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  • Why does ArcGIS Server Feature Service does these specific POST requests 'under the hood'?

I wrote a (Dutch) blog post to explain how you can download data using the ArcGIS REST API, in particular how to do multiple requests when the number of features you want exceeds the server limit.

@arnovananrooij pointed out to me that the Esri ArcGIS Server Feature Service reader does the job very efficiently. As I wrote the post also for readers that do not use FME Desktop, I wondered which requests FME does 'under the hood'.

As it turns out, FME first does one POST request to get all objectIds (the server limit is not a problem for this request):

Endpoint:
https://www.gdngeoservices.nl/arcgis/rest/services/blk/lks_blk_rd/MapServer/1/query?f=json

Body:
where=1=1&outSR=28992&returnIdsOnly=True

Next, FME does multiple POST requests to get all the data. For every new request the objectIds in the `where` query parameter are updated in order to get the next batch of 1.000 features:

Endpoint:
https://www.gdngeoservices.nl/arcgis/rest/services/blk/lks_blk_rd/MapServer/1/query?f=json

Body:
objectIds=18005606,18005621,18005632,18005638,18005657,18005664,18005832,18005838,...,17911868,17911893,17911904&outFields=ADMINISTRATOR_NM,GEOMETRY.LEN,GEOMETRY.AREA,NEN3610_ID_SOIL_LOCATION,STATUS_OORD,STATUSVER,WBB_DOSSIER_DBK,NEN3610_ID_SOIL_MANAGEMENT,SIKB_ID,VERVOLG_WBB,LOCATIECODE_BEVOEGD_GEZAG,TYPE_CD,BIS_LOCCODE

The value of the `objectIds` query parameter actually contains 1.000 (!) objectIds for every request (but the last one).

I am curious to know: Why isn't FME doing multiple GET requests like this one?

https://www.gdngeoservices.nl/arcgis/rest/services/blk/lks_blk_rd/MapServer/1/query?f=json&where=WBB_DOSSIER_DBK>=18005606&outFields=*

Just to be clear: I'm loving the fact that FME does this job so smoothly and 'll keep on using the ArcGIS Server feature service from now on!

But I'm trying to understand how the ArcGIS REST API works internally and what the best way is to query the API when you don't use FME. I was thinking it may have something to do with performance, but I would like to know for sure.

You'll want to look at the parameter resultOffset and resultRecordCount. They use pagination so it skips the first x number of results and only returns the next x based on the parameters I've listed above. FME server also does it this way as well.

You'll want to look at the parameter resultOffset and resultRecordCount. They use pagination so it skips the first x number of results and only returns the next x based on the parameters I've listed above. FME server also does it this way as well.

For this particular service pagination is disabled, so the resultOffset and resultRecordCount query parameters cannot be used:

https://www.gdngeoservices.nl/arcgis/rest/services/blk/lks_blk_rd/MapServer/1/query?where=1=1&outFields=*&resultOffset=1000&recordCount=1000&f=geojson

This is why I was pleasantly surprised that the ArcGIS Server Feature Service reader in this case does support response paging.

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