Read with an after hook implementation fails from Fiori Elements

[rpanneel]

Hello CAP Enthusiasts,

During my local testing I ran into a strange issue using the Fiori Elements front-end.

I've added a virtual spotsAvalaible property to my entity Courses. This virtual property I'm going to fill in the after hook of the READ of the Courses:

srv.after('READ', 'Courses', (courses, req) => {
            // problem from fiori: couses has counted object --> $count
            return courses
                .map(async course => {
                    // Get the reservations for this course
                    const reservations = await cds.transaction(req).run(
                        SELECT.from(Reservations).where({course_ID: course.ID})
                    )
                    // Caluclate spots taken
                    const spotsTaken = reservations.reduce((total, reservation) => total + reservation.quantity, 0)
                    course.spotsAvailable = course.spots - spotsTaken
                })
        })

This works when I use postman and do a get on the courses. (http://localhost:4004/training/Courses)

{
"@odata.context": "$metadata#Courses",
"@odata.metadataEtag": "W/\"BmT9sdj4fnWqz4BxxDN0o+XSNGD5CW69Y8wbhe1uRYk=\"",
"value": [
{
"ID": "ee0b3d38-729d-4237-a7fe-b922f753e87e",
"modifiedAt": null,
"createdAt": "2020-01-18T18:45:57Z",
"createdBy": "anonymous",
"modifiedBy": null,
"title": "Some course",
"days": 1,
"spots": 15,
"courseType": "Technical",
"spotsAvailable": 15,
"trainer_ID": "880331ae-ae41-4a46-b49b-b7a3cbd049b0"
}
]
}

But when using the Fiori elements front-end the hook crashes with following error. For the following request in the $batch:
GET Courses?$count=true&$select=ID,days,spots,title,trainer_ID&$expand=trainer($select=ID,name)&$skip=0&$top=30 HTTP/1.1

`
POST /training/$batch

READ Courses {
'$count': 'true',
'$select': 'ID,days,spots,title,trainer_ID',
'$expand': 'trainer($select=ID,name)',
'$skip': '0',
'$top': '30'
}
READ Courses {
'$count': 'true',
'$select': 'ID,days,spots,title,trainer_ID',
'$expand': 'trainer($select=ID,name)',
'$skip': '0',
'$top': '30'
}
[2020-01-19T14:45:18.101Z | ERROR | 1221510]: Cannot read property 'run' of undefined
TypeError: Cannot read property 'run' of undefined
at C:\repo\CAP\training-reservations\node_modules@sap\cds-services\lib\connect\Transaction.js:84:27
`

When debugging i notice that the after-hook gets called a second time, but this time the courses-parameter is filled with a counted object:

[{counted: 1}]

Is there a way to solve this?

Thanks!

Kind regards,

Robin