JPA EntityManager Methods

Step-by-Step Implementation of JPA Application with the Hibernate Entity Manager

Methods	Definitions
persist(Object entity)	This method can used to make the instance managed and persistent. Usage: Use the persist to save the new entity into the database. Entity can be managed by the persistence context and any changes are made to it will be automatically synchronized with database upon the transaction commit.
merge(Object entity)	This method can be used to merge the state of the given entity into current persistence context. Usage: Use the merge to the update of the exisiting entity instance to the persistence context and it can returns the merged entity which can be the further used for the modification and sychronization with database.
remove(Object entity)	This method can be used to remove the entity instance from the database. Usage: Use the remove to delete the existing the instance from the database.
find(Class<T> entityClass, Object primaryKey)	This method can be used to find the entity by its the primary key. Usage: Use the find to retrieve the entity instance from the database on its the primary key value.It returns the entity instance.
getReference(Class<T> entityClass, Object primaryKey)	This method can be similar to the find but it can returns the reference to the entity instead of the loading it immediately. Usage: Use the getReference to the obtain refrenece to an the entity without actually loading it from the database.
flush()	This method can be used to sychronize the persistence context with underlying the database. Usage: Use the flush to force the EntityManager to the synchronize the changes are made to managed the entities with database.
detach(Object entity)	This method can be used to the detach the entity instance from the persistence context. Usage: Use the detach to the remove an entity from persistence context and it can effectively making it detached.
clear()	This method can be used to clear the persistence context and it can be detaching all the managed entities. Usage: Use the clear to remove all managed entities from persistence context.

Further Subtopics:

JQPL (Java Persistence Query Language): JPQL can be defined as the query language similar to the SQL but the operations on entity objects instead of the database tables and it can allow the developers to write the platform independent queries using the entity attributes and relationships.
Criteria API: The Criteria API can be defined as the programmatic approach for the building queries dynamically using the java codes and it can provide the type of safe way to the construct the queries without the writing SQL or JPQL strings explicitly.
Mapping Inheritance Hierarchies: JPA can supports the different strategies for the mapping the inheritance hierarchies that can including the single table, joined and the table-per-class inheritance. Understanding these strategies is the crucial for the modeling complex object inheritance.
Caching Strategies: Hibernate can offers the various caching strategies to the improve application performance by the reducing the database round trips and these can include the first level-cache and second-level cache.

JPA – Hibernate Entity Manager

JPA in Java persistence can be defined as the Java Persistence API, and it plays an important role in communicating between Java objects and related databases Hibernate is one of the most popular JPA implementations.

JPA and Hibernate Entity Manager

JPA is a specification for managing relational data in Java applications and can provide a variety of interfaces and annotations to perform data manipulation by providing Java objects to database tables.

Hibernate Entity Manager is a JPA service that can be specifically provided by the Hibernate framework and can act as an intermediary between Java objects and the underlying database This JPA can handle CRUD operations, transactions, and entity management of applications.

Similar Reads

Methods Definitions persist(Object entity) This method can used to make the instance managed and persistent. Usage: Use the persist to save the new entity into the database. Entity can be managed by the persistence context and any changes are made to it will be automatically synchronized with database upon the transaction commit. merge(Object entity) This method can be used to merge the state of the given entity into current persistence context. Usage: Use the merge to the update of the exisiting entity instance to the persistence context and it can returns the merged entity which can be the further used for the modification and sychronization with database. remove(Object entity) This method can be used to remove the entity instance from the database. Usage: Use the remove to delete the existing the instance from the database. find(Class entityClass, Object primaryKey) This method can be used to find the entity by its the primary key. Usage: Use the find to retrieve the entity instance from the database on its the primary key value.It returns the entity instance. getReference(Class entityClass, Object primaryKey) This method can be similar to the find but it can returns the reference to the entity instead of the loading it immediately. Usage: Use the getReference to the obtain refrenece to an the entity without actually loading it from the database. flush() This method can be used to sychronize the persistence context with underlying the database. Usage: Use the flush to force the EntityManager to the synchronize the changes are made to managed the entities with database. detach(Object entity) This method can be used to the detach the entity instance from the persistence context. Usage: Use the detach to the remove an entity from persistence context and it can effectively making it detached. clear() This method can be used to clear the persistence context and it can be detaching all the managed entities. Usage: Use the clear to remove all managed entities from persistence context....

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#JPA #Advance Java