topic Re: Query folding handlers reference in Developer

Query folding handlers reference

xli629b — Tue, 07 Feb 2023 15:47:29 GMT

What are all of the query folding handlers (OnTake, OnSkip, OnSelectRows etc.)? I did not find a reference listing all of them.

Which ones are the most important to implement? (I know GetType and GetRows are the mandatory Table.View handlers.)
Or alternatively, what should we consider when deciding which ones to implement?
- Especially in regards to supporting Direct Query? Or Incremental Refresh?

I believe there were past discussions about this in the Issues section of microsoft/DataConnectors on GitHub, which may have answered the above questions. However, this content seems to have been deleted.

Re: Query folding handlers reference

jaweher899 — Wed, 08 Feb 2023 10:57:34 GMT

Query folding handlers are a set of functions in PowerBI's data connector API that allow you to control how data is transferred from a data source to PowerBI. The most commonly used query folding handlers include:

OnTake: controls how many rows are returned from the data source
OnSkip: controls how many rows are skipped before the data is returned
OnSort: controls how the data is sorted before being returned
OnFilter: controls how the data is filtered before being returned
OnColumns: controls which columns are returned from the data source
OnGroup: controls how the data is grouped before being returned
OnSelectRows: combines OnTake, OnSkip, OnSort, OnFilter, OnColumns, and OnGroup into one function call.

The most important handlers to implement depend on the specific use case and the requirements of your data source. However, to support Direct Query, the OnSelectRows and OnGetRows handlers are important. To support Incremental Refresh, the OnGetRows and OnGetSchema handlers are important.

When deciding which handlers to implement, consider the following factors:

The capabilities of your data source: not all data sources support all handlers
The performance and scalability requirements: some handlers can be more resource-intensive than others
The data privacy and security requirements: some handlers may expose sensitive data
The functionality required by PowerBI: some handlers are required to enable certain PowerBI features.

It's recommended to consult the PowerBI documentation and reach out to the PowerBI support team for more information on query folding handlers and best practices for implementation.

Re: Query folding handlers reference

xli629b — Fri, 10 Feb 2023 20:21:12 GMT

FYI:

I found these links (which have been removed from the current documentation without being replaced):
https://github.com/microsoft/DataConnectors/blob/00b30f78143873b0bff60335ed53069288aad6db/docs/table-view.md (in an older version of DataConnectors repo)

https://web.archive.org/web/20200920164149/https://github.com/microsoft/DataConnectors/issues/246