[] map [string] struct错误的Golang分配

Question

As you could probably tell from the below code I am working on a project which creates csv reports from data in mongoDB. After getting the data I need in, I need to structure the data into something more sensible then how it exists in the db, which is fairly horrendous (not my doing) and near impossible to print the way I need it. The structure that makes the most sense to me is a slice (for each document of data) of maps of the name of the data to a structure holding the data for that name. Then I would simply have to loop through the document and stuff values into the structs where they belong.

My implementation of this is

type mongo_essential_data_t struct {
        caution string
        citation string
        caution_note string
}

mongo_rows_struct := make([]map[string]mongo_essential_data_t, len(mongodata_rows))

//setting the values goes like this
mongo_rows_struct[i][data_name].caution_note = fmt.Sprint(k)
//"i" being the document, "k" being the data I want to store

This doesn't work however. When doing "go run" it returns ./answerstest.go:140: cannot assign to mongo_rows_struct[i][data_name].caution_note. I am new to Go and not sure why I am not allowed to do this. I'm sure this is an invalid way to reference that particular data location, if it is even possible to reference it in Go. What is another way to accomplish this setting line? If it is too much work to accomplish this the way I want, I am willing to use a different type of data structure and am open to suggestions.

Answer 1

This is a known issue of Golang, known as issue 3117. You can use a temporary variable to get around it:

var tmp = mongo_rows_struct[i][data_name]
tmp.caution_note = fmt.Sprint(k)
mongo_rows_struct[i][data_name] = tmp