Missing originalValues for collection of primitive types

[mahish]

Hi,
I wanted to discuss an issue I encountered while working with a collection of primitive types. In my case, when an entity has a DataProperty with dp.isScalar === false, the state of the entity correctly changes to "Modified" when the content of the collection has been changed. However, I haven't noticed any effect of this state change in the originalValues map, as described in the originalValues documentation or here

While investigating this issue, I came across this code snippet in the repository

breeze-client/src/default-property-interceptor.ts

Lines 106 to 108 in b450f98

	if (!property.isScalar) {
	throw new Error("Nonscalar data properties are readonly - items may be added or removed but the collection may not be changed.");
	}

First, I'm not recieving this error in my application. Second, the error message is not 100% clear to me so I would like to confirm my understanding here. Does "items may be added or removed but the collection may not be changed" mean that I can change its content but Im not able to change the collection itself => the reference (memory location)?

• if true, is the support for originalValues pending and waiting for implementation in case of collection of primitive types?
• if false, is there no plan to support it at all and I should handle it in my application in whatever way I need to?

I would appreciate any clarification on this matter. Thanks a lot.

[mahish]

I also noticed a change of collection's content does not trigger propertyChange action.

[steveschmitt]

Hi @mahish, the message "items may be added or removed but the collection may not be changed" means what you said: that you can change the content of the collection but not the collection itself. In other words, you should not attempt to replace the collection with a new array.

Part of the reason for this is that Breeze collections are not simple arrays; they are "smart" collections that manage the relationships between entities when they are added or removed from collections.

It seems that that updating the originalValuesMap is not part of the behavior when adding or removing elements from a collection of scalar values. This behavior could be added to Breeze. The difficulty might be when an array element is changed in-place.

[mahish]

@steveschmitt Hi and thank you for the reply. Yeah, I see. Thank you for clarification. I totally understand replacement of the collection itself is not allowed. I was interested in whether a collection's elements has changed (adding, removing). I found out there is _origValues on the collection itself so I use it for my use case alongside the aggregated public entityAspect.originalValues for other data types. Workaround but good enough for now.

I understand the difficulty you mean but I still see a value of adding support for originalValues when manipulating with collections without support for tracking changes of individual collection's elements (eg. observableArray[0] = 'foo'). Quickly checked other libraries with observable arrays and neither of them support such case I believe?

[mahish]

Recently, I've worked with ObservableArray https://github.com/Breeze/breeze-client/blob/b450f982c78e107a798143344d082f8682465138/src/observable-array.ts . I'm listening arrayChanged event on every primitive collection to automatically check for changes on the collection. I can imagine this event might be used internally by Breeze to trigger official entityChanged event via PropertyChange entity action. This action is not triggered by change of collection at the moment. The result would be much more consistent usage of Breeze regarding tracking of changes.

Is there anything I can do about it? Would you welcome PR from me as a starting point? Thanks.

[steveschmitt]

Yes, a PR would be great. Thank you.

[steveschmitt]

@mahish Have you made any progress on this?

[mahish]

@steveschmitt Hi, we are weeks from important release. Part of the release is my set of helpers handling changes of the collection type. I should be able to transform these helpers to the PR during October.