Question

我正在使用Spring Boot实现GraphQL服务器，但是，在为具有多对多关系的模型编写解析器时遇到了一些麻烦。下面的resolver类中的函数getBooks引发以下错误：

package com.example.DemoGraphQL.resolver;

import java.util.Set;
import java.util.stream.Collectors;

import com.coxautodev.graphql.tools.GraphQLResolver;
import com.example.DemoGraphQL.model.Author;
import com.example.DemoGraphQL.model.Book;
import com.example.DemoGraphQL.repository.AuthorRepository;
import com.example.DemoGraphQL.repository.BookRepository;

public class AuthorResolver implements GraphQLResolver<Book> {
    private BookRepository bookRepository;

    public AuthorResolver(BookRepository bookRepository) {
        this.bookRepository = bookRepository;
    }

    public Iterable<Book> getBooks(Author author) {
        Set<Long> ids = author.getBooks().stream().map(book -> book.getId()).collect(Collectors.toSet());
        return bookRepository.findAll(ids);
    }
}

错误消息：

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.example.DemoGraphQL.model.Author.books, could not initialize proxy - no Session

当我仅查询给定模型的一个对象时，便能够实现类似的解析器。任何建议表示赞赏。

Answer 1

我通过将fetch=FetchType.Eager添加到我的多对多装饰器中来解决此问题。

@ManyToMany(fetch = FetchType.EAGER, cascade = { CascadeType.ALL })

这显然不是大规模的解决方案。

Java GraphQL Resolver用于可迭代对象：休眠异常

1 个答案: