Convert expression result list to comma-separated string

Ref: beda-software#33

app/operations/utils.py

@@ -93,8 +93,11 @@ def resolve_string_template(i, env, encode_result=False):
     for exp in exprs:
         data = fhirpath({}, exp["var"][2:-2], env)
         if len(data) > 0:
-            # TODO: pass comma separated values for x-fhir-query
-            vs[exp["var"]] = quote(str(data[0])) if encode_result else str(data[0])
+            # NOTE: http://build.fhir.org/ig/HL7/sdc/expressions.html#x-fhir-query-enhancements
+            # If the expression resolves to a collection of more than one value,
+            # the substitution will be a list of comma-separated values (i.e. behaving as 'or').
+            search_str = ",".join(data)
+            vs[exp["var"]] = quote(search_str) if encode_result else search_str
         else:
             vs[exp["var"]] = ""
     res = i