Hi guys,
Started on an existing project at a new job and they use nhibernate.
They want to implement versioning into the system which I'm having a
bit of a nightmare trying to find a good way to do this.
The idea is that users can create "ammendment packages" to various
entities and after a review process the elements in a package will be
applied to the live system at which point a new "system version" is
created. The complexity comes in because the user is able to run the
system at various versions as business rules state that versions of
the system are still able to be used for up to 2 years after.
I have come up with a workable database schema that should be able to
hold the version data etc however the one thing that is doing my head
in is figuring out how to version relationships or do it in such a way
that we dont have to introduce extra queries everywhere in the app.
For example take class A
public class A : BaseObject
{
public virtual string Title {get;set;}
public virtual string Description {get;set;}
public virtual B B {get;set;}
}
public class B: BaseObject
{
public virtual string Title {get;set;}
public virtual string Description {get;set;}
}
In the database table A (model class A) has a one-to-many foreign key
to table B (model class B).
The way I've headed down so far is that for every entity/table that
needs auditing we have a separate table "{name}Audit" that contains
all of the same fields as {name} and a few more about various meta
data we need to store about a version.
When a user asks for a specific version we query the version table and
return a {name}Audit object that inherits from the {name} entity and
then convert it to a new {name} object by just newing up an instance
of {name} and assigning the common properties across but not doing
anything with the associations)
The problem comes in with how we map the associations so that we only
retrieve the associations as they were at a particular version and not
how they currently are now. I have had a look at Envers and initially
it looked quite good but unfortunately our model works differently
where not every save must be audited as a new row, for instance an
ammendment can go through several updates before being accepted (and
we don't care about the inbetween audits of the ammendment itself),
also it doesn't currently support collections of components.
So ultimately (if the pile of drivel about made no sense) I'm looking
for some advice on how to handle associations in the context of a
version of an entity without having to only ever return ids of
associations and constantly ask for what that association was a X
explicitly.
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