Spring Data JPA 教程：简化数据访问层开发

SpringData

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"SpringDataJPA-ReferenceDocumentation" Spring Data JPA是Spring框架的一部分，它提供了一个高级的Repository抽象层，显著减少了与各种持久化存储进行数据访问层实现时所需的样板代码。这个参考文档详细介绍了如何有效地使用Spring Data JPA来构建高效的数据访问层。 1. **核心概念** - **Repository抽象**：Spring Data通过定义接口，自动实现了常见的CRUD操作，允许开发者专注于业务逻辑而不是数据访问细节。 - **Entity**：在JPA中，实体代表数据库中的表，通过@Entity注解标记。 - **Persistence Context**：JPA的持久化上下文管理对象的状态和事务。 2. **查询方法** - **自定义查询方法**：只需在Repository接口中定义方法名，Spring Data JPA就能自动解析并执行对应的SQL或HQL查询。 - **命名查询**：可以定义预编译的JPA命名查询，提高性能。 3. **定义Repository接口** - **基本接口**：继承JpaRepository或CrudRepository，可以获得基本的CRUD操作。 - **定制接口**：通过添加特定的方法签名，实现更复杂的查询逻辑。 4. **细调Repository定义** - **查询查找策略**：Spring Data提供了多种策略来确定如何从方法名中解析查询。 - **查询创建**：基于方法名的规则，Spring Data可以动态生成SQL或HQL。 - **属性表达式**：使用点号分隔的属性路径来指定查询条件。 - **特殊参数处理**：支持Pageable、Sort等参数来实现分页和排序。 - **限制查询结果**：如使用第一/最后一个结果，或限制返回的记录数。 5. **创建Repository实例** - **XML配置**：在Spring配置文件中声明Repository接口及其实现。 - **使用过滤器**：通过Filter接口来控制哪些Repository实例被创建。 - **JavaConfig**：使用@Configuration类和@EnableJpaRepositories注解进行配置。 - **独立使用**：在没有Spring应用上下文的情况下，直接使用RepositoryFactoryBean创建实例。 6. **自定义Spring Data repositories行为** - **单个Repository的定制**：通过为特定Repository实现一个扩展接口并注入实现。 - **所有Repository的通用定制**：通过RepositoryFactorySupport的子类来全局影响Repository的行为。 7. **Spring Data扩展** - **Web支持**：提供了与Spring MVC的集成，支持网页展示和分页。 - **Hypermedia支持**：对于RESTful服务，支持链接到Pageable结果。 - **Repository populators**：帮助填充Repository实例的数据，用于测试或初始化。 - **Legacy web支持**：包括与旧版Spring MVC的兼容性，以及领域类的Web绑定。 8. **参考文档** - **JPA Repositories**章节详细解释了如何使用JPA的Repository接口，包括其配置、查询和事务管理等方面。以上内容仅是Spring Data JPA参考文档的一部分，实际文档还涵盖了更多主题，如查询构造器、事件监听、审计功能、JPA特定的查询方法等。全面掌握这些知识，能帮助开发者构建出高效、灵活且易于维护的数据访问层。

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Spring Data JPA -

Reference Documentation 6

you can also annotate your repository interface with @RepositoryDefinition. Extending

CrudRepository exposes a complete set of methods to manipulate your entities. If you prefer

to be selective about the methods being exposed, simply copy the ones you want to expose from

CrudRepository into your domain repository.

Note

This allows you to define your own abstractions on top of the provided Spring Data Repositories

functionality.

@NoRepositoryBean

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 1.5 Selectively exposing CRUD methods

In this first step you defined a common base interface for all your domain repositories and exposed

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

of the store of your choice provided by Spring Data ,e.g. in the case if JPA SimpleJpaRepository,

because they are matching the method signatures in CrudRepository. So the UserRepository will

now be able to save users, and find single ones by id, as well as triggering a query to find Users by

their email address.

Note

Note, that the intermediate repository interface is annotated with @NoRepositoryBean. Make

sure you add that annotation to all repository interfaces that Spring Data should not create

instances for at runtime.

1.4 Defining query methods

The repository proxy has two ways to derive a store-specific query from the method name. It can derive

the query from the method name directly, or by using an manually defined query. Available options

depend on the actual store. However, there’s got to be an strategy that decides what actual query is

created. Let’s have a look at the available options.

Query lookup strategies

The following strategies are available for the repository infrastructure to resolve the query. You can

configure the strategy at the namespace through the query-lookup-strategy attribute in case

of XML configuration or via the queryLookupStrategy attribute of the Enable${store}Repositories

annotation in case of Java config. Some strategies may not be supported for particular datastores.

• CREATE attempts to construct a store-specific query from the query method 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”.

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Spring Data JPA -

Reference Documentation 7

• USE_DECLARED_QUERY tries to find a declared query and will throw an exception in case it can’t

find one. The query can be defined by an annotation somewhere or declared by other means.

Consult the documentation of the specific store to find available options for that store. If the repository

infrastructure does not find a declared query for the method at bootstrap time, it fails.

• CREATE_IF_NOT_FOUND (default) combines CREATE and USE_DECLARED_QUERY. It looks up a

declared query first, and if no declared query is found, it creates a custom method name-based query.

This is the default lookup strategy and thus will be used if you do not configure anything explicitly. It

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

declared queries as needed.

Query creation

The query builder mechanism built into Spring Data repository infrastructure is useful for building

constraining queries over entities of the repository. The mechanism strips the prefixes find…By,

read…By, query…By, count…By, and get…By from the method and starts parsing the rest of it. The

introducing clause can contain further expressions such as a Distinct to set a distinct flag on the

query to be created. However, the first By acts as delimiter to indicate the start of the actual criteria. At a

very basic level you can define conditions on entity properties and concatenate them with And and Or.

public interface PersonRepository extends Repository<User, Long> {

List<Person> findByEmailAddressAndLastname(EmailAddress emailAddress, String lastname);

// Enables the distinct flag for the query

List<Person> findDistinctPeopleByLastnameOrFirstname(String lastname, String firstname);

List<Person> findPeopleDistinctByLastnameOrFirstname(String lastname, String firstname);

// Enabling ignoring case for an individual property

List<Person> findByLastnameIgnoreCase(String lastname);

// Enabling ignoring case for all suitable properties

List<Person> findByLastnameAndFirstnameAllIgnoreCase(String lastname, String firstname);

// Enabling static ORDER BY for a query

List<Person> findByLastnameOrderByFirstnameAsc(String lastname);

List<Person> findByLastnameOrderByFirstnameDesc(String lastname);

}

Example 1.6 Query creation from method names

The actual result of parsing the method depends on the persistence store for which you create the query.

However, there are some general things to notice.

• The expressions are usually property traversals combined with operators that can be concatenated.

You can combine property expressions with AND and OR. You also get support for operators such as

Between, LessThan, GreaterThan, Like for the property expressions. The supported operators

can vary by datastore, so consult the appropriate part of your reference documentation.

• The method parser supports setting an IgnoreCase flag for individual properties (for example,

findByLastnameIgnoreCase(…)) or for all properties of a type that support ignoring case (usually

String instances, for example, findByLastnameAndFirstnameAllIgnoreCase(…)). Whether

ignoring cases is supported may vary by store, so consult the relevant sections in the reference

documentation for the store-specific query method.

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