Question

I am working on the domain model for a project. I have a class named user that has a class named UserType as one of the properties. I know when I want to select all users, I will use joins to pick up all corresponding usertypes. How do I do inserts? Do I have to write a handler for userType? Or can I do something like

INSERT INTO users(... usertype_id ...) VALUES(... #{usertype.usertype_id}...)

Please help;

I have spent the whole day trying to figure this out. I am using ibatis 3.0 and I am new to ibatis.

Answer 1

Ibatis is not a full ORM framework, so it doesnt know about objects relationships.
So yes, you must write something like your INSERT if you want to work directly with domain objects that do not fully correspond to a record in your table; that is, if the User object you are mapping in Ibatis does not have a getUsertypeId() method (that returns the value corresponding to the table column usertype_id ) but instead a getUserType() method.

(Of course you can also write a getUsertypeId() method which internally calls getUserType().getId()… but just stop here and don’t pretend to make also a setUserTypeId(int id) which internally tries to load the UsertypeId from the Db, etc, etc… that calls for trouble. You’ll end reinventing JPA/Hibernate.)

I don’t think a TypeHandler is the right approach, that feature is more oriented to converting non-trivial types, not so much for handling relationships.

Another valid approach is to have a layer of relatively low-level-dumb POJOs, roughly one for each table, with properties that map directly to your table columns (say, a UserDb object with a userTypeId property and no getUserType() method, and no bussiness intelligence, dependencies on upper layers or persistence knowledge), and then, on top of that, a layer of richer “real” domain objects, each of which wraps a (usually small) graph of those “dumb” POJOs, and has the intelligence necessary for calling the persistence layer (eg DAO) to load/save the graph (perhaps lazily).

One advantage of this approach is that the core of actual ibatis mappings (the SQL coding) can be done fairly automatically with Ibator – it even creates the code of the POJOs from the DB schema.

For massive reads of data which involves many tables (reports), you can create other trviial ad-hoc POJOs (which corresponds directly to the columns of your SELECT, and perhaps have some rudimentary intelligence to display values – something like a ‘ViewModel’) … or even HashMaps.

PS: You might want to read about DDD (and concepts like “Entities”, “Value objects”, “Views”, “contexts” “rich domain object” vs “anemic domain objects” eg). Ibatis gives you much flexibility to learn and implement along this lines.