database - 聚合以过滤 MongoDB 中的引用

Question

我正在尝试与 Mongoose 进行聚合工作，但我遇到了问题，我得到了这个结果:

[
   {
     _id: new ObjectId("630bb658370cc689973c5bb4"),
     isRead: true,
     user: new ObjectId("630273bbe0f3f82d85b149bd"),
     globalRef: new ObjectId("630bb649370cc689973c5b62"),
   },
   {
     _id: new ObjectId("630bb649370cc689973c5b62"),
     isRead: false,
   },
   {
     _id: new ObjectId("6306bcf16fa60080148fefb6"),
     isRead: false,
   },
   {
     _id: new ObjectId("630273bbe0f3f82d85b149bd"),
     isRead: false,
     user: new ObjectId("630273bbe0f3f82d85b149bd")
   },
   {
     _id: new ObjectId("6306bcf16fa60080148fefb7"),
     isRead: true,
     user: new ObjectId("630273bbe0f3f82d85b149bd")
   }
]

我们可以看到第一个元素对第二个元素有一个引用 (globalRef)，

如果存在另一个元素并以后者作为引用，我想删除元素，这可以通过 $match 实现吗？ $组？ $项目？ $过滤器？

期望的结果:

[
   {
     _id: new ObjectId("630bb658370cc689973c5bb4"),
     isRead: true,
     user: new ObjectId("630273bbe0f3f82d85b149bd"),
     globalRef: new ObjectId("630bb649370cc689973c5b62"),
   },
   {
     _id: new ObjectId("6306bcf16fa60080148fefb6"),
     isRead: false,
   },
   {
     _id: new ObjectId("630273bbe0f3f82d85b149bd"),
     isRead: false,
     user: new ObjectId("630273bbe0f3f82d85b149bd")
   },
   {
     _id: new ObjectId("6306bcf16fa60080148fefb7"),
     isRead: true,
     user: new ObjectId("630273bbe0f3f82d85b149bd")
   }
]

感谢您的帮助

Answer 1

查询

• 您可以使用 globalRef 进行自查找 _id(使 globalRef 上的索引更快)
• 加入后，如果结果为空(未找到匹配项)，则保留文档
• 取消设置以删除结果字段

Playmongo

coll.aggregate(
[{"$lookup": 
   {"from": "coll",
    "localField": "_id",
    "foreignField": "globalRef",
    "as": "results"}},
 {"$match": {"$expr": {"$eq": ["$results", []]}}},
 {"$unset": ["results"]}])