Object Graph with child collection needing 'Replace'

[Chicagoan2016]

We have an object graph, where 'Client' is the main parent object and has a child 'Lineitems' collection.
In one use case, we have to 'replace' the LineItems. By replace, I mean delete and add a new lineItems collection.

The way it works in the UI, we get an instance of our Client object. During interaction with the UI, users can update the entire object graph, including the child LineItems collection. We have provided a dropdown where users have the option to 'replace' the lineItems.
In this 'replace' instance the rest of the object graph will still be the usual update. Only the LineItems need to be deleted and replaced with a new collection.
Any suggestions please?

Kind Regards

[hurcane]

So the UI has a reference to the original Client instance and it has a reference to a separate LineItems collection (e.g. "new line items")? Can we presume that the instances within "new line items" are all "IsNew = True"?

To stick with conventions, I would use the Clear method on the LineItems property of the Client instance and then call AddRange on the same property, passing the "new line items" instance. This will cause all of the previously existing instances to be changed to deleted status. When you save Client, the model DAL code should delete the existing instances and insert the new instances.

[Chicagoan2016]

Thank you @hurcane ,
It gets even better, This code is years old and I didn't describe the use case accurately.
So the child object is actually Cart, with its child collection lineItems where each of the lineItem has lineItemdetails collection.

So the UI has a reference to the original Client instance and it has a reference to a separate LineItems collection (e.g. "new line items")? Can we presume that the instances within "new line items" are all "IsNew = True"?

This only applies to Fetch operation of the whole object graph so is IsNew will be false.

[hurcane]

I have no understanding of your complete use case because you stated, "only applies to fetch operation," and you stated, "interaction with the UI". There is no interaction with the UI during a fetch operation.

My general advice:

• When needing to interact with collections externally (class A needs to manipulate class B's collection, work with the items of the collection. Replacing a collection should always be clearing the existing items and adding the new entities.
• Think about potential database effects of the operation. If it is intended to cause data changes (deletes and inserts), use the collection manipulation operations (remove, add, insert, clear, etc.) to make changes.
• Think about potential issues with other code holding onto a reference of the original collection. If the replace operation is happening on the client, you should manipulate the collection contents, not replace the collection instance.
• If you need to do the replacement during an atomic Fetch operation, then you might consider replacing collection instances with a new collection instance. I can think of an instance where we load a list of default values from a data source, but then the system has configuration parameters to control that the default values should come from a different source. With all of that logic within the same Fetch method, then it would be fine to replace the default collection instance with the alternate collection instance because no other code could possibly yet have a reference to the collection being replaced.

[Chicagoan2016]

@hurcane Thank you Sir.

When needing to interact with collections externally (class A needs to manipulate class B's collection, work with the items of the collection. Replacing a collection should always be clearing the existing items and adding the new entities.

I am going to follow this route. This is an older code base. Does the default implementation of 'DataPortal_Update()'
iterates over the 'DeletedList'?

Kind Regards

[hurcane]

There is no default implementation of that method. But all of the examples in the book and in the repo samples process the deleted items collection first, clear it, then process new and updated items.

[Chicagoan2016]

@hurcane I got it working, I had to use the 'reverse' for loop on the DeletedList.
Out of curiosity, would love to see some sample code about deleted items here.

[Chicagoan2016]

@hurcane I hate to sound contrary, but we do have a default implementation : ).
I removed my own implementation and it still works or I am getting tired.
Kind Regards

[hurcane]

Are you using the child data portal to manage your list? That does have a default implementation. There is another method for async that follows the same process.

I must admit that I don't have any personal experience with using the child data portal. We use object factories, and the child data portal is not a part of that.