Create dynamic query for postgresql in golang with map[string]interface{} input

Question

I have map[string]interface input user like below

user := map[string]interface{}{
       "firstname": firstname,
       "lastname":  lastname,
       "country":   country,
       "email":     email,
   }

Values given above are from other functions as variables hence not indicated in "".

For example, I need to generate a dynamic query as follows from the above interface: "INSERT INTO USERTABLE (key1, key2, key3, key4) VALUES ($1, $2, $3, $4) RETURNING userid", val1, val2, val3, val4)

where the iterator will count keys and values and will generate the query as below

"INSERT INTO USERTABLE (firstname, lastname, country, email) VALUES ($1, $2, $3, $4) RETURNING userid", firstname, lastname, country, email)

Looking to build a dynamic string.

Answer 1

Pure Go

func prepareInsert(table string, params map[string]interface{}) string {
    columns := len(params)
    fieldSlice := make([]string, 0, columns)
    for field, _ := range params {
        fieldSlice = append(fieldSlice, field)
    }
    fields := strings.Join(fieldSlice, ",")

    placeholders := prepareQueryPlaceholders(1, columns)
    return fmt.Sprintf(`INSERT INTO %s (%s) VALUES (%s) RETURNING %s`, table, fields, placeholders, fields)
}

func prepareQueryPlaceholders(start, quantity int) string {
    placeholders := make([]string, 0, quantity)
    end := start + quantity
    for i := start; i < end; i++ {
        placeholders = append(placeholders, strings.Join([]string{"$", strconv.Itoa(i)}, ""))
    }
    return strings.Join(placeholders, ",")
}

PLAYGROUND