Develop Reference

How would I map an #Entity with a hbm.xml?

I in a situation where I need to override some fields in a #Entity class but I can't edit the class. It just so happens that this #Entity class is mapped in a way that I don't think it's possible to partially override it. I was wondering what would be the steps to overriding this class completely or maybe partially if possible.
The class:
org.broadleafcommerce.profile.core.domain.AddressImpl
I've used a hbm.xml and a orm.xml but I'm not exactly sure how to configure them properly.

The book Pro JPA 2 : Mastering the Java Persistence API notes:
The metadata-complete attribute is an attribute on the entity,
mapped-superclass, and embeddable elements. If specified, all
annotations on the specified class and on any fields or properties in
the class will be ignored, and only the metadata in the mapping file
will be considered as the set of metadata for the class. When
metadata-complete is enabled, the same rules that we applied to
annotated entities will still apply when using XML-mapped entities.
For example, the identifier must be mapped, and all relationships must
be specified with their corresponding cardinality mappings inside the
entity element.
So you will need an entry in your orm.xml like the below, adding all other persistent attributes as required (partial override is not possible).
<entity-mappings>
<entity class="com.Foo" metadata-complete="true">
<table name="FOO"/>
<attributes>
<id name="id"/>
</attributes>
</entity>
</entity-mappings>

MyBatis Generator single resultMap

Im using MyBatis Generator to generate JavaBean and Mapper.xml.
But the Mapper.xml is different as I expected .
Mapper.xml contain two resultMap, BaseResultMap and ResultMapWithBLOBs.
I only want one resultMap contain all column.

Tough to know how you have your mybatis generator configuration set up, but the way to do this is through configuring the context's Model Type.
MBG provides an enum called ModelType which allows you to control how the Java Model classes (your beans) are generated. You want to use ModelType.FLAT in your context configuration to avoid any extra bean classes being created.

One option to avoid the creation of "WithBlobs" subclasses is to specify <columnOverride/> to use non-Blob jdbc types in your generator config for the Blob columns.
So, in the example of a TEXT column named "bar" in your table, you can specify VARCHAR instead:
<table tableName='foo' domainObjectName='Foo'>
<property name='useActualColumnNames' value='true' />
<columnOverride column="bar" property="bar" jdbcType="VARCHAR" />
</table>

hibernate simple inheritance - OR - xml property import/include

Final goal:
Have a few java objects sharing the same base class persisted into a database while each one having its own self-contained table with all own/inherited objects, and a simple auto-generated by the database id.
Very simple requirement. Impossible (?) with Hibernate!
What I have so far (using MySQL, Hibernate XML mapping):
map.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping default-access="field"
default-lazy="false">
<class name="xyz.url.hibernate.EntityBase" abstract="true">
<id name="m_id" column="id">
<generator class="identity" />
</id>
<version name="m_version" column="version" type="long" />
<union-subclass name="xyz.url.hibernate.User" table="my_entity">
<property name="name" column="name" type="string" />
</union-subclass>
</class>
</hibernate-mapping>
EntityBase.java
public abstract class EntityBase {
private final long m_id;
private final long m_version;
public EntityBase() {
this.m_id = 0;
this.m_version = 0;
}
public long get_id() {
return this.m_id;
}
public long get_version() {
return this.m_version;
}
}
User.java
public class User extends EntityBase {
public String name;
}
The above does not work unless you change the generator class to increment.
Currently this is the given error:
org.hibernate.MappingException: Cannot use identity column key generation with <union-subclass> mapping for: xyz.url.hibernate.User
Well, why does Hibernate ASSUMES I want a unique ID in a program-wide scope (I've read about some JPA requirement)... what a crap!
Anyway, I insist of having a simple table (per object) that aggregates all the object's (User in this case) properties, and deny using discriminators (again what a crap..) which just complicate the final SQL queries and hit performance.
The only solutions I see here:
Manually map all properties in a one block inside the XML.
Map all properties while "importing" some <propert> items from an external file, thus achieve inheritance (reusage of properties). Possible? How to do?!?
Explore annotations further which as far as I've seen they don't support that simple inheritance requirement.
Dump Hibernate and go with another ORM solution.
Please don't link to the docs - I gave up on that one after reading them a few times!
An example of property import (from external file) would be great.
Thanks and god bless!

First of all you need to decide whether your inheritance relationship should be mapped to the database (to allow polymorphic queries such as from EntityBase, polymorphic realtionships, etc) or not.
As far as I understand in your case it shouldn't be mapped, therefore it doesn't make sense to use inheritance mapping options such as <union-subclass> at all. Now you have the following options:
2. Hibernate doesn't have special support for reuse of XML mappings, but its documentation suggests to use XML entities in this case, see, for example, 10.1.6. Table per concrete class using implicit polymorphism.
3. Annotations certainly support this requirement in form of #MappedSuperclass annotation.
This annotation can be used to mark a class that is not mapped to the database itself, but any mapping annotations defined on its properties take effect for its mapped subclasses, so that you don't need to repeat them.

