I'm having a bear of a time with this and any suggestions would be greatly appreciated.
I have a bi-directional many-to-many association mapping between two entities (FlashCard and Tag) that is currently successfully represented as a java.util.Set. I'd like to change the collection type to a java.util.Map.
Here's an excerpt of the working mappings using Set
Code:
<hibernate-mapping>
<class name="FlashCard" table="FLASHCARD">
<id name="flashCardId" type="int" column="FLASHCARD_ID">
<meta attribute="scope-set">public</meta>
<generator class="native" />
</id>
<property name="question" type="string">
<meta attribute="use-in-tostring">true</meta>
<column name="QUESTION" not-null="true" unique="true" />
</property>
<set name="tags" table="FLASHCARD_TAG">
<meta attribute="field-description">Tags for this FlashCard</meta>
<key column="FLASHCARD_ID" />
<many-to-many class="Tag"
column="TAG_ID" />
</set>
</class>
<class name="Tag" table="TAG">
<id name="tagId" type="int" column="TAG_ID">
<meta attribute="scope-set">public</meta>
<generator class="native" />
</id>
<property name="name" type="string">
<meta attribute="use-in-tostring">true</meta>
<column name="NAME" not-null="true" unique="true" />
</property>
<set name="flashcards" table="FLASHCARD_TAG" inverse="true">
<meta attribute="field-description">FlashCards for this Tag</meta>
<key column="TAG_ID" />
<many-to-many class="FlashCard"
column="FLASHCARD_ID" />
</set>
</class>
</hibernate-mapping>
Ok, so like I said this is working but I'd like to change the collection to type java.util.Map.
I played with the mappings quite a bit and was finally able to get the following to partially work.
Code:
<hibernate-mapping>
<class name="FlashCard" table="FLASHCARD">
<id name="flashCardId" type="int" column="FLASHCARD_ID">
<meta attribute="scope-set">public</meta>
<generator class="native" />
</id>
<property name="question" type="string">
<meta attribute="use-in-tostring">true</meta>
<column name="QUESTION" not-null="true" unique="true" />
</property>
<map name="tags" cascade="all" table="FLASHCARD_TAG">
<meta attribute="field-description">Tags for this FlashCard</meta>
<key column="FLASHCARD_ID" not-null="true" />
<map-key type="String" column="NAME" formula="NAME"/>
<many-to-many column="TAG_ID" class="Tag"/>
</map>
</class>
<class name="Tag" table="TAG">
<id name="tagId" type="int" column="TAG_ID">
<meta attribute="scope-set">public</meta>
<generator class="native" />
</id>
<property name="name" type="string">
<meta attribute="use-in-tostring">true</meta>
<column name="NAME" not-null="true" unique="true" />
</property>
<map name="flashcards" inverse="true" cascade="all" table="FLASHCARD_TAG">
<meta attribute="field-description">FlashCards for this Tag</meta>
<key column="TAG_ID" not-null="true" />
<map-key type="String" column="QUESTION" formula="QUESTION" />
<many-to-many column="FLASHCARD_ID" class="FlashCard"/>
</map>
</class>
</hibernate-mapping>
When I say these mappings "partially work" I mean that I was able use these mapping to generate the database tables and the entity classes. The entity classes did indeed include a collection of type java.util.Map. This all looked find and compiles without errors.
However, when I run the code I get runtime errors from hibernate as follows:
org.hibernate.MappingException: Could not determine type for: String, at table: FLASHCARD_TAG, for columns: [org.hibernate.mapping.Formula( NAME )]
at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:306)
The Hibernate documentation shows an example of a bi-directional many-to-many association but it uses a Set. Here's a
linkto the docs.
Summary
- There are two entities: FlashCard and Tag
- The FlashCard entity has a collection of references to other entities of type Tag
- The Tag entity has a collection of references to other entities of type FlashCard
- This is a many-to-many, bi-directional association
- FLASHCARD_TAG is the association table
- The association is currently represented as a java.util.Set which according to the Hibernate documentation is the most commonly used collection mapping.
- I want to use java.util.Map instead of the java.util.Set
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