com.google.cloud.datastore

Interface Transaction

All Superinterfaces:

DatastoreReader, DatastoreReaderWriter, DatastoreWriter

public interface Transaction
extends DatastoreReaderWriter

A Google cloud datastore transaction. Similar to Batch any write operation that is applied on a transaction will only be sent to the Datastore upon commit(). A call to rollback() will invalidate the transaction and discard the changes. Any read operation that is done by a transaction will be part of it and therefore a commit is guaranteed to fail if an entity was modified outside of the transaction after it was read. Write operation on this transaction will not be reflected by read operation (as the changes are only sent to the Datastore upon commit. A usage example:

 
 Transaction transaction = datastore.newTransaction();
 try {
   Entity entity = transaction.get(key);
   if (!entity.contains("last_name") || entity.isNull("last_name")) {
     String[] name = entity.getString("name").split(" ");
     entity = Entity.newBuilder(entity)
         .remove("name")
         .set("first_name", name[0])
         .set("last_name", name[1])
         .build();
     transaction.update(entity);
     transaction.commit();
   }
 } finally {
   if (transaction.isActive()) {
     transaction.rollback();
   }
 }
  

See Also:

Google Cloud Datastore transactions

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	Transaction.Response

Method Summary

Modifier and Type	Method and Description
List<Entity>	add(FullEntity<?>... entities) Datastore add operation: inserts the provided entities.
Entity	add(FullEntity<?> entity) Datastore add operation: inserts the provided entity.
void	addWithDeferredIdAllocation(FullEntity<?>... entities) Datastore add operation.
Transaction.Response	commit() Commit the transaction.
void	delete(Key... keys) A datastore delete operation.
List<Entity>	fetch(Key... keys) Returns a list with a value for each given key (ordered by input).
Iterator<Entity>	get(Key... key) Returns an Entity for each given Key that exists in the Datastore.
Entity	get(Key key) Returns an Entity for the given Key or null if it doesn't exist.
Datastore	getDatastore() Returns the transaction associated Datastore.
boolean	isActive() Returns true if the transaction is still active (was not committed or rolledback).
List<Entity>	put(FullEntity<?>... entities) A Datastore put (a.k.a upsert) operation: creates an entity if it does not exist, updates it otherwise.
Entity	put(FullEntity<?> entity) A Datastore put (a.k.a upsert) operation: inserts an entity if it does not exist, updates it otherwise.
void	putWithDeferredIdAllocation(FullEntity<?>... entities) Datastore put operation.
void	rollback() Rollback the transaction.
<T> QueryResults<T>	run(Query<T> query) Submits a Query and returns its result.
void	update(Entity... entities) A Datastore update operation.

Method Detail

get

Entity get(Key key)

Returns an Entity for the given Key or null if it doesn't exist. The requested entity will be part of this Datastore transaction (so a commit is guaranteed to fail if entity was changed by others after it was seen by this transaction) but any write changes in this transaction will not be reflected by the returned entity.

Example of getting an entity for a given key.

 
 String keyName = "my_key_name";
 Key key = datastore.newKeyFactory().setKind("MyKind").newKey(keyName);
 Entity entity = transaction.get(key);
 transaction.commit();
 // Do something with the entity
 

Specified by:

get in interface DatastoreReader

Throws:

DatastoreException - upon failure or if no longer active

get

Iterator<Entity> get(Key... key)

Returns an Entity for each given Key that exists in the Datastore. The order of the result is unspecified. Results are loaded lazily, so it is possible to get a DatastoreException from the returned Iterator's hasNext or next methods. The requested entities will be part of this Datastore transaction (so a commit is guaranteed to fail if any of the entities was changed by others after they were seen by this transaction) but any write changes in this transaction will not be reflected by the returned entities.

Example of getting entities for several keys.

