Hibernate: Storing an fixed length array in one database table row - mysql

Question

I have been trying to find a solution to store a fixed length array as a property of an object using hibernate in the same DB table as the object not using a BLOB for the array.
I currently have a class ProductionQCSession which looks like
#Entity
public class ProductionQCSession extends IdEntity {
private Long id;
private Float velocity;
private Float velocityTarget;
private Float[] velocityProfile;
public ProductionQCSession() {
}
#Id #GeneratedValue(strategy=GenerationType.AUTO)
#Override
public Long getId() {
return id;
}
#SuppressWarnings("unused")
public void setId(Long id) {
this.id = id;
}
#Basic
public Float getVelocity() {
return velocity;
}
public void setVelocity(Float velocity) {
this.velocity = velocity;
}
#Basic
public Float[] getVelocityProfile() {
return velocityProfile;
}
public void setVelocityProfile(Float[] velocityProfile) {
this.velocityProfile = velocityProfile;
}
}
Ideally I would like the DB structure to be
id|velocity|VPValue0|VPValue1|VPValue2|VPValue3|...
21| 2.1| 0.1| 0.2| -0.1| 0.3|...
I know with a high certainty that we always have 15 items in the velocityProfile array and those values as just as much properties of the object as any other property therefore I think it makes sense to add them to the database table schema, if it's possible. I would prefer to have it this way as it would be easy to get a overview of the data just doing a raw table print.
The current code just stores the array data as a BLOB.
I have looked http://ndpsoftware.com/HibernateMappingCheatSheet.html mapping cheat sheet, but could not seem to find any good solution.
I'm I just trying to do something nobody else would do?

Answer 1

Essentially, you're trying to have a multi-value field, which is not a relational database concept. A normalized solution would put those into a child table, which Hibernate would let you access directly from the parent row (and return it as a collection).
If you are adamant that it should be in a single table, then you'll need to create 15 individual columns....and hope that in the future you don't suddenly need 16.

Answer 2

The solution ended up being using the standardised method of using a child table even though it makes the data analysis slightly more complicated. The following code was used.
#ElementCollection
#CollectionTable(name ="QCVelocityProfile")
public List<Float> getVelocityProfile() {
return velocityProfile;
}
public void setVelocityProfile(List<Float> velocityProfile) {
this.velocityProfile = velocityProfile;
}