在数组 PyMongo 中查找子文档

Question

I want to query what comments have been made by any User about machine learning book between '2020-03-15' and '2020-04-25', ordered the comments from the most recent to the least recent.

Here is my document.

lib_books = db.lib_books
document_book1 = ({
    "bookid" : "99051fe9-6a9c-46c2-b949-38ef78858dd0",
    "title" : "Machine learning",
    "author" : "Tom Michael",
    "date_of_first_publication" : "2000-10-02",
    "number_of_pages" : 414,
    "publisher" : "New York : McGraw-Hill",
    "topics" : ["Machine learning", "Computer algorithms"],
    "checkout_list" : [
    {
        "time_checked_out" : "2020-03-20 09:11:22",
        "userid" : "ef1234",
        "comments" : [
        {
            "comment1" : "I just finished it and it is worth learning!",
            "time_commented" : "2020-04-01 10:35:13"
        },
        {
            "comment2" : "Some cases are a little bit outdated.",
            "time_commented" : "2020-03-25 13:19:13"
        },
        {
            "comment3" : "Can't wait to learning it!!!",
            "time_commented" : "2020-03-21 08:21:42"
        }]
    },
    {
        "time_checked_out" : "2020-03-04 16:18:02",
        "userid" : "ab1234",
        "comments" : [
        {
            "comment1" : "The book is a little bit difficult but worth reading.",
            "time_commented" : "2020-03-20 12:18:02"
        },
        {
            "comment2" : "It's hard and takes a lot of time to understand",
            "time_commented" : "2020-03-15 11:22:42"
        },
        {
            "comment3" : "I just start reading, the principle of model is well explained.",
            "time_commented" : "2020-03-05 09:11:42"
        }]
    }]
})

I tried this code, but it returns nothing.

query_test = lib_books.find({"bookid": "99051fe9-6a9c-46c2-b949-38ef78858dd0", "checkout_list.comments.time_commented" : {"$gte" : "2020-03-20", "$lte" : "2020-04-20"}})
for x in query_test:
    print(x)

Answer 1

Can you try this

pipeline = [{'$match':{'bookid':"99051fe9-6a9c-46c2-b949-38ef78858dd0"}},//bookid filter
            {'$unwind':'$checkout_list'},
            {'$unwind':'$checkout_list.comments'},
            {'$match':{'checkout_list.comments.time_commented':{"$gte" : "2020-03-20", "$lte" : "2020-04-20"}}},
            {'$project':{'_id':0,'bookid':1,'title':1,'comment':'$checkout_list.comments'}},
            {'$sort':{'checkout_list.comments.time_commented':-1}}]

query_test = lib_books.aggregate(pipeline)
#{"bookid": "99051fe9-6a9c-46c2-b949-38ef78858dd0", "checkout_list.comments.time_commented" : {"$gte" : "2020-03-20", "$lte" : "2020-04-20"}})
for x in query_test:
    print(x)

I would recommend that you maintain comment field as one name, rather than keeping it as 'comment1', 'comment2', etc. If the field had been 'comment', it can be brought to the root itself

Aggregate can be modified as below

pipeline = [{'$match':{'bookid':"99051fe9-6a9c-46c2-b949-38ef78858dd0"}},//bookid filter
            {'$unwind':'$checkout_list'},
            {'$unwind':'$checkout_list.comments'},
            {'$match':{'checkout_list.comments.time_commented':{"$gte" : "2020-03-20", "$lte" : "2020-04-20"}}},
            {'$project':{'_id':0,'bookid':1,'title':1,'comment':'$checkout_list.comments.comment','time_commented':'$checkout_list.comments.time_commented'}},
            {'$sort':{'time_commented':-1}}]

MongoDB Query, in case if required

db.books.aggregate([
{$match:{'bookid':"99051fe9-6a9c-46c2-b949-38ef78858dd0"}},//bookid filter
{$unwind:'$checkout_list'},
{$unwind:'$checkout_list.comments'},
{$match:{'checkout_list.comments.time_commented':{"$gte" : "2020-03-20", "$lte" : "2020-04-20"}}},
{$project:{_id:0,bookid:1,title:1,comment:'$checkout_list.comments.comment',time_commented:'$checkout_list.comments.time_commented'}},
{$sort:{'time_commented':-1}}
])

if there are multiple documents that you need to search, then you can use $in condition.

{$match:{'bookid':{$in:["99051fe9-6a9c-46c2-b949-38ef78858dd0","99051fe9-6a9c-46c2-b949-38ef78858dd1"]}}},//bookid filter