Check If field exists in an sub-document of an Array

Question

I have a schema that is similar to this.

{id: Number,
  line_items: [{ 
    id: String,
    quantity: Number,
    revi         


        

Answer 1

If you just want to get the whole document then as mentioned by @Blakes Seven. You can query using $elemMatch.
But if you want to filter array element and get only those array elements which do not have a certain field then you can use $filter along with $type in aggregation pipeline.

[
    { $match: { "line_items": { "$elemMatch": { "review_request_sent": { "$exists": false } } } } },
    { $project: {
        "line_items": { "$filter": { 
            "input": "$line_items", 
            "as": "item", 
            "cond": { "$eq": [ { "$type": "$$item.review_request_sent" }, "missing" ] }
        } }
    } }
]

Note: $type returns "missing" when used with undefined fields.