JOOQ：如何使用多重集

Posted 2023-02-27

【中文标题】JOOQ：如何使用多重集

【英文标题】：JOOQ: how to use multiset

【发布时间】：2022-01-08 07:52:54

【问题描述】：

鉴于这 3 个具有多对多关系的表

书

book_id	title	isbn	num_pages
1	JOOQ	1234	123
2	SQL	2345	155

book_author

book_id	author_id
1	1
2	1
2	2

作者

author_id	author_name
1	Lucas
2	Jose

还有记录

public record Book(Integer id, String title, String isbn, List<Author> authors) // don't need nr of pages

public record Author(Integer id, String name)

如何使用多重集获取List<Book>？

List<Book> books = dsl.select(
        BOOK_AUTHOR.BOOK_ID,
        select(BOOK.TITLE).from(BOOK).where(BOOK.BOOK_ID.eq(BOOK_AUTHOR.BOOK_ID)).asField("title"),
        select(BOOK.ISBN).from(BOOK).where(BOOK.BOOK_ID.eq(BOOK_AUTHOR.BOOK_ID)).asField("isbn"),
        multiset(
                selectFrom(AUTHOR).where(AUTHOR.AUTHOR_ID.eq(BOOK_AUTHOR.AUTHOR_ID))
        ).as("authors").convertFrom(record -> record.map(Records.mapping(Author::new)))
).from(BOOK_AUTHOR)
 .where(BOOK_AUTHOR.BOOK_ID.in(1, 2))
 .fetchInto(Book.class);

 books.forEach(System.out::println);

预期的列表包含 2 本书，但得到 3 本书！？...

Bookid=1, title='JOOQ', isbn='1234', authors=[Authorname='Lucas']
Bookid=2, title='SQL', isbn='2345', authors=[Authorname='Lucas']
Bookid=2, title='SQL', isbn='2345', authors=[Authorname='Jose']

有什么问题？

生成的SQL：

select "public"."book_author"."book_id", (select "public"."book"."title" from "public"."book" where "public"."book"."book_id" = "public"."book_author"."book_id") as "title", (select "public"."book"."isbn" from "public"."book" where "public"."book"."book_id" = "public"."book_author"."book_id") as "isbn", (select coalesce(jsonb_agg(jsonb_build_array("v0", "v1")), jsonb_build_array()) from (select "public"."author"."author_id" as "v0", "public"."author"."author_name" as "v1" from "public"."author" where "public"."author"."author_id" = "public"."book_author"."author_id") as "t") as "authors" from "public"."book_author" where "public"."book_author"."book_id" in (1, 2)

使用：

JAVA 17 POSTGRESQL spring-boot (2.6.1) 与 spring-boot-starter-jooq JOOQ 3.15.4（允许使用multiset 函数） JOOQ 代码生成（maven 插件）

【参考方案1】：

问题是您从有 3 个条目的 BOOK_AUTHOR 开始。您应该从 BOOK 中选择：

List<Book> books = dsl.select(
   BOOK.BOOK_ID,
   BOOK.TITLE,
   BOOK.ISBN,
   multiset(
     select(AUTHOR.AUTHOR_ID,AUTHOR.AUTHOR_NAME)
         .from(AUTHOR).innerJoin(BOOK_AUTHOR)
         .on(BOOK_AUTHOR.AUTHOR_ID.eq(AUTHOR.AUTHOR_ID))
         .where(BOOK_AUTHOR.BOOK_ID.eq(BOOK.BOOK_ID))
    ).as("authors")
     .convertFrom(record -> record.map(Records.mapping(Author::new)))
    ).from(BOOK)
     .where(BOOK.BOOK_ID.in(1, 2))
     .fetchInto(Book.class);

【讨论】：

谢谢。我收到这段代码的错误......但我明白你的意思

经过一些小改动后工作正常。谢谢！

很高兴您发现了问题