playframework 中的 LazyInitializationException

Question

在为使用 playframework 的网络应用程序编写功能测试时，我创建了

@Before
public void setup() {
    Fixtures.deleteDatabase();
}
@Test
public void testListTagged() {
    Fixtures.loadModels("data.yml");
    Response response = GET("/books/category/science");
    assertNotNull(renderArgs("books"));
    List<Book> books = (List<Book>)renderArgs("books");
    assertEquals(3,books.size());

listTagged 方法检查地图对象的 Cache (String:List）包含属于给定类别的书籍列表，如果地图为空或列表为空，则进行数据库查询并将列表呈现为“书籍”。

public static void listTagged(String category) {
        List<Book> books =null;
        Map<String,List<Book>> tagMap = (Map<String, List<Book>>) Cache.get("tagmap");
        if(tagMap!= null) {
            books = tagMap.get(category);           
        }

        if(tagMap==null || books == null) { 
            books= Book.findTaggedWith(category);
        }
        Book book = null;
        if (books!=null && books.size()>0) {
            book = books.get(0);
        }        
        render(category,book, books);
    }

Book 类

@Entity
public class Book extends Model implements Comparable<Book>{
    @Required
    @Column(unique = true)
    public String isbn;

    @Required
    //@Field
    public String name;
        ...
    @ManyToMany(cascade=CascadeType.PERSIST)
    public Set<Category> categories;
    public Book(String isbn, String name, ...) {
        super();

        this.isbn = isbn;
        this.name = name;
        ...
        this.categories = new TreeSet<Category>();
    }
        ...
public static List<Book> findTaggedWith(String categoryName) {
        Map<String,List<Book>> tagMap = (Map<String, List<Book>>) Cache.get("tagmap");
        if(tagMap==null) {
            tagMap= new HashMap<String,List<Book>>();
        }
        List<Book> books = Book.find("select distinct book from Book book join book.categories as cat where cat.name=:name").bind("name", categoryName).fetch();
        tagMap.put(categoryName, books);
        Cache.add("tagmap", tagMap,"20mn");
        return books;
    }

单独运行上述测试没有造成任何问题。但是当它与一些调用各种书籍的数据库的单元测试一起运行时，会导致延迟初始化异常，

A java.lang.RuntimeException has been caught, java.util.concurrent.ExecutionException: play.exceptions.TemplateExecutionException: failed to lazily initialize a collection of role: models.Book.categories, no session or session was closed

我该如何解决这个问题？有人可以建议吗？

Answer 1

你可以使用：

@ManyToMany(cascade=CascadeType.PERSIST, fetch=FetchType.EAGER)
public Set<Category> categories;

这可能会解决问题。否则，您必须注意会话是否已打开。已测试并正在工作