mongoDB search query - mongodb

Question

For an assignment, we are given the following code:
db.bib.insertMany( [
{type : "book",
"#year": "1994",
"title": "TCP/IP Illustrated",
"author": {
"last": "Stevens",
"first": "W."
},
"publisher": "Addison-Wesley",
"price": "65"
},
{type : "book",
"#year": "1992",
"title": "Unix Programming",
"author": {
"last": "Stevens",
"first": "W."
},
"publisher": "Addison-Wesley",
"price": "65"
},
{type : "book",
"#year": "2000",
"title": "Data on the Web",
"author": [
{
"last": "Abiteboul",
"first": "Serge"
},
{
"last": "Buneman",
"first": "Peter"
},
{
"last": "Suciu",
"first": "Dan"
}
],
"publisher": "Morgan Kaufmann",
"price": "39"
},
{type : "book",
"#year": "1999",
"title": "Digital TV",
"editor": {
"last": "Gerbarg",
"first": "Darcy",
"affiliation": "CITI"
},
"publisher": "Kluwer",
"price": "130"
}
,
{type : "journal",
"title": "Irreproducible results",
"editor": {
"last": "Self",
"first": "W."
},
"publisher": "SV"
}
])
Using mongoDB, we are then asked to complete different search queries in order to find the desired information. The one that I am currently stuck on is
List the titles of books published after 1995 and costing less than 100.
From my understanding, the proper query should be something along the lines of
db.bib.find({price: {$lt: 100}, year: {$gt: 1995}}, {title: 1, _id: 0})
However, this provides a blank result when it should not. Why is this and how can I fix it?

Answer 1

Data type for both of the field is string. you can not compare them as numeric. Try following and it will work. using collation, you can ask MongoDB to treat them as int. you can read more about collation here at mongodb.com.
db.bib.find({$and: [{"#year": {$gt: "1995"}}, {price: {$lt: "100"}}]}).collation({
locale: "en_US",
numericOrdering: true
});