Optional Find in .Find() MongoDB query

Question

My listing may receive a filter parameter, but this parameter is mandatory.

status := r.FormValue("status")
var bet []*Bet

if err := db.C(collectionName).Find(bson.M{"status": status}).Sort("-data-criacao").All(&bet); err != nil {
            http.Error(w, err.Error(), http.StatusInternalServerError)
            return

}

If the parameter was not informed, the query returns no result.

To return all the results, I used to do the following

    var bet []*Bet

    if err := db.C(collectionName).Find(nil).Sort("-data-criacao").All(&bet); err != nil {
                http.Error(w, err.Error(), http.StatusInternalServerError)
                return
}

How can I meet both alternatives?

Answer 1

Simply use an if statement to construct your query based on whether the parameter is supplied.

Something like this:

status := r.FormValue("status")
var bet []*Bet

var filter bson.M
if status != "" {
    filter = bson.M{"status": status}
}

err := db.C(collectionName).Find(filter).Sort("-data-criacao").All(&bet)
if err != nil {
    http.Error(w, err.Error(), http.StatusInternalServerError)
    return
}