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gancw1's avatar
gancw1
Resolver II
1 year ago
Solved

Canvas LMS pagingation problem

I am trying to retrieve the gradebook from Canvas LMS. I asked ChatGPT to generate the code, and the code successfully retrieved the first page. However, the code which includes pagination gives this...
Need Help
Anonymous's avatar
Anonymous
Not applicable
1 year ago

Hi,gancw1 .I am glad to help you.

According to the error message

“We were unable to convert a binary type value to a record type”, the problem may be in the GetNextPageUrl function!
You may need to check your data types!

Perhaps the Value.Metadata Function can help you:

Value.Metadata - Power BI Online Training


below is my suggestions:
Checking the Return Value of Web.Contents: Make sure that the response returned by Web.Contents is in the format you expect. You can check the contents of Web.Contents by outputting its results while debugging. For example:

Response = Web.Contents(url, [
    Headers = [
        Authorization = "Bearer " & ApiToken
    ]
]),
ResponseJson = try Json.Document(Response) otherwise null

2. Try to modify your original code (please make a backup of your original code before modification to avoid data loss)

GetAllPages = (url as text) as table =>
let
    InitialPage = GetPage(url),
    FetchPages = List.Generate(
        () => [CurrentUrl = url, CurrentPage = InitialPage],
        each [CurrentUrl] <> null,
        each [
            Response = Web.Contents([CurrentUrl]),
            ResponseHeaders = Value.Metadata(Response),
            CurrentUrl = GetNextPageUrl(ResponseHeaders),
            CurrentPage = if [CurrentUrl] <> null then GetPage([CurrentUrl]) else null
        ],
        each [CurrentPage]
    ),
    AllPages = Table.Combine(FetchPages)
in
    AllPages

The modified code adds the following section:

 ResponseHeaders = Value.Metadata(Response),

Convert the result of Web.Contents to a record type and pass it to the GetNextPageUrl function.

I hope my suggestions give you good ideas, if you have any more questions, please clarify in a follow-up reply.
Best Regards,
Carson Jian,
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

gancw1's avatar
gancw1
Resolver II
1 year ago
Hi Carson,
First and foremost, thank you for your assistance in troubleshooting the code and suggesting the necessary changes. I truly appreciate your support.
 
I've also been working on the troubleshooting and reached the same conclusion that the code passes the body instead of the header metadata to GetNextPageUrl(). I went ahead and made the change, which indeed fixed the initial error. However, the code only returns the first page and is unable to navigate to the next page.
 
Upon examining the header returned, I noticed that it does not include the 'Link' field which contains the url for the next page
 

Interestingly, when I checked the header using Postman, I observed that the header contains 32 fields, and the Link field is present there.
 

 
Any insights or suggestions on why the returned header does not have the Link field and how to get it to return the full header ? Thanks again for your continued support!

Thanks
Gan