我在JPA中正确使用ManyToMany映射吗？

Question

I am working on a school project, and the goal is to make a JavaEE application for a fictional pharmacy.

Since one drug can cure one or many diseases and one disease can be treated by one or many drugs, I figured it is a @OneToMany relation on the Drug side and a @ManyToMany on the Disease side. I also have a Patient entity. A patient may suffer from one or many diseases, and one disease may afflict many patients. I coded my classes as follows but I get an incompatible-mapping-exception between my Drug and Disease classes when I try to generate tables from entities. I am using a GlassFish server and a Derby connection in Eclipse (everything is well-configured, so it's definitely a code issue). My classes are as follows:

public class Drug implements Serializable{
@OneToMany(targetEntity = Disease.class, mappedBy = "Cures_For_This_Disease")
private List<Disease> Diseases_Cured_By_This_Drug;
//other fields such as the name, price and origin of the drug
}

public class Disease implements Serializable{
@ManyToMany(targetEntity = Drug.class)
private List<Drug> Cures_For_This_Disease;
@ManyToMany(targetEntity = Patient.class)
private List<Patient> Afflicted_Patients;
//other fields such as name of disease etc.
}

public class Patient implements Serializable{
@OneToMany(targetEntity = Disease.class, mappedBy = "AfflictedPatients")
private List<Disease> Current_Diseases;
//other fields such as Patient name, social sec. nubmer etc
}

What am I doing wrong?

Answer 1

You should have @ManyToMany annotation in Drug and Patient classes.

public class Drug implements Serializable{
    @ManyToMany
    private List<Disease> Diseases_Cured_By_This_Drug;

}

public class Disease implements Serializable{
    @ManyToMany(mappedBy="Diseases_Cured_By_This_Drug")
    private List<Drug> Cures_For_This_Disease;
}

This should create a join table between the two corresponding tables.