My understanding of REST is that anything that does not change state to the underlying system (e.g. query) should be a GET request. This also means that query parameters have to be put into the URI like so:
api/SomeMethod/Parameter1/{P1:double}/Parameter2/{P1:double}
or as query strings as discussed here:
REST API Best practice: How to accept list of parameter values as input
Sometimes the query may require a lengthy vector (number of x/y points). How do I overcome the length problem of URIs here? Should I just use a POST? Thanks.
If the vector really is big enough to start worrying about you should really consider moving it out of the query params and represent it as a RESTful resource.
For example, create a collection at:
api/Vector
Then your API clients can POST their large vectors and then in another request refer to it by a single id number.
This reduces the size of the query length drastically, abides by REST, and allows for these vectors to be easily reused. If you are worried about storage you can expire vectors after 30 minutes or longer.
Another option is to go down the JSON-LD road which is similar except you don‘t host the vectors. You just provide an #context object and API clients will host the vector on their own server and reference it to your API by URL in a query parameter.
Related
Say we have a rest api which aggregates data about a Person from other services. One of the Aggregator service routes is GET /person/(person id)/driverinfo which tells us whether the person is a licensed driver or not, license id, expiry date of license and the number of traffic violations. These data can be picked up by the Aggregator from one or more other services. This api will be used by a web page to show the "driver info" about a person. It will also be tested with automation.
Currently, the api gives 204 no content response for persons who never had a driving license. This is because one of the underlying apis gives a 204 for that scenario. So, it was decided that the Aggregator should do the same.
But, I believe that this is not a good response. Instead, we should return 200 with appropriate values for the fields. For example, licensed=false, licenseId = N.A. etc. when the underlying api gives a 204. I.e. the Aggregator should generate these fields and their values.
Which approach do you think is better and why ?
204 means something specific in HTTP; it says that the server found a representation of the requested resource, and that representation is zero bytes long.
Therefore, the real question is more like "Should we use a zero byte long message to describe a situation?". Maybe? If all of the fields in your message schema are optional, and we are trying to describe a representation that means that all of the fields are taking on their default values, then a zero byte array might be the right way to communicate that.
Within the context of HTTP specifically, the headers themselves are already significant in length (compared to zero), so I wouldn't expect there to be particularly compelling performance reasons to squeeze a signal down to zero length. For instance, if we were normally passing around application/json, I would expect that sending an empty object or array to be much more cost effective than sending nothing at all.
Variety of REST practises suggest (i.e. 1, 2, 3) to use plurals in your endpoints and the result is always a list of objects, unless it's filtered by a specific value, such as /users/123 Query parameters are used to filter the list, but still result in a list, nevertheless. I want to know if my case should 'abandon' those best practices.
Let's use cars for my example below.
I've got a database full of cars and each one has a BuildNumber ("Id"), but also a model and build year which combination is unique. If I then query for /cars/ and search for a specific model and year, for example /cars?model=golf&year=2018 I know, according to my previous sentence, my retrieve will always contain a single object, never multiple. My result, however, will still be a list, containing just one object, nevertheless.
In such case, what will be the best practise as the above would mean the object have to be extracted from the list, even though a single object could've been returned instead.
Stick to best practises and export a list
Make a second endpoind /car/ and use the query parameters ?model=golf&year=2018, which are primarily used for filtering in a list, and have the result be a single object, as the singular endpoint states
The reason that I'm asking this is simply for the cleanness of the action: I'm 100% sure my GET request will result in single object, but still have to perform actions to extract it from the list. These steps should've been unnecessary. Aside of that, In my case I don't know the unique identifier, so cars/123 for retrieving a specific car isn't an option. I know, however, filters that will result in one object and one specific object altogether. The additional steps simply feel redundant.
1: https://learn.microsoft.com/en-us/azure/architecture/best-practices/api-design
2: https://blog.mwaysolutions.com/2014/06/05/10-best-practices-for-better-restful-api/
3: https://medium.com/hashmapinc/rest-good-practices-for-api-design-881439796dc9
As you've specifically asked for best practices in regards to REST:
REST doesn't care how you specify your URIs or that semantically meaningful tokens are used inside the URI at all. Further, a client should never expect a certain URI to return a certain type but instead rely on content-type negotiation to tell the server all of the capabilities the client supports.
