Interface Transaction (2.2.10)

public interface Transaction extends DatastoreBatchWriter, 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();
   }
 }

Implements

DatastoreBatchWriter, DatastoreReaderWriter

Methods

<T>run(Query<T> query)

public abstract QueryResults<T> <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();

Parameter

Name	Description
query	`Query<T>`

Returns

Type	Description
QueryResults<T>

add(FullEntity<?> entity)

public abstract 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.

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();

Parameter

Name	Description
entity	`FullEntity<?>`

Returns

Type	Description
Entity

add(FullEntity<?>[] entities)

public abstract 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.

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();

Parameter

Name	Description
entities	`FullEntity<?>[]`

Returns

Type	Description
List<Entity>

addWithDeferredIdAllocation(FullEntity<?>[] entities)

public abstract 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();

Parameter

Name	Description
entities	`FullEntity<?>[]`

commit()

public abstract 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
 }

Returns

Type	Description
Transaction.Response

delete(Key[] keys)

public abstract 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();

Parameter

Name	Description
keys	`Key[]`

fetch(Key[] keys)

public abstract 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 #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();

Parameter

Name	Description
keys	`Key[]`

Returns

Type	Description
List<Entity>

get(Key key)

public abstract 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

Parameter

Name	Description
key	`Key`

Returns

Type	Description
Entity

get(Key[] key)

public abstract 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();

Parameter

Name	Description
key	`Key[]`

Returns

Type	Description
Iterator<Entity>

getDatastore()

public abstract Datastore getDatastore()

Returns the transaction associated Datastore.

Returns

Type	Description
Datastore

getTransactionId()

public abstract ByteString getTransactionId()

Returns

Type	Description
ByteString

isActive()

public abstract 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();
   }
 }

Returns

Type	Description
boolean

put(FullEntity<?> entity)

public abstract 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();

Parameter

Name	Description
entity	`FullEntity<?>`

Returns

Type	Description
Entity

put(FullEntity<?>[] entities)

public abstract 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();

Parameter

Name	Description
entities	`FullEntity<?>[]`

Returns

Type	Description
List<Entity>

putWithDeferredIdAllocation(FullEntity<?>[] entities)

public abstract 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();

Parameter

Name	Description
entities	`FullEntity<?>[]`

rollback()

public abstract 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

update(Entity[] entities)

public abstract 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 operation for entities that were already added or put in this writer. This operation will be converted to #put 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();

Parameter

Name	Description
entities	`Entity[]`