To find documents that contain specific field, use $exists. Let us create a collection with documents −
> db.demo247.insertOne({"ClientDetails":[{"ClientFirstName":"Chris","ClientAge":34}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e46b2a31627c0c63e7dba69") } >db.demo247.insertOne({"ClientDetails":[{"ClientFirstName":"John","ClientLastName":"Smith","ClientAge":31}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e46b2be1627c0c63e7dba6a") } > db.demo247.insertOne({"ClientDetails":[{"ClientFirstName":"David","ClientAge":33}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e46b2cd1627c0c63e7dba6b") } >db.demo247.insertOne({"ClientDetails":[{"ClientFirstName":"David","ClientLastName":"Miller","ClientAge":31}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e46b2de1627c0c63e7dba6c") }
Display all documents from a collection with the help of find() method −
> db.demo247.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5e46b2a31627c0c63e7dba69"), "ClientDetails" : [ { "ClientFirstName" : "Chris", "ClientAge" : 34 } ] } { "_id" : ObjectId("5e46b2be1627c0c63e7dba6a"), "ClientDetails" : [ { "ClientFirstName" : "John", "ClientLastName" : "Smith", "ClientAge" : 31 } ] } { "_id" : ObjectId("5e46b2cd1627c0c63e7dba6b"), "ClientDetails" : [ { "ClientFirstName" : "David", "ClientAge" : 33 } ] } { "_id" : ObjectId("5e46b2de1627c0c63e7dba6c"), "ClientDetails" : [ { "ClientFirstName" : "David", "ClientLastName" : "Miller", "ClientAge" : 31 } ] }
Following is the query to find documents that contains specific field −
> db.demo247.find({"ClientDetails.ClientLastName":{$exists:true}});
This will produce the following output −
{ "_id" : ObjectId("5e46b2be1627c0c63e7dba6a"), "ClientDetails" : [ { "ClientFirstName" : "John", "ClientLastName" : "Smith", "ClientAge" : 31 } ] } { "_id" : ObjectId("5e46b2de1627c0c63e7dba6c"), "ClientDetails" : [ { "ClientFirstName" : "David", "ClientLastName" : "Miller", "ClientAge" : 31 } ] }