Gorm Find result to interface - go

Question

I am trying to build a generic CrudRepository struct using Gorm for my api.
I know generics are coming to GoLang in version 2 but I try to build this lib using reflection or any other lib.
In my CrudRepository:
func (repository *BaseRepository) find(result interface{}, pageSize int, page int) error {
if page < 1 {
return errors.ExceedsMinimumInt("page", "", 0, true, nil)
}
offset := (page - 1) * pageSize
ent := reflect.Zero(reflect.TypeOf(result))
repository.db = repository.db.Limit(pageSize).Offset(offset)
err := repository.db.Find(&ent).Error
result = ent
if err != nil {
return err
}
return nil
}
And calling this method sth like:
func List(){
var entityList []MyEntity
find(entityList, 1, 10)
}
I think, I cannot pass any interface reference into Gorm.db.Find() method
Is there any other way to succeed?

Answer 1

Use a pointer of a slice as input argument of custom find method.
func (repository *BaseRepository) find(result interface{}, pageSize int, page int) error {
if page < 1 {
return errors.ExceedsMinimumInt("page", "", 0, true, nil)
}
if reflect.TypeOf(result).Kind() != reflect.Slice { 👈 check ❗️
return errors.New("`result` is not a slice")
}
offset := (page - 1) * pageSize
db = db.Limit(pageSize).Offset(offset)
if err := db.Find(result).Error; err != nil {
return err
}
return nil
}
usage 👇🏻
var entityList []MyEntity
err := find(&entityList, 10, 1)
Also you have to check input argument (result), because db.Find isn't fit to find single strut 👇🏻 (Retrieving a single object)
If you want to avoid the ErrRecordNotFound error, you could use Find
like db.Limit(1).Find(&user), the Find method accepts both struct and
slice data
For example (Book table is empty):
b := Book{}
rowsAffectedQuantity := db.Find(&b).RowsAffected // 👈 0
err = db.Find(&b).Error // 👈 nil