Select nested fields in mongo db

Question

I have a collection in mongodb where fields are nested under a language root:

{
    en: {
        title: \"eng title\",
        content: \"eng content\",
            


        

Answer 1

You need to aggregate as below:

• Construct a find object to match only the records containing($exists) the language.
• Construct a Projection object to project the fields.

Code:

var currentLang = "en";
var project = {};
project["title"] = "$"+currentLang+".title";
project["content"] = "$"+currentLang+".content";
project["images"] = 1;

var find = {};
find[currentLang] = {"$exists":true};

db.collection.aggregate([
{$match:find},
{$project:project}
])

Answer 2

I'm not sure how you're querying, so I'll assume you're going directly through the mongo client. Assuming you have defined a variable

>currentLang = "en";

You can run an aggregation operation and using the $project operator, restructure the presentation of the document.

Here's an example that I've tested:

> db.test.aggregate({$project: 
        {_id: 0, 
         title: "$" + currentLang + ".title", 
         content: "$" + currentLang + ".content", 
         images: 1
        }
    }).pretty();
{
    "images" : {
        "mainImage" : "dataURL",
        "thumbImage" : "dataURL"
    },
    "title" : "eng title",
    "content" : "eng content"
}

If you want to combine this with an actual query, you can just include it as a $match operator, something like:

> db.test.aggregate(
    {$match: 
        {"en.title": "eng title"}
    }, 
    {$project: 
        {_id: 0, 
         title: "$" + currentLang + ".title", 
         content: "$" + currentLang + ".content", 
         images: 1
        }
    }).pretty();