我在尝试对 mongodb 中嵌入数组的结果进行排序和限制时遇到了最困难的情况。这是场景:
我有一个 post-comment 结构,其中 post 包含一组评论。我想获得一个评论列表,按 createdAt 排序并做一个限制/偏移量......就像给定一个帖子 id 对评论进行分页并将它们返回给我。=]
...继承人的结构示例:
{ "_id" : ObjectId("52707a234f2044b7f2d22083"),
"comments" : [{
"_id" : ObjectId("5270986b4f204f5dd51ada8a"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:26:03.858Z")},
{
"_id" : ObjectId("527098714f204f5dd51ada8b"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:26:09.425Z")
}
],
"createdAt" : ISODate("2013-10-30T03:16:51.745Z"),
"likes" : [ ],
"status" : "simbora!!",
"userid" : NumberLong(1)
}
所以......我可以试试这个查询:
db.post.aggregate([
{$match: {_id: new ObjectId("52707a234f2044b7f2d22083")}},
{$unwind: "$comments"},
{$sort: {"comments.createdAt": -1}},
{$limit: 2}
]);
它给了我这个:
"result" : [
{
"_class" : "models.documents.Post",
"_id" : ObjectId("52707a234f2044b7f2d22083"),
"comments" : {
"_id" : ObjectId("527098714f204f5dd51ada8b"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:26:09.425Z")
},
"createdAt" : ISODate("2013-10-30T03:16:51.745Z"),
"likes" : [ ],
"status" : "simbora!!",
"userid" : NumberLong(1)
},
{
"_class" : "models.documents.Post",
"_id" : ObjectId("52707a234f2044b7f2d22083"),
"comments" : {
"_id" : ObjectId("5270986b4f204f5dd51ada8a"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:26:03.858Z")
},
"createdAt" : ISODate("2013-10-30T03:16:51.745Z"),
"likes" : [ ],
"status" : "simbora!!",
"userid" : NumberLong(1)
}
],
"ok" : 1
请注意,comments 不再是一个数组,而是一个对象……虽然它给了我有序和有限的集合,但它也给了我每个评论的父对象……那不太好。所以我尝试了这个:
db.post.aggregate([
{$match: {_id: new ObjectId("52707a234f2044b7f2d22083")}},
{$unwind: "$comments"},
{$sort: {"comments.createdAt": -1}},
{"$project": {"_id": 0, "comments": "$comments"}},
{"$group": {"_id": "$_id", "comments": {"$push": "$comments"}}},
]);
它给了我这个:
{
"result" : [
{
"_id" : null,
"comments" : [
{
"_id" : ObjectId("527098714f204f5dd51ada8b"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:26:09.425Z")
},
{
"_id" : ObjectId("5270986b4f204f5dd51ada8a"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:26:03.858Z")
},
{
"_id" : ObjectId("527098694f204f5dd51ada89"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:26:01.174Z")
},
{
"_id" : ObjectId("527098674f204f5dd51ada88"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:25:59.795Z")
},
{
"_id" : ObjectId("527098644f204f5dd51ada87"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:25:56.936Z")
},
{
"_id" : ObjectId("527098604f204f5dd51ada86"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:25:52.379Z")
},
{
"_id" : ObjectId("52707a234f2044b7f2d22083"),
"comment" : "asdfasdf asdfasdfa ",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:24:36.539Z")
},
{
"_id" : null,
"comment" : "bla bla",
"userid" : NumberLong(1),
"likes" : [ ],
"createdAt" : ISODate("2013-10-30T05:23:24.037Z")
}
]
}
],
"ok" : 1
}
这也不是很好,因为如果我应用限制并跳过运算符,它将通过帖子限制,而不是评论......
谁能帮我吗??