I've got a model that has been working for versioned objects.
//workspace - users container of versioned items
public class Workspace : IEntity<Guid>
{
public virtual Id { get; protected set; }
public virtual string WorkspaceName { get; set; }
public virtual ICollection<VersionedEntity> VersionableObjects {
get; protected set; }
public virtual User User { get; set; }
public Workspace()
{
this.Id = GuidCombGenerator.Generate();
this.VersionableObjects = new HashSet<VersionedEntity>()
}
}
//base class for all versioned items, allows quick UI display of all
versioned objects, etc.
public abstract class VersionedEntity : IEntity<Guid>
{
public virtual Guid Id { get; protected set; }
public virtual Guid EntityKey { get; protected set; }
public virtual byte[] ConcurrencyVersion { get; protected set; }
public virtual int Version { get; set; }
public virtual string Name { get; set; }
public virtual string Description { get; set }
protected VersionedEntity()
{
this.Id = GuidCombGenerator.Generate();
this.EntityKey = GuidCombGenerator.Generate();
}
//etc...
}
public class RuleContainer: VersionedEntity
{
public IList<Rule> RuleList { get; protected set; }
}
public class Rule : VersionedEntity
{
}
I'm using Table-per-subclass so that for every derived class I've got
an additional table.
Id is the surrogate key and primary key and is generated client side
EntityKey is the object id, or the same id that this entity will have
for it's lifetime
ConcurrencyVersion is used for NHiberate to detect entity changes
A new version is a cloned entity with the version value incremented,
I'm leaving out the fields for status tracking, etc.
Now here is problem I'm trying to find the best solution.
I need to have non-versioned hierarchies.
E.g. a relationship map between objects that follows the entity key
and not the id key, e.g. a weak key reference.
For a Workspace, I map via one-to-many to VersionedEntitiy so that I'm
going to call a strong key reference through a table called
VersionedEntitiesToParentWorkspace
The workspace contains strong key references, but now I need to be
able to track a weak hierarchy/relationship between entities.
Example:
Container A, v1 => Rule A, v1
Container A, v1 => Rule B, v1
Container A, v1 => Rule C, v1
Rule A, v1 => Rule D, v1
Rule B, v1 => Rule A, v1
Rule C, v1 => NULL
Now this relationship needs to be based upon the weak keys, not the strong key.
Hence, only the workspace is used to get the actual version.
There could exist Rule B, version 2, but only in a specific workspace,
I need to reference version 1. But have a data model that allows me to
show all versions of Rule b, version 1 through (n)
Now it's possible that a later version change, Rule B, version 3 now
calls a different set, e.g. a different relationship/hierarchy.
All of this implies that I'm needing a versioned parent/child
relationship per node/entity
VersionedEntity => VersionedHierarchy => VersionedEntity(s)
Or maybe there is a better solution?
One other solution I'm thinking of is the traditional Node/Tree
implementation where it's another table: Nodes
I use Id as a surrogate key, and then use another column as the Entity
Key and have all the Ancestors/Decendants mapped in another table, and
just join to my VersionedEntityTable to get all nodes in that
relationship and have the users be able to choose what version they
want, and save that structure to their workspace.
In an earlier iteration I used composite keys, and the complexity was
very high, switching to a surrogate key, made NHibernate behave
nicely.
The relationships I also had were based upon strong key relationships
on the children objects, but user requirements are that they be weak
key referenced, and the workspace gives the unique versioned item. I'm
trying to avoid a composite key of WorkspaceId, VersionedParentId,
VersionedChildId or something like that.
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