Solving the Realm Swift Error: Cycles containing embedded objects are not currently supported

Discover a solution to the Realm Swift error regarding nested embedded objects, especially when avoiding cascading deletes.
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Understanding the Realm Swift Error: Nested Embedded Objects

If you’re a developer using Realm, you may have encountered the perplexing error message: “Cycles containing embedded objects are not currently supported.” This commonly arises when working with nested embedded objects within your data models.

In this post, we'll dive into the reasons behind this error, and most importantly, we will explore an effective solution to work with nested embedded objects without facing cascading delete issues.

The Issue Explained

Let's break down the problem:

Nested Embedded Objects: You might want a structure where a parent object contains a list of child objects, and those child objects themselves contain a list of further child objects (grandchildren).

Error Occurrence: When you try to create a Realm instance with such a structure, you receive the schema validation error indicating that cycles with embedded objects aren’t supported. This is triggered by having an EmbeddedObject type that contains instances of itself or another EmbeddedObject type that leads back to a cycle.

A Quick Look at the Code

Here’s an example of what that problematic code might look like:

[[See Video to Reveal this Text or Code Snippet]]

The root cause here is the children property in ChildObject, which creates cycles.

The Solution: Using Different Embedded Object Types

To solve this error, you can simply use a different EmbeddedObject type for the children property in ChildObject. Here’s how:

Code Implementation

Define a Grandchild Object: Instead of using the same type for children and grandchildren, create a new class called GrandChildObject.

[[See Video to Reveal this Text or Code Snippet]]

Key Points

Avoid Self-Referencing Types: Ensure that GrandChildObject does not reference back to itself or any parent type that might create a cycle.

No Cascading Deletes: This structure will still help you avoid the overhead of managing cascading deletes while preserving the nested structure you need for your data.

Alternate Approaches

You may consider encoding the child objects to Data, but it is not an ideal approach as it feels hacky and can lead to further issues in data management. This solution is more robust and maintainable.

Conclusion

If you encounter the error “Cycles containing embedded objects are not currently supported” while working with Realm, remember that the key lies in how you structure your embedded objects. By defining distinct classes for levels of your object hierarchy, you will be able to nest objects without running into issues.

Implementing the solution discussed will provide a clear path to organizing your data effectively in Realm, ultimately leading to a better development experience.

Happy coding, and may your Realm databases remain error-free!