MongoDB - How to find all objects within an array?

Question

I\'m trying to find all elements within an array called programme. The result of running db.base.find({\"programme.title\":\"News\"},{\"programme

Answer 1

Projection to a match in MongoDB .find() queries can only return the "first" element matching your conditions.

So to get "multiple" matches your best approach is using .aggregate() and $redact, with first filtering the documents with $match:

db.base.aggregate([
    { "$match": { "programme.title":"News" } },
    { "$redact": {
        "$cond": {
            "if": { "$eq": [ { "$ifNull": [ "$title", "News" ] }, "News" } ],
            "then": "$$DESCEND",
            "else": "$$PRUNE"
        }}
    }}
])

This "removes" ("redacts") any entries from the array that do not match the "title" you are giving.

This is a good approach since you are not creating more documents in the pipeline using $unwind, which is another way to work with arrays.

The catch is that you cannot have another element in your document with the same property name "title", as the $$DECEND walks into the structure and compares the field names at each level.

Answer 2

You can achieve with the help of Aggregation as below :

 db.base.aggregate([
    {$unwind : "$programme"},
    {$match : { "programme.title" : "News" } },
   {$group : { "_id" : "$_id" , "programme" : { $push: "$programme" } } }
]);