Android
Data objects

Query Cookbook

23min

Parse Query Cookbook in Android

Introduction

We’ve already seen how a ParseQuery with get can retrieve a single ParseQuery from Back4App. There are many other ways to retrieve data withParseQueryyou can retrieve many objects at once, use conditions on the objects you wish to retrieve, and more.

In this guide, you will ding deep into the ParseQuery class and see all the methods you can use to build your Queries. You will use a simple database class with some mocked data to perform the Queries using the Javascript Console on Back4App.

You can use Javascript Console on Back4App to create mocked data easily, or you can create your data with your own android app by following this guide.

This tutorial uses an app created in Android Studio 4.1.1 with buildToolsVersion=30.0.2 , Compile SDK Version = 30.0.2 and targetSdkVersion=30

At any time, you can access the complete Android Project built with this tutorial at our Github repositories

Prerequisites

To complete this tutorial, we need:

Goal

Explore the ParseQuery class different methods and learn query types you can create on Android.

The ParseQuery class

Any query operation on Parse uses the ParseQuery object type, which will help you retrieve specific data from your Back4App throughout your app. To create a new ParseQuery, you need to pass as a parameter the desired ParseQuery subclass, which is the one that will contain your query results.

It is crucial to know that a ParseQuery will only resolve after calling a retrieve method (like ParseQuery.find or ParseQuery.get), so a query can be set up and several modifiers can be chained before actually being called.

You can read more about the ParseQuery class here at the official documentation.

Using the JS Console on Back4App

Inside your Back4App application’s dashboard, you will find a very useful API console in which you can run JavaScript code directly. In this guide you will use to store and query data objects from Back4App. On your App main dashboard go to Core->API Console->JS Console.



Document image


Save your Data Objects

To run the queries on this guide you’ll need first to populate your App with some data. Let’s create a sample class called Profile, which mocks a social media profile class using famous people names and the following fields:

  • string type
  • Date type
  • Number (integer) type
  • Array (string array) type
  • Array (Number array) type
  • GeoPoint type
  • Nullable pointer type

Here is the Parse.Object classes creation code, so go ahead and run it in your API console:

Java


After running this code, you should now have a Profile class in your database with six objects created. Your new class should look like this:

Document image


Let’s now take a look at examples from every ParseQuery method, along with brief explanations on what they do. Please note that some methods in this list can take options as an additional argument, but in most cases, it is only related to masterKey usage and not relevant to this guide content, so this possibility will be omitted whenever not relevant.

Query retrievers

These methods are responsible for running the query and retrieving its results, being always present in your query implementation.

This is the java methods:

cancel
count
find
findInBackground
first
get


This is the kotlin methods:

cancel
count
find
findInBackground
first
get


Query conditioners

These methods give you the possibility of applying conditional constraints to your query, which are arguably the most important operations in querying. Remember that these operations can all be chained before the results are retrieved, so many combinations can be achieved to solve your querying needs.

These are Java methods

containedIn
contains
cointansAll
containsAllStartingWith
doesNotExist


These are Kotlin methods

containedIn
contains
cointansAll
containsAllStartingWith
doesNotExist


These are Java methods

canceldoesNotMatchKeyInQuery
doesNotMatchQuery
endsWith
equalTo

exists
fullText
greaterThan
greaterThanOrEqualTo


These are Kotlin methods

canceldoesNotMatchKeyInQuery
doesNotMatchQuery
endsWith
equalTo

exists
fullText
greaterThan
greaterThanOrEqualTo


These are Java methods

lessThan
lessThanOrEqualTo
matches
matchesKeyInQuery
matchesQuery
notEqualTo
startsWith


These are Kotlin methods

lessThan
lessThanOrEqualTo
matches
matchesKeyInQuery
matchesQuery
notEqualTo
startsWith


Query ordering

Essential in most queries, ordering can be easily achieved in Parse and even chained between two or more ordering constraints.

These are Java methods

addAscending
addDescending
ascending
descending


These are Kotlin methods

addAscending
addDescending
ascending
descending


Field selecting

These methods affect which field values can be in your query results.

These are Java methods

include
select


These are Kotlin methods

include
select


Geopoint querying

These are methods specific to GeoPoint querying.

These are Java Methods

near
polygonContains
withinGeoBox
withinKilometers

withinMiles
withinPolygon
withinRadians


These are Kotlin methods

near
polygonContains
withinGeoBox
withinKilometers

withinMiles
withinPolygon
withinRadians


Pagination

These methods are related to pagination utilities, useful for queries that will retrieve a large number of results.

These are Java methods

limit
skip


These are Kotlin methods

limit
skip


Local datastore

These methods enable selecting the source of the queries and using a local datastore.

These are Java methods

fromLocalDatastore
fromNetwork
fromPin
fromPinWithName


These are Kotlin methods

fromLocalDatastore
fromNetwork
fromPin
fromPinWithName


Conclusion

At the end of this guide, you learned how to use different query types in Android.