mysql Pluck 无法使用decimal

[liyuan1125]

GORM Playground Link

https://github.com/go-gorm/playground/pull/437

Description

wallet := UserWallet{UserID: 1, Balance: decimal.NewFromFloat(99.60)}

    if err := DB.Create(&wallet).Error; err != nil {
        t.Errorf("Failed, got error: %v", err)
    }

    var balance decimal.Decimal
    if err := DB.Model(&UserWallet{}).Limit(1).Pluck("balance", &balance).Error; err != nil {
        t.Errorf("Failed, got error: %v", err)
    }

    if err := DB.Model(&UserWallet{}).Limit(1).Pluck("balance", balance).Error; err != nil {
        t.Errorf("Failed, got error: %v", err)
    }

错误：

sql: Scan error on column index 0, name "balance": destination not a pointer

[Heliner]

check the https://gorm.io/docs/advanced_query.html , Pluck return mutilple values .

like this

var balance []decimal.Decimal
if err := DB.Model(&UserWallet{}).Limit(1).Pluck("balance", &balance).Error; err != nil {
t.Errorf("Failed, got error: %v", err)
}

[liyuan1125]

check the https://gorm.io/docs/advanced_query.html , Pluck return mutilple values .

like this

var balance []decimal.Decimal
if err := DB.Model(&UserWallet{}).Limit(1).Pluck("balance", &balance).Error; err != nil {
t.Errorf("Failed, got error: %v", err)
}

var id uint64
if err := DB.Model(&UserWallet{}).Limit(1).Pluck("id", &id).Error; err != nil {
t.Errorf("Failed, got error: %v", err)
}
fmt.Print(id)

output

1

[Heliner]

this cause by Scan.scan() function args this func set this db raw data into result or results, when the type is uint64 or uint32 ... that set this last query raw data into result, when the type is an arrry or slice .. that set this all query raw data into results

var id uint64
if err := DB.Model(&UserWallet{}).Limit(1).Pluck("id", &id).Error; err != nil {
   t.Errorf("Failed, got error: %v", err)
}
fmt.Print(id)

you can use Pluck like this but if limit (n=..), n is greater than 1, an unexpect result will return

    wallet := UserWallet{UserID: 1, Balance: decimal.NewFromFloat(99.60)}
    wallet2 := UserWallet{UserID: 2, Balance: decimal.NewFromFloat(100.60)}

    if err := DB.Create(&wallet).Error; err != nil {
        t.Errorf("Failed, got error: %v", err)
    }
    if err := DB.Create(&wallet2).Error; err != nil {
        t.Errorf("Failed, got error: %v", err)
    }

    var id2 uint64
    if err := DB.Model(&UserWallet{}).Limit(2).Pluck("id", &id2).Error; err != nil {
        t.Errorf("Failed, got error: %v", err)
    }
    fmt.Printf("id:%v", id2)

so, you can use Limit(1).Pluck("id", &id) ,I don't known that is a feature or bug , but that is a special case and doc not recommand use Pluck do like this

[liyuan1125]

this cause by Scan.scan() function args this func set this db raw data into result or results, when the type is uint64 or uint32 ... that set this last query raw data into result, when the type is an arrry or slice .. that set this all query raw data into results

var id uint64
if err := DB.Model(&UserWallet{}).Limit(1).Pluck("id", &id).Error; err != nil {
   t.Errorf("Failed, got error: %v", err)
}
fmt.Print(id)

you can use Pluck like this but if limit (n=..), n is greater than 1, an unexpect result will return

  wallet := UserWallet{UserID: 1, Balance: decimal.NewFromFloat(99.60)}
  wallet2 := UserWallet{UserID: 2, Balance: decimal.NewFromFloat(100.60)}

  if err := DB.Create(&wallet).Error; err != nil {
      t.Errorf("Failed, got error: %v", err)
  }
  if err := DB.Create(&wallet2).Error; err != nil {
      t.Errorf("Failed, got error: %v", err)
  }

  var id2 uint64
  if err := DB.Model(&UserWallet{}).Limit(2).Pluck("id", &id2).Error; err != nil {
      t.Errorf("Failed, got error: %v", err)
  }
  fmt.Printf("id:%v", id2)

so, you can use Limit(1).Pluck("id", &id) ,I don't known that is a feature or bug , but that is a special case and doc not recommand use Pluck do like this

I think its a bug https://github.com/go-gorm/gorm/issues/4457