---
title: Relational Queries
slug: docs/android/data-objects/query-relations
description: In this guide, you will perform relational queries in Parse and implement an Android app using these queries. You will learn how to set up and query realistic data using Back4App and Android.
image: https://www.back4app.com/images/logo-social.png
docTags: 
createdAt: 2024-03-13T15:21:17.973Z
---

# Relational Queries on Android

## Introduction

In this guide, you will perform relational queries in Parse and implement an Android app using these queries. You will learn how to set up and query realistic data using Back4App and Android.

This tutorial uses an app created in Android Studio Arctic Fox -2020.3.1 with <font color="#2166ae">`compileSdk = 30`</font> , <font color="#2166ae">`minSdk = 23`</font> and <font color="#2166ae">`targetSdk = 30`</font>

:::hint{type="success"}
At any time, you can access the complete Android Project built with this tutorial at our Github repositories

- [Kotlin Example Repository](https://github.com/templates-back4app/Android-Parse-Sdk-Kotlin)
- [Java Example Repository](https://github.com/templates-back4app/Android-Parse-Sdk-Java)
:::

## Goal

Our goal is query data stored on <font color="#2166ae">`Back4App`</font> from an <font color="#2166ae">`Android`</font> app.

Here is a preview of what we are gonna achieve:

::Image[]{src="https://api.archbee.com/api/optimize/yD3zCY-NNBBIfd0uqcfR5/r_ztIV4fRNQoI9ol77tTJ_image.png" size="50" width="346" height="750" position="center" showCaption="false"}

## Prerequisites

:::hint{type="info"}
**To complete this tutorial, we need:**

- [Android Studio](https://developer.android.com/studio/index.html)
- An app created on Back4App.
  - **Note:&#x20;**&#x46;ollow the [New Parse App tutorial](https://www.back4app.com/docs/get-started/new-parse-app) to learn how to create a Parse App on Back4App.
- An android app connected to Back4App.
  - **Note:&#x20;**&#x46;ollow the [Install Parse SDK tutoria](https://www.back4app.com/docs/android/parse-android-sdk)l to create an Android Studio Project connected to Back4App.
- A device (or[ virtual device](https://developer.android.com/studio/run/managing-avds.html)) running Android 4.1 (Jelly Bean) or newer.
:::

## Let’s get started!

Before next steps, we need to connect <font color="#2166ae">`Back4App`</font> to our application. You should save the <font color="#2166ae">`appId`</font> and <font color="#2166ae">`clientKey`</font> from the <font color="#2166ae">`Back4App`</font> to <font color="#2166ae">`string.xml`</font> file and then init <font color="#2166ae">`Parse`</font> in our <font color="#2166ae">`App.java`</font> or <font color="#2166ae">`App.kt`</font> file.
Follow the [New Parse App tutorial](https://www.back4app.com/docs/android/parse-android-sdk) if you don’t know how to init <font color="#2166ae">`Parse`</font> to your app.

Or you can download the projects we shared the github links above and edit only the <font color="#2166ae">`appId`</font> and <font color="#2166ae">`clientKey`</font> parts according to you.

:::hint{type="success"}
At any time, you can access the complete Android Project built with this tutorial at our Github repositories

- [Kotlin Example Repository](https://github.com/templates-back4app/Android-Parse-Sdk-Kotlin)
- [Java Example Repository](https://github.com/templates-back4app/Android-Parse-Sdk-Java)
:::

## 1 - Save some data on Back4App

In this step, we will create a Class with the JS Console and Javascript codes provided by <font color="#2166ae">`Parse`</font> and we will create queries for this Class.

Let’s create an assortment of classes, which will be the target of our queries in this guide. The classes are: <font color="#2166ae">`Author`</font>, <font color="#2166ae">`Book`</font>, <font color="#2166ae">`Publisher`</font> and <font color="#2166ae">`BookStore`</font>, in which <font color="#2166ae">`Book`</font> has a 1\:N relation with <font color="#2166ae">`Publisher`</font> and N\:N with <font color="#2166ae">`Author`</font>, and <font color="#2166ae">`BookStore`</font> has an N\:N relation with <font color="#2166ae">`Book`</font>.

