Organizing data layer in android application

Question

I have problems in designing data layer for android applications. More precisely I don't understand what query-like functions should return. I had such solution:

public class NotesDatabase {
    // ...
    public Cursor queryAllNotes() {
        return helper.getReadableDatabase().query(...);
    }
}

There's problem in this approach. To use result you must know query: columns and their types. It's violation of encapsulation. Also this approach creates problems for unit testing.

But I saw another approach:

public class NotesDatabase {
    // ...
    public List<Note> queryAllNotes() {
        Cursor c = helper.getReadableDatabase().query(...);
        ArrayList<Note> notes = new ArrayList<>(c.getCount());
        while (c.moveToNext()) {
            notes.add(new Note(c.getInt(), c.getText() ...));
        }
        return notes;
    }
}

At least we keep encapsulation but I see other problems here. It doesn't seem to be memory performant approach. I can't use CursorAdapter and CursorLoader, can't set autorequerying which is not actually a problem. What a problem is big results. What to do if response is too big to fit in memory? Should I prevent such situation? ~~Should I care?~~

So which approach is preferable? And how to solve these issues?

@juergend My question is how to organize query functions in data layer to keep encapsulation and how to deal with big results of queries? — Nolan, Aug 05 '16 at 20:43

score 1 · Accepted Answer · edited May 23 '17 at 12:01

1

As you noted, the second approach would provide a better encapsulation since the caller would be dealing with a list of familiar domain model (Note) objects instead of a database cursor. To handle the problem of large data sets, this answer may be helpful.

edited May 23 '17 at 12:01

Community

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answered Aug 06 '16 at 01:40

Damodar Periwal

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Organizing data layer in android application

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