Check if value exists for a field in a MongoDB document?

To check if value exists for a field in a MongoDB document, you can use find() along with $exists operator. Let us first create a collection with documents −

> db.checkIfValueDemo.insertOne({"PlayerName":"John Smith","PlayerScores":[5000,98595858,554343]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cc6f507af8e7a4ca6b2ad98")
}
> db.checkIfValueDemo.insertOne({"PlayerName":"John Doe","PlayerScores":[]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cc6f512af8e7a4ca6b2ad99")
}
> db.checkIfValueDemo.insertOne({"PlayerName":"Carol Taylor","PlayerScores":[7848474,8746345353]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cc6f521af8e7a4ca6b2ad9a")
}
> db.checkIfValueDemo.insertOne({"PlayerName":"David Miller","PlayerScores":[]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cc6f531af8e7a4ca6b2ad9b")
}

Following is the query to display all documents from a collection with the help of find() method −

> db.checkIfValueDemo.find().pretty();

This will produce the following output −

{
   "_id" : ObjectId("5cc6f507af8e7a4ca6b2ad98"),
   "PlayerName" : "John Smith",
   "PlayerScores" : [
      5000,
      98595858,
      554343
   ]
}
{
   "_id" : ObjectId("5cc6f512af8e7a4ca6b2ad99"),
   "PlayerName" : "John Doe",
   "PlayerScores" : [ ]
}
{
   "_id" : ObjectId("5cc6f521af8e7a4ca6b2ad9a"),
   "PlayerName" : "Carol Taylor",
   "PlayerScores" : [
      7848474,
      8746345353
   ]
}
{
   "_id" : ObjectId("5cc6f531af8e7a4ca6b2ad9b"),
   "PlayerName" : "David Miller",
   "PlayerScores" : [ ]
}

Following is the query to check if value exists for a field in a document. Here, we are checking for field 'PlayerScores with value [ ] −

> db.checkIfValueDemo.find({'PlayerScores.0' : {$exists: true}}).count();

This will produce the following output

2