Imagine I had a collection called journals containing documents like the following:
{
"article": "id1",
"d": 2
},
{
"article": "id1",
"d": 2
},
{
"article": "id1",
"d": 3
},
{
"article": "id2",
"d": 2
},
...
Where d is kind of a switch and article is a reference. Now I want to have a result like the following:
[
{
"_id": "id1",
"total": 3,
"d2": 2,
"d3": 1
},
{
"_id": "id2",
"total": 1,
"d2": 1,
"d3": 0
}
]
I'm using mongoose and have a model called Journal. What I've got so far is…
Journal.aggregate(
{ $project: {
articleId: 1,
depth2 : { $gte:['$d', 2] },
depth3 : { $eq:['$d', 3] }
}},
{ $group: {
_id: '$article',
total: { $sum: 1 },
d2: { $sum: '$depth2'},
d3: { $sum: '$depth3'}
}
},
function (err, journal) {
console.log(journal);
}
);
which results in:
[
{
"_id": "id1",
"total": 3,
"d2": 0,
"d3": 0
},
{
"_id": "id2",
"total": 1,
"d2": 0,
"d3": 0
}
]
Obviously the error here is that $eq:['$d', 3] is not summed up because that results in a boolean.
So is there a better expression that projects the new depth2 and depth3 fields to 1or 0 instead of true or false?
Or is there a complete and better approach? :)
I'd like to avoid making 3 queries and prepending a matching phase like { $match: { d: 2 } }.
You can use $cond to convert a boolean to a numerical value, but you've also got a $gte where it seems an $eq should be and your docs use article while your code uses articleId:
Journal.aggregate([
{ $project: {
article: 1,
depth2 : { $cond: [{$eq: ['$d', 2]}, 1, 0] },
depth3 : { $cond: [{$eq: ['$d', 3]}, 1, 0] }
}},
{ $group: {
_id: '$article',
total: { $sum: 1 },
d2: { $sum: '$depth2'},
d3: { $sum: '$depth3'}
}
}
]);
Output:
{
"result" : [
{
"_id" : "id2",
"total" : 1,
"d2" : 1,
"d3" : 0
},
{
"_id" : "id1",
"total" : 3,
"d2" : 2,
"d3" : 1
}
],
"ok" : 1
}
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