Parse: How can I get Relation from a local data st

问题:

I am developing an app to serve as a learning and I'm using Parse (parse.com) as a data source.

I am conducting download all objects of my classes in the parse and saving to a local store that has Parse. The following code snippet that performs one of downloads:

public void noticia_getOrUpdate(boolean isUpdate) throws ParseException {
        ParseQuery<Noticia> query = new ParseQuery(Noticia.class);
        query.orderByDescending("createdAt");
        List<Noticia> lNoticias = null;

        try {
            if (isUpdate) {
                lNoticias = query.whereGreaterThan("updatedAt", this.sPref.ultimaAtualizacao_noticia()).find();
                if (!lNoticias.isEmpty())
                    ParseObject.pinAllInBackground(lNoticias);
            } else {
                query.whereEqualTo("ativo", true);
                lNoticias = query.find();

                for (Noticia noticia : lNoticias) {
                    if (noticia.getUpdatedAt().getTime() > this.sPref.ultimaAtualizacao_noticia().getTime())
                        this.sPref.atualiza_noticia(noticia.getUpdatedAt());
                }

                ParseObject.pinAllInBackground(lNoticias);
                this.sPref.atualiza_isUpdate(true);
            }
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }

The problem is I'm downloading all my classes, one is the File type, is a file that works as an image for my news ("Noticia"). I can download and store all on-site data storage, but can not recover using the following code:

public static byte[] NoticiaMidiaRelation(Noticia noticia) {
        try {
            ParseRelation<Midia> relation = noticia.getImagem();
            Midia midia = relation.getQuery().fromLocalDatastore.whereEqualTo("ativo", true).getFirst();

            if (midia != null && midia.getFileData() != null)
                return midia.getFileData();
        } catch (ParseException e) {
            e.printStackTrace();
        }
    return null;
}

If retreat the "fromLocalDatastore" the query, he seeks the server and brings the file correctly, but do not want to pursue it again, because as said, already have the same image stored in the local data store.

Another way to do would be to get the relationship the media Id, after that perform a search for comparing ObjectId within the local store, but I think there's no way the property "parent". But if any, can be used as a solution.

回答1:

You can't according to the documentation:

By default, when fetching an obj ect, related ParseObjects are not fetched

There are work arounds but they might not be practical because by what I understand, you only have one image in your relation per ParseObject in your "Notica" class as you call getFirst(). In this case, using a Pointer would be a better decision but those aren't fetched by default either BUT they are cached to the LocalDatastore. You'll need to add the following code to your query to fetch the Pointer object.

query.include("your_column_key");