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Tag Archives: JPA

How to use Reflection to Document your Data Model based on JPA Annotations

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So using JPA, Hiber­nate or EBeans is cool when you can just anno­tate your Java classes, but haven’t you always wished you could “gen­er­ate” doc­u­men­ta­tion of your data model from the code? Pulling infor­ma­tion of the the JPA / Hiber­nate  and other val­i­da­tion annotations? Assum­ing you have all those nice Anno­ta­tions in your beans:           @Entity @Table(name ...

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JPA 2 | Dynamic Queries Vs Named Queries

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JPA has its own Query language called JPQL. JPQL is very similar to SQL, with one major difference being that JPQL works with entities as defined in the application whereas SQL works with table and column names as defined in the database. JPA provides us with a variety of options when it comes to defining the JPA queries that will ...

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JPA 2 | EntityManagers, Transactions and everything around it

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Introduction One of the most confusing and unclear thing for me, as a Java Developer has been the mystery surrounding the Transaction Management in general and how JPA handles transaction management in particular. When does a transaction get started, when does it end, how entities are persisted, the persistence context and much more. Frameworks like Spring does not help in understanding the ...

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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?

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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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