 
 String firstKeyName = "my_first_key_name";
 String secondKeyName = "my_second_key_name";
 KeyFactory keyFactory = datastore.newKeyFactory().setKind("MyKind");
 Key firstKey = keyFactory.newKey(firstKeyName);
 Key secondKey = keyFactory.newKey(secondKeyName);
 Iterator<Entity> entitiesIterator = transaction.get(firstKey, secondKey);
 List<Entity> entities = Lists.newArrayList();
 while (entitiesIterator.hasNext()) {
   Entity entity = entitiesIterator.next();
   // do something with the entity
   entities.add(entity);
 }
 transaction.commit();
 

Specified by:

get in interface DatastoreReader

Throws:

DatastoreException - upon failure or if no longer active

See Also:

DatastoreReader.get(Key)

fetch

List<Entity> fetch(Key... keys)

Returns a list with a value for each given key (ordered by input). null values are returned for nonexistent keys. When possible prefer using DatastoreReader.get(Key...) to avoid eagerly loading the results. The requested entities will be part of this Datastore transaction (so a commit is guaranteed to fail if any of the entities was changed by others after they were seen by this transaction) but any write changes in this transaction will not be reflected by the returned entities.

Example of fetching a list of entities for several keys.

 
 String firstKeyName = "my_first_key_name";
 String secondKeyName = "my_second_key_name";
 KeyFactory keyFactory = datastore.newKeyFactory().setKind("MyKind");
 Key firstKey = keyFactory.newKey(firstKeyName);
 Key secondKey = keyFactory.newKey(secondKeyName);
 List<Entity> entities = transaction.fetch(firstKey, secondKey);
 for (Entity entity : entities) {
   // do something with the entity
 }
 transaction.commit();
 

Specified by:

fetch in interface DatastoreReader

Throws:

DatastoreException - upon failure or if no longer active

run

<T> QueryResults<T> run(Query<T> query)

Submits a Query and returns its result. The entities returned by the result of this query will be part of this Datastore transaction (so a commit is guaranteed to fail if any of the entities was changed by others after the query was performed) but any write changes in this transaction will not be reflected by the result.

Example of running a query to find all entities with an ancestor.

 
 String parentKeyName = "my_parent_key_name";
 KeyFactory keyFactory = datastore.newKeyFactory().setKind("ParentKind");
 Key parentKey = keyFactory.newKey(parentKeyName);
 // Build a query
 Query<Entity> query = Query.newEntityQueryBuilder()
     .setKind("MyKind")
     .setFilter(PropertyFilter.hasAncestor(parentKey))
     .build();
 QueryResults<Entity> results = transaction.run(query);
 List<Entity> entities = Lists.newArrayList();
 while (results.hasNext()) {
   Entity result = results.next();
   // do something with result
   entities.add(result);
 }
 transaction.commit();
 

Specified by:

run in interface DatastoreReader

Throws:

DatastoreException - upon failure or if no longer active

addWithDeferredIdAllocation

void addWithDeferredIdAllocation(FullEntity<?>... entities)

Datastore add operation. This method will also allocate id for any entity with an incomplete key. As opposed to add(FullEntity) and add(FullEntity...), this method will defer any necessary id allocation to commit time.

Example of adding multiple entities with deferred id allocation.

 
 IncompleteKey key1 = datastore.newKeyFactory().setKind("MyKind").newKey();
 FullEntity.Builder entityBuilder1 = FullEntity.newBuilder(key1);
 entityBuilder1.set("propertyName", "value1");
 FullEntity entity1 = entityBuilder1.build();
 
 IncompleteKey key2 = datastore.newKeyFactory().setKind("MyKind").newKey();
 FullEntity.Builder entityBuilder2 = FullEntity.newBuilder(key2);
 entityBuilder2.set("propertyName", "value2");
 FullEntity entity2 = entityBuilder2.build();
 
 transaction.addWithDeferredIdAllocation(entity1, entity2);
 Response response = transaction.commit();
 

Throws:

DatastoreException - if a given entity with a complete key was already added to this transaction or if the transaction is no longer active

add

Entity add(FullEntity<?> entity)

Datastore add operation: inserts the provided entity. This method will automatically allocate an id if necessary. If entity has a complete key and was already marked for deletion in this writer, the operation will be changed to put(com.google.cloud.datastore.FullEntity<?>).

Example of adding a single entity.

 
 String keyName = "my_key_name";
 Key key = datastore.newKeyFactory().setKind("MyKind").newKey(keyName);
 Entity.Builder entityBuilder = Entity.newBuilder(key);
 entityBuilder.set("propertyName", "value");
 Entity entity = entityBuilder.build();
 transaction.add(entity);
 transaction.commit();
 

Specified by:

add in interface DatastoreWriter

Parameters:

entity - the entity to add

Returns:

an Entity with the same properties and a key that is either newly allocated or the same one if key is already complete

Throws:

DatastoreException - if a given entity with the same complete key was already added to this writer, if the transaction is no longer active or if id allocation for an entity with an incomplete key failed

add

List<Entity> add(FullEntity<?>... entities)

Datastore add operation: inserts the provided entities. This method will automatically allocate id for any entity with an incomplete key. For entities with complete keys that were marked for deletion in this writer the operation will be changed to put(com.google.cloud.datastore.FullEntity<?>).

