title: Is there any whereIn query in Firebase Firestore?
body: <p>I want to find all the users whose phone number is contained in the list.
  It's like searching <code>*</code> from database where email IN phone_numbers.</p>
  
  <p>This is what I am doing.</p>
  
  <pre><code>fun getUsers(persons: List&lt;Person&gt;?): Single&lt;List&lt;User&gt;&gt; {
      return Single.create({ emitter -&gt;
          try {
              val db = FirebaseFirestore.getInstance()
              val userCollection = db.collection(USER_FIREBASE_TABLE)
              var query: Query? = null
              persons?.forEach({ person -&gt;
                  query = if (null == query) userCollection
                          .whereEqualTo("phone", person.phone)
                  else query!!.whereEqualTo("phone", person.phone)
              })
              query?.get()?.addOnCompleteListener({ task: Task&lt;QuerySnapshot&gt; -&gt;
                  emitter.onSuccess(task.getResult().toObjects(User::class.java))
              })
          } catch (exception: Exception) {
              exception.printStackTrace()
              emitter.onError(exception)
          }
      })  
  }
  </code></pre>
  
  <p>As you see I am appending <strong>whereEqualTo</strong> each time to the query. Is there any way to replace it with something like <strong>whereIn</strong> and I pass an array or collection of values to match to?</p>