I have a mongodb (using mongoose) collection ("items") which includes an array ("images") among its properties. Some example documents:
[
{
"_id" : ObjectId("543fa67e9672ec37ebe3d026"),
"name" : "Alice",
"images" : [
{ url: "http://images.com/1.jpg" },
{ url: "http://images.com/2.jpg" },
{ url: "http://images.com/3.jpg" },
]
},
{
"_id" : ObjectId("543fa67e9672ec37ebe3d027"),
"name" : "Bob",
"images" : [
{ url: "http://images.com/4.jpg" },
{ url: "http://images.com/5.jpg" },
]
},
]
I want to implement a query which returns - along with other document properties - the array length (and not the array contents). I know I can get the array length with
db.items.aggregate([
{ "$project" : { "_id" : 0, "imagesLength" : { "$size" : "$images" } } }
])
But I need the imagesLength values along with the documents returned with a find:
db.items.findMany(
{ ...filter },
{ name: 1, imagesCount: 1 }
);
The question is: how can I get the array length along with the find results ?
You can do same as aggregation projection in find's second argument,
Starting in MongoDB 4.4, as part of making find projection consistent with aggregation’s $project stage,
db.items.find(
{ ...filter },
{
_id: 0,
name: 1,
images: { $size: "$images" }
})
You can add a match stage at first in your aggregation to filter the results. Then you can project all fields needed and generate the new ones.
db.items.aggregate([
{ "$match" : { ...filter },
{ "$project" : { "imagesLength" : { "$size" : "$images" }, "name": 1 } }
])