Example of adding multiple entities.

 
 String keyName1 = "my_key_name1";
 String keyName2 = "my_key_name2";
 Key key1 = datastore.newKeyFactory().setKind("MyKind").newKey(keyName1);
 Entity.Builder entityBuilder1 = Entity.newBuilder(key1);
 entityBuilder1.set("propertyName", "value1");
 Entity entity1 = entityBuilder1.build();
 
 Key key2 = datastore.newKeyFactory().setKind("MyKind").newKey(keyName2);
 Entity.Builder entityBuilder2 = Entity.newBuilder(key2);
 entityBuilder2.set("propertyName", "value2");
 Entity entity2 = entityBuilder2.build();
 
 transaction.add(entity1, entity2);
 transaction.commit();
 

Specified by:

add in interface DatastoreWriter

Returns:

a list of Entity ordered by input with the same properties and a key that is either newly allocated or the same one if was already complete

Throws:

DatastoreException - if a given entity with the same complete key was already added to this writer, if the transaction is no longer active or if id allocation for an entity with an incomplete key failed

See Also:

DatastoreWriter.add(FullEntity)

update

void update(Entity... entities)

A Datastore update operation. The operation will fail if an entity with the same key does not already exist. This operation will be converted to put(com.google.cloud.datastore.FullEntity<?>) operation for entities that were already added or put in this writer. This operation will be converted to put(com.google.cloud.datastore.FullEntity<?>) operation for entities that were already added or put in this writer.

Example of updating multiple entities.

 
 String keyName1 = "my_key_name1";
 String keyName2 = "my_key_name2";
 Key key1 = datastore.newKeyFactory().setKind("MyKind").newKey(keyName1);
 Entity.Builder entityBuilder1 = Entity.newBuilder(key1);
 entityBuilder1.set("propertyName", "value3");
 Entity entity1 = entityBuilder1.build();
 
 Key key2 = datastore.newKeyFactory().setKind("MyKind").newKey(keyName2);
 Entity.Builder entityBuilder2 = Entity.newBuilder(key2);
 entityBuilder2.set("propertyName", "value4");
 Entity entity2 = entityBuilder2.build();
 
 transaction.update(entity1, entity2);
 transaction.commit();
 

Specified by:

update in interface DatastoreWriter

Throws:

DatastoreException - if an entity is marked for deletion in this transaction or if the transaction is no longer active

delete

void delete(Key... keys)

A datastore delete operation. It is OK to request the deletion of a non-existing key. This operation will also remove from this batch any prior writes for entities with the same keys. This operation will also remove from this transaction any prior writes for entities with the same keys.

Example of deleting multiple entities.

 
 String keyName1 = "my_key_name1";
 String keyName2 = "my_key_name2";
 Key key1 = datastore.newKeyFactory().setKind("MyKind").newKey(keyName1);
 Key key2 = datastore.newKeyFactory().setKind("MyKind").newKey(keyName2);
 transaction.delete(key1, key2);
 transaction.commit();
 

Specified by:

delete in interface DatastoreWriter

Throws:

DatastoreException - upon failure or if no longer active

putWithDeferredIdAllocation

void putWithDeferredIdAllocation(FullEntity<?>... entities)

Datastore put operation. This method will also allocate id for any entity with an incomplete key. As opposed to put(FullEntity) and put(FullEntity...), this method will defer any necessary id allocation to commit time.

Example of putting multiple entities with deferred id allocation.

 
 IncompleteKey key1 = datastore.newKeyFactory().setKind("MyKind").newKey();
 FullEntity.Builder entityBuilder1 = FullEntity.newBuilder(key1);
 entityBuilder1.set("propertyName", "value1");
 FullEntity entity1 = entityBuilder1.build();
 
 IncompleteKey key2 = datastore.newKeyFactory().setKind("MyKind").newKey();
 FullEntity.Builder entityBuilder2 = FullEntity.newBuilder(key2);
 entityBuilder2.set("propertyName", "value2");
 FullEntity entity2 = entityBuilder2.build();
 
 transaction.putWithDeferredIdAllocation(entity1, entity2);
 Response response = transaction.commit();
 

Throws:

IllegalArgumentException - if any of the given entities is missing a key

DatastoreException - if no longer active

put

Entity put(FullEntity<?> entity)

A Datastore put (a.k.a upsert) operation: inserts an entity if it does not exist, updates it otherwise. This method will automatically allocate an id if necessary. This operation will also remove from this writer any prior writes for the same entity. This operation will also remove from this transaction any prior writes for the same entity.

