Use SELECT COUNT to get number of patients

src/main/java/org/highmed/numportal/service/AqlService.java

@@ -250,19 +250,19 @@ public long getAqlSize(SlimAqlDto aql, String userId) {
 
     validateQuery(aql.getQuery());
 
-    Set<String> ehrIds;
+    int numberOfPatients;
     try {
-      ehrIds =
-          ehrBaseService.retrieveEligiblePatientIds(Aql.builder().query(aql.getQuery()).build());
+      numberOfPatients =
+          ehrBaseService.retrieveNumberOfPatients(Aql.builder().query(aql.getQuery()).build());
     } catch (AqlParseException e) {
       throw new BadRequestException(AqlParseException.class, e.getLocalizedMessage(), e.getMessage());
     }
 
-    if (ehrIds.size() < privacyProperties.getMinHits()) {
+    if (numberOfPatients < privacyProperties.getMinHits()) {
       log.warn(TOO_FEW_MATCHES_RESULTS_WITHHELD_FOR_PRIVACY_REASONS);
       throw new PrivacyException(AqlService.class, TOO_FEW_MATCHES_RESULTS_WITHHELD_FOR_PRIVACY_REASONS);
     }
-    return ehrIds.size();
+    return numberOfPatients;
   }
 
   public List<AqlCategory> getAqlCategories() {

src/main/java/org/highmed/numportal/service/ehrbase/EhrBaseService.java

@@ -11,6 +11,7 @@
 import org.apache.commons.lang3.StringUtils;
 import org.ehrbase.openehr.sdk.aql.dto.AqlQuery;
 import org.ehrbase.openehr.sdk.aql.dto.containment.ContainmentClassExpression;
+import org.ehrbase.openehr.sdk.aql.dto.operand.CountDistinctAggregateFunction;
 import org.ehrbase.openehr.sdk.aql.dto.operand.IdentifiedPath;
 import org.ehrbase.openehr.sdk.aql.dto.path.AqlObjectPath;
 import org.ehrbase.openehr.sdk.aql.dto.select.SelectExpression;
@@ -118,6 +119,51 @@ public Set<String> retrieveEligiblePatientIds(String query) {
     }
   }
 
+  /**
+   * Retrieves the number of patients for the given aql
+   *
+   * @param aql The aql to retrieve patient ids for
+   * @return number of patients
+   * @throws WrongStatusCodeException in case if a malformed aql
+   */
+  public int retrieveNumberOfPatients(Aql aql) {
+    return retrieveNumberOfPatients(aql.getQuery());
+  }
+
+  public int retrieveNumberOfPatients(String query) {
+    log.debug("EhrBase retrieve number of patients for query: {} ", query);
+    AqlQuery dto = AqlQueryParser.parse(query);
+    SelectExpression selectExpression = new SelectExpression();
+
+    var count = new CountDistinctAggregateFunction();
+    selectExpression.setColumnExpression(count);
+
+    IdentifiedPath ehrIdPath = new IdentifiedPath();
+    ehrIdPath.setPath(AqlObjectPath.parse(AqlQueryConstants.EHR_ID_PATH));
+
+    ContainmentClassExpression containmentClassExpression = new ContainmentClassExpression();
+    containmentClassExpression.setType(AqlQueryConstants.EHR_TYPE);
+    containmentClassExpression.setIdentifier(AqlQueryConstants.EHR_CONTAINMENT_IDENTIFIER);
+    ehrIdPath.setRoot(containmentClassExpression);
+
+    count.setIdentifiedPath(ehrIdPath);
+
+    dto.getSelect().setStatement(List.of(selectExpression));
+    log.info("Generated query for retrieveNumberOfPatients {} ", AqlRenderer.render(dto));
+
+    try {
+      List<Record1<Integer>> results = restClient.aqlEndpoint().execute(Query.buildNativeQuery(AqlRenderer.render(dto), Integer.class));
+      return results.get(0).value1();
+    } catch (WrongStatusCodeException e) {
+      log.error(INVALID_AQL_QUERY, e.getMessage(), e);
+      throw new WrongStatusCodeException("EhrBaseService.class", 93, 1);
+    } catch (ClientException e) {
+      log.error(ERROR_MESSAGE, e.getMessage(), e);
+      throw new SystemException(EhrBaseService.class, AN_ERROR_HAS_OCCURRED_CANNOT_EXECUTE_AQL,
+              String.format(AN_ERROR_HAS_OCCURRED_CANNOT_EXECUTE_AQL, e.getMessage()));
+    }
+  }
+
   /**
    * Executes a raw aql query
    *

src/test/java/org/highmed/numportal/service/AqlServiceTest.java

@@ -171,7 +171,7 @@ public void getAqlSizeTest() {
     SlimAqlDto aqlDto = SlimAqlDto.builder()
             .query("select * from dummy_table")
             .build();
-    Mockito.when(ehrBaseService.retrieveEligiblePatientIds(Mockito.any(Aql.class))).thenReturn(new HashSet<>(Arrays.asList("id1", "id2", "id3", "id4")));
+    Mockito.when(ehrBaseService.retrieveNumberOfPatients(Mockito.any(Aql.class))).thenReturn(4);
     aqlService.getAqlSize(aqlDto, "4");
   }
 
@@ -180,7 +180,7 @@ public void shouldHandlePrivacyExceptionWhenGetAqlSize() {
     SlimAqlDto aqlDto = SlimAqlDto.builder()
             .query("select * from dummy_table")
             .build();
-    Mockito.when(ehrBaseService.retrieveEligiblePatientIds(Mockito.any(Aql.class))).thenReturn(new HashSet<>(Arrays.asList("id1")));
+    Mockito.when(ehrBaseService.retrieveNumberOfPatients(Mockito.any(Aql.class))).thenReturn(1);
     aqlService.getAqlSize(aqlDto, "4");
   }