How to get the document inside a field out after "group by" in MongoDB? - mongodb

Question

The documents I work on are like this:
{
"id" : "98syf87erfw8n"
"foo" : { "objectid" : "39", "stuff" : "65" },
"yearpublished" : "1979",
.
.
.
}
This is the query I used:
db.foobar.aggregate([
{ $group : {
_id : '$yearpublished',
myItem: { $first: "$$ROOT" }
}}
])
The final output is in the form:
{
{ "_id" : "1923", "myItem" : {
"id" : "98syf87erfw8n",
"foo" : { "objectid" : "39", "stuff" : "65" },
"yearpublished" : "1979"
}
},
{ "_id" : "1453", "myItem" : {
"id" : "88888888888",
"foo" : { "objectid" : "394", "stuff" : "55" },
"yearpublished" : "1453"
"author" : "Ravi Kiran"
}
}
};
But I want the output as:
{
"id" : "98syf87erfw8n",
"foo" : { "objectid" : "39", "stuff" : "65" },
"yearpublished" : "1979"
},
{
"id" : "88888888888",
"foo" : { "objectid" : "394", "stuff" : "55" },
"yearpublished" : "1453",
"author" : "Ravi Kiran"
}
This means I want to get those documents inside the field myItem out.
How can I do that?

Answer 1

You could use $replaceRoot
Play
db.collection.aggregate({
"$replaceRoot": {
"newRoot": "$myItem"
}
})
There are syntax errors in your output.
"id" : 98syf87erfw8n, is invalid.
It should be "id" : "98syf87erfw8n", Note the quotes
There is comma missing after yearPublished in the second object.

Answer 2

One more project stage after the $group can do the job:
{
$project: {
yearpublished: "$myItem.yearpublished",
foo: "$myItem.foo",
id: "$myItem.id",
_id: 0
}
}
playground