Storing Custom Java Objects with ArrayLists in Firebase Realtime Database

Learn how to effectively store `custom Java objects` containing ArrayLists in Firebase Realtime Database while avoiding common pitfalls.
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This video is based on the question https://stackoverflow.com/q/72150074/ asked by the user 'Ali Tunahan Işık' ( https://stackoverflow.com/u/19059377/ ) and on the answer https://stackoverflow.com/a/72175791/ provided by the user 'Ali Tunahan Işık' ( https://stackoverflow.com/u/19059377/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

Firebase Realtime Database is a powerful tool for mobile app developers, providing a cloud-hosted NoSQL database that allows you to store and sync data seamlessly. However, when it comes to storing custom Java objects containing complex data structures, such as ArrayLists and object references, developers often run into challenges.

One common question is: How do you store custom Java objects with ArrayLists in Firebase Realtime Database? This guide will walk you through the solution while addressing some common pitfalls and errors that can occur in the process.

The Problem

When trying to store custom Java objects in Firebase, developers may encounter errors such as:

CustomClassMapper.convertToPlainJavaTypes

CustomClassMapper.serialize

These errors often stem from the specific requirements Firebase has for the objects you want to store:

Objects must have a default constructor.

Objects should include public getters for each field.

Objects must implement the Serializable interface.

The objects should not reference any non-supported data types. The supported data types are:

String

Long

Double

Boolean

Map<String, Object>

List<Object>

Given these constraints, how can you effectively store your custom objects that contain ArrayLists and other data types?

The Solution

One important factor to consider when designing your Java object structures is how they reference each other.

Understanding Cross References

In this case, the developer had an object called Route, which contained a list of Stop objects. When they tried to include a reference to the Route inside each Stop, the app would crash. The underlying problem was that Firebase tries to store a copy of the object rather than a reference. This setup could lead to infinite recursion if each Stop references the Route and each Route references its Stops.

Steps to Avoid Cross-References

Audit Your Object Relationships:

Before proceeding, examine how your objects interact with one another.

Avoid creating circular references where an object references another that, in turn, references back to the first.

Use Identifiers Instead of References:

Instead of embedding references within your objects, consider using unique identifiers.

For example, just store the Route ID in the Stop objects and use that to fetch the relevant Route as needed.

Ensure Proper Serialization:

Make sure your custom Java classes satisfy all Firebase requirements, especially having default constructors, public getters, and implementing Serializable.

Conclusion

By carefully designing your Java objects and paying attention to how they reference each other, you can successfully store complex structures like custom Java objects with ArrayLists in Firebase Realtime Database without running into common serialization issues. Always strive to avoid circular references and consider using identifiers for related objects to simplify your database operations and maintain app stability.

If you continue to experience issues, revisit the Firebase documentation or community forums for additional tips and insight from other developers.

Feel free to share your experiences with Firebase and custom objects in the comments below! Happy coding!

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