You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: gorp_model.go
    path of file: ./repos/cds/engine/api/application
    
    the code of the file until where you have to start completion: package application

import (
	"database/sql"
	"encoding/json"

	"github.com/go-gorp/gorp"

	"github.com/ovh/cds/engine/api/database/gorpmapping"
	"github.com/ovh/cds/sdk"
)

type dbApplicationVariableAudit sdk.ApplicationVariableAudit

func init() {
	gorpmapping.Register(gorpmapping.New(dbApplication{}, "application", true, "id"))
	gorpmapping.Register(gorpmapping.New(dbApplicationVariableAudit{}, "application_variable_audit", true, "id"))
	gorpmapping.Register(gorpmapping.New(dbApplicationKey{}, "application_key", true, "id"))
	gorpmapping.Register(gorpmapping.New(dbApplicationVariable{}, "application_variable", true, "id"))
	gorpmapping.Register(gorpmapping.New(dbApplicationDeploymentStrategy{}, "application
    
func (ava *dbApplicationVariableAudit) PostGet(db gorp.SqlExecutor) error {
	var before, after sql.NullString
	query := "SELECT variable_before, variable_after from application_variable_audit WHERE id = $1"
	if err := db.QueryRow(query, ava.ID).Scan(&before, &after); err != nil {
		return err
	}

	if before.Valid {
		vBefore := &sdk.ApplicationVariable{}
		if err := sdk.JSONUnmarshal([]byte(before.String), vBefore); err != nil {
			return err
		}
		if sdk.NeedPlaceholder(vBefore.Type) {
			vBefore.Value = sdk.PasswordPlaceholder
		}
		ava.VariableBefore = vBefore

	}

	if after.Valid {
		vAfter := &sdk.ApplicationVariable{}
		if err := sdk.JSONUnmarshal([]byte(after.String), vAfter); err != nil {
			return err
		}
		if sdk.NeedPlaceholder(vAfter.Type) {
			vAfter.Value = sdk.PasswordPlaceholder
		}
		ava.VariableAfter = *vAfter
	}

	return nil
}