Pass mongodb aggregation variable to NodeJs

Question

I am trying to use $gte in aggregation based on property from aggregation in Nodejs.

const twelveHours = 12 * 60 * 60 * 1000;
const pipeline = [
  { $addFields: { 
    twelveHoursBeforeStart: { $subtract: ['$startDate', twelveHours] } } // this works
  },
  { match: { 
    endDate: { $gte: new Date('$twelveHoursBeforeStart') }, // <- HERE pass a variable    
  },
]

I have tried different solutions like:

{ match: { 
  endDate: { $gte: '$twelveHoursBeforeStart' },
},

but non of them actually works

turivishal · Accepted Answer · 2021-04-17 09:51:47Z

1

You can do both the operations in $match stage,

$expr expression match with aggregation $gte operator, first argument is endDate and second subtract condition

const twelveHours = 12 * 60 * 60 * 1000;
const pipeline = [
  {
    $match: {
      $expr: {
        $gte: [
           "$endDate",
           { $subtract: ["$startDate", twelveHours] }
        ]
      }
    }
  }  
]

Playground

edited Apr 17, 2021 at 9:51

answered Apr 17, 2021 at 9:40

turivishal

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4 Comments

IntoTheDeep Over a year ago

This isn't working on Node because it is compiled to: { $expr: { $gte: ['$endDate', { $subtract: ['$startDate', twelveHours] }] } }, Same result will have if compare to undefined. It expects a date object

turivishal Over a year ago

is it string type or date type in your collection?

IntoTheDeep Over a year ago

Isn't it same if we just do { match: { endDate: { $gte: { $subtract: ["$startDate", twelveHours] } } } },

turivishal Over a year ago

no its not same, because $subtract is an aggregation expression operator and we are accessing internal startDate field as well so we can't use internal field in match condition, so that is why it requires to use $expr and there are 2 different syntax for simple $gte and expression $gte

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