I have the following collection
{
"_id": "12345",
"Products": [
"Product1",
"Product2"
],
"State": "active",
}
And would like to project it similar to the output below
_id: "12345"
Products: "Product1, product2"
I tried this but im not getting the desired output of a comman seperated concatenated string
{
_id: 1,
Products: {
$reduce: {
input: "$Products",
initialValue:"0" ,
in: {concat: ["$$value", "$$this"] }
}
}
}
This aggregation query gives the desired result:
db.test.aggregate([{
$project: {
Products: {
$ltrim: {
input: {
$reduce: {
input: "$Products",
initialValue: "",
in: {
$concat: [ "$$value", ", ", "$$this" ]
}
}
},
chars: ", "
}
}
}
}])
The $project is used to transform the Products array of strings into a single concatenated string, using the $reduce array operator.
Note the usage of the $ltrim operator to remove the addition comma from the concatenated string, to give the following result:
[
{
_id: '12345',
Products: 'Product1, Product2'
}
]
The projection of _id field is not explicitly required, it is by default projected.
$ltrim. This is how I would do it programmatically and would prevent the $cond execution on each iteration of reduce element.You can use $reduce and $concat to concatenate the values into one string. The $cond is necessary to determine if a comma is required between the values or not.
db.collection.aggregate([
{
$project: {
"_id": 1,
"Products": {
$reduce: {
input: "$Products",
initialValue: "",
in: {
$concat: [
"$$value",
{
$cond: [
{
$eq: [
"$$value",
""
]
},
"",
","
]
},
"$$this"
]
}
}
}
}
}
])
See HERE for a working example.
Productsis. Is it an array of objects soProducts: [{ '0': 'Product1'}, { '1': 'product2'}]or is it an array of just strings soProducts: ['Product1', 'product2']? It would help if you post an actual sample document.$condis needed becuase you don't want a leading or a trailing comma in the output I assume.