REST API Best practice How to accept list of parameter values as input

Question

We are launching a new REST API and I wanted some community input on best practices around how we should have input parameters formatted   Right now  our API is very JSON-centric  only returns JSON    The debate of whether we want need to return XML is a separate issue   As our API output is JSON centric  we have been going down a path where our inputs are a bit JSON centric and I ve been thinking that may be convenient for some but weird in general   For example  to get a few product details where multiple products can be pulled at once we currently have   http   our api com Product id   101404   7267261     Should we simplify this as   http   our api com Product id 101404 7267261   Or is having JSON input handy  More of a pain   We may want to accept both styles but does that flexibility actually cause more confusion and head aches  maintainability  documentation  etc     A more complex case is when we want to offer more complex inputs   For example  if we want to allow multiple filters on search   http   our api com Search term pumas amp filters   productType    Clothing   Bags    color    Black   Red      We don t necessarily want to put the filter types  e g  productType and color  as request names like this   http   our api com Search term pumas amp productType   Clothing   Bags   amp color   Black   Red     Because we wanted to group all filter input together   In the end  does this really matter   It may be likely that there are so many JSON utils out there that the input type just doesn t matter that much   I know our JavaScript clients making AJAX calls to the API may appreciate the JSON inputs to make their life easier

User · Answer

I will side with nategood s answer as it is complete and it seemed to have please your needs  Though  I would like to add a comment on identifying multiple  1 or more  resource that way   http   our api com Product 101404 7267261  In doing so  you   Complexify the clients by forcing them to interpret your response as an array  which to me is counter intuitive if I make the following request  http   our api com Product 101404  Create redundant APIs with one API for getting all products and the one above for getting 1 or many  Since you shouldn t show more than 1 page of details to a user for the sake of UX  I believe having more than 1 ID would be useless and purely used for filtering the products   It might not be that problematic  but you will either have to handle this yourself server side by returning a single entity  by verifying if your response contains one or more  or let clients manage it   Example  I want to order a book from Amazing  I know exactly which book it is and I see it in the listing when navigating for Horror books    10 000 amazing lines  0 amazing test The return of the amazing monster Let s duplicate amazing code The amazing beginning of the end   After selecting the second book  I am redirected to a page detailing the book part of a list   -------------------------------------------- Book  1 --------------------------------------------     Title  The return of the amazing monster     Summary      Pages      Publisher  --------------------------------------------   Or in a page giving me the full details of that book only   --------------------------------- The return of the amazing monster --------------------------------- Summary  Pages  Publisher  ---------------------------------   My Opinion  I would suggest using the ID in the path variable when unicity is guarantied when getting this resource s details  For example  the APIs below suggest multiple ways to get the details for a specific resource  assuming a product has a unique ID and a spec for that product has a unique name and you can navigate top down     products  id   products  id  specs  name    The moment you need more than 1 resource  I would suggest filtering from a larger collection  For the same example    products ids    Of course  this is my opinion as it is not imposed

User · Answer

You might want to check out RFC 6570   This URI Template spec shows many examples of how  urls can contain parameters

User · Answer

The standard way to pass a list of values as URL parameters is to repeat them   http   our api com Product id 101404 amp id 7267261  Most server code will interpret this as a list of values  although many have single value simplifications so you may have to go looking   Delimited values are also okay   If you are needing to send JSON to the server  I don t like seeing it in in the URL  which is a different format   In particular  URLs have a size limitation  in practice if not in theory    The way I have seen some do a complicated query RESTfully is in two steps    POST your query requirements  receiving back an ID  essentially creating a search criteria resource  GET the search  referencing the above ID optionally DELETE the query requirements if needed  but note that they requirements are available for reuse

User · Answer

First   I think you can do it 2 ways  http   our api com Product  lt id gt    if you just want one record  http   our api com Product        if you want all records  http   our api com Product  lt id1 gt   lt id2 gt   as James suggested can be an option since what comes after the Product tag is a parameter  Or the one I like most is   You can use the the Hypermedia as the engine of application state  HATEOAS  property of a RestFul WS and do a call http   our api com Product that should return the equivalent urls of http   our api com Product  lt id gt  and call them after this   Second  When you have to do queries on the url calls  I would suggest using HATEOAS again   1  Do a get call to http   our api com term pumas productType clothing color black  2  Do a get call to http   our api com term pumas productType clothing bags color black red  3   Using HATEOAS  Do a get call to  http   our api com term pumas productType  -  receive the urls all clothing possible urls -  call the ones you want  clothing and bags  -  receive the possible color urls -  call the ones you want

