Hi,

I am attempting to map a database column to two properties in a hibernate object (see example below). One of those properties is "read-only".

I would like a foreign key ID column to map to both a property for the ID and a property for the object represented in the foreign key table. That way I can query either the ID or the actual object itself. I will only be setting the ID.

See "property_id" column below in the example. I have marked the mapped property as "insert=false" and "update=false" so you cannot set these values in code.

There never is a value for the "property" object. Is this unsupported or am I missing something obvious?

Thanks,

Brent

Just add



to your mapping.

Since the many-to-one is marked false for insert and update this works fine.

Just as an exercise you can remove the false for insert and update with the additional property you'll get an error up on creation of the SessionFactory.

HTH
Ernst

Hmm, maybe I don't understand. If I do what you suggested, I have the following mapping file:



This does not allow me to retrieve the actual UTProperty object that is mapped through the foreign key: "property_id".

Two separate properties (propertyId, property_id) are mapped to the same column (property_id). But I still cannot access the property which represents my UTProperty object. It is always null.

Any suggestions?

Thanks,

Brent

What's the point of having this two lines?


I'd say you have to remove one of them.

HTH
Ernst

OK, so now I understand what you were getting at. I already had a line like you were referring to in your first post. So we you said "add", this line was really a duplicate. Unfortunately, it still does not work.

Which takes us back to the original problem. The value for "property", which is of type UTProperty, is always null. I am using hibernate 2.1.4.

When I do have what I think is the correct XML:



My class looks like this:



The value for "property" which is of type "UTProperty" is always null.

Thanks,

Brent

What happens when you remove the property 'propertyId' mapped to the FK? Can you then retrieve instances of UTDocPropertyValue containing an instance of UTProperty ok?

Why do you need to do this (map a property to the FK of an associated object)? What are you trying to achieve?

If a UTDocPropertyValue has an associated UTProperty then can't you refer to it's id property through the UTProperty instead? There is no need to keep a separate copy in UTDocPropertyValue; it's redundant.

Kevin

Yes, if I remove the "propertyId" property, it returns the actual instantiated version of UTDocPropertyValue.

I was trying to get this working so I could "get" and "set" just the id value, but there were times that I might want to query (not update) the actual UTDocPropertyValue object.

I could obviously load this myself, but I was just seeing if hibernate would do this.

Brent

Get and set the FK in an associated object? But why would you want to do this - Hibernate takes care of this for you through the mapping.

If you want to change the id of an associated object, for example in a 1-1 between A and B, you assign an instance of B to A by calling setB(b) on A (and if the relationship is bidirectional then also call setA(a) on B to maintain the relationship in both directions)

Hibernate takes care of managing the FKs between rows in the tables - this is not something that you should be concerned with or try to manipulate yourself - it is transparent to your code.

Kevin

No, I want to get and set the ID directly in my primary object.

Here is the document table:

document_id
name
property_id

My use case allows me to know the property_id through an external mechanism.

I can accomplish managing this value through the getters and setters.

Document.setPropertyId(Integer )
Integer Document.getPropertyId()

But in a separate use case, I also wanted to be able to be able to query the actual property object as well, as opposed to having to load it.

UTProperty UTDocument.getProperty()

So I will always be "setting" the ID directly, but in some cases I may want to "get" just the ID, in other cases I may want to "get" the whole physical corresponding object.

Like I said, I can manually load the corresponding object, but I thought hibernate would do both for me.

I've some mappings where I have the same requirement (id property and association). I just noticed, that my hbm.xml files do have allways the association first and then the property. So maybe the following works:


HTH
Ernst

I know this is an old thread, but I need to solve the exact same problem. Is there a solution to this issues (specially in Hibernate 3)?

Thanks in advance.

You could use the formula attribute on the many-to-one to achieve this. Here is something that works for me.
DocumentRelations has a many-to-one relation with Document class. In the DocumentRelations object, I can set the documentID and be able to retrieve docRelations.getDocument() and get the same document object. My mapping files are

Document.hbm.xml


and DocRelations.hbm.xml is


Checkout the formula on the many-to-one in the DocumentRElations.hbm.xml. Doing a Testcase like


passes just fine.

Thanks for the response, rajasaur. I will try iur your solution.