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How to determine whether a field exists in MongoDB?
You need to use $exists operator to determine whether a field exists in MongoDB. Let us first create a collection with documents
> db.determineFieldExistsDemo.insertOne({"ClientName":"John"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9eb245d628fa4220163b75")
}
> db.determineFieldExistsDemo.insertOne({"ClientName":"Larry","ClientAge":23});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9eb25cd628fa4220163b76")
}
> db.determineFieldExistsDemo.insertOne({"ClientName":"Mike","ClientCountryName":"UK"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9eb26fd628fa4220163b77")
}
> db.determineFieldExistsDemo.insertOne({"ClientName":"Sam","ClientAge":24});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9eb286d628fa4220163b78")
}Following is the query to display all documents from a collection with the help of find() method
> db.determineFieldExistsDemo.find().pretty();
This will produce the following output
{ "_id" : ObjectId("5c9eb245d628fa4220163b75"), "ClientName" : "John" }
{
"_id" : ObjectId("5c9eb25cd628fa4220163b76"),
"ClientName" : "Larry",
"ClientAge" : 23
}
{
"_id" : ObjectId("5c9eb26fd628fa4220163b77"),
"ClientName" : "Mike",
"ClientCountryName" : "UK"
}
{
"_id" : ObjectId("5c9eb286d628fa4220163b78"),
"ClientName" : "Sam",
"ClientAge" : 24
}Following is the query to determine whether a field exists
> db.determineFieldExistsDemo.find({ClientCountryName:{$exists:true}}).pretty();This will produce the following output
{
"_id" : ObjectId("5c9eb26fd628fa4220163b77"),
"ClientName" : "Mike",
"ClientCountryName" : "UK"
}
Updated on: 30-Jul-2019
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