CODEWITHSUNDEEP
go
Mad Wombat
Mad Wombat

Reputation: 15105

Custom scanner for structs in Go

I am writing a sort of a REST-like API in Go. The database I have is legacy, so I don't control the field names or the structure or for that matter anything. I am abstracting database access methods in a separate package called datastore. The code I have looks like this (skipping all the error handling etc.)

type Datastore struct {}

type Object struct {
  id uint
  name string
  ... zillion more fields here
}

func (Datastore) ObjectList() {
  var objects *[]Object
  db, _ := sqlx.Open("postgres", conn_info)
  rows, _ := sqlx.Queryx("SELECT * FROM object_table")
  defer rows.Close()
  for rows.Next() {
    var obj Object
    rows.Scan(&obj.id, &obj.name)
    objects = append(objects, obj)
  }
  return objects
}

The problem I am currently having is that the object table has dozens and dozens of fields. Some I care about, but some I do not. Some are named the same as Object and some are not. Eventually, I will need to support most of them, but I am working on a proof of concept first. It seems that the Scan code fails if it finds more fields in the row than are present in the arguments for Scan(). I could list the fields I scan for in the query select id, name from object_table, but 1. it makes the code extremely ugly (SQL doesn't get formatted right by gofmt) 2. it adds another place I need to edit when I want to support another field

Is there any way to implement a custom scanner interface that would take the rows object, load some data out of it into a struct and ignore the rest?

Upvotes: 2

Views: 2901

Answers (1)

mpm
mpm

Reputation: 20155

You are already using sqlx so just use *DB.Unsafe() before querying :

var db *sqlx.DB

// exactly the same as the built-in
db = sqlx.Open("sqlite3", ":memory:")
var p Person
udb := db.Unsafe()
err = udb.Get(&p, "SELECT * FROM person, place LIMIT 1;")

Upvotes: 0

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