findOne returning full document - node.js

Question

This is the Data stored in MongoDB database under the collection name of padlos
{
"_id" : ObjectId("60ffb89473dc672be32909c2"),
"courses" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c3"),
"course" : "BCA",
"semesters" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c4"),
"sem" : 1,
"subjects" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c5"),
"subject" : "C++",
"units" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c6"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c7"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ffb89473dc672be32909c8"),
"topic" : "DataTypes"
}
]
}
]
},
{
"_id" : ObjectId("60ffb89473dc672be32909c9"),
"subject" : "IC & IT",
"units" : [
{
"_id" : ObjectId("60ffb89473dc672be32909ca"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ffb89473dc672be32909cb"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ffb89473dc672be32909cc"),
"topic" : "DataTypes"
}
]
}
]
}
]
},
{
"_id" : ObjectId("60ffb89473dc672be32909cd"),
"sem" : 2,
"subjects" : [
{
"_id" : ObjectId("60ffb89473dc672be32909ce"),
"subject" : "Java",
"units" : [
{
"_id" : ObjectId("60ffb89473dc672be32909cf"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ffb89473dc672be32909d0"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ffb89473dc672be32909d1"),
"topic" : "DataTypes"
}
]
}
]
},
{
"_id" : ObjectId("60ffb89473dc672be32909d2"),
"subject" : "SQL",
"units" : [
{
"_id" : ObjectId("60ffb89473dc672be32909d3"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ffb89473dc672be32909d4"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ffb89473dc672be32909d5"),
"topic" : "DataTypes"
}
]
}
]
}
]
}
]
}
],
"__v" : 0
}
This is the code that i am using to query and fetch data
app.get('/',function(req, res)
{
PadhloSchema.findOne(
{"courses.course" : "BCA" , "courses.semesters.sem" : 1, "courses.semesters.subjects.subject" :"C++"},
function(err, courses){
if(!err)
{
res.send(courses);
}
else
{
res.send(err);
}
})
});
I only want to fetch data where the course is BCA ,the semester(sem) is 1 and the subject is C++ and the data in the response must look like this :
{
"_id" : ObjectId("60ff08a977ec48b84ec07b46"),
"subject" : "C++",
"units" : [
{
"_id" : ObjectId("60ff08a977ec48b84ec07b47"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ff08a977ec48b84ec07b48"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ff08a977ec48b84ec07b49"),
"topic" : "DataTypes"
}
]
}
]
}
But rather i am all the data back in the response:
{
"_id" : ObjectId("60ffb89473dc672be32909c2"),
"courses" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c3"),
"course" : "BCA",
"semesters" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c4"),
"sem" : 1,
"subjects" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c5"),
"subject" : "C++",
"units" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c6"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c7"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ffb89473dc672be32909c8"),
"topic" : "DataTypes"
}
]
}
]
},
{
"_id" : ObjectId("60ffb89473dc672be32909c9"),
"subject" : "IC & IT",
"units" : [
{
"_id" : ObjectId("60ffb89473dc672be32909ca"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ffb89473dc672be32909cb"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ffb89473dc672be32909cc"),
"topic" : "DataTypes"
}
]
}
]
}
]
},
{
"_id" : ObjectId("60ffb89473dc672be32909cd"),
"sem" : 2,
"subjects" : [
{
"_id" : ObjectId("60ffb89473dc672be32909ce"),
"subject" : "Java",
"units" : [
{
"_id" : ObjectId("60ffb89473dc672be32909cf"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ffb89473dc672be32909d0"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ffb89473dc672be32909d1"),
"topic" : "DataTypes"
}
]
}
]
},
{
"_id" : ObjectId("60ffb89473dc672be32909d2"),
"subject" : "SQL",
"units" : [
{
"_id" : ObjectId("60ffb89473dc672be32909d3"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ffb89473dc672be32909d4"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ffb89473dc672be32909d5"),
"topic" : "DataTypes"
}
]
}
]
}
]
}
]
}
],
"__v" : 0
}
Please help and tell me where i am doing wrong.I am new and noob in mongoDB.
I am using the latest MongoDB version 5.0.1
UPDATED ANSWER after Comment by Rahul Soni
app.get('/',function(req, res)
{
PadhloSchema.find(
{
courses : {course : "BCA",semesters : {sem : 1 ,subjects :{subject : "C++"}}}
},
function(err, courses){
if(!err)
{
res.send(courses);
}
else
{
res.send(err);
}
})
});
But now it is giving me null array
[]

Answer 1

MongoDB returns data at the document level. https://docs.mongodb.com/manual/tutorial/query-array-of-documents/
Basically, it is working as expected. You are searching for the document and you are getting precisely that. If you are looking for a subdocument, you will need to unwind it like so:
db.tmp.aggregate({$unwind:"$courses"},{$unwind:"$courses.semesters"},{$unwind:"$courses.semesters.subjects"},{$match:{"courses.course":"BCA", "courses.semesters.sem": 1, "courses.semesters.subjects.subject" :"C++"}}).pretty()
NB: I have simply added your document to a database and showing it at a the mongo level. Node.js would work similarly.
{
"_id" : ObjectId("60ffd533bccc96b9985944a9"),
"courses" : {
"_id" : ObjectId("60ffb89473dc672be32909c3"),
"course" : "BCA",
"semesters" : {
"_id" : ObjectId("60ffb89473dc672be32909c4"),
"sem" : 1,
"subjects" : {
"_id" : ObjectId("60ffb89473dc672be32909c5"),
"subject" : "C++",
"units" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c6"),
"unit" : 1,
"topics" : [
{
"_id" : ObjectId("60ffb89473dc672be32909c7"),
"topic" : "Basics"
},
{
"_id" : ObjectId("60ffb89473dc672be32909c8"),
"topic" : "DataTypes"
}
]
}
]
}
}
}
}