On Parse JS Console is possible to run JavaScript code directly, querying and updating your application database contents using the JS SDK commands. Run the code below from your JS Console and insert the data on Back4App. Here is how the JS console looks like in your dashboard:

![](https://api.archbee.com/api/optimize/yD3zCY-NNBBIfd0uqcfR5/5bdz5cp1kW2Hknxagtm5w_image.png)

Go ahead and create the classes with the following example content:

```java
1   // Add objects and create tables
2   // Authors
3   const AuthorA = new Parse.Object('Author');
4   AuthorA.set('name', 'Aaron Writer');
5   await AuthorA.save();
6 
7   const AuthorB = new Parse.Object('Author');
8   AuthorB.set('name', 'Beatrice Novelist');
9   await AuthorB.save();
10
11  const AuthorC = new Parse.Object('Author');
12  AuthorC.set('name', 'Casey Columnist');
13  await AuthorC.save();
14
15  // Publishers
16  const PublisherA = new Parse.Object('Publisher');
17  PublisherA.set('name', 'Acacia Publishings');
18  await PublisherA.save();
19
20  const PublisherB = new Parse.Object('Publisher');
21  PublisherB.set('name', 'Birch Distributions');
22  await PublisherB.save();
23
24  // Books
25  const BookA = new Parse.Object('Book');
26  BookA.set('title', 'A Love Story');
27  BookA.set('publisher', PublisherA);
28  BookA.set('publishingDate', new Date('05/07/1998'));
29  const BookARelation = BookA.relation("authors");
30  BookARelation.add(AuthorA);
31  await BookA.save();
32  
33  const BookB = new Parse.Object('Book');
34  BookB.set('title', 'Benevolent Elves');
35  BookB.set('publisher', PublisherB);
36  BookB.set('publishingDate', new Date('11/31/2008'));
37  const BookBRelation = BookB.relation("authors");
38  BookBRelation.add(AuthorB);
39  await BookB.save();
40
41  const BookC = new Parse.Object('Book');
42  BookC.set('title', 'Can You Believe It?');
43  BookC.set('publisher', PublisherB);
44  BookC.set('publishingDate', new Date('08/21/2018'));
45  const BookCRelation = BookC.relation("authors");
46  BookCRelation.add(AuthorA);
47  BookCRelation.add(AuthorC);
48  await BookC.save();
49
50  // BookStore
51  const BookStoreA = new Parse.Object('BookStore');
52  BookStoreA.set('name', 'Books of Love');
53  const BookStoreARelation = BookStoreA.relation("books");
54  BookStoreARelation.add(BookA);
55  await BookStoreA.save();
56
57  const BookStoreB = new Parse.Object('BookStore');
58  BookStoreB.set('name', 'Fantasy Books');
59  const BookStoreBRelation = BookStoreB.relation("books");
60  BookStoreBRelation.add(BookB);
61  await BookStoreB.save();
62
63  const BookStoreC = new Parse.Object('BookStore');
64  BookStoreC.set('name', 'General Books');
65  const BookStoreCRelation = BookStoreC.relation("books");
66  BookStoreCRelation.add(BookA);
67  BookStoreCRelation.add(BookC);
68  await BookStoreC.save();
69
70  console.log('Success');
```

## 2 - Query the data from Android app

Now that you have populated all the classes, we can now perform some relational queries in it. Let’s begin by filtering <font color="#2166ae">`Book`</font> results by the publisher, searching for the ones that belong to the <font color="#2166ae">`Publisher`</font> “Acacia Publishings” (or “Publisher A”) using the basic <font color="#2166ae">`ParseQuery.equalTo`</font> method:

:::CodeblockTabs
```java
1       progressDialog.show();
2       ParseQuery<ParseObject> publisherQuery = new ParseQuery<>("Publisher");
3       publisherQuery.whereEqualTo("name", "Acacia Publishings");
4       try {
5           ParseObject publisher = publisherQuery.getFirst();
6           ParseQuery<ParseObject> bookQuery = new ParseQuery<ParseObject>("Book");
7           bookQuery.whereEqualTo("publisher", publisher);
8           bookQuery.findInBackground((objects, e) -> {
9               progressDialog.hide();
10              if (e == null) {
11                  initData(objects);
12              } else {
13                  Toast.makeText(this, e.getLocalizedMessage(), Toast.LENGTH_SHORT).show();
14              }
15          });
16      } catch (ParseException e) {
17          progressDialog.hide();
18          e.printStackTrace();
19      }
```

```kotlin
1      progressDialog?.show()
2      val publisherQuery = ParseQuery<ParseObject>("Publisher")
3      publisherQuery.whereEqualTo("name", "Acacia Publishings")
4      try {
5          val publisher = publisherQuery.first
6          val bookQuery = ParseQuery<ParseObject>("Book")
7          bookQuery.whereEqualTo("publisher", publisher)
8          bookQuery.findInBackground { objects: List<ParseObject>?, e: ParseException? ->
9              progressDialog?.hide()
10             if (e == null) {
11                initData(objects!!)
12             } else {
13                 Toast.makeText(this, e.localizedMessage, Toast.LENGTH_SHORT).show()
14             }
15         }
16     } catch (e: ParseException) {
17         progressDialog?.hide()
18         e.printStackTrace()
19     }
```
:::

