need to project nested array using mgo

I m using go lang as the back end of my application and mongoDB as the database.I am facing a problem where i compare the name and project the leave array and inside that i also need to project the certificates for that leave.Since i need only little info from the employee struct i wanted to implement using pipe and project.

 type (
Employee struct {
Name               string
Password           string
EmailAddress       string
Position           string
Gender             string
Nationality        string
Department         string
MaritalStatus      string
Approvedby         string
JoinDate           time.Time
ConfirmationDate   time.Time
EndDate            time.Time
Leave             []*LeaveInfo	
}
LeaveInfo struct {
Total        float64
Id           int
Days         float64
From        time.Time
To          time.Time  
Status       string
Certificate  []*CertificateInfo
}
CertificateInfo struct {
FileName string
FileType string
FileSize int
}

The database structure is as follows

{
"_id" : ObjectId("58213e14927a62f3cf04e05b"),
"name" : "string",
"password" : "string",
"emailaddress" : "string",
"position" : "string",
"gender" : "string",
"maritalstatus" : "string",
"approvedby" : "string",
"nationality" : "german",
"department" : "account",
"joindate" : ISODate("2016-09-19T00:00:00.000Z"),
"confirmationdate" : Date(-62135596800000),
"enddate" : Date(-62135596800000),
"Leave" : [ 
{
"total" : 20.0,
"id" : 0,
"days" : 0.0,
"type" : "",
"from" : ISODate("2016-12-12T00:00:00.000Z"),
"to" : ISODate("2016-12-12T00:00:00.000Z"),
"status" : "",
"certificate" : [
{
"filename" : "malaysia",
"filetype" : ".zip",
"filesize" : 1234
}, 
{
"filename" : "singapore",
"filetype" : ".zip",
"filesize" : 1234
}
]
}, 
{
"total" : 19.0,
"id" : 1,
"days" : 1.0,
"from" : ISODate("2016-12-12T00:00:00.000Z"),
"to" : ISODate("2016-12-12T00:00:00.000Z"),
"applieddate" : ISODate("2016-11-08T02:53:38.902Z"),
"status" : "Processing",
"approveddate" : Date(-62135596800000),
"certificate" : [ 
{
"filename" : "germany",
"filetype" : ".zip",
"filesize" : 1234
}, 
{
"filename" : "england",
"filetype" : ".zip",
"filesize" : 1234
}
]
}, 
{
"total" : 18.0,
"id" : 2,
"days" : 1.0,
"mdays" : 0.0,
"type" : "annualleave",
"daytype" : "FullDay",
"from" : ISODate("2016-12-12T00:00:00.000Z"),
"to" : ISODate("2016-12-12T00:00:00.000Z"),
"applieddate" : ISODate("2016-11-08T05:36:21.579Z"),
"status" : "Processing",
"approveddate" : Date(-62135596800000),
"certificate" : [
{
"filename" : "india",
"filetype" : ".zip",
"filesize" : 1234
}, 
{
"filename" : "france",
"filetype" : ".zip",
"filesize" : 1234
}
]
}
]
}

My code in golang is as follows

pipe3 := c.Pipe([]bson.M{
{
"$match": bson.M{
"name":name
},
},
{
"$unwind": "$leave",
},
{
"$project": bson.M{
"_id":          false,
"name":         1,
"Id":           "$leave.id",
"Total":        "$leave.total",
"Days":         "$leave.days",
"Status":       "$leave.status",
},
},
})

The problem here is i dont know how to retrieve all the info of the certificates related to that particular leave.Please note that the certificate is an array with atleast two index in it...

I need an output similar to this. 
"name":        "John",
"Id":           "1",
"Total":        "10.0",
"Days":         "2.0",
"Status":       "Process",
"Certificate" : [
{
"filename":"certificate1",
"filesize":"size1"
},
{
"filename":"certificate2",
"filesize":"size2"
}
]
"name":        "John",
"Id":           "2",
"Total":        "8.0",
"Days":         "2.0",
"Status":       "Process",
"Certificate" : [
{
"filename":"certificate1",
"filesize":"size1"
},
{
"filename":"certificate2",
"filesize":"size2"
}
]

Is this possible using project.or is there any other way to do this.Appreciate any help.Please.Thanks

Using on your document structure example above, you just have to expose certificate through $project as below:

pipeline := []bson.M{
{"$match": bson.M{"name":"string"}},
{"$unwind": "$Leave"},
{"$project": bson.M{
"_id":          false,
"name":         1,
"Id":           "$Leave.id",
"Total":        "$Leave.total",
"Days":         "$Leave.days",
"Status":       "$Leave.status",
"Certificate":  "$Leave.certificate"},
},
}
pipe := collection.Pipe(pipeline)
response := []bson.M{}
err = pipe.All(&response)

As you already use $unwind on Leave, you have individual documents per leave request. The output of the above aggregation would be:

 {
"name": "string",
"Id": 0,
"Total": 20,
"Days": 0,
"Status": "",
"Certificate": [
{
"filename": "malaysia",
"filetype": ".zip",
"filesize": 1234
},
{
"filename": "singapore",
"filetype": ".zip",
"filesize": 1234
}
]
},
{
"name": "string",
"Id": 1,
"Total": 19,
"Days": 1,
"Status": "Processing",
"Certificate": [
{
"filename": "germany",
"filetype": ".zip",
"filesize": 1234
},
{
"filename": "england",
"filetype": ".zip",
"filesize": 1234
}
]
},
{
"name": "string",
"Id": 2,
"Total": 18,
"Days": 1,
"Status": "Processing",
"Certificate": [
{
"filename": "india",
"filetype": ".zip",
"filesize": 1234
},
{
"filename": "france",
"filetype": ".zip",
"filesize": 1234
}
]
}

Where each leave request, has their own corresponding certificates associated with the leave.