Implement fields fetch for runtime fields (#61995)

This implements the `fields` API in `_search` for runtime fields using doc values. Most of that implementation is stolen from the `docvalue_fields` fetch sub-phase, just moved into the same API that the `fields` API uses. At this point the `docvalue_fields` fetch phase looks like a special case of the `fields` API. While I was at it I moved the "which doc values sub-implementation should I use for fetching?" question from a bunch of `instanceof`s to a method on `LeafFieldData` so we can be much more flexible with what is returned and we're not forced to extend certain classes just to make the fetch phase happy. Relates to #59332
elastic · Sep 15, 2020 · 9a127ad · 9a127ad
1 parent 5075e83
commit 9a127ad
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Showing 107 changed files with 640 additions and 341 deletions.
diff --git a/...es/mapper-extras/src/main/java/org/elasticsearch/index/mapper/RankFeatureFieldMapper.java b/...es/mapper-extras/src/main/java/org/elasticsearch/index/mapper/RankFeatureFieldMapper.java
@@ -183,7 +183,7 @@ private Float objectToFloat(Object value) {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         if (format != null) {
             throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't support formats.");
         }

diff --git a/...s/mapper-extras/src/main/java/org/elasticsearch/index/mapper/RankFeaturesFieldMapper.java b/...s/mapper-extras/src/main/java/org/elasticsearch/index/mapper/RankFeaturesFieldMapper.java
@@ -162,7 +162,7 @@ protected void parseCreateField(ParseContext context) throws IOException {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         if (format != null) {
             throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't support formats.");
         }

diff --git a/...es/mapper-extras/src/main/java/org/elasticsearch/index/mapper/ScaledFloatFieldMapper.java b/...es/mapper-extras/src/main/java/org/elasticsearch/index/mapper/ScaledFloatFieldMapper.java
@@ -397,7 +397,7 @@ private static double objectToDouble(Object value) {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         if (format != null) {
             throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't support formats.");
         }

diff --git a/...apper-extras/src/main/java/org/elasticsearch/index/mapper/SearchAsYouTypeFieldMapper.java b/...apper-extras/src/main/java/org/elasticsearch/index/mapper/SearchAsYouTypeFieldMapper.java
@@ -54,6 +54,7 @@
 import org.elasticsearch.index.query.QueryShardContext;
 import org.elasticsearch.index.similarity.SimilarityProvider;
 import org.elasticsearch.index.similarity.SimilarityService;
+import org.elasticsearch.search.lookup.SearchLookup;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -419,7 +420,7 @@ protected void parseCreateField(ParseContext context) {
         }
 
         @Override
-        public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+        public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
             throw new UnsupportedOperationException();
         }
 
@@ -465,7 +466,7 @@ protected void mergeOptions(FieldMapper other, List<String> conflicts) {
         }
 
         @Override
-        public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+        public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
             throw new UnsupportedOperationException();
         }
 
@@ -588,7 +589,7 @@ protected void parseCreateField(ParseContext context) throws IOException {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         throw new UnsupportedOperationException();
     }
 

diff --git a/...les/mapper-extras/src/main/java/org/elasticsearch/index/mapper/TokenCountFieldMapper.java b/...les/mapper-extras/src/main/java/org/elasticsearch/index/mapper/TokenCountFieldMapper.java
@@ -25,6 +25,7 @@
 import org.apache.lucene.document.FieldType;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.index.analysis.NamedAnalyzer;
+import org.elasticsearch.search.lookup.SearchLookup;
 
 import java.io.IOException;
 import java.util.Iterator;
@@ -159,7 +160,7 @@ protected void parseCreateField(ParseContext context) throws IOException {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         if (format != null) {
             throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't support formats.");
         }

diff --git a/...pper-extras/src/test/java/org/elasticsearch/index/mapper/RankFeatureFieldMapperTests.java b/...pper-extras/src/test/java/org/elasticsearch/index/mapper/RankFeatureFieldMapperTests.java
@@ -147,7 +147,7 @@ public void testRejectMultiValuedFields() throws MapperParsingException, IOExcep
                 e.getCause().getMessage());
     }
 
