I have a aggregation pipeline where i'd like to perform a match only if the intended params is present. For example;

params = { fruit: 'apple', other_params.. }

In my aggregation pipeline:

Some.collection.aggregate([ { "$match": { fruit: 'apple' } } ...other stages ])

So I'd like to run match stage only if i have fruit in params. can it be done?

CodePudding user response：

You can realize this via simple $or logic in the match stage:

db.collection.aggregate([
 {
  $match: {
   $or: [
    {
      fruit: {
        $exists: true,
        $eq: "apple"
      }
    },
    {
      fruit: {
        $exists: false
      }
    }
  ]
 }
}
])

explained:

1. If the key fruit exist it will check if is equal to "apple"
2. If the key do not exist it will not do anything

playground

CodePudding user response：

Mongodb queries are javascript objects, so you can construct them easy and dynamically, with code, based on the params you got. For example i think you need something like

params = { fruit: 'apple', other_params.. }
Some.collection.aggregate([ { "$match": params } ...other stages ])

If you want some of the params to be on the match, start with an empty {} and add the parameters that have to be in the $match.