I am trying to create an Entity that has a byte[12] id in hibernate. It seems like it does not like to have a byte[] as a primary key and as another column it sets it up as a tinyblob in the backing mysql db. I have tried to create a String, but the problem is that the string in java is 2 bytes per char, while it is one byte per char in mysql. I'm looking for something like this
@Entity
public class TestClass {
@Id
@Column(length=12)
private byte[] id;
...
to map to a mysql table like this
Table 'testclass'
Column id - varbinary length 12 primary key
...
I have tried a number of different ways (primarily trying to fiddle with Strings) to do this but it does not seem to work right. Has anyone been able to do this already? Thanks.
As you experienced, this is not supported by standard JPA. From the specification:
2.1.4 Primary Keys and Entity Identity
...
The primary key (or field or property of a composite primary key) should be one of the following types: any Java primitive type; any primitive wrapper type;
java.lang.String;java.util.Date;java.sql.Date. In general, however, approximate numeric types (e.g., floating point types) should never be used in primary keys. Entities whose primary keys use types other than these will not be portable. If generated primary keys are used, only integral types will be portable. Ifjava.util.Dateis used as a primary key field or property, the temporal type should be specified asDATE.
That being said, it appears that you could use a wrapper type around the byte[] and implement a custom user type. The UserType for a byte[] identifier property wiki page provides an implementation.
Refer to the section 2.4.3.2. Type of the Hibernate Annotations documentation to declare and use this custom type with annotations.