-    public void testFetchSourceValue() {
+    public void testFetchSourceValue() throws IOException {
         Settings settings = Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT.id).build();
         Mapper.BuilderContext context = new Mapper.BuilderContext(settings, new ContentPath());
         RankFeatureFieldMapper mapper = new RankFeatureFieldMapper.Builder("field").build(context);

diff --git a/...pper-extras/src/test/java/org/elasticsearch/index/mapper/ScaledFloatFieldMapperTests.java b/...pper-extras/src/test/java/org/elasticsearch/index/mapper/ScaledFloatFieldMapperTests.java
@@ -259,7 +259,7 @@ public void testRejectIndexOptions() {
             containsString("Failed to parse mapping: unknown parameter [index_options] on mapper [field] of type [scaled_float]"));
     }
 
-    public void testFetchSourceValue() {
+    public void testFetchSourceValue() throws IOException {
         Settings settings = Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT.id).build();
         Mapper.BuilderContext context = new Mapper.BuilderContext(settings, new ContentPath());
 

diff --git a/modules/parent-join/src/main/java/org/elasticsearch/join/mapper/MetaJoinFieldMapper.java b/modules/parent-join/src/main/java/org/elasticsearch/join/mapper/MetaJoinFieldMapper.java
@@ -140,7 +140,7 @@ protected void parseCreateField(ParseContext context) throws IOException {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         throw new UnsupportedOperationException("Cannot fetch values for metadata field [" + typeName() + "].");
     }
 

diff --git a/modules/parent-join/src/main/java/org/elasticsearch/join/mapper/ParentIdFieldMapper.java b/modules/parent-join/src/main/java/org/elasticsearch/join/mapper/ParentIdFieldMapper.java
@@ -190,7 +190,7 @@ protected void parseCreateField(ParseContext context) throws IOException {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         throw new UnsupportedOperationException("Cannot fetch values for internal field [" + typeName() + "].");
     }
 

diff --git a/modules/parent-join/src/main/java/org/elasticsearch/join/mapper/ParentJoinFieldMapper.java b/modules/parent-join/src/main/java/org/elasticsearch/join/mapper/ParentJoinFieldMapper.java
@@ -352,7 +352,7 @@ protected void parseCreateField(ParseContext context) throws IOException {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         if (format != null) {
             throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't support formats.");
         }

diff --git a/modules/percolator/src/main/java/org/elasticsearch/percolator/PercolatorFieldMapper.java b/modules/percolator/src/main/java/org/elasticsearch/percolator/PercolatorFieldMapper.java
@@ -79,6 +79,7 @@
 import org.elasticsearch.index.query.QueryShardException;
 import org.elasticsearch.index.query.Rewriteable;
 import org.elasticsearch.index.query.functionscore.FunctionScoreQueryBuilder;
+import org.elasticsearch.search.lookup.SearchLookup;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
@@ -366,7 +367,7 @@ public void parse(ParseContext context) throws IOException {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         if (format != null) {
             throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't support formats.");
         }

diff --git a/...rcolator/src/main/java/org/elasticsearch/percolator/PercolatorHighlightSubFetchPhase.java b/...rcolator/src/main/java/org/elasticsearch/percolator/PercolatorHighlightSubFetchPhase.java
@@ -34,6 +34,8 @@
 import org.elasticsearch.search.fetch.subphase.highlight.Highlighter;
 import org.elasticsearch.search.fetch.subphase.highlight.SearchHighlightContext;
 import org.elasticsearch.search.internal.SearchContext;
+import org.elasticsearch.search.lookup.SearchLookup;
+import org.elasticsearch.search.lookup.SourceLookup;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -54,7 +56,7 @@ final class PercolatorHighlightSubFetchPhase implements FetchSubPhase {
     }
 
     @Override
-    public FetchSubPhaseProcessor getProcessor(SearchContext searchContext) throws IOException {
+    public FetchSubPhaseProcessor getProcessor(SearchContext searchContext, SearchLookup lookup) throws IOException {
         if (searchContext.highlight() == null) {
             return null;
         }
@@ -95,7 +97,7 @@ public void process(HitContext hit) throws IOException {
                             BytesReference document = percolateQuery.getDocuments().get(slot);
                             HitContext subContext = new HitContext(
                                 new SearchHit(slot, "unknown", Collections.emptyMap(), Collections.emptyMap()),
-                                percolatorLeafReaderContext, slot, new HashMap<>()
+                                percolatorLeafReaderContext, slot, new SourceLookup(), new HashMap<>()
                             );
                             subContext.sourceLookup().setSource(document);
                             // force source because MemoryIndex does not store fields

