React Native

Query in React Native using Parse

Introduction

In this guide, you will perform basic queries in Parse and implement a React Native component using these queries. You will learn how to set up and query realistic data using Back4App and React Native.

Prerequisites

To complete this tutorial, you will need:

A React Native App created and connected to Back4App.

If you want to run this guide’s example application, you should set up the react-native-paper library.

Goal

Query data stored on Back4App from a React Native App.

Step 1 - Understanding the Parse.Query class

Any Parse query operation uses the Parse.Query object type, which will help you retrieve specific data from your database throughout your app. It is crucial to know that a Parse.Query will only resolve after calling a retrieve method (like Parse.Query.find or Parse.Query.get), so a query can be set up and several modifiers can be chained before actually being called.

To create a new Parse.Query, you need to pass as a parameter the desired Parse.Object subclass, which is the one that will contain your query results. An example query can be seen below, in which a fictional Profile subclass is being queried.

// This will create your query
let parseQuery = new Parse.Query("Profile");
// The query will resolve only after calling this method
let queryResult = await parseQuery.find();

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

Step 2 - Save some data on Back4App

Let’s create a Profile class, which will be the target of our queries in this guide. 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:

React Native Back4App

Go ahead and create the user Profile class with the following example content:

// Add Profile objects and create table
// Adam Sandler
let Profile = new Parse.Object('Profile');
Profile.set('name', 'Adam Sandler');
Profile.set('birthDay', new Date('09/09/1966'));
Profile.set('friendCount', 2);
Profile.set('favoriteFoods', ['Lobster', 'Bread']);
await Profile.save();

// Adam Levine
Profile = new Parse.Object('Profile');
Profile.set('name', 'Adam Levine');
Profile.set('birthDay', new Date('03/18/1979'));
Profile.set('friendCount', 52);
Profile.set('favoriteFoods', ['Cake', 'Bread']);
await Profile.save();

// Carson Kressley
Profile = new Parse.Object('Profile');
Profile.set('name', 'Carson Kressley');
Profile.set('birthDay', new Date('11/11/1969'));
Profile.set('friendCount', 12);
Profile.set('favoriteFoods', ['Fish', 'Cookies']);
await Profile.save();

// Dan Aykroyd
Profile = new Parse.Object('Profile');
Profile.set('name', 'Dan Aykroyd');
Profile.set('birthDay', new Date('07/01/1952'));
Profile.set('friendCount', 66);
Profile.set('favoriteFoods', ['Jam', 'Peanut Butter']);
await Profile.save();

// Eddie Murphy
Profile = new Parse.Object('Profile');
Profile.set('name', 'Eddie Murphy');
Profile.set('birthDay', new Date('04/03/1961'));
Profile.set('friendCount', 49);
Profile.set('favoriteFoods', ['Lettuce', 'Pepper']);
await Profile.save();

// Fergie
Profile = new Parse.Object('Profile');
Profile.set('name', 'Fergie');
Profile.set('birthDay', new Date('03/27/1975'));
Profile.set('friendCount', 55);
Profile.set('favoriteFoods', ['Lobster', 'Shrimp']);
await Profile.save();

console.log('Success!');

Step 3 - Query the data

Now that you have a populated class, we can now perform some basic queries in it. Let’s begin by filtering Profile results by name, which is a string type field, searching for values that contain the name Adam using the Parse.Query.contains method:

// Create your query
let parseQuery = new Parse.Query('Profile');

// `contains` is a basic query method that checks if string field
// contains a specific substring
parseQuery.contains('name', 'Adam');

// The query will resolve only after calling this method, retrieving
// an array of `Parse.Objects`
let queryResults = await parseQuery.find();

// Let's show the results
for (let result of queryResults) {
  // You access `Parse.Objects` attributes by using `.get`
  console.log(result.get('name'));
};

Let’s now query by the number type field friendCount by using another common query method, Parse.Query.greaterThan. In this case, we want user Profiles in which the friend count is greater than 20.

// Create your query
let parseQuery = new Parse.Query('Profile');

// `greaterThan` is a basic query method that does what it
// says on the tin
parseQuery.greaterThan('friendCount', 20);

// The query will resolve only after calling this method, retrieving
// an array of `Parse.Objects`
let queryResults = await parseQuery.find();

// Let's show the results
for (let result of queryResults) {
  // You access `Parse.Objects` attributes by using `.get`
  console.log(`name: ${result.get('name')}, friend count: ${result.get('friendCount')}`);
};

Other recurring query methods are Parse.Query.ascending and Parse.Query.descending, responsible for ordering your queries. This ordering can be done in most data types, so let’s order a query by the date field birthDay by the youngest.

