java interop and clojure macros

Question

I am facing the following problem. I am trying to construct a function (macro) on top of the hapi-fhir api

function (macro) on topo of hapi-fhir api
  (defmacro search-patient-resource
  "This macro searches for a specified resource based on the
  Patient Id"
  [res id json?]
  (let [tmp (symbol res)]
    (if json?
         `(. (. (. (. (. (. @restful-client search) (forResource ~(symbol res))) encodedJson) (where (. (. ~(resolve tmp)  PATIENT)
                    (hasId (str ~id))))) (returnBundle Bundle)) execute)
    )))

This macros works when a do something like

(let [id 10465]
 (search-patient-resource "Observation" id true))
=>#object[ca.uhn.fhir.model.dstu2.resource.Bundle 0x520a3cc9 "Bundle[id=Bundle/9ca62ae1-82af-488f-a166-5b014f45886e]"]

but not when I do

 (let [id 10465 res "Observation"]
 (search-patient-resource "Observation" id true))
=> CompilerException java.lang.NullPointerException, compiling:(apycare_emrspp/hapi_fhir_helper.clj:122:1)

Of course I cannot write (symbol ~res) because then the reader evaluates (symbol "Observation") at compile time and I get

 CompilerException java.lang.IllegalArgumentException: No matching method found: forResource for class ca.uhn.fhir.rest.client.GenericCl
 ient$SearchInternal, compiling:(apycare_emrspp/hapi_fhir_helper.clj:122:1)

Also neither

   (resolve (symbol ~res)

nor

   (resolve ~(symbol re)

work.

The original java code looks like this

 FhirContext ctx = FhirContext.forDstu2();
 String serverBase = "fhirtest.uhn.ca/baseDstu2";
 IGenericClient client = ctx.newRestfulGenericClient(serverBase); 
 Bundle results = client .search() .forResource(Observation.class) 
.where(Observation.PATIENT.hasId("1234")) 
.returnBundle(ca.uhn.fhir.model.dstu2.resource.Bundle.class) 
.execute();

What I do is attempt to Make the call with

 client
 .search() 
 .forResource(another-resource.class) 
 .where(another-resource.PATIENT.hasId(another-id)) 
 .returnBundle(ca.uhn.fhir.model.dstu2.resource.Bundle.class) 
 .execute();

I don't understand why you are writing this as a macro. It seems you could write it as a function and avoid the problem. — Alan Thompson
– Alan Thompson, Commented Mar 25, 2017 at 20:56
How so? I tried to write it as a function, but how to pass arbirtery method name without the clojure compiler complaining? For instanse lets say I want to pass [Observation] in order to call (. resource Observation). If I pass it as a string then (. resource (symbol "Observation)), will not work unless is expanded from a list through macros. — Heefoo
– Heefoo, Commented Mar 26, 2017 at 5:24
Passing a string and Id as arguments, the string has to be transformed into the java method with the same name and be called at. This works but not when I predefine the string. That is when I pass "Observation" I have the (forResource ~(symbol res)) be transofmed to (forResource Observation) , but if I do (def st "Observation") then I get (forResource st). — Heefoo
– Heefoo, Commented Mar 26, 2017 at 10:19
I tried to create a function to do create the symbol from the string but it doesnt work — Heefoo
– Heefoo, Commented Mar 26, 2017 at 10:22

Heefoo · Accepted Answer · 2017-04-14 15:26:22Z

Ok. The problem I was facing was due too I was neglecting to import the appropriate symbols when calling the code from a defferent namespace. when res = "Resource" in the code above then

 ~(symbol "Resource")

Could not be preperty resolved if I had not first add

(import '(ca.uhn.fhir.model.dstu2.resource.Resource))

In the namespace were the macro was called. This made the code working in most cases. To make it fully functional I had to change

 ~(symbol "Resource")

to (identity ~(symbol "Resource"))

This is the proper translation of java's

Resource.class to clojure code

At the end the macro took the form:

 (defmacro search-patient-resource
 "This macro searches for a specified resource based on the
  Patient Id"
 [res id json?]
 (let [tmp (symbol res)]
   (if json?
     `(. (. (. (. (. (. @restful-client search)
                     (forResource (identity ~(symbol res))))
                  encodedJson)
               (where
                 (.
                  (. ~(resolve tmp)  PATIENT)
                  (hasId (~str ~id)))))
            (returnBundle Bundle))
         execute)
     `(. (. (. (. (. @restful-client search)
                  (forResource (identity ~(symbol res))))
               (where (. (. ~(symbol res)
                            PATIENT)
                         (hasId (str ~id)))))
            (returnBundle Bundle))
         execute))))

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