Mongo aggregate remove group if condition in sub array

Question

At a certain point of my pipeline, I have a structure like this :

[
    {
        _id: 1,
        elems1: [{sub : {date: xxx}}, {sub: {date: yyy}}],
        elems2: [{sub: {date: zzz}}, {sub: {date: qqq}}]
    },
    ...
]

Which comes from a grouping :

{$group: {
    _id: '$user.id',
    elems1: {
        $push: {sub: '$other'}
        },
    elems2: {
        $push: {sub: '$other'}
        }
    }
}}

Now I want to delete the groups that have an element in elems1 OR elems2 with sub.date less than a certain date, how could I do this ?

klhr · Accepted Answer · 2019-03-08 16:11:56Z

1

When you do your $group, you can also track the "minElemDate" and then $match by that in the next pipeline stage.

$group: {
  _id: "$user.id",
  elem1s: ...,
  elem2s: ...
  minElemDate: {
    $min: {
      $cond: [
        { $or: [condition1, condition2] },
       "$user.date",
        null
      ]
    }
  }
},
{ $match: {$gte: ["$minElemDate", minDate]} }

edited Mar 8, 2019 at 16:11

answered Mar 7, 2019 at 20:10

klhr

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6 Comments

HRK44 Over a year ago

I like this idea, can you please elaborate on what to put in condition1 and condition2 ? That's the part where I'm confused

klhr Over a year ago

{$eq: ['$user.name', 'L']} and {$eq: ['$user.name', 'L']} -- it seems like those are the elements that you care about

HRK44 Over a year ago

I will remove this part, maybe it is making it confusing. I care only about the date... I will update my question

klhr Over a year ago

tldr of my answer -- when you do the group, also track the min date. don't try and filter it out afterwards because it'll be harder

HRK44 Over a year ago

The problem is that I don't know what to put in the $min block, since I want the min of the object date inside the array

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