// Create your query
let parseQuery = new Parse.Query('Profile');

// `descending` and `ascending` can and should be chained
// with other query methods to improve your queries
parseQuery.descending('birthDay');

// The query will resolve only after calling this method, retrieving
// an array of `Parse.Objects`
let queryResults = await parseQuery.find();

// Let's show the results
for (let result of queryResults) {
  // You access `Parse.Objects` attributes by using `.get`
  console.log(`name: ${result.get('name')}, birthday: ${result.get('birthDay')}`);
};

As stated here before, you can and should chain query methods to achieve more refined results. Let’s then combine the previous examples in a single query request:

// Create your query
let parseQuery = new Parse.Query('Profile');

parseQuery.contains('name', 'Adam');
parseQuery.greaterThan('friendCount', 20);
parseQuery.descending('birthDay');

// The query will resolve only after calling this method, retrieving
// an array of `Parse.Objects`
let queryResults = await parseQuery.find();

// Let's show the results
for (let result of queryResults) {
  // You access `Parse.Objects` attributes by using `.get`
  console.log(`name: ${result.get('name')}, friend count: ${result.get('friendCount')}, birthday: ${result.get('birthDay')}`);
};

Step 4 - Query from a React Native component

Let’s now use our example queries inside a component in React Native, with a simple interface having a list showing results and also 4 buttons for calling the queries. This is how the component code is laid out, note the doQuery functions, containing the example code form before.

JavaScript
TypeScript

import React, {useState} from 'react';
import {Alert, Image, View, ScrollView, StyleSheet} from 'react-native';
import Parse from 'parse/react-native';
import {
  List,
  Title,
  Button as PaperButton,
  Text as PaperText,
} from 'react-native-paper';

export const BookList = () => {
  // State variable
  const [queryResults, setQueryResults] = useState(null);

  const doQueryByName = async function () {
    // Create our Parse.Query instance so methods can be chained
    // Reading parse objects is done by using Parse.Query
    const parseQuery = new Parse.Query('Profile');

    // `contains` is a basic query method that checks if string field
    // contains a specific substring
    parseQuery.contains('name', 'Adam');

    try {
      let profiles = await parseQuery.find();
      setQueryResults(profiles);
      return true;
    } catch (error) {
      // Error can be caused by lack of Internet connection
      Alert.alert('Error!', error.message);
      return false;
    }
  };

  const doQueryByFriendCount = async function () {
    // Create our Parse.Query instance so methods can be chained
    // Reading parse objects is done by using Parse.Query
    const parseQuery = new Parse.Query('Profile');

    // `greaterThan` is a basic query method that does what it
    // says on the tin
    parseQuery.greaterThan('friendCount', 20);

    try {
      let profiles = await parseQuery.find();
      setQueryResults(profiles);
      return true;
    } catch (error) {
      // Error can be caused by lack of Internet connection
      Alert.alert('Error!', error.message);
      return false;
    }
  };

  const doQueryByOrdering = async function () {
    // Create our Parse.Query instance so methods can be chained
    // Reading parse objects is done by using Parse.Query
    const parseQuery = new Parse.Query('Profile');

    // `descending` and `ascending` can and should be chained
    // with other query methods to improve your queries
    parseQuery.descending('birthDay');

    try {
      let profiles = await parseQuery.find();
      setQueryResults(profiles);
      return true;
    } catch (error) {
      // Error can be caused by lack of Internet connection
      Alert.alert('Error!', error.message);
      return false;
    }
  };

  const doQueryByAll = async function () {
    // Create our Parse.Query instance so methods can be chained
    // Reading parse objects is done by using Parse.Query
    const parseQuery = new Parse.Query('Profile');

    parseQuery.contains('name', 'Adam');
    parseQuery.greaterThan('friendCount', 20);
    parseQuery.descending('birthDay');

    try {
      let profiles = await parseQuery.find();
      setQueryResults(profiles);
      return true;
    } catch (error) {
      // Error can be caused by lack of Internet connection
      Alert.alert('Error!', error.message);
      return false;
    }
  };

  const clearQueryResults = async function () {
    setQueryResults(null);
    return true;
  };

