Question

I have two tables associated by FK.

Table student is mapped like this:

@Entity
@Table(name="student")
public class Student implements Serializable {
  ...
  @Id
  @GeneratedValue
  private int id; 

  @ManyToOne(fetch = FetchType.LAZY, optional = true) 
  @JoinColumn(name = "school_ID", nullable = true, insertable = false, updatable = false)
  private School school;

  private Integer school_ID; 

  @Transient
  private boolean editable = false;
}

Table school:

@Entity
@Table(name="school")
public class School implements Serializable {
  ...
  @OneToMany(fetch = FetchType.LAZY, mappedBy = "school")
  private Set<Student> student = new HashSet<Student>(0);

When I try to insert/update student, which isn’t at any school (student.school_ID is null) it reports:

Exception: java.lang.Exception: org.hibernate.exception.ConstraintViolationException:
could not update: [tables.Student#556758]
...
Caused by: com.microsoft.sqlserver.jdbc.SQLServerException: The UPDATE statement
conflicted with the FOREIGN KEY constraint "FK__student__school_ID__57378E7F". The 
conflict occurred in database "DB", table "dbo.school", column 'id'.

Do I have a possibility to insert also null values on FK?

Shall I define it on:

• entity level or
• database level?

UPDATE:

I’ve change the private School school = new School(), but when I try to insert/update row, it still reports:

SEVERE: Servlet.service() for servlet [Faces Servlet] in context with path [/DB] threw exception [javax.el.PropertyNotFoundException: /view.xhtml @183,102 value="#{item.school.id}": Target Unreachable, 'school' returned null] with root cause
javax.el.PropertyNotFoundException: /view.xhtml @183,102 value="#{item.school.id}": Target Unreachable, 'school' returned null

view.xhtml:

<rich:column>
  <h:outputText value="#{item.school != null ? item.school.name : null}" rendered="#{!item.editable}"/>
  <h:selectOneMenu id="som" tabindex="1" value="#{item.school.id}"  rendered="#{item.editable}">
    <f:selectItems value="#{myDials.schoolList}"/> 
  </h:selectOneMenu>
</rich:column>
<rich:column>

Answer 1

You mapped two different fields on the same school_id column:

private School school;
private Integer school_ID; 

Remove the school_ID field. You don’t need it, since you already have an association to the School entity.

And also remove insertable = false, updatable = false from the association mapping. You should use the school field to create, update or remove the association.