What are best practices for REST nested resources

Question

As far as I can tell each individual resource should have only one canonical path   So in the following example what would good URL patterns be   Take for an example a rest representation of Companies  In this hypothetical example  each company owns 0 or more departments and each department owns 0 or more employees    A department can t exist without an associated company    An employee can t exist without an associated department   Now I d find the natural representation of the resource patterns to be      companies A collection of companies - Accepts put for a new company  Get for the entire collection   companies  companyId  An individual company  Accepts GET  PUT and DELETE  companies  companyId  departments Accepts POST for a new item   Creates a department within the company    companies  companyId  departments  departmentId    companies  companyId  departments  departmentId  employees  companies  companyId  departments  departmentId  employees  empId    Given the constraints  in each of the sections  I feel that this makes sense if a bit deeply nested   However  my difficulty comes if I want to list  GET  all employees across all companies   The resource pattern for that would most closely map to  employees  The collection of all employees   Does that mean that I should have  employees  empId  also because if so then there are two URI s to get the same resource   Or maybe the entire schema should be flattened but that would mean that employees are a nested top-level object   At a basic level  employees  company  companyId  amp department  deptId  returns the exact same view of employees as the most deeply nested pattern   What s the best practice for URL patterns where resources are owned by other resources but should be query-able separately

User · Answer

I ve read all of the above answers but it seems like they have no common strategy  I found a good article about best practices in Design API from Microsoft Documents  I think you should refer      In more complex systems  it can be tempting to provide URIs that   enable a client to navigate through several levels of relationships    such as  customers 1 orders 99 products  However  this level of   complexity can be difficult to maintain and is inflexible if the   relationships between resources change in the future  Instead  try to   keep URIs relatively simple  Once an application has a reference to a   resource  it should be possible to use this reference to find items   related to that resource  The preceding query can be replaced with the   URI  customers 1 orders to find all the orders for customer 1  and   then  orders 99 products to find the products in this order          Tip      Avoid requiring resource URIs more complex than   collection item collection

User · Answer

What you have done is correct   In general there can be many URIs to the same resource - there are no rules that say you shouldn t do that    And generally  you may need to access items directly or as a subset of something else - so your structure makes sense to me   Just because employees are accessible under department   company  companyid  department  departmentid  employees  Doesn t mean they can t be accessible under company too    company  companyid  employees  Which would return employees for that company   It depends on what is needed by your consuming client - that is what you should be designing for    But I would hope that all URLs handlers use the same backing code to satisfy the requests so that you aren t duplicating code

User · Answer

I ve moved what I ve done from the question to an answer where more people are likely to see it    What I ve done is to have the creation endpoints at the nested endpoint  The canonical endpoint for modifying or querying an item is not at the nested resource   So in this example  just listing the endpoints that change a resource    POST  companies  creates a new company returns a link to the created company  POST  companies  companyId  departments when a department is put creates the new department returns a link to  departments  departmentId  PUT  departments  departmentId  modifies a department POST  departments  deparmentId  employees creates a new employee returns a link to  employees  employeeId    So there are root level resources for each of the collections  However the create is in the owning object

User · Answer

Rails provides a solution to this  shallow nesting   I think this is a good because when you deal directly with a known resource  there s no need to use nested routes  as has been discussed in other answers here

User · Answer

I ve tried both design strategies - nested and non-nested endpoints  I ve found that    if the nested resource has a primary key and you don t have its parent primary key  the nested structure requires you to get it  even though the system doesn t actually require it  nested endpoints typically require redundant endpoints  In other words  you will more often than not  need the additional  employees endpoint so you can get a list of employees across departments  If you have  employees  what exactly does   companies departments employees buy you  nesting endpoints don t evolve as nicely  E g  you might not need to search for employees now but you might later and if you have a nested structure  you have no choice but to add another endpoint  With a non-nested design  you just add more parameters  which is simpler  sometimes a resource could have multiple types of parents  Resulting in multiple endpoints all returning the same resource  redundant endpoints makes the docs harder to write and also makes the api harder to learn     In short  the non-nested design seems to allow a more flexible and simpler endpoint schema

