I would like to define a $project aggregation stage where I can instruct it to add a new field and include all existing fields, without having to list all the existing fields.
My document looks like this, with many fields:
{
obj: {
obj_field1: "hi",
obj_field2: "hi2"
},
field1: "a",
field2: "b",
...
field26: "z"
}
I want to make an aggregation operation like this:
[
{
$project: {
custom_field: "$obj.obj_field1",
//the next part is that I don't want to do
field1: 1,
field2: 1,
...
field26: 1
}
},
... //group, match, and whatever...
]
Is there something like an "include all fields" keyword that I can use in this case, or some other way to avoid having to list every field separately?
In 4.2+, you can use the $set
aggregation pipeline operator which is nothing other than an alias to $addFields
added in 3.4
The
$addFields
stage is equivalent to a$project
stage that explicitly specifies all existing fields in the input documents and adds the new fields.
db.collection.aggregate([
{ "$addFields": { "custom_field": "$obj.obj_field1" } }
])