Query DSL: filtered query to support null filter or {} filter (in which case, just the query is executed), closes #1900.

src/main/java/org/elasticsearch/index/query/FilteredQueryBuilder.java

@@ -19,14 +19,13 @@
 
 package org.elasticsearch.index.query;
 
+import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 
 import java.io.IOException;
 
 /**
  * A query that applies a filter to the results of another query.
- *
- *
  */
 public class FilteredQueryBuilder extends BaseQueryBuilder {
 
@@ -40,9 +39,9 @@ public class FilteredQueryBuilder extends BaseQueryBuilder {
      * A query that applies a filter to the results of another query.
      *
      * @param queryBuilder  The query to apply the filter to
-     * @param filterBuilder The filter to apply on the query
+     * @param filterBuilder The filter to apply on the query (Can be null)
      */
-    public FilteredQueryBuilder(QueryBuilder queryBuilder, FilterBuilder filterBuilder) {
+    public FilteredQueryBuilder(QueryBuilder queryBuilder, @Nullable FilterBuilder filterBuilder) {
         this.queryBuilder = queryBuilder;
         this.filterBuilder = filterBuilder;
     }
@@ -61,8 +60,10 @@ public class FilteredQueryBuilder extends BaseQueryBuilder {
         builder.startObject(FilteredQueryParser.NAME);
         builder.field("query");
         queryBuilder.toXContent(builder, params);
-        builder.field("filter");
-        filterBuilder.toXContent(builder, params);
+        if (filterBuilder != null) {
+            builder.field("filter");
+            filterBuilder.toXContent(builder, params);
+        }
         if (boost != -1) {
             builder.field("boost", boost);
         }

src/main/java/org/elasticsearch/index/query/FilteredQueryParser.java

@@ -84,8 +84,9 @@ public class FilteredQueryParser implements QueryParser {
         if (query == null) {
             throw new QueryParsingException(parseContext.index(), "[filtered] requires 'query' element");
         }
+        // we allow for null filter, so it makes compositions on the client side to be simpler
         if (filter == null) {
-            throw new QueryParsingException(parseContext.index(), "[filtered] requires 'filter' element");
+            return query;
         }
 
         // cache if required

src/main/java/org/elasticsearch/index/query/QueryBuilders.java

@@ -23,8 +23,6 @@ import org.elasticsearch.common.Nullable;
 
 /**
  * A static factory for simple "import static" usage.
- *
- *
  */
 public abstract class QueryBuilders {
 
@@ -389,7 +387,7 @@ public abstract class QueryBuilders {
      * @param filterBuilder The filter to apply on the query
      * @deprecated Use filteredQuery instead (rename)
      */
-    public static FilteredQueryBuilder filtered(QueryBuilder queryBuilder, FilterBuilder filterBuilder) {
+    public static FilteredQueryBuilder filtered(QueryBuilder queryBuilder, @Nullable FilterBuilder filterBuilder) {
         return new FilteredQueryBuilder(queryBuilder, filterBuilder);
     }
 
@@ -399,7 +397,7 @@ public abstract class QueryBuilders {
      * @param queryBuilder  The query to apply the filter to
      * @param filterBuilder The filter to apply on the query
      */
-    public static FilteredQueryBuilder filteredQuery(QueryBuilder queryBuilder, FilterBuilder filterBuilder) {
+    public static FilteredQueryBuilder filteredQuery(QueryBuilder queryBuilder, @Nullable FilterBuilder filterBuilder) {
         return new FilteredQueryBuilder(queryBuilder, filterBuilder);
     }
 

src/main/java/org/elasticsearch/index/query/QueryParseContext.java

@@ -208,6 +208,10 @@ public class QueryParseContext {
         }
         token = parser.nextToken();
         if (token != XContentParser.Token.FIELD_NAME) {
+            // empty filter
+            if (token == XContentParser.Token.END_OBJECT || token == XContentParser.Token.VALUE_NULL) {
+                return null;
+            }
             throw new QueryParsingException(index, "[_na] filter malformed, no field after start_object");
         }
         String filterName = parser.currentName();