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Tag Archives: JPA

Mapping enums done right with @Convert in JPA 2.1

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If you ever worked with Java enums in JPA you are definitely aware of their limitations and traps. Using enum as a property of your @Entity is often very good choice, however JPA prior to 2.1 didn’t handle them very well. It gave you 2+1 choices: @Enumerated(EnumType.ORDINAL) (default) will map enum values using Enum.ordinal(). Basically first enumerated value will be ...

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Spring JPA Data + Hibernate + MySQL + Maven

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Development of web-applications with the help of Spring MVC implies creation of several logical layers of architecture. One of the layers is a DAO (Repository) layer. It is responsible for communication with a database. If you developed the DAO layer at least once, you should know that it involves a lot of boilerplate code. A Spring Data take a part ...

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JPA – Querydsl Projections

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In my last post: JPA – Basic Projections – I’ve mentioned about two basic possibilities of building JPA Projections. This post brings you more examples, this time based on Querydsl framework. Note, that I’m referring Querydsl version 3.1.1 here. Reinvented constructor expressions Take a look at the following code:         ... import static com.blogspot.vardlokkur.domain.QEmployee.employee; import javax.persistence.EntityManager; import ...

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JPA – Should I become a laziness extremist?

java-interview-questions-answers

When you spoke with the Developers about mapping objects to relational databases, they very often complain about poor JPA performance, unpredictable behavior of JPA Providers, etc. Usually at some point of the conversation you will hear: “Let’s drop this technology at all, we’ve seen something much better on the conference last month. We will use it in our projects instead ...

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Introducing EclipseLink JPA-RS

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In a previous series of posts I covered how to create a JAX-RS service that leveraged JPA for the persistence layer.  EclipseLink contains a component called JPA-RS that can be used to easily and automatically expose a persistence unit as RESTful service (that supports XML and JSON messages).  MOXy provides the XML and JSON-binding for JPA-RS and things like bidirectional ...

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JPA: Determining the Owning Side of a Relationship

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When using the Java Persistence API (JPA) it is often necessary to create relationships between two entities.  These relationships are defined within the data model (think database) through the use of foreign keys and within our object model (think Java) using annotations to indicate associations. When defining relationships or associations within the object model a common task is identifying the ...

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JPA – Hibernate – Type mapping on package level

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When we are finally mature enough to use some custom types mapping in JPA, we usually stuck with some provider specific solution, because JPA itself doesn’t define any mechanism for doing it. Let me show you an example of custom type mapping definition for one of the JPA providers – Hibernate. Suppose that we use Joda Money in our project, ...

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JPA 2.0 Criteria Query with Hibernate

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Criteria Query has been introduced in JPA 2.0. With the help of criteria queries you can write your queries in a type-safe way. Before criteria queries, developers had to write queries through the construction of object-based query definitions. There might be chances of incorrect syntax while building the queries. The criteria query API provides feature to create structured and nested ...

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JPA and CMT – Why Catching Persistence Exception is Not Enough?

java-interview-questions-answers

Being in EJB and JPA world using CMT (Container Managed Transactions) is very comfortable. Just define few annotations to demarcate transaction boundary (or use the defaults) and that’s it – no fiddling with manual begin, commit or rollback operations. One way to rollback your transaction is to throw non-application exception (or application exception with rollback = true) from your EJB’s ...

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Types of Entity Managers: Application-managed EntityManager

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JPA specification defines few types of EntityManagers / Persistence Contexts. We can have: extended and transactional-scoped EntityManagers, container-managed or application-managed EntityManagers. JTA or resource-local EntityManager, Besides the above distinction, we also have two main contexts in which EntityManager / Persistence Context can exist – Java EE and Java SE. Not every option is available for Java EE and not every ...

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