Example of putting a single entity.

 
 String keyName = "my_key_name";
 Key key = datastore.newKeyFactory().setKind("MyKind").newKey(keyName);
 Entity.Builder entityBuilder = Entity.newBuilder(key);
 entityBuilder.set("propertyName", "value");
 Entity entity = entityBuilder.build();
 transaction.put(entity);
 transaction.commit();
 

Specified by:

put in interface DatastoreWriter

Parameters:

entity - the entity to put

Returns:

an Entity with the same properties and a key that is either newly allocated or the same one if key is already complete

Throws:

DatastoreException - if id allocation for an entity with an incomplete key failed or if the transaction is no longer active

put

List<Entity> put(FullEntity<?>... entities)

A Datastore put (a.k.a upsert) operation: creates an entity if it does not exist, updates it otherwise. This method will automatically allocate id for any entity with an incomplete key. This operation will also remove from this writer any prior writes for the same entities. This operation will also remove from this transaction any prior writes for the same entities.

Example of putting multiple entities.

 
 String keyName1 = "my_key_name1";
 String keyName2 = "my_key_name2";
 Key key1 = datastore.newKeyFactory().setKind("MyKind").newKey(keyName1);
 Entity.Builder entityBuilder1 = Entity.newBuilder(key1);
 entityBuilder1.set("propertyName", "value1");
 Entity entity1 = entityBuilder1.build();
 
 Key key2 = datastore.newKeyFactory().setKind("MyKind").newKey(keyName2);
 Entity.Builder entityBuilder2 = Entity.newBuilder(key2);
 entityBuilder2.set("propertyName", "value2");
 Entity entity2 = entityBuilder2.build();
 
 transaction.put(entity1, entity2);
 transaction.commit();
 

Specified by:

put in interface DatastoreWriter

Returns:

a list of updated or inserted Entity, ordered by input. Returned keys are either newly allocated or the same one if was already complete.

Throws:

DatastoreException - if id allocation for an entity with an incomplete key failed or if the transaction is no longer active

commit

Transaction.Response commit()

Commit the transaction.

Example of committing a transaction.

 
 // create an entity
 KeyFactory keyFactory = datastore.newKeyFactory().setKind("MyKind");
 Key key = datastore.allocateId(keyFactory.newKey());
 Entity entity = Entity.newBuilder(key).set("description", "commit()").build();
 
 // add the entity and commit
 try {
   transaction.put(entity);
   transaction.commit();
 } catch (DatastoreException ex) {
   // handle exception
 }
 

Throws:

DatastoreException - if could not commit the transaction or if no longer active

rollback

void rollback()

Rollback the transaction.

Example of rolling back a transaction.

 
 // create an entity
 KeyFactory keyFactory = datastore.newKeyFactory().setKind("MyKind");
 Key key = datastore.allocateId(keyFactory.newKey());
 Entity entity = Entity.newBuilder(key).set("description", "rollback()").build();
 
 // add the entity and rollback
 transaction.put(entity);
 transaction.rollback();
 // calling transaction.commit() now would fail
 

Throws:

DatastoreException - if transaction was already committed

isActive

boolean isActive()

Returns true if the transaction is still active (was not committed or rolledback).

Example of verifying if a transaction is active.

 
 // create an entity
 KeyFactory keyFactory = datastore.newKeyFactory().setKind("MyKind");
 Key key = datastore.allocateId(keyFactory.newKey());
 Entity entity = Entity.newBuilder(key).set("description", "active()").build();
 // calling transaction.active() now would return true
 try {
   // add the entity and commit
   transaction.put(entity);
   transaction.commit();
 } finally {
   // if committing succeeded
   // then transaction.active() will be false
   if (transaction.isActive()) {
     // otherwise it's true and we need to rollback
     transaction.rollback();
   }
 }
 

getDatastore

Datastore getDatastore()

Returns the transaction associated Datastore.