How Can I Parse YAML with Dynamic Keys in Golang?

Parsing YAML with Dynamic Keys in Golang

When working with YAML files that contain dynamically defined keys, the type system of Go can present challenges. This article explores how to parse such YAML effectively while maintaining the desired type structure.

We encountered an example where the YAML file contained variable keys (e.g., "V1", "V2", etc.). The initial approach of parsing this as an Environment type faltered, leading us to seek a custom solution.

The solution lies in implementing a custom UnmarshalYAML method for our Environment type. This method allows us to intercept the unmarshaling process and handle the dynamic keys. The updated code:

<code class="go">type Environment struct {
    SkipHeaderValidation bool
    Versions             map[string]MajorVersion
}

func (e *Environment) UnmarshalYAML(unmarshal func(interface{}) error) error {
    var params struct {
        SkipHeaderValidation bool `yaml:"skip-header-validation"`
    }
    if err := unmarshal(&params); err != nil {
        return err
    }
    var versions map[string]MajorVersion
    if err := unmarshal(&versions); err != nil {
        // Here we expect an error because a boolean cannot be converted to a
        // a MajorVersion
        if _, ok := err.(*yaml.TypeError); !ok {
            return err
        }
    }
    e.SkipHeaderValidation = params.SkipHeaderValidation
    e.Versions = versions
    return nil
}</code>

By defining a map[string]MajorVersion for the Versions property, we enable dynamic key parsing. The custom UnmarshalYAML method dynamically populates this map based on the YAML content.

Now, when we unmarshal the YAML, we obtain a map[string]Environment as the root type, with each environment having a filled Versions map. This addresses the challenge of parsing and representing dynamically defined keys in YAML.

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