How Can I Efficiently Read Nested Slices of Maps in Golang Using Viper?

Reading a Slice of Maps with Golang Viper

Reading nested data structures, like a slice of maps, in Golang is a common task. This article will show you how to use the Viper library to easily access and manage such data.

The Problem: Reading a Nested Slice of Maps

Consider a configuration file in HCL that contains a slice of maps representing groups of targets. The Viper GetStringMap function retrieves the "group" key as a single map, but we need to access the slice of maps within it.

Solution: Using Viper Unmarshalling

Instead of manually casting and parsing the raw data, we can take advantage of Viper's unmarshalling capabilities. Unmarshalling translates the config into a custom struct that mirrors the desired data structure.

To achieve this:

1. Define a Config Struct: Define a Go struct that corresponds to the expected config data structure. It should include fields for the interval, statsd prefix, and a slice of group structs.

   type config struct {
       interval int `mapstructure:"Interval"`
       statsdPrefix string `mapstructure:"statsd_prefix"`
       groups []group
   }
   
   type group struct {
       group string `mapstructure:"group"`
       targetPrefix string `mapstructure:"target_prefix"`
       targets []target
   }
   
   type target struct {
       target string `mapstructure:"target"`
       hosts []string `mapstructure:"hosts"`
   }

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2. Unmarshal the Config: Use Viper's Unmarshal function to decode the configuration file into the defined struct.

   var C config
   
   err := viper.Unmarshal(&C)
   if err != nil {
       // Handle error
   }

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By following these steps, you can effectively read and manage nested slices of maps in your Golang application using Viper.

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