  return (
    <>
      <View style={Styles.header}>
        <Image
          style={Styles.header_logo}
          source={ {
            uri:
              'https://blog.back4app.com/wp-content/uploads/2019/05/back4app-white-logo-500px.png',
          } }
        />
        <PaperText style={Styles.header_text}>
          <PaperText style={Styles.header_text_bold}>
            {'React Native on Back4App - '}
          </PaperText>
          {' Basic Queries'}
        </PaperText>
      </View>
      <ScrollView style={Styles.wrapper}>
        <View>
          <Title>{'Result List'}</Title>
          {/* Book list */}
          {queryResults !== null &&
            queryResults !== undefined &&
            queryResults.map((profile) => (
              <List.Item
                key={profile.id}
                title={profile.get('name')}
                description={`Friend count: ${profile.get(
                  'friendCount',
                )}, Birthday: ${profile.get('birthDay')}`}
                titleStyle={Styles.list_text}
                style={Styles.list_item}
              />
            ))}
          {queryResults === null ||
          queryResults === undefined ||
          (queryResults !== null &&
            queryResults !== undefined &&
            queryResults.length <= 0) ? (
            <PaperText>{'No results here!'}</PaperText>
          ) : null}
        </View>
        <View>
          <Title>{'Query buttons'}</Title>
          <PaperButton
            onPress={() => doQueryByName()}
            mode="contained"
            icon="search-web"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Query by name'}
          </PaperButton>
          <PaperButton
            onPress={() => doQueryByFriendCount()}
            mode="contained"
            icon="search-web"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Query by friend count'}
          </PaperButton>
          <PaperButton
            onPress={() => doQueryByOrdering()}
            mode="contained"
            icon="search-web"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Query by ordering'}
          </PaperButton>
          <PaperButton
            onPress={() => doQueryByAll()}
            mode="contained"
            icon="search-web"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Query by all'}
          </PaperButton>
          <PaperButton
            onPress={() => clearQueryResults()}
            mode="contained"
            icon="delete"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Clear Results'}
          </PaperButton>
        </View>
      </ScrollView>
    </>
  );
};

// These define the screen component styles
const Styles = StyleSheet.create({
  header: {
    alignItems: 'center',
    paddingTop: 30,
    paddingBottom: 50,
    backgroundColor: '#208AEC',
  },
  header_logo: {
    height: 50,
    width: 220,
    resizeMode: 'contain',
  },
  header_text: {
    marginTop: 15,
    color: '#f0f0f0',
    fontSize: 16,
  },
  header_text_bold: {
    color: '#fff',
    fontWeight: 'bold',
  },
  wrapper: {
    width: '90%',
    alignSelf: 'center',
  },
  list_button: {
    marginTop: 6,
    marginLeft: 15,
    height: 40,
  },
  list_item: {
    borderBottomWidth: 1,
    borderBottomColor: 'rgba(0, 0, 0, 0.12)',
  },
  list_text: {
    fontSize: 15,
  },
});

import React, {FC, ReactElement, useState} from 'react';
import {Alert, Image, View, ScrollView, StyleSheet} from 'react-native';
import Parse from 'parse/react-native';
import {
  List,
  Title,
  Button as PaperButton,
  Text as PaperText,
} from 'react-native-paper';

export const QueryList: FC<{}> = ({}): ReactElement => {
  // State variable
  const [queryResults, setQueryResults] = useState(null);

  const doQueryByName = async function (): Promise<boolean> {
    // Create our Parse.Query instance so methods can be chained
    // Reading parse objects is done by using Parse.Query
    const parseQuery: Parse.Query = new Parse.Query('Profile');

    // `contains` is a basic query method that checks if string field
    // contains a specific substring
    parseQuery.contains('name', 'Adam');

    try {
      let profiles: [Parse.Object] = await parseQuery.find();
      setQueryResults(profiles);
      return true;
    } catch (error) {
      // Error can be caused by lack of Internet connection
      Alert.alert('Error!', error.message);
      return false;
    }
  };

  const doQueryByFriendCount = async function (): Promise<boolean> {
    // Create our Parse.Query instance so methods can be chained
    // Reading parse objects is done by using Parse.Query
    const parseQuery: Parse.Query = new Parse.Query('Profile');

    // `greaterThan` is a basic query method that does what it
    // says on the tin
    parseQuery.greaterThan('friendCount', 20);

    try {
      let profiles: [Parse.Object] = await parseQuery.find();
      setQueryResults(profiles);
      return true;
    } catch (error) {
      // Error can be caused by lack of Internet connection
      Alert.alert('Error!', error.message);
      return false;
    }
  };

  const doQueryByOrdering = async function (): Promise<boolean> {
    // Create our Parse.Query instance so methods can be chained
    // Reading parse objects is done by using Parse.Query
    const parseQuery: Parse.Query = new Parse.Query('Profile');

