Query cookbook
React Query Cookbook for Parse
Introduction
We’ve already seen how a Parse.Query with get can retrieve a single Parse.Object from Back4App. There are many other ways to retrieve data with Parse.Query - you 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 Parse.Query 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.
Prerequisites
To complete this tutorial, you will need:
Goal
Explore the Parse.Query class different methods.
The Parse.Query class
Any query operation on Parse uses the Parse.Query object type, which will help you retrieve specific data from your Back4App throughout your app. 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.
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.
You can read more about the Parse.Query 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.
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 name;
- Date type birthDay;
- Number (integer) type friendCount;
- Array (string array) type favoriteFoods;
- Array (Number array) type luckyNumbers;
- GeoPoint type lastLoginLocation;
- Nullable pointer type premiumMembership, related to a Membership class containing string name and Date expirationDate fields.
Here is the Parse.Object classes creation code, so go ahead and run it in your API console:
1 // Add Profile objects and create table
2 // Adam Sandler
3 let Profile = new Parse.Object('Profile');
4 Profile.set('name', 'Adam Sandler');
5 Profile.set('birthDay', new Date('09/09/1966'));
6 Profile.set('friendCount', 2);
7 Profile.set('favoriteFoods', ['Lobster', 'Bread']);
8 Profile.set('luckyNumbers', [2, 7]);
9 Profile.set('lastLoginLocation', new Parse.GeoPoint(37.38412167489413, -122.01268034622319));
10 await Profile.save();
11
12 // Britney Spears
13 Profile = new Parse.Object('Profile');
14 Profile.set('name', 'Britney Spears');
15 Profile.set('birthDay', new Date('12/02/1981'));
16 Profile.set('friendCount', 52);
17 Profile.set('favoriteFoods', ['Cake', 'Bread']);
18 Profile.set('luckyNumbers', [22, 7]);
19 Profile.set('lastLoginLocation', new Parse.GeoPoint(37.38412167489413, -122.01268034622319));
20 await Profile.save();
21
22 // Carson Kressley
23 Profile = new Parse.Object('Profile');
24 Profile.set('name', 'Carson Kressley');
25 Profile.set('birthDay', new Date('11/11/1969'));
26 Profile.set('friendCount', 12);
27 Profile.set('favoriteFoods', ['Fish', 'Cookies']);
28 Profile.set('luckyNumbers', [8, 2]);
29 Profile.set('lastLoginLocation', new Parse.GeoPoint(37.38412167489413, -122.01268034622319));
30 await Profile.save();
31
32 // Dan Aykroyd
33 // Creates related object Membership for this user only
34 let Membership = new Parse.Object('Membership');
35 Membership.set('name', 'Premium');
36 Membership.set('expirationDate', new Date('10/10/2030'))
37 await Membership.save();
38 Profile = new Parse.Object('Profile');
39 Profile.set('name', 'Dan Aykroyd');
40 Profile.set('birthDay', new Date('07/01/1952'));
41 Profile.set('friendCount', 66);
42 Profile.set('favoriteFoods', ['Jam', 'Peanut Butter']);
43 Profile.set('luckyNumbers', [22, 77]);
44 Profile.set('lastLoginLocation', new Parse.GeoPoint(37.38412167489413, -122.01268034622319));
45 Profile.set('premiumMembership', Membership);
46 await Profile.save();
47
48 // Eddie Murphy
49 Profile = new Parse.Object('Profile');
50 Profile.set('name', 'Eddie Murphy');
51 Profile.set('birthDay', new Date('04/03/1961'));
52 Profile.set('friendCount', 49);
53 Profile.set('favoriteFoods', ['Lettuce', 'Pepper']);
54 Profile.set('luckyNumbers', [6, 5]);
55 Profile.set('lastLoginLocation', new Parse.GeoPoint(-27.104919974838154, -52.61428045237739));
56 await Profile.save();
57
58 // Fergie
59 Profile = new Parse.Object('Profile');
60 Profile.set('name', 'Fergie');
61 Profile.set('birthDay', new Date('03/27/1975'));
62 Profile.set('friendCount', 55);
63 Profile.set('favoriteFoods', ['Lobster', 'Shrimp']);
64 Profile.set('luckyNumbers', [13, 7]);
65 Profile.set('lastLoginLocation', new Parse.GeoPoint(-27.104919974838154, -52.61428045237739));
66 await Profile.save();
67
68 console.log('Success!');
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:
Let’s now take a look at examples from every Parse.Query 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 quick method is used to retrieve a single Parse.Object instance when you know its objectId.
1 let query = new Parse.Query('Profile');
2 // Since objectId is randomly set in your database, make sure to inform a
3 // valid one when testing this method
4 let queryResult = await query.get('C6ENdLnFdQ');
5 console.log(queryResult); 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.
// Filters objects in which a key value is contained in the provided array of values.
1 let query = new Parse.Query('Profile');
2 // containedIn can be used on any data type such as numbers and strings
3 query.containedIn('luckyNumbers', [2, 7]);
4 let queryResult = await query.find();
5 console.log(queryResult);// Filters objects in which a key value is not set.
1 let query = new Parse.Query('Profile');
2 query.doesNotExist('premiumMembership');
3 let queryResult = await query.find();
4 console.log(queryResult);// Filters objects in which a specific key’s value is equal to the provided value.