You should furthermore not think of REST in terms of object orientation but more in terms of affordance and statemachines where a client get served every information needed in order to make an educated decision on what to do next.
The best sample to give here is probably to take a close look at the Web and how it's done for HTML pages. How can you filter for a specific car and how it will be presented to you? The same concepts that are used in the Web also apply to REST as both use the same interaction model. In regards to your car sample, the API should initially return some control-structures that teach a client how a request needs to be formed and what options could be filtered for. In HTML this is done via forms. For non-HTML based REST APIs dedicated media-types should be defined that translate the same approach to non-HTML structures. On sending the request to the server, your client would include all of the supported media-types it supports in an Accept HTTP header, which informs the server about the capabilities of the client. Media-types are just human-readable specification on how to process payloads of such types. Such specifications may include hints on type information a link relation might return. In order to gain wide-usage of media-types they should be defined as generic as possible. Instead of defining a media-type specific for a car, which is possible, it probably would be more convenient to use an existing or define a new general data-container format (similar to HTML).
All of the steps mentioned here should help you to design and implement an API that is free to evolve without having to risk to break clients, that furthermore is also scalable and minimizes interoperability concerns.
Unfortunately your question targets something totally different IMO, something more related to RPC. You basically invoke a generic method via HTTP on an endpoint, similar like SOAP, RMI or CORBA work. Whether you respect the semantics of HTTP operations or not is only of sub-interest here. Even if you'd reached level 3 of the Richardson Maturity Model (RMM) it does not mean that you are compliant to REST. Your client might still break if the server changes anything within the response. The RMM further doesn't even consider media-types at all, hence I consider it as rather useless.
However, regardless if you use a (true) REST or RPC/CRUD client, if retrieving single items is your preference instead of feeding them into a collection you should consider to include the URI of the items of interest instead of its data directly into the collection, as Evert also has suggested. While most people seem to be concerned on server performance and round-trip-times, it actually is very elegant in terms of caching. Further certain link-relation names such as prefetch may inform the client that it may fetch the targets payload early as it is highly possible that it's content will be requested next. Through caching a request might not even have to be triggered or sent to the server for processing, which is probably the best performance gain you can achieve.
1) If you use query like cars/where... - use CARS
2) If you whant CAR - make method GetCarById
You might not get a perfect answer to this, because all are going to be a bit subjective and often in a different way.
My general thought about this is that every item in my system will have its own unique url, for example /cars/1234. That case is always singular.
But this specific item might appear as a member in collections and search results. When /cars/1234 apears in these, they will always appear as a list with 1 item (or 0 or more depending on the query).
I feel that this is ultimately the most predictable.
In my case though, if a car appears as a member of a search or colletion, it's 'true url' will still be displayed.
I am wondering if it is possible to adhere to REST principles when creating what will essentially amount to a BI tool.
In my scenario I have high data volume with 100,000's of IDs (frankly more than this but for the sake of this example let's go with that.). These are presented in a traditional table that allows for necessary features when accessing large data sets such as pagination. The user also has the ability to filter by one, or many of these ID's to drill down the data set as they see fit.
It is theoretically possible that the user would want to filter on 100 of the ID's, thus rendering a GET URI incredibly long. Which as I understand it would kind of break the resource identification principle of a REST API. Not to mention could potentially bump into the character limit in a GET request for certain browsers since the ID's may be quite long. Normally I would just use a POST since I can add all of the applied filters in the body and generate a where clause on the server.
Since a POST in a REST API is supposed to
Create a new entry in the collection.
By definition it would appear, at least to me that generating a complex query for something like this would mean that a REST API is not possible. Or does this perhaps mean that I am approaching the solution wrong (totally plausible).
It would seem that in my scenario using a GET simply isn't possible due to the potential length of the parameters. Thus I am forced to use a POST. Though using a POST as I am seems to violate REST style, which isn't the end of the world. I mostly just wanted to double check that I am not missing something and there is not a solution using a GET.
To follow the resources principle, make a search like resource. POST your ids in a body wto this endpoint and it will prepare a list of results for you and redirect you to searchresults/{id}.