User · Answer

I disagree with this kind of path  GET  companies  companyId  departments   If you want to get departments  I think it s better to use a  departments resource  GET  departments companyId 123   I suppose you have a companies table and a departments table then classes to map them in the programming language you use  I also assume that departments could be attached to other entities than companies  so a  departments resource is straightforward  it s convenient to have resources mapped to tables and also you don t need as many endpoints since you can reuse  GET  departments companyId 123   for any kind of search  for instance   GET  departments name xxx GET  departments companyId 123 amp name xxx etc    If you want to create a department  the   POST  departments   resource should be used and the request body should contain the company ID  if the department can be linked to only one company

User · Answer

How your URLs look have nothing to do with REST  Anything goes  It actually is an  implementation detail   So just like how you name your variables  All they have to be is unique and durable    Don t waste too much time on this  just make a choice and stick to it be consistent  For example if you go with hierarchies then you do it for all your resources  If you go with query parameters   etc just like naming conventions in your code   Why so   As far as I know a  RESTful  API is to be browsable  you know    Hypermedia as the Engine of Application State    therefore an API client does not care about what your URLs are like as long as they re valid  there s no SEO  no human that needs to read those  friendly urls   except may be for debugging      How nice understandable a URL is in a REST API is only interesting to you as the API developer  not the API client  as would the name of a variable in your code be   The most important thing is that your API client know how to interpret your media type   For example it knows that     your media type has a links property that lists available related links  Each link is identified by a relationship  just like browsers know that link rel  stylesheet   means its a style sheet or rel favico is a link to a favicon     and it knowns what those relationships mean   companies  mean a list of companies  search  means a templated url for doing a search on a list of resource   departments  means departments of the current resource     Below is an example HTTP exchange  bodies are in yaml since it s easier to write    Request  GET   HTTP 1 1 Host  api acme io Accept  text yaml  text acme-mediatype yaml   Response  a list of links to main resource  companies  people  whatever      HTTP 1 1 200 OK Date  Tue  05 Apr 2016 15 04 00 GMT Last-Modified  Tue  05 Apr 2016 00 00 00 GMT Content-Type  text acme-mediatype yaml    body  this is your API s entrypoint  like a homepage    links      could be some random path https   api acme local modskmklmkdsml     the only thing the API client cares about is the key  or rel   companies    companies  https   api acme local companies   people  https   api acme local people   Request  link to companies  using previous response s body links companies   GET  companies HTTP 1 1 Host  api acme local Accept  text yaml  text acme-mediatype yaml   Response  a partial list of companies  under items   the resource contains related links  like link to get the next couple of companies  body links next  an other  templated  link to search  body links search   HTTP 1 1 200 OK Date  Tue  05 Apr 2016 15 06 00 GMT Last-Modified  Tue  05 Apr 2016 00 00 00 GMT Content-Type  text acme-mediatype yaml    body  representation of a list of companies links      link to the next page   next  https   api acme local companies page 2     templated link for search   search  https   api acme local companies query  query     you could provide available actions related to this resource actions    add      href  https   api acme local companies     method  POST items    - name  company1     links        self  https   api acme local companies 8er13eo         and here is the link to departments         again the client only cares about the key department       department  https   api acme local companies 8er13eo departments   - name  company2     links        self  https   api acme local companies 9r13d4l         or could be in some other location          department  https   api2 acme local departments company 8er13eo   So as you see if you go the links relations way how you structure the path part of your URLs does t have any value to your API client  And if your are communicating the structure of your URLs to your client as documentation  then your are not doing REST  or at least not Level 3 as per  Richardson s maturity model

[rest] What are best practices for REST nested resources?

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