    // `descending` and `ascending` can and should be chained
    // with other query methods to improve your queries
    parseQuery.descending('birthDay');

    try {
      let profiles: [Parse.Object] = await parseQuery.find();
      setQueryResults(profiles);
      return true;
    } catch (error) {
      // Error can be caused by lack of Internet connection
      Alert.alert('Error!', error.message);
      return false;
    }
  };

  const doQueryByAll = async function (): Promise<boolean> {
    // Create our Parse.Query instance so methods can be chained
    // Reading parse objects is done by using Parse.Query
    const parseQuery: Parse.Query = new Parse.Query('Profile');

    parseQuery.contains('name', 'Adam');
    parseQuery.greaterThan('friendCount', 20);
    parseQuery.descending('birthDay');

    try {
      let profiles: [Parse.Object] = await parseQuery.find();
      setQueryResults(profiles);
      return true;
    } catch (error) {
      // Error can be caused by lack of Internet connection
      Alert.alert('Error!', error.message);
      return false;
    }
  };

  const clearQueryResults = async function (): Promise<boolean> {
    setQueryResults(null);
    return true;
  };

  return (
    <>
      <View style={Styles.header}>
        <Image
          style={Styles.header_logo}
          source={ {
            uri:
              'https://blog.back4app.com/wp-content/uploads/2019/05/back4app-white-logo-500px.png',
          } }
        />
        <PaperText style={Styles.header_text}>
          <PaperText style={Styles.header_text_bold}>
            {'React Native on Back4App - '}
          </PaperText>
          {' Basic Queries'}
        </PaperText>
      </View>
      <ScrollView style={Styles.wrapper}>
        <View>
          <Title>{'Result List'}</Title>
          {/* Book list */}
          {queryResults !== null &&
            queryResults !== undefined &&
            queryResults.map((profile: Parse.Object) => (
              <List.Item
                key={profile.id}
                title={profile.get('name')}
                description={`Friend count: ${profile.get(
                  'friendCount',
                )}, Birthday: ${profile.get('birthDay')}`}
                titleStyle={Styles.list_text}
                style={Styles.list_item}
              />
            ))}
          {queryResults === null ||
          queryResults === undefined ||
          (queryResults !== null &&
            queryResults !== undefined &&
            queryResults.length <= 0) ? (
            <PaperText>{'No results here!'}</PaperText>
          ) : null}
        </View>
        <View>
          <Title>{'Query buttons'}</Title>
          <PaperButton
            onPress={() => doQueryByName()}
            mode="contained"
            icon="search-web"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Query by name'}
          </PaperButton>
          <PaperButton
            onPress={() => doQueryByFriendCount()}
            mode="contained"
            icon="search-web"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Query by friend count'}
          </PaperButton>
          <PaperButton
            onPress={() => doQueryByOrdering()}
            mode="contained"
            icon="search-web"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Query by ordering'}
          </PaperButton>
          <PaperButton
            onPress={() => doQueryByAll()}
            mode="contained"
            icon="search-web"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Query by all'}
          </PaperButton>
          <PaperButton
            onPress={() => clearQueryResults()}
            mode="contained"
            icon="delete"
            color={'#208AEC'}
            style={Styles.list_button}>
            {'Clear Results'}
          </PaperButton>
        </View>
      </ScrollView>
    </>
  );
};

// These define the screen component styles
const Styles = StyleSheet.create({
  header: {
    alignItems: 'center',
    paddingTop: 30,
    paddingBottom: 50,
    backgroundColor: '#208AEC',
  },
  header_logo: {
    height: 50,
    width: 220,
    resizeMode: 'contain',
  },
  header_text: {
    marginTop: 15,
    color: '#f0f0f0',
    fontSize: 16,
  },
  header_text_bold: {
    color: '#fff',
    fontWeight: 'bold',
  },
  wrapper: {
    width: '90%',
    alignSelf: 'center',
  },
  list_button: {
    marginTop: 6,
    marginLeft: 15,
    height: 40,
  },
  list_item: {
    borderBottomWidth: 1,
    borderBottomColor: 'rgba(0, 0, 0, 0.12)',
  },
  list_text: {
    fontSize: 15,
  },
});

This is how the component should look like after rendering and querying by all the query functions:

React Native Back4App

Conclusion

At the end of this guide, you learned how basic data queries work on Parse and how to perform them on Back4App from a React Native App. In the next guide, you will explore the Parse.Query full potential using all the methods available on this class.

One to one Relationship

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