diff --git a/...olator/src/main/java/org/elasticsearch/percolator/PercolatorMatchedSlotSubFetchPhase.java b/...olator/src/main/java/org/elasticsearch/percolator/PercolatorMatchedSlotSubFetchPhase.java
@@ -36,6 +36,7 @@
 import org.elasticsearch.search.fetch.FetchSubPhase;
 import org.elasticsearch.search.fetch.FetchSubPhaseProcessor;
 import org.elasticsearch.search.internal.SearchContext;
+import org.elasticsearch.search.lookup.SearchLookup;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -56,7 +57,7 @@ final class PercolatorMatchedSlotSubFetchPhase implements FetchSubPhase {
     static final String FIELD_NAME_PREFIX = "_percolator_document_slot";
 
     @Override
-    public FetchSubPhaseProcessor getProcessor(SearchContext searchContext) throws IOException {
+    public FetchSubPhaseProcessor getProcessor(SearchContext searchContext, SearchLookup lookup) throws IOException {
 
         List<PercolateContext> percolateContexts = new ArrayList<>();
         List<PercolateQuery> percolateQueries = locatePercolatorQuery(searchContext.query());

diff --git a/...tor/src/test/java/org/elasticsearch/percolator/PercolatorHighlightSubFetchPhaseTests.java b/...tor/src/test/java/org/elasticsearch/percolator/PercolatorHighlightSubFetchPhaseTests.java
@@ -52,9 +52,9 @@ public void testHitsExecutionNeeded() throws IOException {
         Mockito.when(searchContext.highlight()).thenReturn(new SearchHighlightContext(Collections.emptyList()));
         Mockito.when(searchContext.query()).thenReturn(new MatchAllDocsQuery());
 
-        assertNull(subFetchPhase.getProcessor(searchContext));
+        assertNull(subFetchPhase.getProcessor(searchContext, null));
         Mockito.when(searchContext.query()).thenReturn(percolateQuery);
-        assertNotNull(subFetchPhase.getProcessor(searchContext));
+        assertNotNull(subFetchPhase.getProcessor(searchContext, null));
     }
 
     public void testLocatePercolatorQuery() {

diff --git a/...r/src/test/java/org/elasticsearch/percolator/PercolatorMatchedSlotSubFetchPhaseTests.java b/...r/src/test/java/org/elasticsearch/percolator/PercolatorMatchedSlotSubFetchPhaseTests.java
@@ -40,6 +40,7 @@
 import org.elasticsearch.search.fetch.FetchSubPhase.HitContext;
 import org.elasticsearch.search.fetch.FetchSubPhaseProcessor;
 import org.elasticsearch.search.internal.SearchContext;
+import org.elasticsearch.search.lookup.SourceLookup;
 import org.elasticsearch.test.ESTestCase;
 
 import java.util.Collections;
@@ -66,7 +67,7 @@ public void testHitsExecute() throws Exception {
                 LeafReaderContext context = reader.leaves().get(0);
                 // A match:
                 {
-                    HitContext hit = new HitContext(new SearchHit(0), context, 0,  new HashMap<>());
+                    HitContext hit = new HitContext(new SearchHit(0), context, 0, new SourceLookup(), new HashMap<>());
                     PercolateQuery.QueryStore queryStore = ctx -> docId -> new TermQuery(new Term("field", "value"));
                     MemoryIndex memoryIndex = new MemoryIndex();
                     memoryIndex.addField("field", "value", new WhitespaceAnalyzer());
@@ -77,7 +78,7 @@ public void testHitsExecute() throws Exception {
                     SearchContext sc = mock(SearchContext.class);
                     when(sc.query()).thenReturn(percolateQuery);
 
-                    FetchSubPhaseProcessor processor = phase.getProcessor(sc);
+                    FetchSubPhaseProcessor processor = phase.getProcessor(sc, null);
                     assertNotNull(processor);
                     processor.process(hit);
 
@@ -87,7 +88,7 @@ public void testHitsExecute() throws Exception {
 
                 // No match:
                 {
-                    HitContext hit = new HitContext(new SearchHit(0), context, 0,  new HashMap<>());
+                    HitContext hit = new HitContext(new SearchHit(0), context, 0, new SourceLookup(), new HashMap<>());
                     PercolateQuery.QueryStore queryStore = ctx -> docId -> new TermQuery(new Term("field", "value"));
                     MemoryIndex memoryIndex = new MemoryIndex();
                     memoryIndex.addField("field", "value1", new WhitespaceAnalyzer());
@@ -98,7 +99,7 @@ public void testHitsExecute() throws Exception {
                     SearchContext sc = mock(SearchContext.class);
                     when(sc.query()).thenReturn(percolateQuery);
 
