Who is flush entity

Except when you explicitly flush , there are absolutely no guarantees about when the entity manager executes the JDBC calls, only the order in which they are executed. However, Hibernate does guarantee that the Query.

It is possible to change the default behavior so that flush occurs less frequently. The FlushModeType for an entity manager defines two different modes: only flush at commit time or flush automatically using the explained routine unless flush is called explicitly.

I have an EJB where I am saving an object to the database. In an example I have seen, once this data is saved EntityManager. The object I am saving is not attached and not used later in the method. In fact, once saved the method returns and I would expect the resources to be released.

The example code does this on a remove call as well. A call to EntityManager. So, when you call EntityManager. Any constraint failures column width, data types, foreign key will be known at this time. The EntityManager. By default JPA does not normally write changes to the database until the transaction is committed. This is normally desirable as it avoids database access, resources and locks until required.

It also allows database writes to be ordered, and batched for optimal database access, and to maintain integrity constraints and avoid deadlocks. So when you call EntityManager. An Explicit flush will make the entity now residing in the Persistence Context to be moved to the database using a SQL. Without flush , this moving of entity from Persistence Context to the database will happen when the Transaction to which this Persistence Context is associated is committed.

Persistence framework usually manages transactions behind the scene. So there is no guaranty that flushed queries will be successfully committed.

That means you won't get auto generated IDs after persist. You just pass persisted object and eventually after later flush it gets ID. A real proxy class override ALL public methods along the lines of the getName method shown below:. Traversing the object graph for parts that are lazy-loaded will easily trigger lots of SQL queries and will perform badly if used to heavily.

Make sure to use DQL to fetch-join all the parts of the object-graph that you need as efficiently as possible. As a result the persistent state of such an entity will subsequently be properly synchronized with the database when EntityManager flush is invoked. Doctrine applies a strategy called transactional write-behind, which means that it will delay most SQL commands until EntityManager flush is invoked which will then issue all necessary SQL statements to synchronize your objects with the database in the most efficient way and a single, short transaction, taking care of maintaining referential integrity.

You can not rely on a generated identifier to be available directly after invoking persist. The inverse is also true. You can not rely on a generated identifier being not available after a failed flush operation. Do not pass detached entities to the persist operation. By applying the remove operation on some entity, that entity becomes REMOVED, which means that its persistent state will be deleted once EntityManager flush is invoked. The entity will be deleted on the next invocation of EntityManager flush that involves that entity.

This means that entities scheduled for removal can still be queried for and appear in query and collection results. After an entity has been removed its in-memory state is the same as before the removal, except for generated identifiers.

Removing an entity will also automatically delete any existing records in many-to-many join tables that link this entity. The action taken depends on the value of the joinColumn mapping attribute onDelete.

Deleting an object with all its associated objects can be achieved in multiple ways with very different performance impacts. Calling remove on an entity will remove the object from the identity map and therefore detach it. Querying the same entity again, for example via a lazy loaded relation, will return a new object. Changes made to the detached entity, if any including removal of the entity , will not be synchronized to the database after the entity has been detached.

There are several situations in which an entity is detached automatically without invoking the detach method:. The detach operation is usually not as frequently needed and used as persist and remove.

Merging entities refers to the merging of usually detached entities into the context of an EntityManager so that they become managed again. The state of the passed entity will be merged into a managed copy of this entity and this copy will subsequently be returned.

The reason for this is, if you serialize a class that was a proxy instance before, the private variables won't be serialized and a PHP Notice is thrown. The merge operation will throw an OptimisticLockException if the entity being merged uses optimistic locking through a version field and the versions of the entity being merged and the managed copy don't match.

This usually means that the entity has been modified while being detached. The merge operation is usually not as frequently needed and used as persist and remove. The most common scenario for the merge operation is to reattach entities to an EntityManager that come from some cache and are therefore detached and you want to modify and persist such an entity. If you need to perform multiple merges of entities that share certain subparts of their object-graphs and cascade merge, then you have to call EntityManager clear between the successive calls to EntityManager merge.

Otherwise you might end up with multiple copies of the same object in the database, however with different ids. If you load some detached entities from a cache and you do not need to persist or delete them or otherwise make use of them without the need for persistence services there is no need to use merge.

The state of persistent entities is synchronized with the database on flush of an EntityManager which commits the underlying UnitOfWork. The synchronization involves writing any updates to persistent entities and their relationships to the database. Thereby bidirectional relationships are persisted based on the references held by the owning side of the relationship as explained in the Association Mapping chapter.

When EntityManager flush is called, Doctrine inspects all managed, new and removed entities and will perform the following operations. As soon as you begin to change the state of entities, call persist or remove the contents of the UnitOfWork and the database will drive out of sync.

They can only be synchronized by calling EntityManager flush. This section describes the effects of database and UnitOfWork being out of sync. EntityManager flush is never called implicitly by Doctrine. You always have to trigger it manually. For all initialized relationships of the new or managed entity the following semantics apply to each associated entity X:. The flush operation applies to a removed entity by deleting its persistent state from the database.

The size of a Unit of Work mainly refers to the number of managed entities at a particular point in time. The size represents the number of managed entities in the Unit of Work. This size affects the performance of flush operations due to change tracking see Change Tracking Policies and, of course, memory consumption, so you may want to check it from time to time during development.

This is an anti-pattern and unnecessarily reduces the performance of your application. Instead, form units of work that operate on your objects and call flush when you are done.