issue #74: enabling field extractor only if there are extractable fie…

…lds in the schema.

src/main/java/de/gwdg/metadataqa/api/calculator/CalculatorFactory.java

@@ -47,7 +47,7 @@ private void configure() {
   }
 
   private void addExtractor() {
-    if (configuration.isFieldExtractorEnabled())
+    if (configuration.isFieldExtractorEnabled() && !schema.getExtractableFields().isEmpty())
       calculators.add(new FieldExtractor(schema));
   }
 

src/test/java/de/gwdg/metadataqa/api/calculator/CalculatorFactoryTest.java

@@ -0,0 +1,49 @@
+package de.gwdg.metadataqa.api.calculator;
+
+import de.gwdg.metadataqa.api.configuration.MeasurementConfiguration;
+import de.gwdg.metadataqa.api.interfaces.Calculator;
+import de.gwdg.metadataqa.api.json.JsonBranch;
+import de.gwdg.metadataqa.api.schema.BaseSchema;
+import de.gwdg.metadataqa.api.schema.Format;
+import de.gwdg.metadataqa.api.schema.Schema;
+import org.junit.Test;
+
+import java.util.List;
+
+import static org.junit.Assert.*;
+
+public class CalculatorFactoryTest {
+
+  @Test
+  public void createWithExtractable() {
+    Schema schema = new BaseSchema()
+      .setFormat(Format.CSV)
+      .addField(new JsonBranch("url"))
+      .addField(new JsonBranch("name").setExtractable());
+
+    MeasurementConfiguration config = new MeasurementConfiguration()
+      .enableFieldExtractor()
+      .enableCompletenessMeasurement();
+
+    List<Calculator> calculators = CalculatorFactory.create(config, schema);
+    assertEquals(2, calculators.size());
+    assertEquals("fieldExtractor", calculators.get(0).getCalculatorName());
+    assertEquals("completeness", calculators.get(1).getCalculatorName());
+  }
+
+  @Test
+  public void createWithoutExtractable() {
+    Schema schema = new BaseSchema()
+      .setFormat(Format.CSV)
+      .addField(new JsonBranch("url"))
+      .addField(new JsonBranch("name"));
+
+    MeasurementConfiguration config = new MeasurementConfiguration()
+      .enableFieldExtractor()
+      .enableCompletenessMeasurement();
+
+    List<Calculator> calculators = CalculatorFactory.create(config, schema);
+    assertEquals(1, calculators.size());
+    assertEquals("completeness", calculators.get(0).getCalculatorName());
+  }
+}