Change default format for date_nanos field

docs/reference/mapping/types/date_nanos.asciidoc

@@ -18,15 +18,7 @@ back to a string depending on the date format that is associated with the field.
 Date formats can be customised, but if no `format` is specified then it uses
 the default:
 
-    "strict_date_optional_time||epoch_millis"
-
-This means that it will accept dates with optional timestamps, which conform
-to the formats supported by
-<<strict-date-time,`strict_date_optional_time`>> including up to nine second
-fractionals or milliseconds-since-the-epoch (thus losing precision on the
-nano second part). Using <<strict-date-time,`strict_date_optional_time`>> will 
-format the result up to only three second fractionals. To
-print and parse up to nine digits of resolution, use <<strict-date-time-nanos,`strict_date_optional_time_nanos`>>.
+    "strict_date_optional_time_nanos||epoch_millis"
 
 For instance:
 
@@ -74,7 +66,7 @@ GET my-index-000001/_search
   "docvalue_fields" : [
     {
       "field" : "date",
-      "format": "strict_date_time" <7>
+      "format": "strict_date_optional_time_nanos" <7>
     }
   ]
 }

qa/rolling-upgrade/src/test/resources/rest-api-spec/test/old_cluster/10_basic.yml

@@ -256,3 +256,24 @@
   - do:
       indices.get_index_template:
         name: my-it
+
+---
+"Verify date_nanos default format":
+  - do:
+      indices.create:
+        index: index_nanos
+        body:
+          mappings:
+            properties:
+              date:
+                type: date
+              date_nanos:
+                type: date_nanos
+
+  - do:
+      index:
+        index: index_nanos
+        id: 0
+        body:
+          date: "2015-01-01T12:10:30.123456789Z"
+          date_nanos: "2015-01-01T12:10:30.123456789Z"

qa/rolling-upgrade/src/test/resources/rest-api-spec/test/upgraded_cluster/10_basic.yml

@@ -186,3 +186,16 @@
   - match: {component_templates.0.component_template.template.settings: {index: {number_of_shards: '1', number_of_replicas: '0'}}}
   - is_true: component_templates.0.component_template.template.mappings
   - match: {component_templates.0.component_template.template.aliases: {aliasname: {}}}
+
+---
+"Verify date_nanos default format":
+  - do:
+      search:
+        index: index_nanos
+        body:
+          fields: ["date_nanos", "date"]
+
+  - match: { hits.total.value: 1 }
+  - match: { hits.hits.0._id: "0" }
+  - match: { hits.hits.0.fields.date: [ "2018-10-29T12:12:12.123Z" ] }
+  - match: { hits.hits.0.fields.date_nanos: [ "2018-10-29T12:12:12.123456789Z" ] }

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

@@ -64,6 +64,7 @@ public final class DateFieldMapper extends FieldMapper {
     public static final String CONTENT_TYPE = "date";
     public static final String DATE_NANOS_CONTENT_TYPE = "date_nanos";
     public static final DateFormatter DEFAULT_DATE_TIME_FORMATTER = DateFormatter.forPattern("strict_date_optional_time||epoch_millis");
+    public static final DateFormatter DEFAULT_DATE_TIME_NANOS_FORMATTER = DateFormatter.forPattern("strict_date_optional_time_nanos||epoch_millis");
     private static final DateMathParser EPOCH_MILLIS_PARSER = DateFormatter.forPattern("epoch_millis").toDateMathParser();
 
     public enum Resolution {
@@ -216,8 +217,7 @@ public static class Builder extends FieldMapper.Builder {
 
         private final Parameter<Map<String, String>> meta = Parameter.metaParam();
 
-        private final Parameter<String> format
-            = Parameter.stringParam("format", false, m -> toType(m).format, DEFAULT_DATE_TIME_FORMATTER.pattern());
+        private final Parameter<String> format;
         private final Parameter<Locale> locale = new Parameter<>("locale", false, () -> Locale.ROOT,
             (n, c, o) -> LocaleUtils.parse(o.toString()), m -> toType(m).locale);
 
@@ -235,6 +235,10 @@ public Builder(String name, Resolution resolution, DateFormatter dateFormatter,
             this.indexCreatedVersion = indexCreatedVersion;
             this.ignoreMalformed
                 = Parameter.boolParam("ignore_malformed", true, m -> toType(m).ignoreMalformed, ignoreMalformedByDefault);
+
+            DateFormatter defaultFormat = resolution == Resolution.MILLISECONDS ?
+                DEFAULT_DATE_TIME_FORMATTER : DEFAULT_DATE_TIME_NANOS_FORMATTER;
+            this.format = Parameter.stringParam("format", false, m -> toType(m).format, defaultFormat.pattern());
             if (dateFormatter != null) {
                 this.format.setValue(dateFormatter.pattern());
                 this.locale.setValue(dateFormatter.locale());

server/src/test/java/org/elasticsearch/index/mapper/DateFieldMapperTests.java

@@ -319,6 +319,17 @@ public void testFetchDocValuesMillis() throws IOException {
         assertEquals(List.of(date), fetchFromDocValues(mapperService, ft, format, 1589578382123L));
     }
 
+    public void testFormatPreserveNanos() throws IOException {
+        MapperService mapperService = createMapperService(
+            fieldMapping(b -> b.field("type", "date_nanos"))
+        );
+        DateFieldMapper.DateFieldType ft = (DateFieldMapper.DateFieldType) mapperService.fieldType("field");
+        assertEquals(ft.dateTimeFormatter, DateFieldMapper.DEFAULT_DATE_TIME_NANOS_FORMATTER);
+        DocValueFormat format = ft.docValueFormat(null, null);
+        String date = "2020-05-15T21:33:02.123456789Z";
+        assertEquals(List.of(date), fetchFromDocValues(mapperService, ft, format, date));
+    }
+
     public void testFetchDocValuesNanos() throws IOException {
         MapperService mapperService = createMapperService(
             fieldMapping(b -> b.field("type", "date_nanos").field("format", "strict_date_time||epoch_millis"))
@@ -494,7 +505,7 @@ private MapperService dateNanosMapperService() throws IOException {
     }
 
     private String randomIs8601Nanos(long maxMillis) {
-        String date = DateFieldMapper.DEFAULT_DATE_TIME_FORMATTER.formatMillis(randomLongBetween(0, maxMillis));
+        String date = DateFieldMapper.DEFAULT_DATE_TIME_NANOS_FORMATTER.formatMillis(randomLongBetween(0, maxMillis));
         date = date.substring(0, date.length() - 1);  // Strip off trailing "Z"
         return date + String.format(Locale.ROOT, "%06d", between(0, 999999)) + "Z";  // Add nanos and the "Z"
     }