[英]How to query single document which contains specific value of some element in array of arrays MongoDB
[英]How to query element of array of document in mongodb
我只是花了整个晚上试图弄清楚这一点,我在 db 中有这样的用户:
[
{
"_id": "5fcff6ed224670346c8b60de",
"name": "john",
"password": "147",
"data": [
{
"_id": "5fd000356d5df538d0338db4",
"comment": "comment1",
"date": "2020-12-08T22:37:41.740Z"
},
{
"_id": "5fd0003e6d5df538d0338db6",
"comment": "comment2",
"date": "2020-12-08T22:37:50.271Z"
},
{
"_id": "5fd000476d5df538d0338dba",
"comment": "comment3",
"date": "2020-12-08T22:37:59.128Z"
}
],
"__v": 6
},
{
"_id": "5fcff6f5224670346c8b60df",
"name": "Samantha",
"password": "123",
"data": [],
"__v": 0
},
]
当用户“john”登录时,他想检索第 1 条评论,我该怎么做?
我想出了如何删除它,但不知道如何找回它
router.delete("/:id", auth, async (req, res) => {
let user = await User.findByIdAndUpdate(
req.user._id,
{
$pull: {
data: { _id: req.params.id },
},
},
{ new: true }
);
res.send(user.data);
});
我什至放弃了,试图只检索整个用户,然后过滤数据,但它没有用
router.get("/:id", auth, async (req, res) => {
let user = await User.findById(req.user._id);
let arr = user.data
arr = arr.filter(e => e._id === req.params.id)
res.send(arr)
});
您可以像这样使用查询和投影:
db.getCollection('users').find({
"data": {
$elemMatch: {
comment: "comment1"
}
},
"name": "john"
},
{
"data.$": 1
})
使用$elemMatch
,您可以在嵌入文档上指定多个条件。
然后,您将结果投影为仅返回具有以下条件的第一个元素
{comment: "comment1"}
和{name: "john"}
您将获得只有一个索引的数据数组,这正是您所要求的。
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