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Mongodb Tutorial

MongoDB Element Query Operator - $exists

Description

In this page we are going to discuss the usage of $exists operator. The $exists operator is used to allow the user to retrieve documents from a collection either a specific field is exists or not into those documents.

Insert the following document into the collection 'testtable':

>db.testtable.insert({"user_id":"user5","password":"user5", "sex":"Male","age":21, "date_of_join":"17/08/2011", "education":"MCA", "profession":"S.W. Engineer","interest":"SPORTS","extra":{"community_name" :["ATHELATIC", "GAMES FAN GYES","FAVOURIT GAMES"]}});

Our database name is 'myinfo' and our collection name is 'testtable'. Here, is the collection bellow.

Sample collection "testtable"

{
        "_id" : ObjectId("528f4e630fe5e6467e58ae7b"),
        "user_id" : "user1",
        "password" : "1a2b3c",
        "sex" : "Male",
        "age" : 17,
        "date_of_join" : "16/10/2010",
        "education" : "M.C.A.",
        "profession" : "CONSULTANT",
        "interest" : "MUSIC",
        "extra" : {
                "community_name" : [
                        "MODERN MUSIC",
                        "CLASSICAL MUSIC",
                        "WESTERN MUSIC"
                ],
                "community_moder_id" : [
                        "MR. Alex",
                        "MR.   Dang",
                        "MR Haris"
                ],
                "community_members" : [
                        700,
                        200,
                        1500
                ],
                "friends" : {
                        "valued_friends_id" : [
                                "kumar",
                                "harry",
                                "anand"
                        ],
                        "ban_friends_id" : [
                                "Amir",
                                "Raja",
                                "mont"
                        ]
                }
        }
}
{
        "_id" : ObjectId("528f4e720fe5e6467e58ae7c"),
        "user_id" : "user2",
        "password" : "11aa1a",
        "sex" : "Male",
        "age" : 24,
        "date_of_join" : "17/10/2009",
        "education" : "M.B.A.",
        "profession" : "MARKETING",
        "interest" : " MUSIC",
        "extra" : {
                "community_name" : [
                        "MODERN MUSIC",
                        "CLASSICAL MUSIC",
                        "WESTERN MUSIC"
                ],
                "co mmunity_moder_id" : [
                        "MR. Roy",
                        "MR. Das",
                        "MR Doglus"
                ],
                "community_members" : [
                        500,
                        300,
                        1400
                ],
                "friends" : {
                        "valued_friends_id" : [
                                "pal",
                                "viki",
                                "john"
                        ],
                        "ban_friends_id" : [
                                "jalan",
                                "mono j",
                                "evan"
                        ]
                }
        }
}
{
        "_id" : ObjectId("528f4e7e0fe5e6467e58ae7d"),
        "user_id" : "user3",
        "password" : "b1c1d1",
        "sex" : "Female",
        "age" : 19,
        "date_of_join" : "16/10/2010",
        "education" : "M.C.A.",
        "profession" : "IT COR.",
        "interest" : "AR T",
        "extra" : {
                "community_name" : [
                        "MODERN ART",
                        "CLASSICAL ART",
                        "WESTERN ART"
                ],
                "community_mo der_id" : [
                        "MR. Rifel",
                        "MR. Sarma",
                        "MR Bhatia"
                ],
                "community_members" : [
                        5000,
                        2000,
                        1500
                ],
                "friends" : {
                        "valued_friends_id" : [
                                "philip",
                                "anant",
                                "alan"
                        ],
                        "ban_friends_id" : [
                                "Amir",
                                "Raja",
                                "mont"
                        ]
                }
        }
}
{
        "_id" : ObjectId("528f4e910fe5e6467e58ae7e"),
        "user_id" : "user4",
        "password" : "abczyx",
        "sex" : "Female",
        "age" : 22,
        "date_of_join" : "17/8/2009",

        "education" : "M.B.B.S.",
        "profession" : "DOCTOR",
        "interest" : "SPORTS",
        "extra" : {
                "community_name" : [
                        "ATHELATIC",
                        "GAMES FAN GYES",
                        "FAVOURIT GAMES"
                ],
                "community_moder_id" : [
                        "MR. Paul",
                        "MR. Das",
                        "MR Doglus"
                ],
                "community_members" : [
                        2500,
                        2200,
                        3500
                ],
                "friends" : {
                        "valued_friends_id" : [
                                "vinod",
                                "viki",
                                "john"
                        ],
                        "ban_friends_id" : [
                                "jalan",
                                "monoj",
                                "evan"
                        ]
                }
        }
}
{
        "_id" : ObjectId("528f4f8a0fe5e6467e58ae7f"),
        "user_id" : "user5",
        "password" : "user5",
        "sex" : "Male",
        "age" : 21,
        "date_of_join" : "17/08/2011",
        "education" : "MCA",
        "profession" : "S.W. Engineer",
        "interest" : "SPORTS",
        "extra" : {
                "community_name" : [
                        "ATHELATIC",
                        "GAMES FAN GYES",
                        "FAVOURIT GAMES"
                ]
        }
}

