如何使用 TypeORM 查询多对多关系

Question

Note与Subject具有多对多关系

查询它的最佳方法是什么？ 我想写以下内容，让所有主题都记在一张纸条上：

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

但这会返回所有主题，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[];

执行的查询为：

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和显式连接的方法

Answer 1

您尝试让 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.这在repo.find中是不可能的

在撰写本文时，无法使用repo.find(...)在连接的表上创建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，所以要小心这些子句。

2. 重新选择注释实体

如果您想要给定note的所有subject，则需要使用查询构建器，如您所指出的，或者您需要重新选择具有关系的注释对象。

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

3. 使用TypeORM懒惰关系

如果要避免重新选择，则需要使用TypeORM惰性关系，但这会强制您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，您需要await在每次使用之前加载链接的注释，但不需要提供与find方法的关系数组。

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