Go struct reflection

September 20, 2023

What's inside this article ⌄

Golang get struct field names
Golang check struct field null by name
Golang get struct field type by name
Golang get struct field tag
Golang check struct field empty
Golang struct reflection

You can use this piece of code to get this information from the structure using reflection and print it in tabular form. This code also takes into account pointer types, and it finds the origin type:

package main

import (
   "fmt"
   "os"
   "reflect"
   "strconv"
   "text/tabwriter"
)

func main() {
   type Test struct {
      Name    string  `db:"tag1"` // filled value
      Surname *string `db:"tag2"` // pointer to non-empty string
      Address string  `db:"tag3"` // non-filled value (will be defaulted by empty string)
      Zip     *string `db:"tag4"` // non-filled pointer
      Phone   *string `db:"tag5"` // pointer to empty string
   }

    surname := "surname"
    phone := ""
    test := &Test{
        Name:    "name",
        Surname: &surname,
        Phone:   &phone,
    }

    structRef := reflect.ValueOf(test).Elem()
    structRefType := structRef.Type()

    table := tabwriter.NewWriter(os.Stdout, 1, 1, 1, ' ', 0)
    fmt.Fprintln(table, "field_name \tfield_type \tfield_tag \tis_empty_or_null")

    for i := 0; i < structRef.NumField(); i++ {
        fieldRefValue := structRef.Field(i)
        fieldRefType := structRefType.Field(i)
        isPointer := fieldRefValue.Kind() == reflect.Ptr

        varName := fieldRefType.Name
        varTag := string(fieldRefType.Tag.Get("db"))
        varType := fieldRefType.Type
        var varEmptyOrNull string
        if isPointer {
            varEmptyOrNull = strconv.FormatBool(fieldRefValue.IsNil() || fieldRefValue.Elem().IsZero())
        } else {
            varEmptyOrNull = strconv.FormatBool(fieldRefValue.IsZero())
        }

        fmt.Fprintf(table, "%v \t%v \t%v \t%v \n", varName, varType, varTag, varEmptyOrNull)
    }
    table.Flush()
}