You can also use XML Entity Reference, see:
https://n1njahacks.wordpress.com/2014/09/19/hibernate-xml-mapping-fragment-re-use/
http://xml.silmaril.ie/includes.html

Java ORM: Multiple (interface) inheritance

I'd like to map a domain model to a relational database using one of the ORM frameworks for Java. Unfortunately, none of them seem to have adequate support for classes implementing multiple interfaces. Say I want to map something like:
public interface Quotable {
}
public interface Tradable {
}
// StockIndex only implements Quotable as it cannot be trade directly
public class StockIndex implements Quotable {
}
// Stock implements both interfaces as there are market quotes and can be traded
public class Stock implements Quotable, Tradable {
}
public class Quote {
private Quotable quotable;
}
public class Trade {
private Tradable tradable;
}
So what I'm trying to achieve is that a Quote can reference any Quotable (Stock, StockIndex and others) while a Trade can only reference Tradable entities. I've tried OpenJPA and (plain) Hibernate with no luck even though the latter's support for interfaces looked promising.
Is there any framework that can handle my scenario? Or are there any good reasons why this shouldn't be mapped to a database? If so, how should my model be modified?
My initial Hibernate mapping looked something like this (I'm not showing any OpenJPA stuff as it doesn't support interface inheritance or at least I couldn't figure out how):
<hibernate-mapping package="com.foo">
<class name="Quotable" table="quotable" >
<id type="java.lang.Long" column="id">
<generator class="sequence" />
</id>
<discriminator column="type" type="string" />
<subclass name="StockIndex">
<join table="stock_index" >
<key column="id"/>
<property name="name" column="name" access="field" />
</join>
</subclass>
<subclass name="Stock">
<join table="stock" >
<key column="id"/>
<property name="name" column="name" access="field" />
</join>
</subclass>
</class>
</hibernate-mapping>
This is pretty much identical to the example in the Hibernate documentation and results in a table quotable with an id and a string discriminator column, a table stock_index with an id and the index' name and a table stock with an id and the stock's name. So far so good...
But what shall I do with the Tradeable interface? I would have to setup a separate hierarchy and map Stock in both hierarchies. I did try this but had to define different entity names for Stock (and needed to include this patch) but this also didn't work due to foreign key violations. I tried a couple of other obscure things that didn't work either.
Anyway, mapping Stock twice wouldn't be a good solution as the application would have to remember adding Stock instances twice - once for each interface. I'd rather have the framework handle this automaticaly.
Ideally Hibernate would allow extending multiple interfaces, i.e. something like (note the extends attribute on the subclass element):
<subclass name="Stock" extends="Quotable, Tradable" >
<join table="stock" >
<key column="id"/>
<property name="name" column="name" access="field" />
</join>
</subclass>
Any other ideas how my example can be mapped? I've now learned about the <any> element which looks like it might work for me but I have yet to understand all its implications.
How about other frameworks? I've heard EclipseLink also has some support for interfaces but it's not well documented.

I don't think you will find any ORM able to handle interfaces hierarchy nicely.
So I won't talk about ORMs here but I'm going to show you how to implement your example using Qi4j.
Qi4j is an implementation of Composite Oriented Programming, using the standard Java platform and a framework for domain centric application development, including evolved concepts from AOP, DI and DDD. See http://qi4j.org
In Qi4j, domain state is modeled using Entities and Values. In the following code sample I assume that everything is an Entity but your mileage may vary.
As Entities are declared using only interfaces, your use case should fit in nicely.
interface Quotable { ... }
interface Tradable { ... }
interface StockIndex extends Quotable { ... }
interface Stock extends Quotable, Tradable { ... }
interface Quote {
Association<Quotable> quotable();
}
interface Trade {
Association<Tradable> tradable();
}
You can then store theses in an EntityStore and use the Query API to retrieve them easily (and in a fully polymorphic way).
Note that Qi4j EntityStores are not only SQL based but support NoSQL databases too. See the available extensions here: http://qi4j.org/latest/extensions.html
See the Qi4j documentation if you have more questions.

org.hibernate.InstantiationException: How to tell Hibernate which class to use for object instantiation

