MongoDB: $filter multiple arrays

Question

I have an collection like:

{
   _id: 0,
   items: [
     { item_id: 43, quantity: 2, price: 10 },
     { item_id: 2, quantity: 1, price: 240 }
   ],
   T: [
     { item_id: 2993, quantity: 3, price: 110 },
     { item_id: 90103, quantity: 4, price: 5 },
     { item_id: 398, quantity: 1, price: 300 }
    ]
}
{
   _id: 1,
   items: [
     { item_id: 23, quantity: 3, price: 110 },
     { item_id: 103, quantity: 4, price: 5 },
     { item_id: 38, quantity: 1, price: 300 }
   ],
   T: [
     { item_id: 23, quantity: 3, price: 110 },
     { item_id: 103, quantity: 4, price: 5 },
     { item_id: 38, quantity: 1, price: 300 }
     ]
}
{
    _id: 2,
    items: [
       { item_id: 4, quantity: 1, price: 23 }
    ],
   T: [
     { item_id: 203, quantity: 3, price: 110 },
     { item_id: 003, quantity: 4, price: 5 },
     { item_id: 398, quantity: 1, price: 300 }
     ]
}

I want to return a all the items in the items array with a price >= 100. That is done with the following:

   $project: {
         items: {
            $filter: {
               input: "$items",
               as: "item",
               cond: { $gte: [ "$$item.price", 100 ] }
            }
         }
      }

How can I expand this expression to $filter on the items array and the T array all elements that have a price >= 100?

Hi JohnnyHK, i want to basically filter on both the T and items array with the same condition. So I expect the output to be all the documents with the T and items array only containing elements with a price >= 100 — johhny B
– johhny B, Commented May 9, 2016 at 14:12

JohnnyHK · Accepted Answer · 2016-05-09 14:16:58Z

1

You can include both the items and T fields in the same $project, each with its own $filter:

db.test.aggregate([
    {$project: {
        items: {
            $filter: {
               input: "$items",
               as: "item",
               cond: { $gte: [ "$$item.price", 100 ] }
            }
        },
        T: {
            $filter: {
               input: "$T",
               as: "t",
               cond: { $gte: [ "$$t.price", 100 ] }
            }
        }
    }}
])

answered May 9, 2016 at 14:16

JohnnyHK

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