Unmarshalling a bson.D object (Golang)

Question

I'll try to be as clear as possible. I'm building a simple audit logging API, using MongoDB, and Model-Vew-Controller architecture. As part of the functionality, the user can request data using a http endpoint. When the endpoint is hit, the controller package calls the model package, and the code below is executed:

// The GetResourceData function takes the resource, and provides the log data for that resource, sorted by // date and time. It also takes a context.context, and a *mongo.Client as parameters.

func GetResourceData(ctx context.Context, CL *mongo.Client, Resource string) error { ourDatabase := CL.Database("Event_Database") eventsCollection := ourDatabase.Collection("Events")

opts := options.Find()
opts.SetSort(bson.D{{"Date", -1}, {"Time", -1}})

filterCursor, err := eventsCollection.Find(
    ctx,
    bson.M{"Resource": Resource},
    opts)

if err != nil {

    log.Fatal(err)
}

defer filterCursor.Close(ctx)
for filterCursor.Next(ctx) {

    var eventsFiltered []bson.D
    if err = filterCursor.All(ctx, &eventsFiltered); err != nil {
        log.Fatal(err)
    }

    fmt.Println(eventsFiltered)

}

return err
}

This works fine, and as you can see, I've printed the eventsFiltered to the terminal. It doesn't do much good there however, and I need to print it to the screen. I have a function that's ready to do this in the view package with a http.ResponseWriter, BUT - I cannot figure out how to convert the bson.D to a string format so I can cleanly pass this in as a parameter. If I try bson.Unmarshall;

            var cookie []byte
    bson.Unmarshal(cookie, eventsFiltered)
    s := string(cookie)
    fmt.Println("Events filtered as a string is: ", s)
    fmt.Println("Events filtered as a byte slice is: ", cookie)

I get the following;

Users filtered as a string is:

Users filtered as a byte slice is: []

...an empty string, or an empty byte slice. I know there is something really simple I'm missing, but I can't see it!

Any help would be greatly appreciated. Please ask if you have any questions.

Thanks, A

Answer 1

First of all, if you use filterCursor.All(ctx, &eventsFiltered), you don't need to either iterate trough all the collection or close the cursor (cursor method All(...) will do it for you).

---

What about your question, you can do for example something like this:

        var eventsFiltered []bson.D
        if err = filterCursor.All(ctx, &eventsFiltered); err != nil {
            log.Fatal(err)
        }
        for _, event := range eventsFiltered {
            for _, keyValPair := range event {
                fmt.Printf("key is %s; val is %v", keyValPair.Key, keyValPair.Value)
            }
        }

Or, in case an order of elements doesn't matter, consider unmarshalling into bson.M:

        var eventsFiltered []bson.M
        if err = filterCursor.All(ctx, &eventsFiltered); err != nil {
            log.Fatal(err)
        }
        for _, event := range eventsFiltered {
            for key, val := range event {
                fmt.Printf("key is %s; val is %v", key, val)
            }
        }

So, the whole solution would be:

func GetResourceData(ctx context.Context, CL *mongo.Client, Resource string) error {
    ourDatabase := CL.Database("Event_Database")
    eventsCollection := ourDatabase.Collection("Events")

    opts := options.Find()
    opts.SetSort(bson.D{{"Date", -1}, {"Time", -1}})

    filterCursor, err := eventsCollection.Find(
        ctx,
        bson.M{"Resource": Resource},
        opts)

    if err != nil {
        log.Fatal(err)
    }

    if filterCursor.Next(ctx) {
        var eventsFiltered []bson.M
        if err = filterCursor.All(ctx, &eventsFiltered); err != nil {
            log.Fatal(err)
        }
        // If you need ordered print, uncomment the following lines and comment out following uncommented for loop
        //        for _, event := range eventsFiltered {
        //            for _, keyValPair := range event{
        //                fmt.Printf("key is %s; val is %v", keyValPair.Key, keyValPair.Value)
        //            }
        //        }
        for _, event := range eventsFiltered {
            for key, val := range event {
                fmt.Printf("key is %s; val is %v", key, val)
            }
        }

    }
    return nil
}