I am currently trying to replace my own database controller implementation with Hibernate and I have the following problem creating an appropriate mapping file.
(I am very new to Hibernate, so please be gentle :-) - I've read through the whole Hibernate Reference documentation but I don't have any practical experience yet).
(The whole thing should represent the relationship between email accounts and their server settings).
I have a class called MailAccount which has 2 properties (see code below):
public class MailAccount{
long id;
IncomingMailServer incomingServer;
OutgoingMailServer outgoingServer;
public MailAccount(){
super();
}
// Getter and setter omitted
}
The server class hierachy looks like this:
MailServer.java
public abstract class MailServer {
String password;
String host;
String username;
String port;
// Getter and setter omitted
}
IncomingMailServer.java
public abstract class IncomingMailServer extends MailServer {
}
OutgoingMailServer.java
public abstract class OutgoingMailServer extends MailServer {
}
Pop3Server.java
public class Pop3Server extends IncomingMailServer{
public Pop3Server(){
super();
}
}
ImapServer.java
public class ImapServer extends IncomingMailServer{
public ImapServer(){
super();
}
}
SmtpServer.java
public class SmtpServer extends OutgoingMailServer{
public SmtpServer(){
super();
}
}
The properties incomingServer and outgoingServer in MailAccount.java of course only hold instances of either Pop3Server, ImapServer (for incomingServer) or SmtpServer (for outgoingServer).
Now, I tried to create the mapping file for MailAccount:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="test.account">
<class name="MailAccount" table="MAILACCOUNTS" dynamic-update="true">
<id name="id" column="MAIL_ACCOUNT_ID">
<generator class="native" />
</id>
<component name="incomingServer" class="test.server.incoming.IncomingMailServer">
<property name="password" column="INCOMING_SERVER_PASSWORD" />
<property name="host" column="INCOMING_SERVER_PASSWORD" />
<property name="username" column="INCOMING_SERVER_PASSWORD" />
<property name="port" column="INCOMING_SERVER_PASSWORD" />
</component>
<component name="outgoingServer" class="test.server.outgoing.OutgoingMailServer">
<property name="password" column="OUTGOING_SERVER_PASSWORD" />
<property name="host" column="OUTGOING_SERVER_PASSWORD" />
<property name="username" column="OUTGOING_SERVER_PASSWORD" />
<property name="port" column="OUTGOING_SERVER_PASSWORD" />
</component>
</class>
</hibernate-mapping>
Note: Since I got a 1:1 relation between MailAccount and IncomingMailServer as well as MailAccount and OutgoingMailServer, I want everything in 1 table in order to prevent unnecessary joins.
The problem: Whenever I tell Hibernate to save an instance of MailAccount, like this:
session = getSession();
transaction = session.beginTransaction();
session.save(mailAccount);
transaction.commit();
.. I get the following exception:
org.hibernate.InstantiationException:
Cannot instantiate abstract class or
interface:
test.server.incoming.IncomingMailServer
This totally makes sense since abstract classes cannot be instantiated.
However, here comes my question: How can I tell Hibernate to create an instance of the right class (Pop3Server, SmtpServer, ImapServer) instead of the abstract ones?
Example: If the property incomingServer holds an instance of Pop3Server, then Hiberante should store that into my database and when I load the according MailAccount back, I want Hibernate to recreate an instance of Pop3Server.

The problem is occurring because a component is not a stand-alone entity, but "a class whose instances are stored as an intrinsic part of an owning entity and share the identity of the entity". In JPA terms it is considered an Embeddable class. These classes are usually used to create a class object out of a number of table columns that would normally have to be stored as individual attributes in an entity (you can almost look at it as grouping).
While there are a number of benefits to this approach, there are some restrictions. One of these restrictions are that the component or embeddable cannot be an abstract class. The reason being that there isn't any way for hibernate to associate a particular concrete subclass with the value you are trying to store or read. Think of it this way: would you be able to tell what instance to create by only looking at the column data? It's usually not that straight forward, especially for the persistence engine.
In order to get the functionality you desire, you will want to look into storing MailServer data as a separate entity with its own primary key field. Doing so allows you to manage the data with subclasses using various inheritance methods such as including a DiscriminatorColumn or separate tables (depending on your configuration).
Here are some links that should help you with setting up these mappings and using entity inheritance:
One-to-One mapping example
(useful if not reusing MailServer
data.
Inheritance overview
Useful Hibernate examples (not
latest spec, but gives you good
overview)
Hope this helps.
http://www.vaannila.com/hibernate/hibernate-example/hibernate-example.html
If you were to use this approach using Hibernate (I personally prefer JPA-based Annotation configurations), you could configure MailServer as an abstract entity that would define the common column mappings between the classes and a DiscriminatorColumn (if using same table inheritance). The subclasses would be built off of this definition, adding custom attributes as needed.