Go and MongoDB: generic DAO implementation issue - mongodb

Question

In the current project we use Go and MongoDB via mgo driver.
For every entity we have to implement DAO for CRUD operations, and it's basically copy-paste, e.g.
func (thisDao ClusterDao) FindAll() ([]*entity.User, error) {
session, collection := thisDao.getCollection()
defer session.Close()
result := []*entity.User{} //create a new empty slice to return
q := bson.M{}
err := collection.Find(q).All(&result)
return result, err
}
For every other entity it's all the same but the result type.
Since Go has no generics, how could we avoid code duplication?
I've tried to pass the result interface{} param instead of creating it in the method, and call the method like this:
dao.FindAll([]*entity.User{})
but the collection.Find().All() method need a slice as the input, not just interface:
[restful] recover from panic situation: - result argument must be a slice address
/usr/local/go/src/runtime/asm_amd64.s:514
/usr/local/go/src/runtime/panic.go:489
/home/dds/gopath/src/gopkg.in/mgo.v2/session.go:3791
/home/dds/gopath/src/gopkg.in/mgo.v2/session.go:3818
Then I tried to make this param result []interface{}, but in that case it's impossible to pass []*entity.User{}:
cannot use []*entity.User literal (type []*entity.User) as type []interface {} in argument to thisDao.GenericDao.FindAll
Any idea how could I implement generic DAO in Go?

Answer 1

You should be able to pass a result interface{} to your FindAll function and just pass it along to mgo's Query.All method since the argument's would have the same type.
func (thisDao ClusterDao) FindAll(result interface{}) error {
session, collection := thisDao.getCollection()
defer session.Close()
q := bson.M{}
// just pass result as is, don't do & here
// because that would be a pointer to the interface not
// to the underlying slice, which mgo probably doesn't like
return collection.Find(q).All(result)
}
// ...
users := []*entity.User{}
if err := dao.FindAll(&users); err != nil { // pass pointer to slice here
panic(err)
}
log.Println(users)