Query Cookbook
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
To complete this tutorial, we need:
- An app created on Back4App.
- An android app connected to Back4App.
- Note: Follow the Install Parse SDK tutorial to create an Android Studio Project connected to Back4App.
Explore the ParseQuery class different methods and learn query types you can create on Android.
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.
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.
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:
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 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.
These methods are responsible for running the query and retrieving its results, being always present in your query implementation.
This is the java methods:
This is the kotlin methods:
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
These are Kotlin methods
These are Java methods
These are Kotlin methods
These are Java methods
These are Kotlin methods
Essential in most queries, ordering can be easily achieved in Parse and even chained between two or more ordering constraints.
These are Java methods
These are Kotlin methods
These methods affect which field values can be in your query results.
These are Java methods
These are Kotlin methods
These are methods specific to GeoPoint querying.
These are Java Methods
These are Kotlin methods
These methods are related to pagination utilities, useful for queries that will retrieve a large number of results.
These are Java methods
These are Kotlin methods
These methods enable selecting the source of the queries and using a local datastore.
These are Java methods
These are Kotlin methods
At the end of this guide, you learned how to use different query types in Android.