Returning no Metadata if Metadata Spec is Empty (#271)

* actually returning 0 results if spec is empty. This is backwards-compatible because all metadata is fetched if the provided spec is null


Former-commit-id: 06a7812

build.gradle

@@ -11,7 +11,7 @@ allprojects {
     group = 'org.vitrivr'
 
     /* Our current version, on dev branch this should always be release+1-SNAPSHOT */
-    version = '3.8.2'
+    version = '3.8.3'
 
     apply plugin: 'java-library'
     apply plugin: 'maven-publish'

cineast-api/src/main/java/org/vitrivr/cineast/api/messages/query/TemporalQuery.java

@@ -29,6 +29,9 @@ public class TemporalQuery extends Query {
    */
   private final Float maxLength;
 
+  /**
+   * Provide an empty list to fetch no metadata at all. If the field is not filled (i.e. null), all metadata is provided for backwards-compatibility
+   */
   private final List<MetadataAccessSpecification> metadataAccessSpec;
 
   @JsonCreator

cineast-core/src/main/java/org/vitrivr/cineast/core/db/dao/MetadataAccessSpecification.java

@@ -3,7 +3,7 @@
 import com.fasterxml.jackson.annotation.JsonProperty;
 
 /**
- * Use '*' in either domain or key to retrieve simply all information
+ * Use '*' in either domain or key to retrieve simply all information. In general, if an empty specification list is provided, no metadata is returned.
  */
 public class MetadataAccessSpecification {
 

cineast-core/src/main/java/org/vitrivr/cineast/core/db/dao/reader/AbstractMetadataReader.java

@@ -60,6 +60,10 @@ public List<R> findBySpec(List<String> ids, List<MetadataAccessSpecification> sp
       LOGGER.warn("provided id-list {} or spec {} is null, returning empty list", ids, spec);
       return new ArrayList<>();
     }
+    if (spec.size() == 0) {
+      LOGGER.trace("Not returning any metadata since spec was an empty list.");
+      return new ArrayList<>();
+    }
     StopWatch watch = StopWatch.createStarted();
     ids = sanitizeIds(ids);
     spec = sanitizeSpec(spec);
@@ -69,6 +73,14 @@ public List<R> findBySpec(List<String> ids, List<MetadataAccessSpecification> sp
   }
 
   public List<R> findBySpec(List<MetadataAccessSpecification> spec) {
+    if (spec == null) {
+      LOGGER.warn("Provided spec is null, returning empty list");
+      return new ArrayList<>();
+    }
+    if (spec.size() == 0) {
+      LOGGER.trace("Not returning any metadata since spec was an empty list.");
+      return new ArrayList<>();
+    }
     StopWatch watch = StopWatch.createStarted();
     spec = sanitizeSpec(spec);
     List<Map<String, PrimitiveTypeProvider>> results = selector.getMetadataBySpec(spec);