DATAMONGO-2149 - Fix $slice in fields projection when pointing to array of DBRefs.

We now no longer try to convert the actual slice parameters into a DBRef.

Original pull request: #623.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java

@@ -18,6 +18,7 @@ package org.springframework.data.mongodb.core.convert;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map.Entry;
@@ -270,7 +271,7 @@ public class QueryMapper {
 	 */
 	protected DBObject getMappedKeyword(Field property, Keyword keyword) {
 
-		boolean needsAssociationConversion = property.isAssociation() && !keyword.isExists();
+		boolean needsAssociationConversion = property.isAssociation() && !keyword.isExists() && keyword.mayHoldDbRef();
 		Object value = keyword.getValue();
 
 		Object convertedValue = needsAssociationConversion ? convertAssociation(value, property)
@@ -544,10 +545,12 @@ public class QueryMapper {
 	static class Keyword {
 
 		private static final String N_OR_PATTERN = "\\$.*or";
+		private static final Set<String> NON_DBREF_CONVERTING_KEYWORDS = new HashSet<String>(Arrays.asList("$", "$size", "$slice", "$gt", "$lt"));
 
 		private final String key;
 		private final Object value;
 
+
 		public Keyword(DBObject source, String key) {
 			this.key = key;
 			this.value = source.get(key);
@@ -607,6 +610,15 @@ public class QueryMapper {
 		public <T> T getValue() {
 			return (T) value;
 		}
+
+		/**
+		 *
+		 * @return {@literal true} if key may hold a DbRef.
+		 * @since 1.10.18
+		 */
+		public boolean mayHoldDbRef() {
+			return !NON_DBREF_CONVERTING_KEYWORDS.contains(key);
+		}
 	}
 
 	/**

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/AbstractPersonRepositoryIntegrationTests.java

@@ -23,7 +23,9 @@ import static org.springframework.data.geo.Metrics.*;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashSet;
+import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -56,6 +58,7 @@ import org.springframework.data.geo.Polygon;
 import org.springframework.data.mongodb.core.MongoOperations;
 import org.springframework.data.mongodb.core.geo.GeoJsonPoint;
 import org.springframework.data.mongodb.core.query.BasicQuery;
+import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.repository.Person.Sex;
 import org.springframework.data.mongodb.repository.SampleEvaluationContextExtension.SampleSecurityContextHolder;
 import org.springframework.data.querydsl.QSort;
@@ -1181,4 +1184,48 @@ public abstract class AbstractPersonRepositoryIntegrationTests {
 		assertThat(repository.findByFirstnameRegex(Pattern.compile(fn)), hasSize(0));
 		assertThat(repository.findByFirstnameRegex(Pattern.compile(fn, Pattern.CASE_INSENSITIVE)), hasSize(1));
 	}
+
+	@Test // DATAMONGO-2149
+	public void annotatedQueryShouldAllowSliceInFieldsProjectionWithDbRef() {
+
+		operations.remove(new Query(), User.class);
+
+		List<User> users = new ArrayList<User>();
+
+		for (int i = 0; i < 10; i++) {
+
+			User user = new User();
+			user.id = "id" + i;
+			user.username = "user" + i;
+
+			users.add(user);
+
+			operations.save(user);
+		}
+
+		alicia.fans = new ArrayList<User>(users);
+		operations.save(alicia);
+
+		Person target = repository.findWithSliceInProjection(alicia.getId(), 0, 5);
+		assertThat(target.getFans(), hasSize(5));
+	}
+
+	@Test // DATAMONGO-2149
+	public void annotatedQueryShouldAllowPositionalParameterInFieldsProjection() {
+
+		Set<Address> addressList = new LinkedHashSet<Address>();
+
+		for (int i = 0; i < 10; i++) {
+			  addressList.add(new Address("street-" + i, "zip", "lnz"));
+		}
+
+		alicia.setShippingAddresses(addressList);
+		operations.save(alicia);
+
+		Person target = repository.findWithArrayPositionInProjection(1);
+
+		assertThat(target, notNullValue());
+		assertThat(target.getShippingAddresses(), hasSize(1));
+	}
+
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/PersonRepository.java

@@ -328,4 +328,10 @@ public interface PersonRepository extends MongoRepository<Person, String>, Query
 	void deleteByThePersonsFirstname(String firstname);
 
 	List<Person> findByFirstnameRegex(Pattern pattern);
+
+	@Query(value = "{ 'id' : ?0 }", fields = "{ 'fans': { '$slice': [ ?1, ?2 ] } }")
+	Person findWithSliceInProjection(String id, int skip, int limit);
+
+	@Query(value = "{ 'shippingAddresses' : { '$elemMatch' : { 'city' : { '$eq' : 'lnz' } } } }", fields = "{ 'shippingAddresses.$': ?0 }")
+	Person findWithArrayPositionInProjection(int position);
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/query/StringBasedMongoQueryUnitTests.java

@@ -529,6 +529,18 @@ public class StringBasedMongoQueryUnitTests {
 		assertThat(query.getQueryObject(), is((DBObject) new BasicDBObject().append("arg0", null)));
 	}
 
+	@Test // DATAMONGO-2149
+	public void shouldParseFieldsProjectionWithSliceCorrectly() throws Exception {
+
+		StringBasedMongoQuery mongoQuery = createQueryForMethod("findWithSliceInProjection", String.class, int.class,
+				int.class);
+		ConvertingParameterAccessor accessor = StubParameterAccessor.getAccessor(converter, "Bruce Banner", 0, 5);
+
+		org.springframework.data.mongodb.core.query.Query query = mongoQuery.createQuery(accessor);
+
+		assertThat(query.getFieldsObject(), is(equalTo(JSON.parse("{ \"fans\" : { \"$slice\" : [0, 5] } }"))));
+	}
+
 	private StringBasedMongoQuery createQueryForMethod(String name, Class<?>... parameters) throws Exception {
 
 		Method method = SampleRepository.class.getMethod(name, parameters);
@@ -623,5 +635,11 @@ public class StringBasedMongoQueryUnitTests {
 
 		@Query("{ arg0 : ?#{[0]} }")
 		List<Person> findByUsingSpel(Object arg0);
+
+		@Query("{ 'lastname' : { '$regex' : ?#{[0].lastname} } }")
+		Person findByPersonLastnameRegex(Person key);
+
+		@Query(value = "{ 'id' : ?0 }", fields = "{ 'fans': { '$slice': [ ?1, ?2 ] } }")
+		Person findWithSliceInProjection(String id, int skip, int limit);
 	}
 }