Building Graphs with Business Objects

Patrick posted on Wednesday, February 20, 2008

Hi,

I have a challenge and was wondering how other solved (would solve) this with CSLA.NET

I have a graph structure of nodes and edges:

Every node can have multiple parents connected by an edge
And every node can have multiple children again connected by an edge
There is always one root node and it's not allowed to create cycles.

The prototype looks like this:

Tables:
Edges:
- NodeId (int)
- ChildNodeId (int)
Nodes:
- NodeId (int)
- NodeName (varchar())
- ...
Business objects:
- NodeList (EditableRootList)
-- Node (EditableChild)
--- EdgeList (EditableChildList)
---- Edge (EditableChild)

NodeList properties:

GetNodeList(int rootId): Get's all nodes and connected child edges through a recursive CTE. So we end up with a list of nodes each having a EdgeList with their children Edges (but otherwise unconnected to the actual children nodes).
RootNodeId: Property is set via GetNodeList(int rootId)

Node properties

Parents: gets nodes by asking the NodeList to return all Nodes which have the current node as a child
Children: gets all child nodes by looping through the Edges in its EdgeList and then using the ChildNodeId property of the Edge to look up the Node in NodeList

This works quite ok but the there are some difficulties with persisting the graph:

When calling NodeList.Update - NodeList cycles through the dirty Nodes and persists them with their corresponding EdgeList. This doesn't work for new inserted Nodes as all Nodes need to be inserted first before any new Edge is inserted (foreign key constraint)
The primary key of the Node is set after it's inserted. Now all parent and child edges need to get the new primary key before they can be persisted

Other point which this solution doesn't cover:

Node's don’t get notification when a child changes
There is the requirement for nodes to be able to summarize their children’s value for a certain property e.g. price.
There is the requirement for nodes to be able to inherit values from their parents e.g. color.

I was wondering what other approaches you might have taken or would take. Smile [:)]

Thanks a lot for your feedback,
Patrick

JoeFallon1 replied on Thursday, February 21, 2008

Patrick,

1. Your posts are always interesting.

2. One thing you might consider is creating a Use Case Controller object. This is a normal root level BO which contains the other BOs you are discussing.

When you Create a New controller BO you might pass it the rootID and then it instantiates all the other BOs as normal.

The advantage you now have is that the controller has access to all the Bos in side of it and can enforce rules and such.

In this case you can also call DataPortal_Update on the controller BO and then you can decide within its Update method how to do the save of your objects.

Since the standard Save of your root BO fails you can now step back and do something different.

e.g. Loop over a child collection and insert all new nodes first, then insert Edges.

Joe

Patrick replied on Thursday, February 21, 2008

JoeFallon1:
1. Your posts are always interesting.

Thank you

JoeFallon1:
2. One thing you might consider is creating a Use Case Controller object.

Yes very good idea.

Here are some more threads on the topic

I'm still looking forward to some more feedback :)

Thanks a lot,
Patrick