Every available object in the ws module is written up as a resource. The resource class defines the properties that are exposed and the setters that are available. The class also defines the representations and what goes in them (ref vs default vs full, see below for more on representations)
See documentation about resources and their URIs here: REST Web Service Resources
You can also see some generated URI documentation on the "Help" page that the module puts into its Administration page section.
There is a "catalog" uri that lists off the currently available resources in the installation (including module-provided resources):
There are some objects that are not defined or do not make sense apart from another parent object. These we refer to as subresources. Examples are PersonNames, PersonAddresses, ConceptNames, etc. You can act on subresources under the parent url:
A subresource can have only one parent. If it feels like you want to add something to two parents, perhaps that should be a top-level resource. E.g. "encounters" should not be a subresource of "patient" + "location" (answering questions of "all encounters of a patient" and "all encounters at a location"). Instead, these should be queries on the encounter resource: /ws/rest/v1/encounter?patient=349234-2349234 and /ws/rest/v1/encounter?location=3423482-34923-23
Because there are so many options when creating REST urls, we have laid out a set of conventions that all REST developers should follow. This will keep our web service api looking neat and uniform across all different types of objects and modules.
- For resource,
- GET /ws/rest/resource?q=query = search
- GET /ws/rest/resource/uuid = retrieve
- POST /ws/rest/resource = create
- Request body contains data to persist (not in request params)
- POST /ws/rest/resource/uuid = partial update of the resource
- Request body contains just the fields to update (not in request params)
- PUT = replace value of entire object (we don't use this yet)
- DELETE /ws/rest/resource/uuid = void for data, retire for metadata
- DELETE /ws/rest/resource/uuid?purge=true = purge (aka delete from the database entirely)
- Do not put verbs into the URL. Represent this idea with sub-resources.
- For example, instead of addNameToPerson we POST to /ws/rest/person/uuid/names
- Are prefixed with /ws/rest/ due to servlet forwarding in openmrs
- The URL should be written in all-lowercase ASCII letters
- No special characters (e.g. no spaces or underscores)
- Hyphens are ok if absolutely necessary
- No extensions allowed (acceptHeader will be used to specify json or xml content. All json for release 1.0)
- Sub-resources (i.e. things like personname or patientidentifier which belong to a parent resource) should have their URIs inside the URI of their parent (like /ws/rest/person/uuid/names/nameuuid)
- Domain objects that are separately managed get their own URI. (e.g. /ws/rest/enrollment/uuid instead of /ws/rest/program/uuid/enrollments/uuid)
- Hide (aka don't expose) "helper" classes as much as possible (e.g. web service clients should never see ConceptSet, etc)
- Resource names should usually be the same as the domain objects they represent, but they may differ if the domain object name is confusing.
- For example org.openmrs.PatientProgram is /ws/rest/enrollment
When saving or editing a property on a "Concept" object, the conceptDatatype property can be simply the uuid. In addition, for most metadata, the "name" is unique across all active metadata, so that can also be used in place of the uuid when saving as well (POST or PUT).
The objects returned by web service calls are variable in their properties. In general there are three different representations that exist: ref, default, full. It is possible for modules to provide more representations for their objects. (TODO: document what method to call to get the available reps)
To change between representations, use the "v" query parameter:
...?v=default is invalid. Simply leave that parameter off.
Web service calls that return lists of objects will put those objects into the "ref" representation.
When an object is a child resource on another object (e.g. conceptDatatype property on Concept object) the full ConceptDatatype object is not returned by default. Instead a "ref" kind of class with String properties for
links, and a
display fills the concept.conceptDatatype property. The ref looks like this:
To fetch the full ConceptDatatype data, a second call to the links.self uri:
http:/../openmrs/ws/rest/conceptdatatype/8d4a4488-c2cc-11de-8d13-0010c6dffd0f is needed.
This representation is returned for objects when there is no "v=" parameter given. Most properties will be included and "refs" of some subobjects will also be listed.
The full representation is meant when to be used when subsequent calls are not desired or you need some uncommonly needed properties (like audit info).
Nearly every method in the OpenMRS API requires authentication, therefore, some every method in the webservices module needs to have an authenticated user in order to work.
There is a filter defined on the module that intercepts all calls and authenticates the given request.
Currently only BASIC authentication is supported. Header arguments values of ___ and ___ are expected.
Alternatively, a session token can be used. GET /openmrs/ws/rest/session with the BASIC credentials will return the current token value. This token should be passed with all subsequent calls as a cookie named jsessionid=token.
A resource can have any number of "links" in the links attribute. Generally these will be links to other representations (see above) but could be to other types of relationships between objects: things like "parent", etc.
A "ref" representation will contain a link to "self" that is the default rep. A "default" rep will have a link to "full" that is the same object expect with all properties included.
The full representation of object contains a property called auditInfo. You can find the creator, changer, and voider/retirer information here.
If the object is data and so is voidable, you will additionally see:
If the object is metadata and so is retirable, you will see:
The "retired" and "voided" boolean properties are on the ref/default/full representations. The ref rep will only contain the property if the object if isVoided/isRetired returns true.
The OpenMRS API will change over time and this will necessitate the rest representations and urls to be modified as well. The first release of the module will be version "v1". The entire rest api is versioned with this same number:
If/when (hopefully never) we make a major change to the entire rest setup, we will change this to v2. (e.g. change from json to kson)
Each resource can also refer to different underlying api object versions. Each object declares a resourceVersion property that specifies which version of the API it is required to work in. This works similar to an @since annotation.
The actual visible version of the '''module''' will be incremented independenty from openmrs AND from the version of the rest api.
There were discussions about using the Media-Type header instead of a number in the uri. However, looking at a lot of major players in the api space, we decided to go with a global api version in the uri.
(available with OpenMRS v1.8.1 or higher due to the Spring Framework 3.0.5 requirement)
The module also adds an ETag to response headers when presenting resources to clients. ETags have been implemented in shallow-mode (i.e. they save client bandwidth, but not server-side processing). As described here, as a client application you may want to look at ETag when making REST calls.
From the wikipedia article:
In typical usage, when a URL is retrieved the web server will return the resource along with its corresponding ETag value, which is placed in an HTTP "ETag" field:
The client may then decide to cache the resource, along with its ETag. Later, if the client wants to retrieve the same URL again, it will send its previously saved copy of the ETag along with the request in a "If-None-Match" field.
On this subsequent request, the server may now compare the client's ETag with the ETag for the current version of the resource. If the ETag values match, meaning that the resource has not changed, then the server may send back a very short response with an HTTP 304 Not Modified status. The 304 status tells the client that its cached version is still good and that it should use that.
However, if the ETag values do not match, meaning the resource has likely changed, then a full response including the resource's content is returned, just as if ETags were not being used. In this case the client may decide to replace its previously cached version with the newly returned resource and the new ETag.
Example using curl:
RESPONSE HEADER IS:
RESPONSE HEADER IS:
We see that both the ETag are same and hence the client knows that the response would be the same and can save bandwidth.
After some days, if Darius's records have not been updated then, the client can send the ETag and check for modifications:
From the 304 Not Modified, we know that the records are the same and the client doesn't have to get the data again.