REST API: Offset parameter larger then resultset size causes weird behavior

[Matthias Vandermaesen]

Hi,

I accidentally generated this API call which returns a weird, inconsistent resultset:

http://www.europeana.eu/api/v2/search.json?query=who:(Copy+after+Jan+van+Eyck)&qf=TYPE:IMAGE&rows=20&start=20&wskey=api2demo

Response:

{

apikey: "api2demo",

action: "search.json",

success: true,

requestNumber: 999,

itemsCount: 0,

totalResults: 3

}

The problem here is that totalResults says that there are 3 items, but no "items" property is present.  If you app relies on a check if totalResults > 0 before proceeding to parse the "items" property, then you are going to run into breaking errors.

The cause of this bug is the start=20 parameter.  In this case: I'm trying to fetch items starting from an offset position (20) which is larger then the totalResults parameter (3)

Any application should of course check itemCount as well because that shows the number of items returned in the current call.

I would like to suggest an improvement:  Always return the "items" property but return an empty array of items if itemscount = 0.  That way, the API avoids breaking dependent applications because a property is suddenly not present anymore.

With regards,

Matthias Vandermaesen

Digitale dataconservator | Vlaamse Kunstcollectie VZW

matthias.v...@vlaamsekunstcollectie.be

http://www.vlaamsekunstcollectie.be 

Abrahamstraat 13

9000 Gent

M +32 (0)486 75 56 23

T +32 (0)9 225 49 34

[Gordea Sergiu]

Well …

 

I see no inconsistence here, with regard to the request and response…

I don’t think that the API should be responsible for preventing inconsistencies in the search queries …. Especially because you have many possible combinations.

 

It is a common/standard practice in JSON serialization to not serialize null properties. So … how would the empty array help client to understand that actually start is greater than total results?

As the query is technically correct and the response is also consistent with the query, I would say that it is not appropriate to respond with an error message.

 

What might be useful from my perspective is to add a “range” in the response, for which [-1 , -1] would mean “out of range”, if the goal is to better understand the meaning of the results.

 

BR,

 

Sergiu

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[Vladimir Alexiev]

Agree with Sergiu, you can easily check whether an "items" key is present before accessing it