sql server - hibernate - allow null value on FK -

i have 2 tables associated fk.

table student mapped 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 try insert/update student, isn't @ school (student.school_id null) reports:

exception: java.lang.exception: org.hibernate.exception.constraintviolationexception: not update: [tables.student#556758] ... caused by: com.microsoft.sqlserver.jdbc.sqlserverexception: update statement conflicted foreign key constraint "fk__student__school_id__57378e7f".  conflict occurred in database "db", table "dbo.school", column 'id'. 

do have possibility insert null values on fk?

shall define on:

• entity level or
• database level?

update:

i've change private school school = new school(), when try insert/update row, still reports:

severe: servlet.service() servlet [faces servlet] in context path [/db] threw exception [javax.el.propertynotfoundexception: /view.xhtml @183,102 value="#{item.school.id}": target unreachable, 'school' returned null] 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> 

you mapped 2 different fields on same school_id column:

private school school; private integer school_id;  

remove school_id field. don't need it, since have association school entity.

and remove insertable = false, updatable = false association mapping. should use school field create, update or remove association.