Let’s now query which <font color="#2166ae">`BookStore`</font> objects contain <font color="#2166ae">`Book`</font> objects with publishing date greater than 01/01/2010, using an inner query with the <font color="#2166ae">`ParseQuery.whereGreaterThan`</font> method and then the <font color="#2166ae">`ParseQuery.whereMatchesQuery`</font> method:

:::CodeblockTabs
```java
1       progressDialog.show();
2       ParseQuery<ParseObject> bookQuery = new ParseQuery<>("Book");
3
4       Calendar calendar = Calendar.getInstance();
5       calendar.set(2010,1,1,59,59,59);
6       Date date = calendar.getTime();
7
8       bookQuery.whereGreaterThan("publishingDate", date);
9
10      ParseQuery<ParseObject> bookStoreQuery = new ParseQuery<>("BookStore");
11      bookStoreQuery.whereMatchesQuery("books",bookQuery);
12      bookStoreQuery.findInBackground((objects, e) -> {
13          progressDialog.hide();
14          if (e==null){
15              initData(objects);
16          } else {
17              Toast.makeText(this, e.getLocalizedMessage(), Toast.LENGTH_SHORT).show();
18          }
19      });
```

```kotlin
1      progressDialog?.show()
2      val bookQuery = ParseQuery<ParseObject>("Book")
3      val calendar = Calendar.getInstance()
4      calendar[2010, 1, 1, 59, 59] = 59
5      val date = calendar.time
6      bookQuery.whereGreaterThan("publishingDate", date)
7      val bookStoreQuery = ParseQuery<ParseObject>("BookStore")
8      bookStoreQuery.whereMatchesQuery("books", bookQuery)
9      bookStoreQuery.findInBackground { objects: List<ParseObject>?, e: ParseException? ->
10         progressDialog?.hide()
11         if (e == null) {
12             initData(objects!!)
13         } else {
14             Toast.makeText(this, e.localizedMessage, Toast.LENGTH_SHORT).show()
15         }
16     }
```
:::

Now lets create a more complex relational query, looking for <font color="#2166ae">`BookStore`</font> objects that have at least one <font color="#2166ae">`Book`</font> written by <font color="#2166ae">`Author`</font> “Aaron Writer” (or “AuthorA”), using <font color="#2166ae">`whereEqualTo`</font> and <font color="#2166ae">`whereMatchesQuery`</font>:

:::CodeblockTabs
```java
1       progressDialog.show();
2       ParseQuery<ParseObject> authorQuery = new ParseQuery<>("Author");
3       authorQuery.whereEqualTo("name","Aaron Writer");
4       try {
5           ParseObject authorA = authorQuery.getFirst();
6           ParseQuery<ParseObject> bookQuery = new ParseQuery<>("Book");
7           bookQuery.whereEqualTo("authors",authorA);
8
9           ParseQuery<ParseObject> bookStoreQuery = new ParseQuery<>("BookStore");
10          bookStoreQuery.whereMatchesQuery("books",bookQuery);
11
12          bookStoreQuery.findInBackground((objects, e) -> {
13             progressDialog.hide();
14             if (e==null){
15                  initData(objects);
16             } else {
17                 Toast.makeText(this, e.getLocalizedMessage(), Toast.LENGTH_SHORT).show();
18             }
19         });
20
21
22     } catch (ParseException e) {
23         progressDialog.hide();
24         e.printStackTrace();
25     }
```

```kotlin
1      progressDialog?.show()
2     val authorQuery = ParseQuery<ParseObject>("Author")
3     authorQuery.whereEqualTo("name", "Aaron Writer")
4     try {
5         val authorA = authorQuery.first
6         val bookQuery = ParseQuery<ParseObject>("Book")
7         bookQuery.whereEqualTo("authors", authorA)
8         val bookStoreQuery = ParseQuery<ParseObject>("BookStore")
9         bookStoreQuery.whereMatchesQuery("books", bookQuery)
10        bookStoreQuery.findInBackground { objects: List<ParseObject>?, e: ParseException? ->
11            progressDialog?.hide()
12            if (e == null) {
13                initData(objects!!)
14            } else {
15                Toast.makeText(this, e.localizedMessage, Toast.LENGTH_SHORT).show()
16            }
17        }
18    } catch (e: ParseException) {
19        progressDialog?.hide()
20        e.printStackTrace()
21    }
```
:::

## It’s done!

At the end of this guide, you learned how relational queries work on Parse and how to perform them on Back4App from an Android App.