Why are the foreign keys in ejb declared as objects(entities)? - sql

Question

I'am developing a java web EE application using EJB, JPA and netbeans. I've created a table with sql named users for registration and login and another table named prescripts which has 3 foreign keys refering to the primary key idusers of users(docid, pharmid, patid).
I also created with net beans entity bean named users and a session bean named UsersFacade and for prescripts an entity bean: prescripts and session bean: PrescriptsFacade.
My question is this:
Why in users ejb all variables(columns) are declared as they are(string for string, integer for integer etc) and in prescripts are declared as users?
//users.java
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "idusers")
private Integer idusers;
#Column(name = "user_type")
private String userType;
#Column(name = "name")
private String name;
#Column(name = "nickname")
private String nickname;
//prescripts.java
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "idprescripts")
private Integer idprescripts;
#Column(name = "data")
private String data;
#JoinColumn(name = "pharm_id", referencedColumnName = "idusers")
#ManyToOne
private Users users;
#JoinColumn(name = "doc_id", referencedColumnName = "idusers")
#ManyToOne
private Users users1;
#JoinColumn(name = "pat_id", referencedColumnName = "idusers")
#ManyToOne
private Users users2;
For users i use this code in a servlet to insert a row in sql base:
Users currentUsers;
currentUsers = new Users();
String Type = request.getParameter("user_type");
String Name = request.getParameter("name");
String Nickname = request.getParameter("nickname");
currentUsers.setUserType(Type);
currentUsers.setName(Name);
currentUsers.setNickname(Nickname);
UsersFacade.create(currentUsers);
How am i supposed to insert a row in prescripts this way?
This doesn't work(it shows error null pointer exception):
currentPresc = new Prescripts();
String PatID = request.getParameter("pat_id");
String DocID = request.getParameter("doc_id");
String PharmID = request.getParameter("pharm_id");
String Data = request.getParameter("data");
int patid = Integer.parseInt(PatID);
int docid = Integer.parseInt(DocID);
int pharmid = Integer.parseInt(PharmID);
currentUsers = UsersFacade.find(patid);
currentPresc.setUsers(currentUsers);
currentUsers = UsersFacade.find(docid);
currentPresc.setUsers1(currentUsers);
currentUsers = UsersFacade.find(pharmid);
currentPresc.setUsers2(currentUsers);
currentPresc.setData(Data);
PrescriptsFacade.create(currentPresc);
I skipped the set and get methods and some variables for simplifying reasons. Please any help is really very appreciated, i am stucked with this 2 weeks now :'(
I send you the whole classes of users and prescripts:
Prescripts.java
package entities;
import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
#Entity
#Table(name = "prescripts")
#NamedQueries({
#NamedQuery(name = "Prescripts.findAll", query = "SELECT p FROM Prescripts p"),
#NamedQuery(name = "Prescripts.findByIdprescripts", query = "SELECT p FROM Prescripts p WHERE p.idprescripts = :idprescripts"),
#NamedQuery(name = "Prescripts.findByData", query = "SELECT p FROM Prescripts p WHERE p.presc = :presc")})
public class Prescripts implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "idprescripts")
private Integer idprescripts;
#JoinColumn(name = "doc_id", referencedColumnName = "idusers")
#ManyToOne
private Users doc_id;
#JoinColumn(name = "pat_id", referencedColumnName = "idusers")
#ManyToOne
private Users pat_id;
#JoinColumn(name = "pharm_id", referencedColumnName = "idusers")
#ManyToOne
private Users pharm_id;
#Column(name = "presc")
private String presc;
public Prescripts() {
}
public Prescripts(Users pat_id, Users pharm_id, Users doc_id, String presc) {
this.pharm_id = pharm_id;
this.doc_id = doc_id;
this.pat_id = pat_id;
this.presc = presc;
}
public Integer getIdprescripts() {
return idprescripts;
}
public void setIdprescripts(Integer idprescripts) {
this.idprescripts = idprescripts;
}
public String getPresc() {
return presc;
}
public void setPresc(String presc) {
this.presc = presc;
}
public Users getPharmId() {
return pharm_id;
}
public void setPharmId(Users pharm_id) {
this.pharm_id = pharm_id;
}
public Users getDocId() {
return doc_id;
}
public void setDocId(Users doc_id) {
this.doc_id = doc_id;
}
public Users getPatId() {
return pat_id;
}
public void setPatId(Users pat_id) {
this.pat_id = pat_id;
}
#Override
public int hashCode() {
int hash = 0;
hash += (idprescripts != null ? idprescripts.hashCode() : 0);
return hash;
}
#Override
public boolean equals(Object object) {
// TODO: Warning - this method won't work in the case the id fields are not set
if (!(object instanceof Prescripts)) {
return false;
}
Prescripts other = (Prescripts) object;
if ((this.idprescripts == null && other.idprescripts != null) || (this.idprescripts != null && !this.idprescripts.equals(other.idprescripts))) {
