Complex sorting for search in realm, union of multiple RealmResults

Question

I replaced sqlite with realm in my open source Linux Command Library project. Everything went fine so far, but now I\'m facing a problem.

I\'m using a RealmBaseAdapt

Answer 1

Thank you guys, you both helped me alot to solve the problem. @Mateusz Herych @EpicPandaForce

Here is the custom adapter:

public abstract class RealmMultiAdapter<T extends RealmObject> extends BaseAdapter {

    private final RealmChangeListener<T> realmChangeListener = new RealmChangeListener<T>() {
        @Override
        public void onChange(RealmResults<T> t) {
            notifyDataSetChanged();
        }
    };

    protected LayoutInflater inflater;
    protected List<RealmResults<T>> realmResults;
    protected Context context;

    public RealmMultiAdapter(Context context, List<RealmResults<T>> realmResults, boolean automaticUpdate) {
        if (context == null) {
            throw new IllegalArgumentException("Context cannot be null");
        }
        this.context = context;
        this.realmResults = realmResults;
        this.inflater = LayoutInflater.from(context);
        for(RealmResults<T> results : realmResults) {
            results.addChangeListener(realmChangeListener);
        }
    }

    /**
     * Returns how many items are in the data set.
     *
     * @return count of items.
     */
    @Override
    public int getCount() {
        if (realmResults == null) {
            return 0;
        }
        int count = 0;
        for(RealmResults<T> realmResult : realmResults) {
            count += realmResult.size();
        }
        return count;
    }

    /**
     * Returns the item associated with the specified position.
     *
     * @param i index of item whose data we want.
     * @return the item at the specified position.
     */
    @Override
    public T getItem(int i) {
        if (realmResults == null || realmResults.size()==0) {
            return null;
        }
        int count = 0;
        for(RealmResults<T> realmResult : realmResults) {
            if(i<realmResult.size()+count) {
                return realmResult.get(i-count);
            }
            count += realmResult.size();
        }
        return null;
    }

    /**
     * Returns the current ID for an item. Note that item IDs are not stable so you cannot rely on the item ID being the
     * same after {@link #notifyDataSetChanged()} or {@link #updateRealmResults(List<RealmResults<T>>)} has been called.
     *
     * @param i index of item in the adapter.
     * @return current item ID.
     */
    @Override
    public long getItemId(int i) {
        // TODO: find better solution once we have unique IDs
        return i;
    }

    /**
     * Updates the RealmResults associated to the Adapter. Useful when the query has been changed.
     * If the query does not change you might consider using the automaticUpdate feature.
     *
     * @param queryResults the new RealmResults coming from the new query.
     */
    public void updateRealmResults(List<RealmResults<T>> queryResults) {
        for(RealmResults<T> results : realmResults) {
            if(results.isValid()) {             
                results.removeChangeListener(realmChangeListener);
            }
        }
        this.realmResults = queryResults;
        for(RealmResults<T> results : realmResults) {
            results.addChangeListener(realmChangeListener);
        }
        notifyDataSetChanged();
    }
}

Basically I replaced the single RealmResult with a list of RealmResults and modified the getItem() and getCount() method.

    // before
    protected RealmResults<T> realmResults;
    // after
    protected List<RealmResults<T>> realmResults;

And this is how I update the search

    List<RealmResults<Command>> results = new ArrayList<>();
    results.add(mRealm.where(Command.class).equalTo("name", query).findAll());
    results.add(mRealm.where(Command.class).beginsWith("name", query).notEqualTo("name", query).findAll());
    results.add(mRealm.where(Command.class).contains("name", query).not().beginsWith("name", query).notEqualTo("name", query).findAll());

    mAdapter.updateRealmResults(results);

Answer 2

Not sure if there isn't a better/more-performant way for that but you can try making 3 different queries and then concatenating their results.

    List<Command> commands = new ArrayList<>();

    commands.addAll(realm.where(Command.class)
            .equalTo("name", query)
            .findAll());

    commands.addAll(realm.where(Command.class)
            .beginsWith("name", query)
            .notEqualTo("name", query)
            .findAll());

    commands.addAll(realm.where(Command.class)
            .contains("name", query)
            .not().beginsWith("name", query)
            .findAll());

This obviously involves changing your Adapter implementation from RealmBaseAdapter to something more regular. Please keep in mind that while your Realm objects reside in a regular list, they still keep a connection to your Realm database, so you can't close your realm instance while your ListView is displaying data.

Update: As @EpicPandaForce pointed out in comments, this solution doesn't work well with Realm's autoupdating. It may appear that some Commands are removed / have changed names and this won't be reflected by your Adapter in that case. Make sure to copy your objects first and setup a change listener on your realm results.