How Can I Marshal Dynamic JSON Field Tags in Go?

Marshaling Dynamic JSON Field Tags in Go

When generating JSON for a Terraform file using the JSON format, you may encounter the challenge of using dynamic JSON keys for resources with random or variable names. This arises because Terraform's field tags for JSON marshalling require static identifiers.

Traditionally, one might consider using custom code to roll their own JSON, however, using the existing marshalling capabilities is preferable. The question arises: how can you create dynamic JSON keys with Go's field tags?

Solution

Unfortunately, using field tags to generate dynamic JSON keys is not possible in Go. However, an alternative solution exists: using a map.

Using a Map

Maps in Go allow for dynamic keys, making them ideal for this situation. Here's an example:

type Resource struct {
    AWSInstance map[string]AWSInstance `json:"aws_instance"`
}

type AWSInstance struct {
    // Your instance properties here
}

In this example, the AWSInstance field within the Resource struct is a map using dynamic string keys to store individual AWSInstance values.

Example Usage

r := Resource{
    AWSInstance: map[string]AWSInstance{
        "web1": AWSInstance{
            // Initialize your instance properties
        },
        // ... add other instances with dynamic keys
    },
}

Playground Example

You can explore an interactive example on the Go Playground: https://go.dev/play/p/e9d2O-cLsjX

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