Add support for deriving source field from docValues for DateFieldMapper

Signed-off-by: Shreyansh Ray <rayshrey@amazon.com>

Author: rayshrey

server/src/main/java/org/opensearch/index/mapper/DateFieldMapper.java

@@ -36,7 +36,9 @@
 import org.apache.lucene.document.SortedNumericDocValuesField;
 import org.apache.lucene.document.StoredField;
 import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.PointValues;
+import org.apache.lucene.index.SortedNumericDocValues;
 import org.apache.lucene.search.BoostQuery;
 import org.apache.lucene.search.IndexOrDocValuesQuery;
 import org.apache.lucene.search.IndexSortSortedNumericDocValuesRangeQuery;
@@ -74,6 +76,7 @@
 import java.time.ZonedDateTime;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -330,7 +333,8 @@ public DateFieldMapper build(BuilderContext context) {
                 buildFormatter(),
                 resolution,
                 nullValue.getValue(),
-                meta.getValue()
+                meta.getValue(),
+                true
             );
             ft.setBoost(boost.getValue());
             Long nullTimestamp = parseNullValue(ft);
@@ -372,15 +376,29 @@ public DateFieldType(
             DateFormatter dateTimeFormatter,
             Resolution resolution,
             String nullValue,
-            Map<String, String> meta
+            Map<String, String> meta,
+            boolean derivedSourceSupported
         ) {
-            super(name, isSearchable, isStored, hasDocValues, TextSearchInfo.SIMPLE_MATCH_ONLY, meta);
+            super(name, isSearchable, isStored, hasDocValues, TextSearchInfo.SIMPLE_MATCH_ONLY, meta, derivedSourceSupported);
             this.dateTimeFormatter = dateTimeFormatter;
             this.dateMathParser = dateTimeFormatter.toDateMathParser();
             this.resolution = resolution;
             this.nullValue = nullValue;
         }
 
+        public DateFieldType(
+            String name,
+            boolean isSearchable,
+            boolean isStored,
+            boolean hasDocValues,
+            DateFormatter dateTimeFormatter,
+            Resolution resolution,
+            String nullValue,
+            Map<String, String> meta
+        ) {
+            this(name, isSearchable, isStored, hasDocValues, dateTimeFormatter, resolution, nullValue, meta, false);
+        }
+
         public DateFieldType(String name) {
             this(name, true, false, true, getDefaultDateTimeFormatter(), Resolution.MILLISECONDS, null, Collections.emptyMap());
         }
@@ -800,4 +818,18 @@ public boolean getIgnoreMalformed() {
     public Long getNullValue() {
         return nullValue;
     }
+
+    @Override
+    protected String[] deriveSource(LeafReader leafReader, int docId) throws IOException {
+        SortedNumericDocValues sortedNumericDocValues = leafReader.getSortedNumericDocValues(name());
+        if (sortedNumericDocValues.advanceExact(docId)) {
+            int size = sortedNumericDocValues.docValueCount();
+            String[] values = new String[size];
+            DateFormatter dateFormatter = fieldType().dateTimeFormatter;
+            for (int i = 0; i < size; i++)
+                values[i] = dateFormatter.formatMillis(sortedNumericDocValues.nextValue());
+            return values;
+        }
+        return null;
+    }
 }

server/src/main/java/org/opensearch/index/mapper/FieldMapper.java

@@ -35,6 +35,7 @@
 import org.apache.lucene.document.Field;
 import org.apache.lucene.document.FieldType;
 import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.LeafReader;
 import org.opensearch.common.annotation.PublicApi;
 import org.opensearch.common.settings.Setting;
 import org.opensearch.common.settings.Setting.Property;
@@ -571,6 +572,17 @@ protected static String indexOptionToString(IndexOptions indexOption) {
 
     protected abstract String contentType();
 
+    public Object getDerivedSource(LeafReader leafReader, int docId) throws IOException{
+        if (mappedFieldType.isDerivedSourceSupported() == false)
+            throw new UnsupportedOperationException("Derived source field is not supported for [" + name() + "] field");
+        return deriveSource(leafReader, docId);
+    }
+
+    // generic implementation, override in subclasses for specific implementation
+    protected Object deriveSource(LeafReader leafReader, int docId) throws IOException {
+        return null;
+    }
+
     /**
      * Multi field implementation used across field mappers
      *

server/src/main/java/org/opensearch/index/mapper/MappedFieldType.java

@@ -94,14 +94,16 @@ public abstract class MappedFieldType {
     private float boost;
     private NamedAnalyzer indexAnalyzer;
     private boolean eagerGlobalOrdinals;
+    private final boolean derivedSourceSupported;
 
     public MappedFieldType(
         String name,
         boolean isIndexed,
         boolean isStored,
         boolean hasDocValues,
         TextSearchInfo textSearchInfo,
-        Map<String, String> meta
+        Map<String, String> meta,
+        boolean derivedSourceSupported
     ) {
         setBoost(1.0f);
         this.name = Objects.requireNonNull(name);
@@ -110,6 +112,18 @@ public MappedFieldType(
         this.docValues = hasDocValues;
         this.textSearchInfo = Objects.requireNonNull(textSearchInfo);
         this.meta = meta;
+        this.derivedSourceSupported = derivedSourceSupported;
+    }
+
+    public MappedFieldType(
+        String name,
+        boolean isIndexed,
+        boolean isStored,
+        boolean hasDocValues,
+        TextSearchInfo textSearchInfo,
+        Map<String, String> meta
+    ) {
+        this(name, isIndexed, isStored, hasDocValues, textSearchInfo, meta, false);
     }
 
     /**
@@ -158,6 +172,10 @@ public boolean hasDocValues() {
         return docValues;
     }
 
+    public boolean isDerivedSourceSupported() {
+        return derivedSourceSupported;
+    }
+
     public NamedAnalyzer indexAnalyzer() {
         return indexAnalyzer;
     }