问题描述
我试图找出使用 type-graphql 和 typeorm 和 postgresql db(使用 apollo 服务器和 express)处理一对多关系的最佳方法.我有一个与课程表具有一对多关系的用户表.我目前处理此问题的方法是使用 @RelationId 字段创建一列 userCourseIds,然后使用 @FieldResolver 和 dataloader 批量获取属于该用户的课程.我的问题是,对于 @RelationId 字段,无论我是否实际查询 userCourses,都会进行一个单独的查询来获取关系 ID.有没有办法解决这个问题,它不会产生额外的查询,或者有没有更好的方法来处理一对多关系?
I'm trying to figure out the best way to handle a one-to-many relationship using type-graphql and typeorm with a postgresql db (using apollo server with express). I have a user table which has a one-to-many relation with a courses table. The way I am currently handling this is to use the @RelationId field to create a column of userCourseIds and then using @FieldResolver with dataloader to batch fetch the courses that belong to that user(s). My issue is that with the @RelationId field, a separate query is made to get the relationids whether or not I actually query for userCourses. Is there a way to handle this where it won't make that extra query or is there a better way to go about handling one-to-many relationships?
关系的用户端:
@OneToMany(() => Course, (course) => course.creator, { cascade: true })
userCourses: Course[];
@RelationId((user: User) => user.userCourses)
userCourseIds: string;
关系的课程方面:
@Field()
@Column()
creatorId: string;
@ManyToOne(() => User, (user) => user.userCourses)
creator: User;
userCourses FieldResolver:
userCourses FieldResolver:
@FieldResolver(() => [Course], { nullable: true })
async userCourses(@Root() user: User, @Ctx() { courseLoader }: MyContext) {
const userCourses = await courseLoader.loadMany(user.userCourseIds);
return userCourses;
}
推荐答案
userCourses
字段可以使用 @TypeormLoader 装饰器编写如下所示://github/slaypni/type-graphql-dataloader" rel="nofollow noreferrer">type-graphql-datalaoader.
userCourses
field can be written like below using @TypeormLoader
decorator provided by type-graphql-datalaoader.
@ObjectType()
@Entity()
class User {
...
@Field((type) => [Course])
@OneToMany(() => Course, (course) => course.creator, { cascade: true })
@TypeormLoader((course: Course) => course.creatorId, { selfKey: true })
userCourses: Course[];
}
@ObjectType()
@Entity()
class Course {
...
@ManyToOne(() => User, (user) => user.userCourses)
creator: User;
@RelationId((course: Course) => course.creator)
creatorId: string;
}
由于省略了 userCourseIds
,因此不会再发出其他查询.虽然 creatorId
和 @RelationId
存在,但它不会发出额外的查询,因为实体有自己的值.
Additional queries will not be issued anymore since userCourseIds
is omitted. Although creatorId
with @RelationId
exists, it will not issue extra queries since the entity has the value by its own.
@TypeormLoader
不再需要参数.因此 @RelationId
可以完全省略,如果愿意的话.
@TypeormLoader
no longer needs arguments. Therefore @RelationId
can be completely omitted, if preferred.
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