API Resource Listing Best Practice#

This section provides best practices when using API GET requests when listing resources. The best practices for the use of a number of API request parameters and parameter values are examined.

For further details on API parameters, refer to the API Guide.

The list of API request parameters for resource listing are:

Parameter	Description	Value	Default
`skip`	The list resource offset as a number.		0
`limit`	The maximum number of resources returned. The maximum value is 2000. If the `Range` request header is used, it will override this parameter.	1-2000	50
`count`	Specify if the number of resources should be counted. If false, the `pagination` object in the response shows the `total` as 0, so no total is calculated and the API performance is improved.	true, false	true
`order_by`	The summary attribute field to sort on.		First summary attribute
`direction`	The direction of the summary attribute field sort (asc:ascending, desc: descending).	asc, desc	asc
`summary`	Only summary data is returned in the data object.	true, false	true
`policy_name`	Return a model form schema where the Field Display Policy with name [FDP name] is applied to it. Use `policy` with the parameters `schema` and `format=json`.	[FDP name]
`cached`	System will respond with resource information where the data was obtained from cache. (Functionally only applicable to device models and data models).	true, false	true

Consider the following comments and best practices for the parameters below:

count: The value of count=true is very expensive in terms of performance, and more so as the size of the resource grows. The first count query of for example a 36 000 Data Number Inventory resource can take as long as a minute to return a response. However, subsequent calls should decrease in execution time.

The value count=true should only be used if it is unavoidable. An alternative is to iterate over pages (limit=200) until the request returns less than 200 instances, or to simply paginate until no more resources are returned.
order_by: no performance change if another summary attribute is specified.
direction: no performance change if either values asc or desc are used.
policy_name: the parameter is used by the GUI for display purposes. Timing data shows that the initial call with this parameters takes longer thank subsequent ones, possibly because of cache priming after a restart. Subsequent calls shows the execution time is on par with requests that do not include the parameter.
summary: depending on the data required by the request, time can be saved if the value summary=true, so that only the summary data is returned.
limit: execution time and memory consumption is impacted if the limit value is large.

To summarize, the recommended parameter values for an optimal API list request (GET) are:

cached=true
summary=true
count=false
policy_name not used

Example results with various parameter values (36 000 Data Number Inventory resource):

count:true, skip:0, policy_name:, limit:200, summary:false in 6.51744103432 s
count:true, skip:0, policy_name:, limit:200, summary:true in 5.6118888855 s
count:false, skip:0, policy_name:, limit:200, summary:false in 1.55350899696 s
count:false, skip:0, policy_name:policy_name=HcsDNInventoryDatFDP, limit:200,
     summary:true in 5.17663216591 s
count:false, skip:0, policy_name:, limit:200, summary:true in 1.09510588646 s