CPS-1391: Impact analysis on CPS core API's due to changes of CPS-341

Overview

In CPS-341 the POST operation to create a new data node was updated to bring support for a multiple data trees under a single anchor (or a single root "/" node). In order to achieve this, the JSON data containing multiple data trees are parsed into a Collection of data nodes.

This collection of data nodes is then converted to a List of Fragment Entities which is stored into the database.

From the above description it is clear that when a GET operation will be performed on an anchor containing multiple data trees to retrieve one or all data trees, it will be returned as a List of Fragment Entities as opposed to a single Fragment Entity being returned earlier.

It is to be noted here that the methods used for GET operation are not limited to Get a Node API and are reused in other API's as well. All the APIS discussed below internally call the getFragmentWithoutDescendantsByXpath()to retrieve the data trees. This epic covers the impact on all the API's due to the above mentioned changes in CPS core.

A common task across the API's is to maintain backwards compatibility as well.

References

Open Issues and Decisions

S. No	API	Issue	Decisions	Final Outcome
1	Get a Node	Get operation should return all the data trees under the root when xpath is set to "/"	25 Nov 2022 after discussion with Toine Siebelink it was decided to give priority to the GET operation first, before heading for other API's. A discussion with the architects is to be scheduled to discuss upon the following points: should a separate end point be created which returns all the data trees under the root node impact of ongoing versioning issue with CPS on the above point and backwards compatibility
2	CPS Core API's under this link	The remaining CPS core API's might require modification with respect to decisions made for the GET operation. Based upon the decisions for the above Issue this table will be updated from time to time.	25 Nov 2022 in the meeting it was decided to focus on GET operation first as the work on remaining API's seemed different from the one for the GET API. Also it was decided to first have a discussion with the architects regarding the GET API and then have a separate discussion for the remaining API;s.

List of impacted API's

Operation	API	Issues	Possible Solution
GET	Get a Node	should return all the data trees when xpath is set to root(/) currently returns only the first data tree	modify the existing code for Get a Node API so it returns a List of fragment entities this impacts other API's as well which make use of the Get operation a separate API can be developed to return all the data trees, similar to Get all anchors and Get one anchor API in CPS
PUT	Replace a node with descendants Replace list content	currently when the replace action is performed with xpath set to root, it will first perform a get operation internally to retrieve the first data tree and then execute the replace operation but with support for multiple data trees under root when the API is called with xpath set to "/", it will first get all the data trees once all the data trees are returned the PUT operation will be performed if xpath is set to "/" and the number of data trees on which the replace operation is being performed is less than the total number of data trees the operation of retrieving all the data trees does not seems to be feasible	when xpath is set to "/" the replace operation can return an error message the user can specify the data tree for which Replace operation is to be performed, but if the number of data trees on which replace operation is to be performed is significantly high
DELETE	Delete a datanode		when delete operation is performed with xpath set to root all the data trees must be deleted
PATCH	Update node leaves	when the API is called and xpath is set to "/", first the get operation is executed internally to retrieve all the data trees once all the data trees are returned in a List the API proceeds to perform the Patch operation if xpath is set to "/" and the number of data trees on which the patch operation is being performed is less than the total number of data trees the operation of retrieving all the data trees is not feasible	when xpath is set to "/" the patch operation can return an error message the user can specify the data tree for which patch operation is to be performed, but the drawback of this approach is, when the number of data trees on which patch operation is to be performed is significantly big
POST	Add list element to existing list	when the API is called and xpath is set to "/", first the get operation is executed internally to retrieve all the data trees once all the data trees are returned in a List the API proceeds to perform the Post operation retrieving all the data trees does not seems feasible with xpath set to root, given the scenario where new list element is getting added to few of the data trees	with xpath set to root, the API should return an error message the POST operation can be performed on particular data trees by specifying their respective xpaths.

The existing GET operation

//Returns single fragment entity
default FragmentEntity findFirstRootByDataspaceAndAnchor(@NonNull DataspaceEntity dataspaceEntity,
                                                             @NonNull AnchorEntity anchorEntity) {
        return findRootsByDataspaceAndAnchor(dataspaceEntity.getId(), anchorEntity.getId()).stream().findFirst()
            .orElseThrow(() -> new DataNodeNotFoundException(dataspaceEntity.getName(), anchorEntity.getName()));

The updated GET operation is as follows to retrieve all the data trees under root

//Now returns a List of Fragment entities
default List<FragmentEntity> findFirstRootByDataspaceAndAnchor(@NonNull DataspaceEntity dataspaceEntity,
                                                                   @NonNull AnchorEntity anchorEntity) {
        final List<FragmentEntity> fragmentEntities = new ArrayList<>(findRootsByDataspaceAndAnchor(dataspaceEntity.getId(), anchorEntity.getId()));
        if (! fragmentEntities.isEmpty()){
            return  fragmentEntities;
        } else{
            throw new DataNodeNotFoundException(dataspaceEntity.getName(), anchorEntity.getName());
        }
    }

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