Mongodb comparing object arrays keys

You would require another array that contains just the mapped paths and this can be derived using JavaScript's .map() method. This array will then be used in the mongo query as the $in operator value. The following demonstrates this:

var dynFiles = [          
       {_id: "1", path:"C:\folder\textfile01.txt"},
       {_id: "2", path:"C:\folder\textfile02.txt"},
       {_id: "3", path:"C:\folder\textfile03.txt"},
       {_id: "4", path:"C:\Filename04.txt"},
    ],
    paths = dynFiles.map(function(f){ return f.path; });

db.collection.find({"files.path": {"$in": paths }})

Using the .aggregate() method.

First you need to return an array of "path" using the .map() method.

> var dynFiles = [          
...        {_id: "1", path:"C:\folder\textfile01.txt"},
...        {_id: "2", path:"C:\folder\textfile02.txt"},
...        {_id: "3", path:"C:\folder\textfile03.txt"},
...        {_id: "4", path:"C:\Filename04.txt"},
...   ];
> var paths = dynFiles.map(function(element) {
... return element.path;
... });
> paths
[
        "C:\folder\textfile01.txt",
        "C:\folder\textfile02.txt",
        "C:\folder\textfile03.txt",
        "C:Filename04.txt"
]

Then comes the aggregation query:

You only need one stage in your pipeline which is the $project stage where you use the $map operator to return an array of sub-documents that where "path" is in "dynFiles". To check if a given "path" is in "dynFiles" you use the $setIsSubset operator in $cond expression. The reason you need the $setIsSubset is because you can't use the $in operator in $cond expression. Of course the $setIsSubset operator takes two arrays as parameter you need to use the $map operator to return one element array. Of course the $literal operator let you assign a literal array to the "input" in $map. Also you need to use the $setDifference here to filter out all false from the array which is fine as long as the data being filtered is "unique".

db.paths.aggregate([
    { "$project": { 
        "files": { 
            "$setDifference": [
                { "$map": { 
                    "input": "$files", 
                    "as": "file", 
                    "in": { 
                        "$cond": [ 
                            { "$setIsSubset": [ 
                                { "$map": {
                                    "input": { "$literal": [ "A" ] },
                                    "as": "el", 
                                    "in": "$$file.path"
                                }}, 
                                paths
                            ] },
                            "$$file",
                            false 
                        ]
                    }
                }}, 
                [false]
            ]
        }
    }}
])

Another way and probably the easiest way is by using the $filter operator new in MongoDB 3.2

db.paths.aggregate([
    { "$project": { 
        "files": {
            "$filter": { 
                "input": "$files", 
                "as": "file",  
                "cond": {
                    "$setIsSubset": [
                        { "$map": {
                            "input": { "$literal": [ "A" ] }, 
                            "as": "el", 
                            "in": "$$file.path"
                        }}, 
                        paths 
                    ]
                }
            }
        }
    }}
])

Both queries yield the same result:

{
        "_id" : "3213dsadsa812321",
        "files" : [
                {
                        "_id" : "99303",
                        "path" : "C:Filename04.txt"
                }
        ]
}