See for example: https://gooroo.io/GoorooTHINK/Article/16583/HTTP-Patterns---Bouncer/25829#.W3aBsugzaUk
It seems to me that REST has clean and clear semantics for basic CRUD and for listing resources, but I've seen no discussion of how to handle large lists of resources. It doesn't scale to dump an entire database table over the network in a resource-oriented architecture (imagine a customer table with a million customers!), especially if you only need a few items. So it seems that some semantics should exist to filter, map and reduce a list of resources on the server-side.
So, do you know any tried and true ways to do the following kinds of requests in REST:
1) Retrieve just the count of the resources?
I could imagine doing something like GET /api/customer?result=count
Is that how it's usually done?
I could also imagine modifying the URL (/api/count/customer or /api/customer/count, for example), but that seems to either break the continuity of the resource paths or inflict an ugly hack on the expected ID field.
2) Filter the results on the server-side?
I could imagine using query parameters for this, in a context-specific way (such as GET /api/customer?country=US&state=TX).
It seems tricky to do it in a flexible way, especially if you need to join other tables (for example, get customers who purchased in the last 6 months).
I could imagine using the HTTP OPTIONS method to return a JSON string specifying possible filters and their possible values.
Has anyone tried this sort of thing?
If so, how complex did you get (for example, retrieving the items purchased year-to-date by female customers between 18 and 45 years old in Massachussetts, etc.)?
3) Mapping to just get a limited set of fields or to add fields from joined tables?
4) More complicated reductions than count (such as average, sum, etc.)?
EDIT: To clarify, I'm interested in how the request is formulated rather than how to implement it on the server-side.
I think the answer to your question is OData! OData is a generic protocol for querying and interacting with information. OData is based on REST but extends the semantics to include programatic elemements similar to SQL.
OData is not always URL-based only as it use JSON payloads for some scenarios. But it is a standard (OASIS) so it well structured and supported by many APIs.
A few general links:
https://en.wikipedia.org/wiki/Open_Data_Protocol
http://www.odata.org/
The most common ways of handling large data sets in GET requests are (afaict) :
1) Pagination. The request would be something like GET /api/customer?country=US&state=TX&firstResult=0&maxResults=50. This way the client has the freedom to choose the size of the data chunk he needs (this is often useful for UI-based clients).
2) Exposing a size service, so that the client gets to know how large the data set is before actually requesting it. The service would be something like
GET /api/customer/size?country=US&state=TX
Obviously the two can (and imho should) be used together, so that when/if a client (be it mobile or web or whatever) waints to fill its UI with content, he can choose what's the best data chunk size based also on the size of whole data set (e.g. to avoid creating 100 pages for the user to navigate).
I have already gone through this
How best to design a REST API with multiple filters?
This does help when you have say 3 or 4 filtering criteria and you can accomodate that in the query String.
However let's take this example
You want to get call details about 20 telephone numbers, between a certain startdate and enddate.
Now I do agree ideally one should be advised to make individual queries for each number and then on the client side collate all data.
However for certain Live systems that would mean 20 rounds of queries on the switches or cdr databases. That is 20 request-response cycles plus the client having to collate and order them again based on time. While in the database level it would have been a simple single query that can return an ordered data and transformed back into a REST xml response that the client can embed on their system.
If we are to use GET the query string will get really confusing and has a limit as well.
Any suggestions to get around this issue.
Of course we can send a POST request with an xml having all numbers in it but that is against REST Get principles.
In case of GET use OData queries. For example when your start and end dates represented as numbers (unix time) URI could look like:
GET http://operatorcalls.com/Calls/Details?$filter=Date le 1342699200 and Date gt 1342526400
What you seem to be missing is an important concept of REST, caching. This can be done, as an example, in the browser, for a single client. Or it can be done as a shared cache between all the clients and the live production system (whatever it may be). Thus reducing queries against a live production system, or in your example, actual switches.
You should really take some time to read Fieldings thesis, and understand that REST is an architectural style.
I found a solution here Handling multiple parameters in a URI (RESTfully) in Java
but not quite happy with it.
So in effect we will end up using /cdr?numbers=number1,number2,number3 ...
However not too pleased with it as there is a limit to Query String in the url and also doesn't really seem to be an elegant solution. Anyone found any solution to this in their own implementation?
Basically not using POST for this kind of Fetch requests and also not using cumbresome and lengthy Query Strings.
We are using Jersey but also open to using CXF or Spring REST