Error while performing compound queries in firestore - firebase

Question

I want to perform a compound query in firestore where I would like to get all documents with field bloodgroup equal to A+ and with field createdBy not equal to email. This email is that of the logged in user. When I perform the query I get NullPointerException. How to perform the query correctly 021-07-24 19:50:24.746 17550-17550/com.example.bloodbankcompany E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.bloodbankcompany, PID: 17550 java.lang.NullPointerExceptionatcom.example.bloodbankcompany.UserlistActivity$EventChangeListener3$1.onEvent(UserlistActivity.kt:217) I am storing the document snapshot inside the userArrayList array. Without the whereNotEqualTo query I am getting output where my documents get listed in recyclerview.
private fun EventChangeListener2(){
val sharedPreferences1 = getSharedPreferences("email", Context.MODE_PRIVATE)
val email: String? = sharedPreferences1.getString("email","null")?.trim()
Toast.makeText(this, "ssrae$email", Toast.LENGTH_SHORT ).show()
mFireStore.collection("applicationForm").whereNotEqualTo("createdBy",email).whereEqualTo("bloodgroup","A+").addSnapshotListener(object : EventListener<QuerySnapshot>{
override fun onEvent(value: QuerySnapshot?, error: FirebaseFirestoreException?) {
if (error!= null){
Log.e("firestore error", error.message.toString())
}
for(dc: DocumentChange in value?.documentChanges!!){
if (dc.type== DocumentChange.Type.ADDED){
userArrayList.add(dc.document.toObject(User1::class.java))
var number=userArrayList
var number1 =userArrayList
}
// Toast.makeText(applicationContext,userArrayList.toString(), Toast.LENGTH_SHORT).show()
}
myAdapter.notifyDataSetChanged()
}
})
}

Answer 1

Well, I have edited a little bit of your code, if it still doesn't work add a comment.
Also, an explanation about changes is commented below.
private fun EventChangeListener2() {
val sharedPreferences1 = getSharedPreferences("email", Context.MODE_PRIVATE)
val email: String? = sharedPreferences1.getString("email", "null")?.trim()
Log.d("firestore email", email.toString())
Toast.makeText(this, "ssrae$email", Toast.LENGTH_SHORT).show()
// try and catch will avoid your app to crash.
try {
//ref
var ref = mFireStore.collection("applicationForm")
.whereEqualTo("bloodgroup", "A+")
/**
* I believe since your email is of type nullable and there may be
* maybe a chance that email is null and is given to whereNotEqualTo
* I am just making an assumption here since I don't know what you
* recieve from sharedPreferences and whether it is null or not
*
* So, what I have done here is,
* firstly, I have split the firestore call into 2 parts and
* Secondly, I have a null-check for email, if it is
* not-null ref will also include this query
*
*/
//null Check for email
if (email != null) ref = ref.whereNotEqualTo("createdBy", email)
// Snapshot Listener
ref.addSnapshotListener(object : EventListener<QuerySnapshot> {
override fun onEvent(value: QuerySnapshot?, error: FirebaseFirestoreException?) {
if (error != null) {
Log.e("firestore error", error.message.toString())
}
for (dc: DocumentChange in value?.documentChanges!!) {
if (dc.type == DocumentChange.Type.ADDED) {
userArrayList.add(dc.document.toObject(User1::class.java))
var number = userArrayList
var number1 = userArrayList
}
// Toast.makeText(applicationContext,userArrayList.toString(), Toast.LENGTH_SHORT).show()
}
myAdapter.notifyDataSetChanged()
}
})
} catch (e: Exception) {
Log.e("firestore error", "Error", e)
}
}
EDIT:
According to firebase docs,
https://firebase.google.com/docs/firestore/query-data/indexing#exemptions
If you attempt a compound query with a range clause that doesn't map to an existing index, you receive an error. The error message includes a direct link to create the missing index in the Firebase console.