Project with Match in aggregate not working in mongodb

[问题]

2down votefavorite

I am trying to fetch data based on some match condition.
First I've tried this: Here ending_date is full date format

Offer.aggregate([

{

$match: {

carer_id : req.params.carer_id,

status : 3

}

},

{

$group : {

_id : { year: { $year : "$ending_date" }, month:
{ $month : "$ending_date" }},

count : { $sum : 1 }

}

}],

function (err, res)

{ if (err) ; // TODO handle error

console.log(res);

});

which gives me following output:

[ { _id: {
year: 2015, month: 11 }, count: 2 } ]

Now I want to check year also, so I am trying this:

Offer.aggregate([

{

$project: {

myyear: {$year: "$ending_date"}

}

},

{

$match: {

carer_id : req.params.carer_id,

status : 3,

$myyear : "2015"

}

},

{

$group : {

_id : { year: { $year : "$ending_date" }, month:
{ $month : "$ending_date" }},

count : { $sum : 1 }

}

}],

function (err, res)

{ if (err) ; // TODO handle error

console.log(res);

});

which gives me following output:

[]

as you can see, _id has 2015 as a year, so when I match
year it should be come in array. But I am getting null array. Why this?

Is there any other way to match only year form whole
datetime?

Here is the sample data

{

"_id": {

"$oid": "56348e7938b1ab3c382d3363"

},

"carer_id": "55e6f647f081105c299bb45d",

"user_id": "55f000a2878075c416ff9879",

"starting_date": {

"$date": "2015-10-15T05:41:00.000Z"

},

"ending_date": {

"$date": "2015-11-19T10:03:00.000Z"

},

"amount": "850",

"total_days": "25",

"status": 3,

"is_confirm": false,

"__v": 0

}

{

"_id": {

"$oid": "563b5747d6e0a50300a1059a"

},

"carer_id": "55e6f647f081105c299bb45d",

"user_id": "55f000a2878075c416ff9879",

"starting_date": {

"$date": "2015-11-06T04:40:00.000Z"

},

"ending_date": {

"$date": "2015-11-16T04:40:00.000Z"

},

"amount": "25",

"total_days": "10",

"status": 3,

"is_confirm": false,

"__v": 0

}

[回答]

You forgot to project the fields that you're using in $match and $group later
on. For a quick fix, use this query instead:

Offer.aggregate([

{

    $project: {

        myyear: { $year: "$ending_date" },

        carer_id: 1,

        status: 1,

        ending_date: 1

    }

},

{ 

    $match: { 

        carer_id: req.params.carer_id,

        myyear: 2015,

        status: 3

    }

},

{

    $group: {

        _id: {

            year: { $year: "$ending_date" },

            month: { $month: "$ending_date" }

        }, 

        count: { $sum: 1 }

    }

}], 

function (err, res)

{

    if (err) {} // TODO handle error 

    console.log(res); 

});

That said, Blakes Seven explained how to make a better query in her answer. I think you should try and use her approach instead.

也就是说,project的字段中必须包含match中用到的字段.

来自: https://stackoverflow.com/questions/33752817/project-with-match-in-aggregate-not-working-in-mongodb