-                    FetchSubPhaseProcessor processor = phase.getProcessor(sc);
+                    FetchSubPhaseProcessor processor = phase.getProcessor(sc, null);
                     assertNotNull(processor);
                     processor.process(hit);
 
@@ -107,7 +108,7 @@ public void testHitsExecute() throws Exception {
 
                 // No query:
                 {
-                    HitContext hit = new HitContext(new SearchHit(0), context, 0,  new HashMap<>());
+                    HitContext hit = new HitContext(new SearchHit(0), context, 0, new SourceLookup(), new HashMap<>());
                     PercolateQuery.QueryStore queryStore = ctx -> docId -> null;
                     MemoryIndex memoryIndex = new MemoryIndex();
                     memoryIndex.addField("field", "value", new WhitespaceAnalyzer());
@@ -118,7 +119,7 @@ public void testHitsExecute() throws Exception {
                     SearchContext sc = mock(SearchContext.class);
                     when(sc.query()).thenReturn(percolateQuery);
 
-                    FetchSubPhaseProcessor processor = phase.getProcessor(sc);
+                    FetchSubPhaseProcessor processor = phase.getProcessor(sc, null);
                     assertNotNull(processor);
                     processor.process(hit);
 

diff --git a/...ysis-icu/src/main/java/org/elasticsearch/index/mapper/ICUCollationKeywordFieldMapper.java b/...ysis-icu/src/main/java/org/elasticsearch/index/mapper/ICUCollationKeywordFieldMapper.java
@@ -735,7 +735,7 @@ protected void parseCreateField(ParseContext context) throws IOException {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         if (format != null) {
             throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't support formats.");
         }

diff --git a/...icu/src/test/java/org/elasticsearch/index/mapper/ICUCollationKeywordFieldMapperTests.java b/...icu/src/test/java/org/elasticsearch/index/mapper/ICUCollationKeywordFieldMapperTests.java
@@ -317,7 +317,7 @@ public void testUpdateIgnoreAbove() throws IOException {
         assertEquals(0, fields.length);
     }
 
-    public void testFetchSourceValue() {
+    public void testFetchSourceValue() throws IOException {
         Settings settings = Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT.id).build();
         Mapper.BuilderContext context = new Mapper.BuilderContext(settings, new ContentPath());
 

diff --git a/...Test/java/org/elasticsearch/index/mapper/annotatedtext/AnnotatedTextFieldMapperTests.java b/...Test/java/org/elasticsearch/index/mapper/annotatedtext/AnnotatedTextFieldMapperTests.java
@@ -678,7 +678,7 @@ public void testEmptyName() throws IOException {
         assertThat(e.getMessage(), containsString("name cannot be empty string"));
     }
 
-    public void testFetchSourceValue() {
+    public void testFetchSourceValue() throws IOException {
         Settings settings = Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT.id).build();
         Mapper.BuilderContext context = new Mapper.BuilderContext(settings, new ContentPath());
 

diff --git a/.../src/main/java/org/elasticsearch/index/mapper/annotatedtext/AnnotatedTextFieldMapper.java b/.../src/main/java/org/elasticsearch/index/mapper/annotatedtext/AnnotatedTextFieldMapper.java
@@ -46,6 +46,7 @@
 import org.elasticsearch.index.mapper.ValueFetcher;
 import org.elasticsearch.index.mapper.annotatedtext.AnnotatedTextFieldMapper.AnnotatedText.AnnotationToken;
 import org.elasticsearch.index.similarity.SimilarityProvider;
+import org.elasticsearch.search.lookup.SearchLookup;
 
 import java.io.IOException;
 import java.io.Reader;
@@ -589,7 +590,7 @@ protected void parseCreateField(ParseContext context) throws IOException {
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         if (format != null) {
             throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't support formats.");
         }

diff --git a/...pper-murmur3/src/main/java/org/elasticsearch/index/mapper/murmur3/Murmur3FieldMapper.java b/...pper-murmur3/src/main/java/org/elasticsearch/index/mapper/murmur3/Murmur3FieldMapper.java
@@ -153,7 +153,7 @@ protected void parseCreateField(ParseContext context)
     }
 
