13 - What is Entity Manager and How to use with Spring MVC? |

Описание: #Hibernate #EntityManager #JPA #SpringMVC

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What is Entity Manager in Hibernate ?
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--- Hibernate Entity Manager implements the programming interfaces and lifecycle rules as defined by the JPA 2.0 specification.
--- Together with Hibernate Annotations, this wrapper implements a complete (and standalone) JPA persistence solution on top of the mature Hibernate Core.
--- The Entity Manager API is used to access a database in a particular unit of work. This interface is similar to the Session in Hibernate.
--- It is used to create and remove persistent entity instances, to find entities by their primary key identity, and to query over all entities.
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What is Entity Manager Factory?
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--- An entity manager factory provides entity manager instances, all instances are configured to connect to the same database, to use the same default settings as defined by the particular implementation, etc.
--- Interface used to interact with the entity manager factory for the persistence unit. When the application has finished using the entity manager factory, and/or at application shutdown, the application should close the entity manager factory.
--- You can prepare several entity manager factories to access several data stores. This interface is similar to the Session Factory in native Hibernate.
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What is Local Container Entity Manager Factory Bean?
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--- FactoryBean that creates a JPA EntityManagerFactory according to JPA’s standard container bootstrap contract.
--- This is the most powerful way to set up a shared JPA EntityManagerFactory in a Spring application context.
--- The EntityManagerFactory can then be passed to JPA-based DAOs via dependency injection.
Note that switching to a JNDI lookup or to a LocalEntityManagerFactoryBean definition is just a matter of configuration.
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What is Persistence context?
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--- The scope of this context can either be the transaction, or an extended unit of work.
--- Entities are managed by javax.persistence.EntityManager instance using persistence context.
--- Each EntityManager instance is associated with a persistence context.
--- Within the persistence context, the entity instances and their lifecycle are managed.
--- Persistence context defines a scope under which particular entity instances are created, persisted, and removed.
--- A persistence context is like a cache which contains a set of persistent entities, So once the transaction is finished, all persistent objects are detached from the EntityManager’s persistence context and are no longer managed.
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What is HibernateJpaVendorAdapter?
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--- JpaVendorAdapter implementation for Hibernate EntityManager.
--- Its kind of one property of EntityManager and contains some configuration like generate DDL, show SQL, format SQL etc.
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What is JpaTransactionManager?
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--- This transaction manager is appropriate for applications that use a single JPA EntityManagerFactory for transactional data access.
--- JTA (usually through JtaTransactionManager) is necessary for accessing multiple transactional resources within the same transaction.
--- This transaction manager also supports direct DataSource access within a transaction.
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