ColumnExpr doesn't work in Relation function

[irmarini]

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Hi, I'm using go-pg to add prefix to a value of a column in a relation but I always get error column not found. My model:

type BankAccount struct {
	tableName  struct{}  `pg:"bank_account"`
	ID         int       `json:"id" pg:"id,pk"`
	Name       string    `json:"name" pg:"name"`
	Number     string    `json:"number" pg:"number"`
	BankCode   string    `json:"bank_code" pg:"bank_code"`
	Bank       *Bank     `json:"bank,omitempty" pg:"rel:has-one"`
}

type Bank struct {
	tableName struct{} `pg:"bank"`
	Code      string   `json:"code" pg:"code,pk"`
	Name      string   `json:"name" pg:"name"`
	Image     string   `json:"image" pg:"image"`
}

I want to add prefix into column image in table bank like this:

var banks []*BankAccount

err := db.Model(&banks).
Relation("Bank", func(q *orm.Query) (*orm.Query, error) {
	return q.Column("bank.*").
		ColumnExpr("?||image as image", viper.GetString("base_url")), nil
}).Select()
...

but it always return me error like this:
"error": "pg: can't find column=code in model=BankAccount (prefix the column with underscore or use discard_unknown_columns)"

Expected Behavior

The return under the Relation must be the bank table with prefix on column bank.image
So I expect to get output like this:

{
  "id": 1,
  "name": "John Doe",
  "number": "123",
  "bank_code": "bank",
  "bank": {
      "code": "bank",
      "name": "Bank Name",
      "image": "http://localhost/bank.png"
}

Current Behavior

The return in Relation function always referring to bank_account not bank and give me this error:
"error": "pg: can't find column=code in model=BankAccount (prefix the column with underscore or use discard_unknown_columns)"

Context (Environment)

I'm using v10