Data;
var cur = Activity.ManagedQuery (contData, null, null, null, null);
Contact myContact = null;
var lookupKeyList = new List<string> ();
while (cur.MoveToNext ()) {
lookupKeyList.Add (cur.GetString (cur.GetColumnIndexContactsContract.Contacts.InterfaceConsts.LookupKey)));
}
myContact = book.Where (c => c.Id == lookupKeyList [0]).First ();
This code is part of picking a contact from the phone book and receiving the data on OnActivityResult method.
Unfortunately, this code is taking up too much time on some devices and is instantaneous on others. I guess its related to Contact Aggregation but I am not sure. Any pointers?

Sounds like an Android issue, not necessarily a Xamarin issue. Take a look at the question Getting name and email from contact list is very slow. One of the things this answer does is use a Projection in the query to get all the columns in one go.