如何使用 TypeORM 查询多对多关系

Question

Note 与 Subject

存在多对多关系

查询它的最佳方式是什么？我会喜欢写下下面的内容以获得给定笔记上的所有主题:

  const subjectRepo = connection.getRepository(Subject);
  const response = await subjectRepo.find({
    relations: ['notes'],
    where: { note }
  });

但是 returns 所有主题，而不仅仅是笔记上的主题。

Reln 定义为：

  @ManyToMany(() => Subject, (subject: Subject) => subject.notes)
  subjects: Subject[];

-- 和--

  @ManyToMany(() => Note, note => note.subjects)
  @JoinTable()
  notes: Note[];

执行的查询是：

SELECT "Subject"."id" AS "Subject_id", "Subject"."name" AS "Subject_name", "Subject"."description" AS "Subject_description", "Subject"."createdDate" AS "Subject_createdDate", "Subject"."updatedDate" AS "Subject_updatedDate", "Subject"."notebookId" AS "Subject_notebookId", "Subject"."measurementsId" AS "Subject_measurementsId", "Subject_notes"."id" AS "Subject_notes_id", "Subject_notes"."content" AS "Subject_notes_content", "Subject_notes"."notedAt" AS "Subject_notes_notedAt", "Subject_notes"."createdDate" AS "Subject_notes_createdDate", "Subject_notes"."updatedDate" AS "Subject_notes_updatedDate", "Subject_notes"."notebookId" AS "Subject_notes_notebookId" FROM "subject" "Subject" LEFT JOIN "subject_notes_note" "Subject_Subject_notes" ON "Subject_Subject_notes"."subjectId"="Subject"."id" LEFT JOIN "note" "Subject_notes" ON "Subject_notes"."id"="Subject_Subject_notes"."noteId"

---

注意：您可以这样做：

  return subjectRepo
    .createQueryBuilder('subject')
    .leftJoin('subject.notes', 'note')
    .where('note.id = :id', { id: note.id })
    .getMany();

但我希望有一种字符串更少且显式连接的方法

Answer 1

你试图让TypeORM生成的SQL大致如下

SELECT *
FROM subject
JOIN subject_note AS jt on jt.subject_id = subject.id
WHERE jt.note_id = :id

1。 repo.find

这是不可能的

在撰写本文时，无法使用 repo.find(...) 在联接的 table 上创建 where 子句。您可以 join (doc) 但 where 子句仅影响存储库的实体。

TypeORM 也会默默地忽略无效的 where 子句，所以要小心那些。

2。重新select注释实体

如果您想要给定 note 的所有 subject，您将需要使用查询生成器，如您所述，或者您需要重新 select注意对象及其关系。

note = await noteRepo.find({
    relations: ['subjects'],
    where: { id: note.id }
});
const subjects = note.subjects

3。使用TypeORM 惰性关系

如果你想避免重新selection，你需要使用TypeORM Lazy relations但是这迫使你将两个实体中的类型更改为Promise

// note entity
@ManyToMany(() => Subject, (subject: Subject) => subject.notes)
subjects: Promise<Subject[]>;

// subject entity
@ManyToMany(() => Note, note => note.subjects)
@JoinTable()
notes: Promise<Note[]>;

使用这种惰性关系，您将需要 await 在每次使用前加载链接的注释，但您不需要向 find 方法提供关系数组。

const note = await noteRepo.find({
    where: { id: someId }
});
const subjects = await note.subjects