venmo/cursor-utils

Working with Android SQLite Cursors is less than ideal. Code can easily be duplicated throughout your codebase if you're not careful to keep the translation of SQLite columns into Java objects. Iterating across the returned data from a Cursor is another area which can lead to code duplication. Sometimes you actually want a Cursor to be a List, yet other times a List to be a Cursor.

This library was designed to encapsulate the repeatable actions for Android Cursors and treat them as if they were closer to a Java object rather than a conglomerate of dicts/hashes.

Here is a presentation from the NYC Android Meetup on August 27, 2014, about the library on SlideShare.

IterableCursor (and IterableCursorWrapper)

At minimum, you should use an IterableCursorWrapper and never look at a plain old Android Cursor again.

public class User {
    public User(String name, String bio) { /* ... */ }
}

public class UserCursor extends IterableCursorWrapper<User> {

    public UserCursor(Cursor c) {
        super(c);
    }

    public User peek() {
        String name = getString(COLUMN_USER_NAME, "Default Name");
        String bio = getLong(COLUMN_USER_BIO, "No bio yet");
        return new User(name, bio);
    }
    
}

public class MyDatabase extends SQLiteOpenHelper {

    // ...
    
    public IterableCursor<User> queryAllUsers() {
        Cursor cursor = getReadableDatabase().query(TABLE_USERS, null, null, null, null, null,
                null, null);
        return new UserCursor(cursor);
    }
    
}

Voilà! Now you can use an enhanced for loop to access all Users at once:

IterableCursor<User> users = myDb.queryAllUsers();
for (User user : users) {
    if (user.isMyBestFriend()) giveSomeCake(user);
}
users.close();

This also simplifies using SQL-backed CursorAdapters (via IterableCursorAdapter<T>:

@Override
public void bindView(View v, Context context, User user) {
    ViewHolder holder = v.getTag();
    holder.textView.setText(user.getFullName());
}

IterableCursorAdapter is a combination of the newView() / bindView() API of CursorAdapter, with the direct item access of ArrayAdapter<T>.

CursorList

Often, certain queries are difficult to express in SQL constraints and it's much simpler to defer to Java to do filtering. But what happens when you're done filtering: you're left with a List but you want to use your favorite CursorAdapter. To solve this issue, mask your List as a CursorList:

IterableCursor<User> users = myDb.queryAllUsers();
List<User> bestFriends = new LinkedList<User>();
for (User user : users) {
    if (user.isMyBestFriend()) bestFriends.add(user);
}

IterableCursor<User> bestFriendCursor = new CursorList<User>(bestFriends);
bestFriendsListView.setAdapter(new UserCursorAdapter(bestFriendsCursor));

CursorList is an instance of both android.database.Cursor and java.util.List; it's the best of both worlds.

IterableCursor + IterableCursor

What if you wanted to have one master ListView that prioritized best friends first, but then listed everyone alphabetically?

List<User> bestFriendsList = computeBestFriendsFromCursor(); // see above
IterableCursor<User> bestFriends = new CursorList(bestFriendsList);
IterableCursor<User> allUsers = myDb.queryAllUsers();

IterableCursor<User> mergedCursor = new IterableMergeCursor<User>(bestFriends, allUsers);
listView.setAdapter(new UserCursorAdapter(mergedCursor));

The adapter has no idea that it's getting two cursors - it still gets to peek() for a User and doesn't need to know that you already did some sorting.

Cursor helper methods

Getting data at a particular column of a Cursor is a pain. And what happens if you have a custom query that only returns certain columns and not the full row?

String field1 = cursor.getString(cursor.getColumnIndex(COLUMN_FIELD1));
int field2 = cursor.getInt(cursor.getColumnIndex(COLUMN_FIELD2));
try {
    boolean field3 = cursor.getBoolean(cursor.getColumnIndex(COLUMN_FIELD3));
} catch (Exception) {
    // oh no, field3 wasn't returned this time! what should I do???
}
// ...

IterableCursorWrapper provides convenience methods which remove this headache with simpler methods and default values.

public User peek() {
    String field1 = getString(COLUMN_FIELD1, "default");
    int field2 = getInteger(COLUMN_FIELD2, 0);
    boolean field3 = getBoolean(COLUMN_FIELD3, DEFAULT_FIELD3_VALUE);
}

Cursor → Collection

If the cursor size isn't too big and you just want to deal with a Collection instead, CursorUtils has some methods to translate the IterableCursor into your favorite collection:

IterableCursor<User> cursor1 = queryAllUsers();
ArrayList<User> all = CursorUtils.consumeToArrayList(cursor1);
// also comes with consumeToLinkedList()

IterableCursor<Tweet> cursor2 = queryAllTweetsAndRetweets();
LinkedHashSet<User> noRepeats = CursorUtils.consumeToLinkedHashSet(cursor2);

IterableCursor<GooglePlusUser> cursor3 = queryComplicatedDataSet();
CoolGuavaCollection<GooglePlusUser> hashMultiQueue = Guava.newAwesome();
CursorUtils.consumeToCollection(hashMultiQueue, cursor3);

Download

Gradle:

compile 'com.venmo.cursor:library:0.4'

Maven:

<dependency>
  <groupId>com.venmo.cursor>
  <artifactId>library</artifactId>
  <version>0.4</version>
</dependency>

Jar: [direct download link]

Contributing

We'd love to see your ideas for improving this library! The best way to contribute is by submitting a pull request – we'll do our best to respond to your patch as soon as possible. You can also submit an issue if you find bugs or have any questions.

Please make sure to follow our general coding style and add test coverage for new features!

Contributors

@tpoulos for an awesome logo!