Project with Match in aggregate not working after use substr in mongodb - mongodb

Question

I have face one use with mongodb.
below is my sample record.
{
"_id" : ObjectId("56fa21da0be9b4e3328b4567"),
"us_u_id" : "1459169911J4gPxpYQ7A",
"us_dealer_u_id" : "1459169911J4gPxpYQ7A",
"us_corporate_dealer_u_id" : "1459169173rgSdxVeMLa",
"us_oem_u_id" : "1459169848CK5yOpXito",
"us_part_number" : "E200026",
"us_sup_part_number" : "",
"us_alter_part_number" : "",
"us_qty" : 0,
"us_sale_qty" : 2,
"us_date" : "20160326",
"us_source_name" : "BOMAG",
"us_source_address" : "",
"us_source_city" : "",
"us_source_state" : "",
"us_zip_code" : "",
"us_alternet_source_code" : "",
"updated_at" : ISODate("2016-03-29T06:34:02.728Z"),
"created_at" : ISODate("2016-03-29T06:34:02.728Z")
}
I have try to get all recored having unique date
So, I have made below query using aggregate
.aggregate(
[
{
"$match":{
"yearSubstring":"2016",
"monthSubstring":"03",
"us_dealer_u_id":"1459169911J4gPxpYQ7A"
}
},
{
"$project":
{
"yearSubstring":{"$substr":["$us_date",0,4]},
"monthSubstring":{"$substr":["$us_date",4,2]},
"daySubstring":{"$substr":["$us_date",6,2]}
}
},
{
"$group":
{
"_id":{"monthSubstring":"$monthSubstring",
"yearSubstring":"$yearSubstring",
"daySubstring":"$daySubstring"
},
"daySubstring":{"$last":"$daySubstring"}
}
},
{"$sort":{"us_date":1}}
]
)
I have try both way to pass year and month (as string and as int)
but I have get blank result.
if I'm remove month and year from condition then record came.
mostly I have try all the diff. diff. solution but result is same.
Thank in advance.

Answer 1

You have written incorrect query.
You don't have yearSubstring and monthSubstring fields on this stage.
{
"$match":{
"yearSubstring":"2016",
"monthSubstring":"03",
"us_dealer_u_id":"1459169911J4gPxpYQ7A"
}
},
You should write as following:
.aggregate(
[
{
"$match":{
"us_dealer_u_id":"1459169911J4gPxpYQ7A"
}
},
{
"$project":
{
"yearSubstring":{"$substr":["$us_date",0,4]},
"monthSubstring":{"$substr":["$us_date",4,2]},
"daySubstring":{"$substr":["$us_date",6,2]}
}
},
{
"$match":{
"yearSubstring":"2016",
"monthSubstring":"03"
}
},
{
"$group":
{
"_id":{"monthSubstring":"$monthSubstring",
"yearSubstring":"$yearSubstring",
"daySubstring":"$daySubstring"
},
"daySubstring":{"$last":"$daySubstring"}
}
},
{"$sort":{"us_date":1}}
]
)
If you want to get other fields, you should include them into projection stage.