User · Answer

A Step Back  First and foremost  REST describes a URI as a universally unique ID   Far too many people get caught up on the structure of URIs and which URIs are more  restful  than others   This argument is as ludicrous as saying naming someone  Bob  is better than naming him  Joe      both names get the job of  identifying a person  done   A URI is nothing more than a universally unique name     So in REST s eyes arguing about whether  id   101404   7267261   is more restful than  id 101404 7267261 or  Product 101404 7267261 is somewhat futile     Now  having said that  many times how URIs are constructed can usually serve as a good indicator for other issues in a RESTful service   There are a couple of red flags in your URIs and question in general   Suggestions   Multiple URIs for the same resource and Content-Location     We may want to accept both styles but does that flexibility actually cause more confusion and head aches  maintainability  documentation  etc      URIs identify resources   Each resource should have one canonical URI   This does not mean that you can t have two URIs point to the same resource but there are well defined ways to go about doing it   If you do decide to use both the JSON and list based formats  or any other format  you need to decide which of these formats is the main canonical URI   All responses to other URIs that point to the same  resource  should include the Content-Location header   Sticking with the name analogy  having multiple URIs is like having nicknames for people   It is perfectly acceptable and often times quite handy  however if I m using a nickname I still probably want to know their full name     the  official  way to refer to that person   This way when someone mentions someone by their full name   Nichloas Telsa   I know they are talking about the same person I refer to as  Nick    Search  in your URI     A more complex case is when we want to offer more complex inputs  For example  if we want to allow multiple filters on search      A general rule of thumb of mine is  if your URI contains a verb  it may be an indication that something is off   URI s identify a resource  however they should not indicate what we re doing to that resource   That s the job of HTTP or in restful terms  our  uniform interface    To beat the name analogy dead  using a verb in a URI is like changing someone s name when you want to interact with them   If I m interacting with Bob  Bob s name doesn t become  BobHi  when I want to say Hi to him   Similarly  when we want to  search  Products  our URI structure shouldn t change from   Product      to   Search         Answering Your Initial Question   Regarding   101404   7267261   vs 101404 7267261  My suggestion here is to avoid the JSON syntax for simplicity s sake  i e  don t require your users do URL encoding when you don t really have to    It will make your API a tad more usable   Better yet  as others have recommended  go with the standard application x-www-form-urlencoded format as it will probably be most familiar to your end users  e g   id   101404 amp id   7267261    It may not be  pretty   but Pretty URIs does not necessary mean Usable URIs   However  to reiterate my initial point though  ultimately when speaking about REST  it doesn t matter   Don t dwell too heavily on it  Your complex search URI example can be solved in very much the same way as your product example   I would recommend going the application x-www-form-urlencoded format again as it is already a standard that many are familiar with   Also  I would recommend merging the two      Your URI      Search term pumas amp filters   productType    Clothing   Bags    color    Black   Red          Your URI after being URI encoded      Search term pumas amp filters  7B 22productType 22 3A 5B 22Clothing 22 2C 22Bags 22 5D 2C 22color 22 3A 5B 22Black 22 2C 22Red 22 5D 7D   Can be transformed to      Product term pumas amp productType   Clothing amp productType   Bags amp color   Black amp color   Red   Aside from avoiding the requirement of URL encoding and making things look a bit more standard  it now homogenizes the API a bit   The user knows that if they want to retrieve a Product or List of Products  both are considered a single  resource  in RESTful terms   they are interested in  Product     URIs

User · Answer

First case   A normal product lookup would look like this  http   our api com product 1  So Im thinking that best practice would be for you to do this  http   our api com Product 101404 7267261  Second Case  Search with querystring parameters - fine like this  I would be tempted to combine terms with AND and OR instead of using      PS This can be subjective  so do what you feel comfortable with   The reason for putting the data in the url is so the link can pasted on a site  shared between users  If this isnt an issue  by all means use a JSON  POST instead   EDIT  On reflection I think this approach suits an entity with a compound key  but not a query for multiple entities

[api] REST API Best practice: How to accept list of parameter values as input

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