how can I get an object of array by index
example:
{ "_id" : 1, "name" : "bob", colors: [ "red", "blue", "green"] }
{ "_id" : 2, "name" : "jim", colors: ["yellow", "black" ] }
my query: something like
db.users.find({name: "bob"}, {colors: 2})
result:
{ "_id" : 1, "name" : "bob", colors: "blue" }
You can try below aggregation
db.collection.aggregate([
{ "$match": { "name": "bob" }},
{ "$project": {
"name": 1,
"color": { "$slice": [ "$colors", 1, 1 ] }
}},
{ "$unwind": "$color" }
])
Above query will return
[
{
"_id": 1,
"color": "blue",
"name": "bob"
}
]
You can use $arrayElemAt to get the n-th item in array:
db.users.aggregate([
{$match: {name: "bob"}},
{$project: {name: "$name", color: {$arrayElemAt: ['$colors', 1]}}}
])
Note that the index is 0-based.