     @Override
-    public ValueFetcher valueFetcher(MapperService mapperService, String format) {
+    public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
         if (format != null) {
             throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't support formats.");
         }

diff --git a/rest-api-spec/src/main/resources/rest-api-spec/test/search/240_date_nanos.yml b/rest-api-spec/src/main/resources/rest-api-spec/test/search/240_date_nanos.yml
@@ -110,8 +110,15 @@ setup:
         rest_total_hits_as_int: true
         index: date*
         body:
-          docvalue_fields: [ { "field": "date", "format" : "strict_date_optional_time" }, { "field": "date", "format": "epoch_millis" }, { "field" : "date", "format": "uuuu-MM-dd'T'HH:mm:ss.SSSSSSSSSX" } ]
-          sort: [ { "date": "desc" } ]
+          docvalue_fields:
+            - field: date
+              format: strict_date_optional_time
+            - field: date
+              format: epoch_millis
+            - field: date
+              format: uuuu-MM-dd'T'HH:mm:ss.SSSSSSSSSX
+          sort:
+            - date: desc
 
   - match: { hits.total: 2 }
   - length: { hits.hits: 2 }

diff --git a/...er/src/internalClusterTest/java/org/elasticsearch/search/fetch/FetchSubPhasePluginIT.java b/...er/src/internalClusterTest/java/org/elasticsearch/search/fetch/FetchSubPhasePluginIT.java
@@ -39,6 +39,7 @@
 import org.elasticsearch.search.SearchExtBuilder;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.search.internal.SearchContext;
+import org.elasticsearch.search.lookup.SearchLookup;
 import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.test.ESIntegTestCase.ClusterScope;
 import org.elasticsearch.test.ESIntegTestCase.Scope;
@@ -114,7 +115,7 @@ private static final class TermVectorsFetchSubPhase implements FetchSubPhase {
         private static final String NAME = "term_vectors_fetch";
 
         @Override
-        public FetchSubPhaseProcessor getProcessor(SearchContext searchContext) {
+        public FetchSubPhaseProcessor getProcessor(SearchContext searchContext, SearchLookup lookup) {
             return new FetchSubPhaseProcessor() {
                 @Override
                 public void setNextReader(LeafReaderContext readerContext) {

diff --git a/server/src/main/java/org/elasticsearch/index/fielddata/IndexNumericFieldData.java b/server/src/main/java/org/elasticsearch/index/fielddata/IndexNumericFieldData.java
@@ -32,10 +32,10 @@
 import org.elasticsearch.index.fielddata.fieldcomparator.LongValuesComparatorSource;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.MultiValueMode;
-import org.elasticsearch.search.sort.BucketedSort;
-import org.elasticsearch.search.sort.SortOrder;
 import org.elasticsearch.search.aggregations.support.CoreValuesSourceType;
 import org.elasticsearch.search.aggregations.support.ValuesSourceType;
+import org.elasticsearch.search.sort.BucketedSort;
+import org.elasticsearch.search.sort.SortOrder;
 
 import java.io.IOException;
 import java.util.function.LongUnaryOperator;

diff --git a/server/src/main/java/org/elasticsearch/index/fielddata/LeafFieldData.java b/server/src/main/java/org/elasticsearch/index/fielddata/LeafFieldData.java
@@ -21,6 +21,10 @@
 
 import org.apache.lucene.util.Accountable;
 import org.elasticsearch.common.lease.Releasable;
+import org.elasticsearch.index.mapper.DocValueFetcher;
+import org.elasticsearch.search.DocValueFormat;
+
+import java.io.IOException;
 
 /**
  * The thread safe {@link org.apache.lucene.index.LeafReader} level cache of the data.
@@ -37,4 +41,26 @@ public interface LeafFieldData extends Accountable, Releasable {
      */
     SortedBinaryDocValues getBytesValues();
 
+    /**
+     * Return a value fetcher for this leaf implementation.
+     */
+    default DocValueFetcher.Leaf getLeafValueFetcher(DocValueFormat format) {
+        SortedBinaryDocValues values = getBytesValues();
+        return new DocValueFetcher.Leaf() {
+            @Override
+            public boolean advanceExact(int docId) throws IOException {
+                return values.advanceExact(docId);
+            }
+
+            @Override
+            public int docValueCount() throws IOException {
+                return values.docValueCount();
+            }
+
+            @Override
+            public Object nextValue() throws IOException {
+                return format.format(values.nextValue());
+            }
+        };
+    }
 }