How to query any table of RDS using Golang SDK - sql-server

Question

I am writing an AWS lambda to query 10 different tables from RDS(SQL Server) using Golang SDK. What I have learned so far is we have to create a similar struct for the table to query it. But as I want to query 10 tables, So I don't want to create the struct for every table, even the table schema may get changed someday.
Lately, I want to create a CSV file per table as the backup with the queried data and upload it to S3. So is it possible to directly import the CSV file into a lambda, so that I can directly upload it to S3?
You can see my current code below
func executeQuery(dbconnection *sql.DB) {
println("\n\n----------Executing Query ----------")
query := "select TOP 5 City,State,Country from IMBookingApp.dbo.Address"
rows, err := dbconnection.Query(query)
if err != nil {
fmt.Println("Error:")
log.Fatal(err)
}
println("rows", rows)
defer rows.Close()
count := 0
for rows.Next() {
var City, State, Country string
rows.Columns
err := rows.Scan(&City, &State, &Country)
if err != nil {
fmt.Println("Error reading rows: " + err.Error())
}
fmt.Printf("City: %s, State: %s, Country: %s\n", City, State, Country)
count++
}
}
This code can only work for the Address table, and not for other tables
I have also tried it with GORM
package main
import (
"fmt"
"github.com/jinzhu/gorm"
_ "github.com/jinzhu/gorm/dialects/mssql"
)
type Currency struct {
CurrencyId int `gorm:"column:CurrencyId;"`
Code string `gorm:"column:Code;"`
Description string `gorm:"column:Description;"`
}
func main() {
db, err := gorm.Open("mssql", "sqlserver://***")
db.SingularTable(true)
gorm.DefaultTableNameHandler = func(dbVeiculosGorm *gorm.DB, defaultTableName string) string {
return "IMBookingApp.dbo.Currency"
}
fmt.Println("HasTable-Currency:", db.HasTable("ClientUser"))
var currency Currency
db.Debug().Find(&currency)
fmt.Println("Currency:", currency)
fmt.Println("Error", err)
defer db.Close()
}
With both the approaches I couldn't find any way to make the code generic for multiple tables. I would appreciate it if anyone can give me some suggestions or if you can point to some resources.

Answer 1

I did not test this code but is should give you an idea how to fetch Rows into strings array.
defer rows.Close()
columns, err := rows.Columns()
if err != nil {
panic(err)
}
for rows.Next() {
receiver := make([]*string, len(columns))
err := rows.Scan(receiver)
if err != nil {
fmt.Println("Error reading rows: " + err.Error())
}
}
GO internally converts many types into strings - https://github.com/golang/go/blob/master/src/database/sql/convert.go#L219
If data is cannot be converted you have 2 options:
Easy - update your SQL query to return strings or string compatible data
Complicated. Use slice of interface{} instead of slice of *string and fill it in with default values of correct type based on rows.ColumnTypes(). Later you will have to convert real values into strings to save into csv.

Answer 2

Below code worked for me -
conn, _ := getConnection() // Get database connection
rows, err := conn.Query(query)
if err != nil {
fmt.Println("Error:")
log.Fatal(err)
}
defer rows.Close()
columns, err := rows.Columns()
if err != nil {
panic(err)
}
for rows.Next() {
receiver := make([]string, len(columns))
is := make([]interface{}, len(receiver))
for i := range is {
is[i] = &receiver[i]
// each is[i] will be of type interface{} - compatible with Scan()
// using the underlying concrete `*string` values from `receiver`
}
err := rows.Scan(is...)
if err != nil {
fmt.Println("Error reading rows: " + err.Error())
}
fmt.Println("receiver", receiver)
Reference:- sql: expected 3 destination arguments in Scan, not 1 in Golang