Cheat Sheet: New Features in JPA 2.1

JPA 2.1 introduced 12 new features, like StoreProcedureQueries, Entity Graphs and Attribute Converter, to make your work with the database easier and more efficient.
Download your free New Features in JPA 2.1 cheat sheet now, to get all the information you need to improve your database access.

This 5 page cheat sheet brings you:

- a short description and
- code snippets for each feature,
- links to more detailed articles.

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Showing posts with label JPA2.1. Show all posts
Showing posts with label JPA2.1. Show all posts

Result Set Mapping: Constructor Result Mappings

This is the third part of my series about SQL result set mappings:
In the first post of this series, we had a look at some mapping definition between the query result and one entity. The mapping definitions got more complex in the second part, as we mapped the query result to multiple entities and handled additional columns. 
In this post, we will have a look at the Constructor Result Mappings introduced in JPA 2.1. This feature allows us to call the constructor of a value object with the result of the query, similar to the JPQL constructor expressions. This is often used, if we want to provide a specific view of our domain model to the client.

JPA 2.1 - 12 features every developer should know

If you are a regular reader of this blog, you know that I wrote several articles about features and enhancements introduced with JPA 2.1. One thing that was missing, was a general overview about all the changes. So here it is :-)
The following paragraphs provide a description of the 12 features and enhancements introduced with JPA 2.1. And as a special bonus, I created a cheat sheet with a short description and additional code snippets for each change, which you can download for free.

5 ways to initialize lazy relations and when to use them

Lazy loading of relations between entities is a well established best practice in JPA. Its main goal is to retrieve only the requested entities from the database and load the related entities only if needed. That is a great approach, if we only need the requested entities. But it creates additional work and can be the cause of performance problems, if we also need some of the related entities.

Lets have a look at the different ways to trigger the initialization and their specific advantages and disadvantages.

Testing with Aliens: How to test a JPA type converter with Arquillian

This post was written together with +Aslak Knutsen (@aslakknutsen).

JPA type converters provide an easy way to define how an entity attribute gets persisted to the database. You can use them to implement lots of different features, e.g. to encrypt your data as I showed in a previous post: How to use a JPA Type Converter to encrypt your data
But writing the type converter is not enough. We also need to make sure, that it is working correctly.

In general, there are two ways to test a type converter. We could write a unit test to check, if the conversion works correctly. But a unit test performs a test of the isolated class without putting it into the real execution environment. That means that we will still not know, if the converter works in one of our applications. If everything is set up correctly, the persistence provider will call the converter before writing to and after reading from the database. So we also need to check if the type converter gets called by the persistence provider and if everything works fine under that condition. We need to test the converter inside of the container we want to use for our application.
We will have a look at how this can be done with Arquillian and its persistence extension.

How to use a JPA Attribute Converter to encrypt your data

A few days ago, I read an interesting article by Bear Giles about Database encryption using JPA listeners from 2012. He discusses his requirements for an encryption solution and provides a code example with JPA listeners. His main requirements are:
  • provide a transparent encryption that does not affect the application,
  • be able to add the encryption at deployment time,
  • develop application and security/encryption by two different teams/persons.
And I completely agree with him. But after 1.5 years and a spec update to JPA 2.1, JPA listeners are not the only solution anymore. JPA 2.1 introduced Attribute Converter, which can be used to create a maybe better solution.

JPA 2.1 Entity Graph - Part 2: Define lazy/eager loading at runtime

This is my second post on Entity Graphs, one of the features introduced with JPA 2.1. The first post described the usage of named entity graphs. These can be used to define a graph of entities and/or attributes at compile time that shall be fetched with a find or query method. Dynamic entity graphs do to the same but in a dynamic way. This means you can use the EntityGraph API to define your entity graph at runtime.
If you have missed the first post and want to read how to define a named entity graph or how lazy loading issues were solved with JPA 2.0, check this post: JPA 2.1 Entity Graph - Part 1: Named entity graphs

JPA 2.1 Entity Graph - Part 1: Named entity graphs

Lazy loading was often an issue with JPA 2.0. You have to define at the entity if you want to use FetchType.LAZY (default) or FetchType.EAGER to load the relation and this mode is always used. FetchType.EAGER is only used if we want to always load the relation. FetchType.LAZY is used in almost all of the cases to get a well performing and scalable application.
But this is not without drawbacks. If you have to use an element of the relation, you need to make sure, that the relation gets initialized within the transaction that load the entity from the database. This can be done by using a specific query that reads the entity and the required relations from the database. But this will result in use case specific queries. Another option is to access the relation within your business code which will result in an additional query for each relation. Both approaches are far from perfect.

JPA 2.1 entity graphs are a better solution for it. The definition of an entity graph is independent of the query and defines which attributes to fetch from the database. An entity graph can be used as a fetch or a load graph. If a fetch graph is used, only the attributes specified by the entity graph will be treated as FetchType.EAGER. All other attributes will be lazy. If a load graph is used, all attributes that are not specified by the entity graph will keep their default fetch type.

Lets have a look how to define and use an entity graph.

JPA 2.1 Attribute Converter - The better way to persist enums

Persisting enums with JPA 2.0 is possible, but there is no nice way to do it. Using the @Enumerated annotation, you can use EnumType.ORDINAL or EnumType.STRING to map the enum value to its database representation. But both options have their drawbacks. The ordinal of an Enum depends on the ordering of its values and can create problems, if we need to add new ones. The String representation of an Enum is often quite verbose and renaming a value will break the database mapping. These drawbacks can be avoided by using an Attribute Converter.

Criteria Update/Delete - The easy way to implement bulk operations with JPA2.1

With JPA2.1 the Criteria API was extended by CriteriaUpdate and CriteriaDelete. The two classes can be used to implement bulk update and delete operations using the Criteria API.

JPA 2.1 - How to implement an Attribute Converter

JPA 2.1 brings several improvements. One of them is the Attribute Converter. It allows the developer to specify methods to convert between the database and the Java representation of an attribute.