return false;
}
return true;
}
#Override
public String toString() {
return "entities.Prescripts[idprescripts=" + idprescripts + "]";
}
}
Users.java
package entities;
import java.io.Serializable;
import java.util.Collection;
import java.util.List;
import javax.persistence.*;
import javax.xml.bind.annotation.XmlTransient;
#Entity
#Table(name = "users")
#NamedQueries({
#NamedQuery(name = "Users.findAll", query = "SELECT u FROM Users u"),
#NamedQuery(name = "Users.findByIdusers", query = "SELECT u FROM Users u WHERE u.idusers = :idusers"),
#NamedQuery(name = "Users.findByUserType", query = "SELECT u FROM Users u WHERE u.userType = :userType"),
#NamedQuery(name = "Users.findByNickname", query = "SELECT u FROM Users u WHERE u.nickname = :nickname"),
#NamedQuery(name = "Users.findByName", query = "SELECT u FROM Users u WHERE u.name = :name"),
#NamedQuery(name = "Users.findByPassword", query = "SELECT u FROM Users u WHERE u.password = :password"),
#NamedQuery(name = "Users.findByEmail", query = "SELECT u FROM Users u WHERE u.email = :email"),
#NamedQuery(name = "Users.findByCity", query = "SELECT u FROM Users u WHERE u.city = :city"),
#NamedQuery(name = "Users.findByStreet", query = "SELECT u FROM Users u WHERE u.street = :street"),
#NamedQuery(name = "Users.findByAt", query = "SELECT u FROM Users u WHERE u.at = :at"),
#NamedQuery(name = "Users.findByAmka", query = "SELECT u FROM Users u WHERE u.amka = :amka"),
#NamedQuery(name = "Users.findByAfm", query = "SELECT u FROM Users u WHERE u.afm = :afm"),
#NamedQuery(name = "Users.findByVerify", query = "SELECT u FROM Users u WHERE u.verify = :verify")})
public class Users implements Serializable {
#OneToMany(mappedBy = "pat_id")
private List<Prescripts> prescriptsList;
#OneToMany(mappedBy = "doc_id")
private List<Prescripts> prescriptsList1;
#OneToMany(mappedBy = "pharm_id")
private List<Prescripts> prescriptsList2;
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "idusers")
private Integer idusers;
#Column(name = "user_type")
private String userType;
#Column(name = "name")
private String name;
#Column(name = "nickname")
private String nickname;
#Column(name = "password")
private String password;
#Column(name = "email")
private String email;
#Column(name = "city")
private String city;
#Column(name = "street")
private String street;
#Column(name = "AT")
private String at;
#Column(name = "AMKA")
private String amka;
#Column(name = "AFM")
private String afm;
#Column(name = "verify")
private Boolean verify;
public Users() {
}
public Users( String userType,String name,String nickname, String password, String email, String city, String street, String at,
String amka, String afm, Boolean verify)
{
this.userType= userType;
this.name= name;
this.nickname= nickname;
this.password= password;
this.email = email;
this.city = city;
this.street = street;
this.at = at;
this.amka = amka;
this.afm = afm;
this.verify=verify;
}
public Integer getIdusers() {
return idusers;
}
public void setIdusers(Integer idusers) {
this.idusers = idusers;
}
public String getUserType() {
return userType;
}
public void setUserType(String userType) {
this.userType = userType;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getNickname() {
return nickname;
}
public void setNickname(String nickname) {
this.nickname = nickname;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getStreet() {
return street;
}
public void setStreet(String street) {
this.street = street;
}
public String getAt() {
return at;
}
public void setAt(String at) {
this.at = at;
}
public String getAmka() {
return amka;
}
public void setAmka(String amka) {
this.amka = amka;
}
public String getAfm() {
return afm;
}
public void setAfm(String afm) {
this.afm = afm;
}
public Boolean getVerify() {
return verify;
}
public void setVerify(Boolean verify) {
this.verify = verify;
}
#Override
public int hashCode() {
int hash = 0;
hash += (idusers != null ? idusers.hashCode() : 0);
return hash;
}
#Override
public boolean equals(Object object) {
// TODO: Warning - this method won't work in the case the id fields are not set
if (!(object instanceof Users)) {
return false;
}
Users other = (Users) object;
if ((this.idusers == null && other.idusers != null) || (this.idusers != null && !this.idusers.equals(other.idusers))) {
return false;
}
return true;
}
#Override
public String toString() {
return "entities.Users[idusers=" + idusers + "]";
}
public List<Prescripts> getPrescriptsList() {
return prescriptsList;
}
public void setPrescriptsList(List<Prescripts> prescriptsList) {
this.prescriptsList = prescriptsList;
}
public List<Prescripts> getPrescriptsList1() {
return prescriptsList1;
}
public void setPrescriptsList1(List<Prescripts> prescriptsList1) {
this.prescriptsList1 = prescriptsList1;
}
public List<Prescripts> getPrescriptsList2() {
return prescriptsList2;
}
public void setPrescriptsList2(List<Prescripts> prescriptsList2) {
this.prescriptsList2 = prescriptsList2;
}
}

