Скачать или смотреть How to Set a Default JSON Property Using Jolt Only If It Does Not Exist

Learn how to use Jolt to set default JSON properties when they don't exist, while preserving values of properties that do, with easy-to-follow examples.
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How to Set a Default JSON Property Using Jolt Only If It Does Not Exist

When working with JSON data, it is common to need default values for properties when they do not exist. This situation often arises when you want to ensure your output JSON structure remains consistent, even if certain properties are missing in the input. Today, we will explore how to effectively set a default value using Jolt, while avoiding unwanted overrides when a property's value is explicitly set to null.

The Problem Statement

Imagine you have a scenario where your input JSON might look like this:

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

You want the output to automatically include a default value for lastName, such as [empty], if lastName does not exist, resulting in:

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

However, if your input JSON contains:

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

You'd want the output to preserve the null value for lastName, like this:

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

With these requirements in mind, how do we set default values only if a property does not exist, regardless of its value?

The Solution: Using Jolt Specifications

To address this problem, we can utilize Jolt's modify-default-beta operation alongside the isNull function. Here’s how it can be structured.

Step-by-Step Jolt Specification

Modify-Default-Beta Operation: This is the core operation we will be using to define default behaviors for missing properties.

IsNull Function: This function allows us to check whether the property we are interested in is null.

Here’s a straightforward Jolt spec to implement the solution:

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

Breakdown of the Specification

Operation: The modify-default-beta operation is used here to define the default behavior.

Spec Details:

lastName: This specifies that we are targeting the lastName attribute.

Function Call:

@ (1,&): This notation tells Jolt to look at the current attribute's value. Here, & indicates a reference to lastName.

isNull(): The function checks if the value of lastName is null. If it is null, we return [empty]; otherwise, the current value (even if it’s null) is preserved.

Conclusion

By applying this Jolt spec, you can efficiently manage defaults for JSON properties without unintentionally overriding existing values. This approach adheres to the best practices of maintaining data integrity while providing the flexibility needed for dynamic JSON structures.

Now you can confidently use Jolt to handle default values in JSON inputs, ensuring your applications run smoothly regardless of input variations.