[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-772) null in maps are handled inconsistently

[Ferenc Gratzer (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-772?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=42167#action_42167 ] 

Ferenc Gratzer commented on HHH-772:
------------------------------------

I want to share how this old and insane hibernate issue could be circumvented fairly easy.

Let's take the next example:
public class Owner {
 private Map<KeyClass, ValueClass> mapping = new HashMap<KeyClass, ValueClass>();

 public ValueClass getMappingValue(KeyClass keyClass) {
  return mapping.get(keyClass);
 }

 public void addMapping(KeyClass keyClass, ValueClass valueClass) {
  mapping.put(keyClass, valueClass);
 }
}

This wouldn't work if the value of the map is null.
owner.addMapping(keyClass, null)

1) Add a new dummy boolean column to the mapping table:
ALTER TABLE MAPPING_TABLE ADD DUMMY SMALLINT DEFAULT 0 NOT NULL;

2) Add a <composite-element> as the value of the map:
<map name="mapping" cascade="all" fetch="select" lazy="true" mutable="true" inverse="false" table="MAPPING_TABLE">
 <cache usage="read-write" />
 <key column="OWNER_ID" not-null="true" />
 <map-key-many-to-many class="KeyClass" column="KEY_ID" />
 <!-- This composite element is only created as Hibernate doesn't allow null as map value, see HHH-772 -->
 <composite-element class="MapValueClass">
  <many-to-one name="mapValue" column="VALUE_ID" class="ValueClass" />
  <property name="dummy" column="DUMMY" not-null="true" type="boolean" />
 </composite-element>
</map>

3) Create a MapValueClass class:
public class MapValueClass {
 private ValueClass valueClass;
 @SuppressWarnings("unused")
 private boolean dummy;

 @SuppressWarnings("unused")
 private MapValueClass() {
    // Hibernate
 }

 public MapValueClass(ValueClass valueClass) {
  this.valueClass = valueClass;
 }

 public ValueClass getValueClass() {
  return valueClass;
 }
}
4) Change the mapping configuration in Owner class:
class Owner {
  Map<KeyClass, MapValueClass> mapping = new HashMap<KeyClass, MapValueClass>();

 public ValueClass getMappingValue(KeyClass keyClass) {
  return mapping.get(keyClass).getValueClass();
 }

 public void addMapping(KeyClass keyClass, ValueClass valueClass) {
  mapping.put(keyClass, new MapValueClass(valueClass));
 }
}

Now the owner.addMapping(keyObject, null) works fine.


> null in maps are handled inconsistently
> ---------------------------------------
>
>                 Key: HHH-772
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-772
>             Project: Hibernate Core
>          Issue Type: Improvement
>          Components: core
>            Reporter: Max Rydahl Andersen
>             Fix For: 3.1 beta 1
>
>
> regarding case 00004729.
> group.getUsers().put("something", null);
> Does not result in any insert.
> Inserting "something", null manually into the underlying table and
> when hibernate reads the map will have "something"->null in the map.

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