[英]Filter documents from two collections in mongoDB using mongoose
I have two collections: "message" and "group_message_map". 我有两个集合:“消息”和“ group_message_map”。 _id column of message collection I am storing in the group_message_map.
我存储在group_message_map中的消息集合的_id列。 Few of the group_message_map entry if I am deleting so, only the remaining common entry from both the collections I am trying to fetch but getting the response as empty.
如果我要删除group_message_map条目,则很少,只有我试图获取的两个集合中剩余的公共条目,但响应为空。 Here is my method:
这是我的方法:
getLimitedMessages(receiverId, senderId, page, size, callback) {
var messages = [];
GroupMessageMap.find({
groupId: receiverId,
userSId: senderId
})
.skip(parseInt(((size * page) - size)))
.limit(parseInt(size))
.sort({ $natural: -1 })
.exec(function(err, maps) {
if (err) {
console.log('err is maps ', err);
} else {
maps.map((map) => {
Message.find({
_id: map.messageId
}, function(err, message) {
if (err) {
console.log('messages err ', err);
} else {
messages.push(message);
}
});
});
}
});
console.log('filtered messages: ' + messages);
};
Why not using $lookup or populate 为什么不使用$ lookup或填充
maps.map((map) will not wait for async db call and before getting db response, you will get empty response maps.map((map)将不等待异步数据库调用,并且在获得数据库响应之前,您将获得空响应
Refer these links 参考这些链接
https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/ http://mongoosejs.com/docs/populate.html https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/ http://mongoosejs.com/docs/populate.html
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