DATAMONGO-550 - Fixed potential NullPointerExceptions in MongoTemplate.

Guarded access to results of mappingContext.getPersistentEntity(…) to prevent NullPointerExceptions in case the template is used with non-entity types like a plain DBObject. Added some custom logic for plain BasicDBObjects to get the _id field populated appropriately.

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

@@ -505,13 +505,12 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 	}
 
 	public <T> T findById(Object id, Class<T> entityClass) {
-		MongoPersistentEntity<?> persistentEntity = mappingContext.getPersistentEntity(entityClass);
+		return findById(id, entityClass, determineCollectionName(entityClass));
-		return findById(id, entityClass, persistentEntity.getCollection());
 	}
 
 	public <T> T findById(Object id, Class<T> entityClass, String collectionName) {
 		MongoPersistentEntity<?> persistentEntity = mappingContext.getPersistentEntity(entityClass);
-		MongoPersistentProperty idProperty = persistentEntity.getIdProperty();
+		MongoPersistentProperty idProperty = persistentEntity == null ? null : persistentEntity.getIdProperty();
 		String idKey = idProperty == null ? ID : idProperty.getName();
 		return doFindOne(collectionName, new BasicDBObject(idKey, id), null, entityClass);
 	}
@@ -795,7 +794,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 
 		assertUpdateableIdIfNotSet(objectToSave);
 
-		BasicDBObject dbDoc = new BasicDBObject();
+		DBObject dbDoc = new BasicDBObject();
 
 		maybeEmitEvent(new BeforeConvertEvent<T>(objectToSave));
 		writer.write(objectToSave, dbDoc);
@@ -982,7 +981,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 		Assert.notNull(object);
 
 		MongoPersistentEntity<?> entity = mappingContext.getPersistentEntity(object.getClass());
-		MongoPersistentProperty idProp = entity.getIdProperty();
+		MongoPersistentProperty idProp = entity == null ? null : entity.getIdProperty();
 
 		if (idProp == null) {
 			throw new MappingException("No id property found for object of type " + entity.getType().getName());
@@ -1438,6 +1437,12 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 			return;
 		}
 
+		if (savedObject instanceof BasicDBObject) {
+			DBObject dbObject = (DBObject) savedObject;
+			dbObject.put(ID, id);
+			return;
+		}
+
 		MongoPersistentProperty idProp = getIdPropertyFor(savedObject.getClass());
 
 		if (idProp == null) {
@@ -1555,7 +1560,8 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 	}
 
 	private MongoPersistentProperty getIdPropertyFor(Class<?> type) {
-		return mappingContext.getPersistentEntity(type).getIdProperty();
+		MongoPersistentEntity<?> persistentEntity = mappingContext.getPersistentEntity(type);
+		return persistentEntity == null ? null : persistentEntity.getIdProperty();
 	}
 
 	private <T> String determineEntityCollectionName(T obj) {

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateTests.java

@@ -42,6 +42,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.core.convert.converter.Converter;
 import org.springframework.dao.DataAccessException;
 import org.springframework.dao.DataIntegrityViolationException;
+import org.springframework.dao.InvalidDataAccessApiUsageException;
 import org.springframework.dao.OptimisticLockingFailureException;
 import org.springframework.data.annotation.Id;
 import org.springframework.data.annotation.PersistenceConstructor;
@@ -63,6 +64,7 @@ import org.springframework.data.mongodb.core.query.Update;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 
+import com.mongodb.BasicDBObject;
 import com.mongodb.DBCollection;
 import com.mongodb.DBCursor;
 import com.mongodb.DBObject;
@@ -143,6 +145,7 @@ public class MongoTemplateTests {
 		template.dropCollection(TestClass.class);
 		template.dropCollection(Sample.class);
 		template.dropCollection(MyPerson.class);
+		template.dropCollection("collection");
 	}
 
 	@Test
@@ -1352,6 +1355,44 @@ public class MongoTemplateTests {
 		template.save(null);
 	}
 
+	/**
+	 * @see DATAMONGO-550
+	 */
+	@Test
+	public void savesPlainDbObjectCorrectly() {
+
+		DBObject dbObject = new BasicDBObject("foo", "bar");
+		template.save(dbObject, "collection");
+
+		assertThat(dbObject.containsField("_id"), is(true));
+	}
+
+	/**
+	 * @see DATAMONGO-550
+	 */
+	@Test(expected = InvalidDataAccessApiUsageException.class)
+	public void rejectsPlainObjectWithOutExplicitCollection() {
+
+		DBObject dbObject = new BasicDBObject("foo", "bar");
+		template.save(dbObject, "collection");
+
+		template.findById(dbObject.get("_id"), DBObject.class);
+	}
+
+	/**
+	 * @see DATAMONGO-550
+	 */
+	@Test
+	public void readsPlainDbObjectById() {
+
+		DBObject dbObject = new BasicDBObject("foo", "bar");
+		template.save(dbObject, "collection");
+
+		DBObject result = template.findById(dbObject.get("_id"), DBObject.class, "collection");
+		assertThat(result.get("foo"), is(dbObject.get("foo")));
+		assertThat(result.get("_id"), is(dbObject.get("_id")));
+	}
+
 	static class MyId {
 
 		String first;