Use abstract super class as parameter for Spring data repository
Solution 1:
If you aren't using table inheritance on the database side (e.g. super class table with descriminator column), AFAIK, and based off reading the JPA tutorial, this can't be done (i.e. simply using @MappedSuperclass annotation for your abstract class)
Mapped superclasses cannot be queried and cannot be used in EntityManager or Query operations. You must use entity subclasses of the mapped superclass in EntityManager or Query operations. Mapped superclasses can't be targets of entity relationships
Note, the JPA repository abstraction uses an EntityManager under the hood. I did a simple test, and what you will get (in the case of Hibernate implementation) an "IllegalArgumentException : not an entity AbstractClass"
On the other hand, if you do use table inheritance, then you can use the abstract type. I know you said "with just the minimal change" (and I guess my short answer is I don't think it's possible - probably for the reasons you guessed), so I guess the rest of this answer is for other inquiring minds ;-)
An example of a table inheritance strategy would be something like this (disclaimer: this is not the correct visualization for erd inheritance, but MySQL Workbench doesn't support it, but what I have below forward engineered the model to MYSQL the way it needs to be)
Where CountryCatalog has a FK/PK reference to the AbstractCatalog table pk (id). The AbstractCatalog table has a descriminatorColumn that will be used to determine to which subtype the supertype occurrence is related.
In terms of how you would code that, it would look something like
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(name="descriminatorColumn")
@Table(name="AbstractCatalog")
public abstract class AbstractCatalog {
@Id
private long id;
...
}
@Entity
@Table(name = "CountryCatalog")
public class CountryCatalog extends AbstractCatalog {
// id is inherited
...
}
public interface AbstractCatalogRepository
extends JpaRepository<AbstractCatalog, Long> {
}
@Repository
public class CountryCatalogServiceImpl implements CountryCatalogService {
@Autowired
private AbstractCatalogRepository catalogRepository;
@Override
public List<CountryCatalog> findAll() {
return (List<CountryCatalog>)(List<?>)catalogRepository.findAll();
}
@Override
public CountryCatalog findOne(long id) {
return (CountryCatalog)catalogRepository.findOne(id);
}
}
Basically, in conclusion, what you are trying to do won't work if you don't have table inheritance. The class type for the repository needs to be an entity. If your tables aren't set up this way for inheritance, it just comes down to whether or not you want to change the tables. It may be a bit much just to avoid multiple repositories though.
Some references I used are here and here
Note: Everything in this answer is tested against Hibernate provider
Solution 2:
Oke, new project and I'm following this set up a little bit.
The problem was :
We want to add attachments, but an attachment can be uploading a file, a link or a mail.
Pojo classes :
Attachment.java :
@Entity
@Table(name = "T_ATTACHMENT")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(name = "DISCRIMINATOR", discriminatorType = DiscriminatorType.STRING)
public abstract class Attachment {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "ATTACHMENT_SID")
private Long id;
@ManyToOne
@JoinColumn(name = "TASK_SID", referencedColumnName = "TASK_SID", nullable = false, unique = false, insertable = true, updatable = true)
private Task task;
@ManyToOne
@JoinColumn(name = "USER_SID", referencedColumnName = "USER_SID", nullable = false, unique = false, insertable = true, updatable = true)
private User user;
public Task getTask() {
return task;
}
public void setTask(Task task) {
this.task = task;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
}
FileAttachment.java :
@Entity
@Table(name = "T_FILE_ATTACHMENT")
@DiscriminatorValue("FILE")
public class FileAttachment extends Attachment {
@Column(name = "NAME", nullable = false, unique = false)
private String fileName;
@Lob
@Basic
@Column(name = "FILE", nullable = false, unique = false)
private byte[] file;
public String getFileName() {
return fileName;
}
public void setFileName(String fileName) {
this.fileName = fileName;
}
public byte[] getFile() {
return file;
}
public void setFile(byte[] file) {
this.file = file;
}
}
MailAttachment.java :
@Entity
@Table(name = "T_MAIL_ATTACHMENT")
@DiscriminatorValue("MAIL")
public class MailAttachment extends Attachment {
@Column(name = "RECIPIENT", nullable = false, unique = false)
private String to;
@Column(name = "CC", nullable = true, unique = false)
private String cc;
@Column(name = "BCC", nullable = true, unique = false)
private String bcc;
@Column(name = "TITLE", nullable = true, unique = false)
private String title;
@Column(name = "MESSAGE", nullable = true, unique = false)
private String message;
public String getTo() {
return to;
}
public void setTo(String to) {
this.to = to;
}
public String getCc() {
return cc;
}
public void setCc(String cc) {
this.cc = cc;
}
public String getBcc() {
return bcc;
}
public void setBcc(String bcc) {
this.bcc = bcc;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
}
LinkAttachment.java :
@Entity
@Table(name = "T_LINK_ATTACHMENT")
@DiscriminatorValue("LINK")
public class LinkAttachment extends Attachment {
@Column(name = "DESCRIPTION", nullable = true, unique = false)
private String description;
@Column(name = "LINK", nullable = false, unique = false)
private String link;
public String getDescription() {
return description == null ? getLink() : description;
}
public void setDescription(String description) {
this.description = description;
}
public String getLink() {
return link;
}
public void setLink(String link) {
this.link = link;
}
}
Spring data repo's :
AttachmentRepository.java:
public interface AttachmentRepository extends CustomRepository<Attachment, Long> {
List<Attachment> findByTask(Task task);
}
CustomRepository.java :
public interface CustomRepository<E, PK extends Serializable> extends
PagingAndSortingRepository<E, PK>,
JpaSpecificationExecutor<E>,
QueryDslPredicateExecutor<E> {
@Override
List<E> findAll();
}
And at last the service :
@Service
public class AttachmentServiceImpl implements AttachmentService {
@Inject
private AttachmentRepository attachmentRepository;
@Override
public List<Attachment> findByTask(Task task) {
return attachmentRepository.findByTask(task);
}
@Override
@Transactional
public Attachment save(Attachment attachment) {
return attachmentRepository.save(attachment);
}
}
This results in :
I can save to the abstract repo with any implementation I created, JPA will do it correct.
If I call findByTask(Task task) I get a List<Attachment> of all the subclasses, and they have the correct subclass in the back.
This means, you can make a renderer who do instanceof and you can customize your rendering for each subclass.
Downside is, you still need to create custom specific repository's, but only when you want to query on a specific property what is in the subclass or when you only want 1 specific implementation in stead of all implementations.
Solution 3:
What DB are you using?
If it's JPA, take a look at Can I use a generic Repository for all children of a MappedSuperClass with Spring Data JPA?
If it's Mongo you need to properly tune Jackson polymorphism configuration http://wiki.fasterxml.com/JacksonPolymorphicDeserialization
So this is possible.