Why Iam getting this value as a NULL - mongodb

Question

I am getting the below erro, when I provide the findOne function. It is displaying NULL, couldn't find the solution as there are records with the title.
db.links.findOne({title: "MongoDB TUtor"});
{
"_id" : ObjectId("54f3ea83663952fddd7aaa54"),
"title" : "MongoDB TUtor",
"url" : "mongo.com",
"comment" : "document-oriented db"
}
> db.links.findOne({title: "true"});
null
> db.links.findOne({title: 1});
null
--
Records in links collection
db.links.find().forEach(printjson)
{
"_id" : ObjectId("54f3ea83663952fddd7aaa54"),
"title" : "MongoDB TUtor",
"url" : "mongo.com",
"comment" : "document-oriented db"
}
{
"_id" : ObjectId("54f3ebe7663952fddd7aaa55"),
"title" : "Mongo DB handson",
"url" : "https://university.mongo.com",
"comment" : [
"NoSQL",
"Document-based"
],
"filed_on" : ISODate("2015-03-02T04:47:02.131Z"),
"meta" : {
"browser" : [
"Google Chrome",
"MAC Safari"
],
"version" : "13.4.3.7"
}
}
{
"_id" : ObjectId("54f3f77e663952fddd7aaa5a"),
"title" : "MongoDB_database",
"url" : "mongo.com",
"comment" : "document-oriented db"
}
{
"_id" : ObjectId("54f3f7b7663952fddd7aaa5c"),
"title" : "database",
"url" : "mongo.com",
"comment" : "document-oriented db"
}
{ "_id" : ObjectId("54f3fa5f663952fddd7aaa5d"), "title" : "Rocky" }
{
"_id" : ObjectId("54f3facf663952fddd7aaa5e"),
"title" : "Arnold",
"userId" : ObjectId("54f3fa5f663952fddd7aaa5d")
}
> db.links.find().pretty()
{
"_id" : ObjectId("54f3ea83663952fddd7aaa54"),
"title" : "MongoDB TUtor",
"url" : "mongo.com",
"comment" : "document-oriented db"
}
{
"_id" : ObjectId("54f3ebe7663952fddd7aaa55"),
"title" : "Mongo DB handson",
"url" : "https://university.mongo.com",
"comment" : [
"NoSQL",
"Document-based"
],
"filed_on" : ISODate("2015-03-02T04:47:02.131Z"),
"meta" : {
"browser" : [
"Google Chrome",
"MAC Safari"
],
"version" : "13.4.3.7"
}
}
{
"_id" : ObjectId("54f3f77e663952fddd7aaa5a"),
"title" : "MongoDB_database",
"url" : "mongo.com",
"comment" : "document-oriented db"
}
{
"_id" : ObjectId("54f3f7b7663952fddd7aaa5c"),
"title" : "database",
"url" : "mongo.com",
"comment" : "document-oriented db"
}
{ "_id" : ObjectId("54f3fa5f663952fddd7aaa5d"), "title" : "Rocky" }
{
"_id" : ObjectId("54f3facf663952fddd7aaa5e"),
"title" : "Arnold",
"userId" : ObjectId("54f3fa5f663952fddd7aaa5d")
}

Answer 1

That's not how you do it. The way you are querying this it is looking for an actual document that either has "title": true or "title": 1. Of course, none of your documents meet that condition.
When you want to find out if that field is "actually there" then you use the $exists operator to test for the presence:
db.links.findOne({ "title": { "$exists": true } })
Or naturally with the reverse case when looking for documents that do not have the matching field.