GreenDAO is an ORM (Object Relational Mapping) library that uses code generation to provide a faster alternative to reflection-based ORMs for Android. It works by mapping Java objects to SQLite database tables to allow for CRUD (create, read, update, delete) operations on the data. The library includes a schema definition and code generator that automatically generates DAO classes to manage database access and queries. This avoids the performance overhead of reflection and allows for compiler checks of the database schema.

1. greenDAO
Kewang

2. Agenda
● SQL syntax
● SQLite @ Android
● ORM
● greenDAO

3. SQL syntax

4. SELECT
● SELECT Persons.LastName, Persons.FirstName,
Orders.OrderNo FROM Persons INNER JOIN
Orders ON Persons.P_Id=Orders.P_Id ORDER BY
Persons.LastName
● SELECT * FROM Persons WHERE LastName
BETWEEN 'Hansen' AND 'Pettersen'
● SELECT Customer,OrderDate,SUM(OrderPrice)
FROM Orders GROUP BY Customer,OrderDate

5. INSERT
● INSERT INTO Persons (P_Id, LastName, FirstName)
VALUES (5, 'Tjessem', 'Jakob')
● INSERT INTO Persons VALUES (4,'Nilsen', 'Johan',
'Bakken 2', 'Stavanger')

6. UPDATE
● UPDATE Persons SET Address='Nissestien 67',
City='Sandnes' WHERE LastName='Tjessem' AND
FirstName='Jakob'
● UPDATE Persons SET Address='Nissestien 67',
City='Sandnes'

7. DELETE
● DELETE FROM Persons WHERE
LastName='Tjessem' AND FirstName='Jakob'

8. SQLite @ Android

9. 4 components
● SQLiteOpenHelper
● SQLiteDatabase
● SQLiteQueryBuilder
● Cursor

10. SQLiteOpenHelper
A helper class to manage database
creation and version management.

11. SQLiteDatabase + SQLiteQueryBuilder
delete * 1
append * 3
insert * 3
replace(update) * 4
open * 5
query * 15

12. Oh my god, I'm a professional DBA!!!

13. Never mind, we have......
execSQL * 2
db.execSQL("CREATE TABLE IF NOT EXISTS person (personid integer primary
key autoincrement, name varchar(20), age INTEGER)");

14. and
rawQuery * 4
db.rawQuery("select count(*) from person", null);

15. Cursor
Recordsets returned by a query

16. Cursor
getDataType * 16
movePosition * 6
isXXX * 6

17. Sample code - Controller
datasource = new CommentsDataSource(this);
datasource.open();
List<Comment> values = datasource.getAllComments();
ArrayAdapter<Comment> adapter = new
ArrayAdapter<Comment>(this,
android.R.layout.simple_list_item_1, values);
open

18. Sample code - Controller
String[] comments = new String[] { "Cool", "Very nice",
"Hate it" };
int nextInt = new Random().nextInt(3);
comment = datasource.createComment(comments[nextInt]);
adapter.add(comment);
insert

19. Sample code - Controller
if (getListAdapter().getCount() > 0) {
comment = (Comment) getListAdapter().getItem(0);
datasource.deleteComment(comment);
adapter.remove(comment);
}
delete

20. Sample code - Model
@Override
public void onCreate(SQLiteDatabase database) {
database.execSQL("create table " + TABLE_COMMENTS +
"(" + COLUMN_ID + " integer primary key autoincrement, "
+ COLUMN_COMMENT + " text not null);");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_COMMENTS);
onCreate(db);
}

21. Sample code - Model
public Comment createComment(String comment) {
ContentValues values = new ContentValues();
values.put("comment", comment);
long id = database.insert("comments", null, values);
Cursor cursor = database.query("comments", allColumns,
"_id" + " = " + id, null, null, null, null);
cursor.moveToFirst();
cursor.close();
return cursorToComment(cursor);
}

22. Sample code - Model
public void deleteComment(Comment comment) {
long id = comment.getId();
database.delete("comments", "_id" + " = " + id, null);
}

23. Sample code - Model
private Comment cursorToComment(Cursor cursor) {
Comment comment = new Comment();
comment.setId(cursor.getLong(0));
comment.setComment(cursor.getString(1));
return comment;
}

24. Sample code - Model
public List<Comment> getAllComments() {
List<Comment> comments = new ArrayList<Comment>();
Cursor cursor = database.query("comments", allColumns,
null, null, null, null, null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
comments.add(cursorToComment(cursor));
cursor.moveToNext();
}
cursor.close();
return comments;
}

25. No better choice ?

26. ORM
Object-relational mapping

28. Record maps to Java Object

29. Rails sample

30. We use SQLite @ Android
OrmLite
greenDAO

31. greenDAO

32. Architecture

33. Structure

34. How to use...
private void initDatabase() {
helper = new DaoMaster.DevOpenHelper(this, NAME, null);
master = new DaoMaster(helper.getWritableDatabase());
session = master.newSession();
cityDao = session.getCityDao();
townDao = session.getTownDao();
storeDao = session.getStoreDao();
}

35. How to use...
cityDao.insert(new City(1L, "台北市"));
storeDao._queryTown_Stores(townId).isEmpty()
town =
townDao.queryBuilder().where(TownDao.Properties.Name.eq(
"新莊區"), TownDao.Properties.CityId.eq(5)).unique();

36. At first, generate code to use it.
public static void main(String[] args) {
schema = new Schema(4, "tw.kewang.smile319.model");
addCity();
addTown();
addStore();
new DaoGenerator().generateAll(schema, "../Prj/src-gen");
}

37. At first, generate code to use it.
private static void addTown() {
Entity town = schema.addEntity("Town");
town.addIdProperty().columnName("id");
town.addStringProperty("name").notNull();
town.addDoubleProperty("latitude");
town.addDoubleProperty("longitude");
Property cityId =
town.addLongProperty("cityId").notNull().getProperty();
ToMany cityToTowns = city.addToMany(town, cityId);
cityToTowns.setName("towns");
}

38. What is generator ?

39. Generator contains...
● A schema at least
● A schema has many entities (models)
● A entity has many property (data type, not null,
autoincrement, index......etc.)
● 2 entities have a relationship (optional)
● Project has a leader
● Leader belongs to a project

40. QueryBuilder
● whereXXX
● joinXXX
● orderXXX
● listXXX
● uniqueXXX
● or, and
● limit, offset, count

41. FAQ

42. 1. Why use generator ?

43. Typically, annotation & reflection
BUT
1.can't compiler check
2.reflection is very slow @ Android

44. 2. Why use greenDAO ?

45. Speed up !
1.generator instead of reflection
2.refine SQLiteCursor
3.custom LongHashMap @ LUT

46. 3. What about OrmLite ?

48. References
● http://greendao-orm.com/
● https://github.com/greenrobot/greenDAO
● http://www.slideshare.net/droidcon/green-dao

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