Selection of multiple columns unsing spring data JPA and JPQL - spring

Question

I am trying to select two columns which are in two separate tables. One table is users and other one is privillages. I need to fetch username from users and pname from privillages. My model classes are like follows,
#Entity
#Table(name = "users")
public class Users implements Serializable{
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
public String username;
public String password;
public Integer privid;
#OneToMany(cascade = CascadeType.ALL, mappedBy = "pid")
private Collection<Privillages> priviJoin;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
#Column(name = "username")
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
#Column(name = "password")
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
#Column(name = "privid")
public Integer getPrivid() {
return privid;
}
public void setPrivid(Integer privid) {
this.privid = privid;
}
public Collection<Privillages> getPriviJoin() {
return priviJoin;
}
public void setPriviJoin(Privillages priviJoin) {
this.priviJoin = (Collection<Privillages>) priviJoin;
}
public Users() {
}
#Override
public String toString() {
return String.format("Users[id=%d, username='%s', password='%s']", id,
username, password);
}
}
And my Privillages class is,
#Entity
#Table(name = "privillages")
public class Privillages implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
public Integer id;
public String pname;
#ManyToOne(optional = false)
#JoinColumn(name = "pid", referencedColumnName = "privid")
public Users pid;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
#Column(name = "pname")
public String getPname() {
return pname;
}
public void setPname(String pname) {
this.pname = pname;
}
#Column(name = "pid")
public Users getPid() {
return pid;
}
public void setPid(Users pid) {
this.pid = pid;
}
public Privillages(){
}
}
And my Users repository is,
public interface UsersRepository extends CrudRepository<Users, Integer>
{
#Query("select u from Users ug join ug.priviJoin u")
List<Users> findByUsername();
}
And My Privillage repository is:
public interface PrivillagesRepository extends CrudRepository<Privillages,
Integer> {
}
My controller file is:
#RequestMapping(value = "/joinResult", method = RequestMethod.GET)
public ModelAndView joinResultShow(Model model)
{
List<Privillages> privillages = (List<Privillages>)privillagesRepo.findAll();
model.addAttribute("joinData",privillages);
ModelAndView viewObj = new ModelAndView("fleethome");
return viewObj;
}
And displaying like:
<table>
<tr th:each="message : ${joinData}">
<td th:text="${message.pname}"></td>
<td th:text="${message.pid.username}"></td>
</tr>
</table>
And getting error like:
There was an unexpected error (type=Internal Server Error, status=500).
No message available
Stacktrace is:
java.lang.NullPointerException: null
at
com.central.controller.WebController.joinResultShow(WebController.java:58) ~
[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~
[na:1.8.0_141]
at sun.reflect.NativeMethodAccessorImpl.invoke
(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_141]
at sun.reflect.DelegatingMethodAccessorImpl.
invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_141]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_141]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke
(InvocableHandlerMethod.java:205) ~[spring-web-
4.3.11.RELEASE.jar:4.3.11.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.
invokeForRequest(InvocableHandlerMethod.java:133) ~[spring-web-
4.3.11.RELEASE.jar:4.3.11.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.
ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.
java:97) ~[spring-webmvc-4.3.11.RELEASE.jar:4.3.11.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.
RequestMappingHandlerAdapter.invokeHandlerMethod
(RequestMappingHandlerAdapter .java:827)
~[spring-webmvc-4.3.11.RELEASE.jar:4.3.11.RELEASE]
at org.springframework.web.servlet.mvc.method.
annotation.RequestMappingHandlerAdapter.handleInternal
(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-
4.3.11.RELEASE.jar:4.3.11.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.
handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-
4.3.11.RELEASE.jar:4.3.11.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.
doDispatch(DispatcherServlet.java:967) ~[spring-webmvc-
4.3.11.RELEASE.jar:4.3.11.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService
(DispatcherServlet.java:901) ~[spring-webmvc-
4.3.11.RELEASE.jar:4.3.11.RELEASE]
I need to retrieve username from users and pname column from privillages. How should I change my code?

Answer 1

First of all, you should create privillages repository:
public interface PrivillagesRepository extends CrudRepository<Privillages, Integer> {
}
Then you can do find all privillages in your controller:
List<Privillages> privillages = privillages.findAll();
model.addAttribute("joinData",privillages);
After that, change your template:
<table>
<tr th:each="message : ${joinData}">
<td th:text="${message.pname}"></td>
<td th:text="${message.pid.username}"></td>
</tr>
</table>
As you can see, to print username, you need to use nested field "pid" (Users class)

Answer 2

I just explored the context that, Use the same repository as the Userrepository along with the JPQL query. And modify the view file according to that for displaying username with using the pid from Privillages Model class. I am adding the code need to modify with certain changes.
My controller file is,
UsersRepository userRepo;
#RequestMapping(value = "/joinResult", method = RequestMethod.GET)
public ModelAndView joinResultShow(Model model)
{
List<Users> use = (List<Users>) userRepo.findByUsername();
model.addAttribute("joinData",use);
ModelAndView viewObj = new ModelAndView("fleethome");
return viewObj;
}
And the repository ,
public interface UsersRepository extends CrudRepository<Users, Integer>
{
Users findByUsernameAndPassword(String username,String password);
#Query("select u from Users ug join ug.priviJoin u")
List<Users> findByUsername();
}
And My Privillage repository,
public interface PrivillagesRepository extends CrudRepository<Privillages,
Integer> {
}
And modify the View file with,
<table>
<th> Username </th>
<th> Privillage Name </th>
<tr th:each="message : ${joinData}">
<td th:text="${message.pid.username}"></td>
<td th:text="${message.pname}"></td>
</tr>
</table>