How to Create a JSON Schema with Unique Pattern Properties

Discover how to enforce unique property names in your JSON Schema using techniques to validate JSON objects effectively.
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Understanding the Problem: Unique Pattern Properties in JSON Schema

If you’re working with JSON Schema, you may find yourself in a situation where you want to define properties with arbitrary names while ensuring that those names remain unique. This can be quite tricky, as the built-in JSON Schema capabilities, specifically patternProperties, do not inherently enforce the uniqueness of property names.

In this post, we’ll explore how to create a JSON Schema that allows for arbitrary properties but ensures those property names are unique by employing some extra validation techniques.

The Challenge

Let's review an example scenario that highlights this issue. Consider the following JSON Schema:

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

When applied to this JSON object:

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

The schema validates the JSON object despite the fact that property1 appears twice with different values. This is counter to our goal of having unique property names within the object.

The Solution: Detecting Duplicate Properties

Current Limitations of JSON Schema

As it stands, JSON Schema does not provide any built-in method to validate that property names within a JSON object are unique. While the JSON specification allows duplicate property names—which is not recommended—this flexibility creates complications for developers who need strict validation rules.

However, we can create a workaround by utilizing additional code to check for duplicate names after the initial schema validation step.

Validating JSON with Custom Logic

To effectively enforce unique property names in your JSON objects, you can implement a custom validation logic that checks for duplicates. Here is a sample implementation in C# using the Newtonsoft.Json library:

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

Explanation of the Code

Parsing the Schema: We define a JSON Schema using the JsonSchema.Parse method, allowing arbitrary properties through patternProperties.

Loading the JSON Object: When loading the JSON object, we set DuplicatePropertyNameHandling to Error. This ensures that an exception will be thrown if duplicate property names exist.

Catching Exceptions: In the event of a duplicate property name, a JsonReaderException is caught, providing feedback about the nature of the error. For instance, if property1 appears twice, the message would indicate that a property with that name already exists.

Validating the JSON: The schema validation process can now inform you if the object violates the unique property name rule.

Conclusion

While JSON Schema itself lacks the ability to inherently detect duplicate properties, combining it with additional validation logic allows you to enforce unique property names in your JSON objects. This ensures greater data integrity and aligns with best practices in JSON usage.

By utilizing the outlined methods, developers can confidently implement unique pattern properties in their JSON schemas, maintaining robust and reliable data structures.

If you have further inquiries or need help with your JSON Schema validation, feel free to leave your comments below!