$exists
operator is used to get the documents that contain specific field.
Syntax
{
field: { $exists: <boolean> } }
When
boolean is true, then exists operator matches all documents that contains given
field, including documents where the field value is null.. When Boolean is
false, then exists operator matches all documents that don’t contain given
field.
> db.employee.find() { "_id" : 1, "firstName" : "Joel", "lastName" : "chelli", "salary" : 25000, "hobbies" : [ "watching movies", "playing games" ] } { "_id" : 2, "firstName" : "Ananad", "lastName" : "Bandaru", "salary" : 200000, "hobbies" : [ "car drivinig", "watching movies" ] } { "_id" : 3, "firstName" : "Gopi", "lastName" : "Battu", "salary" : 65000, "hobbies" : [ "climbing hills", "dancing", "singing" ] } { "_id" : 4, "firstName" : "Ritwik", "lastName" : "Mohenthy", "salary" : 50000, "hobbies" : [ "watching movies", "watching movies", "watching movies" ] } { "_id" : 5, "firstName" : "RamaKrishna", "lastName" : "Gurram", "salary" : 150000, "hobbies" : [ "hackning sites", "Reading books", "listening music" ] } { "_id" : 6, "firstName" : "BalaKrishna", "lastName" : "Gurram", "salary" : 80000, "hobbies" : [ "roaming around", "eating food" ] } { "_id" : ObjectId("54ba2de1f1c8f2149c000740"), "name" : "Krishna", "project" : "A350" } { "_id" : ObjectId("54ba2dfcf1c8f2149c000741"), "name" : "Krishna", "project" : 4 }
1.Get documents
that contain field “name”.
> db.employee.find({"name" : {$exists:true}}) { "_id" : ObjectId("54ba2de1f1c8f2149c000740"), "name" : "Krishna", "project" : "A350" } { "_id" : ObjectId("54ba2dfcf1c8f2149c000741"), "name" : "Krishna", "project" : 4 }
2. Get documents
that don’t contain field “name”.
> db.employee.find({"name" : {$exists:false}}) { "_id" : 1, "firstName" : "Joel", "lastName" : "chelli", "salary" : 25000, "hobbies" : [ "watching movies", "playing games" ] } { "_id" : 2, "firstName" : "Ananad", "lastName" : "Bandaru", "salary" : 200000, "hobbies" : [ "car drivinig", "watching movies" ] } { "_id" : 3, "firstName" : "Gopi", "lastName" : "Battu", "salary" : 65000, "hobbies" : [ "climbing hills", "dancing", "singing" ] } { "_id" : 4, "firstName" : "Ritwik", "lastName" : "Mohenthy", "salary" : 50000, "hobbies" : [ "watching movies", "watching movies", "watching movies" ] } { "_id" : 5, "firstName" : "RamaKrishna", "lastName" : "Gurram", "salary" : 150000, "hobbies" : [ "hackning sites", "Reading books", "listening music" ] } { "_id" : 6, "firstName" : "BalaKrishna", "lastName" : "Gurram", "salary" : 80000, "hobbies" : [ "roaming around", "eating food" ] }
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