Spring Data JPA 1.3参考文档：入门与高级特性

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Spring Data JPA 是一个强大的框架，它将 Java Persistence API (JPA) 与 Spring 框架集成，简化了在 Spring 应用程序中使用 JPA 进行数据持久化的操作。Spring Data JPA 1.3.0.RELEASE 版本提供了丰富的文档，由 Oliver Gierke 编写，他是 SpringSource 的高级顾问，隶属于 VMware。该文档详细介绍了 Spring Data JPA 的核心概念和使用方法，包括以下几个主要部分： 1. **项目元数据**：这部分涵盖了如何设置项目的配置，如定义产品名称，这对于文档生成和配置文件是至关重要的。 2. **Repository 接口**：Spring Data JPA 的核心是 Repository 接口，它为开发者提供了一种声明式的方式来定义数据访问方法，如查询、保存和删除操作。文档首先介绍 Repository 接口的概念，然后说明如何定义接口，以及如何精细调整其行为，例如定义查询方法，选择查询策略，处理特殊参数等。 - **定义 repository 接口**：用户需要创建特定于数据模型的接口，这些接口遵循特定的命名约定（如 `CrudRepository` 或自定义扩展）。 - **查询方法**：包括基本的 CRUD（Create, Read, Update, Delete）操作，以及更复杂的查询如分页、排序和聚合函数。 - **查询策略**：允许开发者选择使用 JPA 的原生 SQL 查询或使用更高级的查询构造器（QBC，Querydsl 等）。 - **参数处理**：处理查询中的参数，支持类型安全的参数绑定。 3. **创建 repository 实例**：文档讨论了两种配置方式，XML 配置和 Java Config，以及在单独应用程序中的使用场景。 4. **定制实现**：允许开发者扩展 Repository 接口，为单个或所有 repository 添加自定义行为，如通用功能或业务逻辑。 5. **扩展性**：Spring Data JPA 提供了丰富的扩展机制，以便于与其他库集成，如对 DomainClass（领域类）的特殊处理。 Spring Data JPA 1.3.0.RELEASE 的参考文档为开发者提供了一个全面的指南，帮助他们高效地使用 JPA 在 Spring 环境中进行数据操作，包括设计和配置 repository 接口、执行复杂查询，以及定制和扩展框架的功能。通过阅读这份文档，开发者可以更好地理解并利用 Spring Data JPA 的优势，提升开发效率和代码质量。

please define productname in your docbook file!

1.3.0.RELEASE

Spring Data JPA -

Reference Documentation 4

public interface PersonRepository extends Repository<User, Long> { … }

2. Declare query methods on the interface.

List<Person> findByLastname(String lastname);

3. Setup Spring to create proxy instances for those interfaces.

<?xml version="1.0" encoding="UTF-8"?>

<beans:beans xmlns:beans="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns="http://www.springframework.org/schema/data/jpa"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/data/jpa

http://www.springframework.org/schema/data/jpa/spring-jpa.xsd">

</beans>

Note

Note that we use the JPA namespace here just by example. If you're using the repository

abstraction for any other store you need to change this to the appropriate namespace

declaration of your store module which should be exchanging jpa in favor of e.g. mongodb.

4. Get the repository instance injected and use it.

public class SomeClient {

@Autowired

private PersonRepository repository;

public void doSomething() {

List<Person> persons = repository.findByLastname("Matthews");

}

At this stage we barely scratched the surface of what's possible with the repositories but the general

approach should be clear. Let's go through each of these steps and figure out details and various options

that you have at each stage.

Defining repository interfaces

As a very first step you define a domain class specific repository interface. It's got to extend Repository

and be typed to the domain class and an ID type. If you want to expose CRUD methods for that domain

type, extend CrudRepository instead of Repository.

Fine tuning repository definition

Usually you will have your repository interface extend Repository, CrudRepository or

PagingAndSortingRepository. If you don't like extending Spring Data interfaces at all you can also

annotate your repository interface with @RepositoryDefinition. Extending CrudRepository will

expose a complete set of methods to manipulate your entities. If you would rather be selective about

please define productname in your docbook file!

1.3.0.RELEASE

Spring Data JPA -

Reference Documentation 5

the methods being exposed, simply copy the ones you want to expose from CrudRepository into

your domain repository.

interface MyBaseRepository<T, ID extends Serializable> extends Repository<T, ID> {

T findOne(ID id);

T save(T entity);

}

interface UserRepository extends MyBaseRepository<User, Long> {

User findByEmailAddress(EmailAddress emailAddress);

}

Example 1.3 Selectively exposing CRUD methods

In the first step we define a common base interface for all our domain repositories and expose

findOne(…) as well as save(…).These methods will be routed into the base repository implementation

of the store of your choice because they are matching the method signatures in CrudRepository.

So our UserRepository will now be able to save users, find single ones by id as well as triggering

a query to find Users by their email address.

Defining query methods

Query lookup strategies

The next thing we have to discuss is the definition of query methods. There are two main ways that the

repository proxy is able to come up with the store specific query from the method name. The first option

is to derive the query from the method name directly, the second is using some kind of additionally

created query. What detailed options are available pretty much depends on the actual store, however,

there's got to be some algorithm that decides what actual query is created.

There are three strategies available for the repository infrastructure to resolve the query. The strategy

to be used can be configured at the namespace through the query-lookup-strategy attribute.

However, It might be the case that some of the strategies are not supported for specific datastores.

Here are your options:

CREATE

This strategy will try to construct a store specific query from the query method's name. The general

approach is to remove a given set of well-known prefixes from the method name and parse the rest of

the method. Read more about query construction in the section called “Query creation”.

USE_DECLARED_QUERY

This strategy tries to find a declared query which will be used for execution first. The query could be

defined by an annotation somewhere or declared by other means. Please consult the documentation

of the specific store to find out what options are available for that store. If the repository infrastructure

does not find a declared query for the method at bootstrap time it will fail.

CREATE_IF_NOT_FOUND (default)

This strategy is actually a combination of CREATE and USE_DECLARED_QUERY. It will try to lookup a

declared query first but create a custom method name based query if no declared query was found. This

is the default lookup strategy and thus will be used if you don't configure anything explicitly. It allows

quick query definition by method names but also custom tuning of these queries by introducing declared

queries as needed.

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