我有两个模型Book和Author,Book有一个指向Author的引用,如果一个Author被删除,那么我只想检索那些有作者的书:
BookSchema包含以下字段:
name: String,
author: {
type: Schema.Types.ObjectId,
ref: 'Author',
required: [true, 'A book must have an author']
}
AuthorSchema 带有以下字段
name: String
我需要使用 $lookup 操作符完成这个任务。我已经得到了期望的结果,但是不确定这是否是最佳方式。这是我的解决方案:
const books = await Book.aggregate([
{ $lookup: {
from: 'authors',
localField: 'author',
foreignField: '_id',
as: 'bookAuthor'
}
},
{ $match: { bookAuthor: { $not: { $size: 0 } } } },
{ $unwind: '$bookAuthor' },
{ $project: {
name: 1,
bookAuthor: { name: 1 }
}
}
]);