1 let query = new Parse.Query('Profile');
2 // equalTo can be used in any data type
3 query.equalTo('friendCount', 2);
4 let queryResult = await query.find();
5 console.log(queryResult);// Filters objects in which a specific key’s value is greater than or equal to the provided value.
1 let query = new Parse.Query('Profile');
2 // greaterThanOrEqualTo can be used on numbers and dates
3 query.greaterThanOrEqualTo('friendCount', 49);
4 let queryResult = await query.find();
5 console.log(queryResult);// Requires that a key’s value matches a value in an object returned by a different Parse.Query. Useful for multi-object querying.
1 let query = new Parse.Query('Profile');
2 // Multiple queries can be combined using this, useful when there are more objects
3 // related, not our example case
4 query.matchesKeyInQuery('friendCount', 'friendCount', new Parse.Query('Profile').lessThan('friendCount', 50));
5 query.greaterThan('friendCount', 10);
6 let queryResult = await query.find();
7 console.log(queryResult);// Filters objects in which a string key’s value starts with the provided text value.
1 let query = new Parse.Query('Profile');
2 // This is faster than other string searches by using backend index
3 query.startsWith('name', 'Brit');
4 let queryResult = await query.find();
5 console.log(queryResult);Query ordering
Essential in most queries, ordering can be easily achieved in Parse and even chained between two or more ordering constraints.
// Sort the results in ascending order, this can be chained without overwriting previous orderings. Multiple keys can be used to solve ordering ties.
1 let query = new Parse.Query('Profile');
2 query.ascending('friendCount');
3 let queryResult = await query.find();
4 console.log(queryResult);Field selecting
These methods affect which field values can be in your query results.
// Return only the specified fields in the returned objects.
1 let query = new Parse.Query('Profile');
2 query.select('name');
3 let queryResult = await query.find();
4 console.log(queryResult[0].get('birthDay') === undefined);
5 console.log(queryResult[0].get('name'));Geopoint querying
These are methods specific to GeoPoint querying.
// Find objects whose key value is near the given GeoPoint and within the maxDistance value. The sorted boolean value determines if the results should be sorted by distance ascending.
1 let query = new Parse.Query('Profile');
2 query.withinKilometers('lastLoginLocation', new Parse.GeoPoint(37.38412167489413, -122.01268034622319), 100, true);
3 let queryResult = await query.find();
4 console.log(queryResult);// Find objects whose key value is near the given GeoPoint and within the maxDistance value. The sorted boolean value determines if the results should be sorted by distance ascending.
1 let query = new Parse.Query('Profile');
2 query.withinRadians('lastLoginLocation', new Parse.GeoPoint(37.38412167489413, -122.01268034622319), 1.5, true);
3 let queryResult = await query.find();
4 console.log(queryResult);Pagination
These methods are related to pagination utilities, useful for queries that will retrieve a large number of results.
// Sets a flag that will wrap or not the query response in an object containing results, holding the array of Parse.Object and count integer holding the total number of results.
1 let query = new Parse.Query('Profile');
2 query.withCount(true);
3 let queryResult = await query.find();
4 console.log(queryResult);Response handling
These methods are helpers for handling the query responses, making it possible to queue callbacks that will be called after your query is resolved. They act as query resolvers as well, like find and first.
// Iterates over each result from the query and calls a callback for each one, in an unspecified order. Note that execution will halt on a rejected promise, so make sure to handle this case if using promises. Differs from each for passing more parameters down on callback execution and by allowing direct accumulator handling.
// The initialValue is the value to use as the first argument to the first call of the callback. If no initialValue is supplied, the first object in the query will be used and skipped.
1 let query = new Parse.Query('Profile');
2 let queryResult = await query.reduce((accumulator, currentObject, index) => console.log(`${index} - ${currentObject} - ${accumulator}`));
3 console.log(queryResult);Compound query
These methods will create compound queries, which can combine more than one Parse.Query instance to achieve more complex results.
// Compose a compound query that is the OR of the passed queries.
1 let query1 = new Parse.Query('Profile');
2 query1.greaterThan('friendCount', 10);
3 let query2 = new Parse.Query('Profile');
4 query1.lessThan('friendCount', 50);
5 let query = Parse.Query.or(query1, query2);
6 let queryResult = await query.find();
7 console.log(queryResult);Database related
These methods are related to the database preferences and operations.
// Executes an aggregate query, retrieving objects over a set of input values. Please refer to MongoDB documentation on aggregate(https://docs.mongodb.com/v3.2/reference/operator/aggregation/)for better understanding.
1 let query = new Parse.Query('Profile');
2 let queryResult = await query.aggregate({ limit: 5 });
3 console.log(queryResult);Local datastore
These methods enable selecting the source of the queries and using a local datastore.
// Changes the source of this query to a specific group of pinned objects.
1 let query = new Parse.Query('Profile');
2 query.fromPinWithName('pinnedObjects');
3 let queryResult = await query.find();
4 console.log(queryResult);JSON specifics
Methods that allow queries to be represented as JSON and retrieved.
// Returns a JSON representation of this query operations.
1 let query = new Parse.Query('Profile');
2 query.greaterThan('friendCount', 10);
3 let queryJSON = await query.toJSON();
4 console.log(queryJSON);Conclusion
At the end of this guide, you learned how to perform every data query method in Parse. In the next guide, you will learn about relational Parse querying in React.