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查找文档

Overview

在本指南中，您可以学习；了解如何使用MongoDB Extension for Hibernate ORM运行数据库查询，以从MongoDB集合中检索文档。

要查询MongoDB数据，请在会话或实体管理器上调用 createQuery() 方法。然后，以 Hibernate Query Language (HQL) 或 Jakarta Persistence Query Language (JPQL)声明指定您的查询。

检索所有文档

要从集合中检索所有文档，请将 select声明传递给 createQuery() 方法。在此声明中，指定表示要查询的集合的实体。

The following example retrieves the title values of all documents from the sample_mflix.movies collection by querying the Movie entity:

var allDocs = session.createQuery("select title from Movie", String.class)
                           .getResultList();
for (var t : allDocs) {
    System.out.println("Title: " + t);
}

Title: A Corner in Wheat
Title: Gertie the Dinosaur
Title: The Perils of Pauline
Title: Civilization
Title: Where Are My Children?
...

var allDocs = entityManager.createQuery("select m.title from Movie m", String.class)
                           .getResultList();
for (var t : allDocs) {
    System.out.println("Title: " + t);
}

Title: A Corner in Wheat
Title: Gertie the Dinosaur
Title: The Perils of Pauline
Title: Civilization
Title: Where Are My Children?
...

检索匹配文档

要检索匹配特定条件的文档，请将带有 where 子句的 SELECT声明传递给 createQuery() 方法。在此声明中，指定表示要查询的集合的实体以及匹配条件。

The following example retrieves documents that have a title value of "Romeo and Juliet" from the sample_mflix.movies collection:

var matchingDocs = session.createQuery("from Movie where title = :t", Movie.class)
                          .setParameter("t", "Romeo and Juliet")
                          .getResultList();
for (var m : matchingDocs) {
    System.out.println("Title: " + m.getTitle() + ", Year: " + m.getYear());
}

Title: Romeo and Juliet, Year: 1936
Title: Romeo and Juliet, Year: 1968

var matchingDocs = entityManager.createQuery("select m from Movie m where m.title = :t", Movie.class)
                                .setParameter("t", "Romeo and Juliet")
                                .getResultList();
for (var m : matchingDocs) {
    System.out.println("Title: " + m.getTitle() + ", Year: " + m.getYear());
}

Title: Romeo and Juliet, Year: 1936
Title: Romeo and Juliet, Year: 1968

Retrieve One Document

要检索匹配特定条件的单个文档，请将 getSingleResult() 方法链接到 createQuery() 方法。

The following example retrieves a single document that has a title value of "Best in Show" from the sample_mflix.movies collection:

var singleResult = session.createQuery("from Movie where title = :t", Movie.class)
                          .setParameter("t", "Best in Show")
                          .getSingleResult();
System.out.println("Title: " + singleResult.getTitle() + ", Year: " + singleResult.getYear());

var singleResult = entityManager.createQuery("select m from Movie m where m.title = :t", Movie.class)
                                .setParameter("t", "Best in Show")
                                .getSingleResult();
System.out.println("Title: " + singleResult.getTitle() + ", Year: " + singleResult.getYear());

重要

NonUniqueResultException 错误

如果查询匹配多个文档，则 getSingleResult() 方法会引发 NonUniqueResultException 错误。要避免此错误，请确保查询仅匹配一个文档或查询结果限制为一个文档。

运行条件API查询

您可以使用 Jakarta Persistence Criteria API 以编程方式构建类型安全的查询，而不是使用 HQL 或 JPQL 声明创建查询筛选条件。

要使用 Criteria API创建查询，请完成以下步骤：

从会话或实体经理创建 CriteriaBuilder对象。
从构建器创建一个 CriteriaQuery对象，并指定要查询的实体。
使用 CriteriaQuery 类提供的查询方法来指定查询条件。

提示

要学习；了解有关 Criteria API 的更多信息，请参阅 Jakarta EE 文档中的使用 Criteria API创建查询。

The following example uses the Criteria API to retrieve all documents that have a year value of 1925 from the sample_mflix.movies collection:

CriteriaBuilder cb = session.getCriteriaBuilder();
CriteriaQuery<Movie> cq = cb.createQuery(Movie.class);
Root<Movie> movieRoot = cq.from(Movie.class);
cq.select(movieRoot).where(cb.equal(movieRoot.get("year"), 1925));
session.createQuery(cq).getResultList()
    .forEach(m -> System.out.println(m.getTitle()));

Lady Windermere's Fan
Clash of the Wolves
Grass: A Nation's Battle for Life

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Movie> cq = cb.createQuery(Movie.class);
Root<Movie> movieRoot = cq.from(Movie.class);
cq.select(movieRoot).where(cb.equal(movieRoot.get("year"), 1925));
entityManager.createQuery(cq).getResultList()
    .forEach(m -> System.out.println(m.getTitle()));

Lady Windermere's Fan
Clash of the Wolves
Grass: A Nation's Battle for Life

运行原生查询

要运行Hibernate ORM 扩展当前不支持的MongoDB查询，您可以将查询作为MongoDB查询语言 (MQL)声明传递给 createNativeQuery() 方法。

要学习了解如何运行原生查询，请参阅执行原生查询指南。