Answer 1

The main question seems to be why variables in the User-class is declared as Integer, but the "user_id-variable" in Prescript is declared as User.
This is simply the way EJB3 works. You are thinking to much in terms of sql and relational databases. You define the primary key of tables (e.g. Users.idusers) as if it was a column, but references to other objects (entities, to be precise) are defined using the natural object. Therefore the Prescripts.users is declared as a Users-object. The EJB platform will take care of transforming this into a database column (in this case probably named users_idusers), with the correct type (in this case Integer), but this is taken care of and you shouldn't need to care about that.
You should go through a EJB3 tutorial or two - there are plenty of these, and make sure you complete the tutorials. You seemed to have missed some of the basics. Also note that your code could have been much simpler. The "#Column"-annotations are usually not needed, mapped_by is usually not needed, column-names ditto, etc. Also use singular names (User instead of Users). The common standard for primarykeys is simply #Id Long id, making it easy to remember the name of the primary key for all entities (but some prefer distinct names).
To answer your actual problem we would need more information, including what is on TestServlet.java line 233. Your code seems more or less correct, but it is hard for others to verify that. Finding the Users-object from EntityManger/facade and then setting it into the Prescipts-object is the correct way to do it.

Answer 2

In java, relations between entities (in a entity-relationship model) is represented as references to objects, (one-to-one) or lists of references to objects (one-to-many)
A relational database implements relations between entities (rows in tables) as foreign keys, that matches the primary key for a row in another table.
(The word "relational" in a "relational database" does actually just mean that the columns (tuples) in a table is related to each other...The foreign key stuff is an addition.)
I generally considered smart to start with a proper entity-relationshop model before designing database tables all willy nilly...