Document written in command prompt

MongoDB $exists operator with 'true' keyword

If we want to fetch documents from the collection "testtable" where the field "community_members" is exists, the following mongodb command can be used :

>db.testtable.find({"extra.community_members" : { $exists : true } } ).pretty();

N.B. find() method displays the documents in a non structured format but to display the results in a formatted way, the pretty() method can be used.

Output of the command:

{
        "_id" : ObjectId("528f4e630fe5e6467e58ae7b"),
        "user_id" : "user1",
        "password" : "1a2b3c",
        "sex" : "Male",
        "age" : 17,
        "date_of_join" : "16/10/2010",
        "education" : "M.C.A.",
        "profession" : "CONSULTANT",
        "interest" : "MUSIC",
        "extra" : {
                "community_name" : [
                        "MODERN MUSIC",
                        "CLASSICAL MUSIC",
                        "WESTERN MUSIC"
                ],
                "community_moder_id" : [
                        "MR. Alex",
                        "MR.   Dang",
                        "MR Haris"
                ],
                "community_members" : [
                        700,
                        200,
                        1500
                ],
                "friends" : {
                        "valued_friends_id" : [
                                "kumar",
                                "harry",
                                "anand"
                        ],
                        "ban_friends_id" : [
                                "Amir",
                                "Raja",
                                "mont"
                        ]
                }
        }
}
{
        "_id" : ObjectId("528f4e720fe5e6467e58ae7c"),
        "user_id" : "user2",
        "password" : "11aa1a",
        "sex" : "Male",
        "age" : 24,
        "date_of_join" : "17/10/2009",
        "education" : "M.B.A.",
        "profession" : "MARKETING",
        "interest" : " MUSIC",
        "extra" : {
                "community_name" : [
                        "MODERN MUSIC",
                        "CLASSICAL MUSIC",
                        "WESTERN MUSIC"
                ],
                "co mmunity_moder_id" : [
                        "MR. Roy",
                        "MR. Das",
                        "MR Doglus"
                ],
                "community_members" : [
                        500,
                        300,
                        1400
                ],
                "friends" : {
                        "valued_friends_id" : [
                                "pal",
                                "viki",
                                "john"
                        ],
                        "ban_friends_id" : [
                                "jalan",
                                "mono j",
                                "evan"
                        ]
                }
        }
}
{
        "_id" : ObjectId("528f4e7e0fe5e6467e58ae7d"),
        "user_id" : "user3",
        "password" : "b1c1d1",
        "sex" : "Female",
        "age" : 19,
        "date_of_join" : "16/10/2010",
        "education" : "M.C.A.",
        "profession" : "IT COR.",
        "interest" : "AR T",
        "extra" : {
                "community_name" : [
                        "MODERN ART",
                        "CLASSICAL ART",
                        "WESTERN ART"
                ],
                "community_mo der_id" : [
                        "MR. Rifel",
                        "MR. Sarma",
                        "MR Bhatia"
                ],
                "community_members" : [
                        5000,
                        2000,
                        1500
                ],
                "friends" : {
                        "valued_friends_id" : [
                                "philip",
                                "anant",
                                "alan"
                        ],
                        "ban_friends_id" : [
                                "Amir",
                                "Raja",
                                "mont"
                        ]
                }
        }
}
{
        "_id" : ObjectId("528f4e910fe5e6467e58ae7e"),
        "user_id" : "user4",
        "password" : "abczyx",
        "sex" : "Female",
        "age" : 22,
        "date_of_join" : "17/8/2009",

        "education" : "M.B.B.S.",
        "profession" : "DOCTOR",
        "interest" : "SPORTS",
        "extra" : {
                "community_name" : [
                        "ATHELATIC",
                        "GAMES FAN GYES",
                        "FAVOURIT GAMES"
                ],
                "community_moder_id" : [
                        "MR. Paul",
                        "MR. Das",
                        "MR Doglus"
                ],
                "community_members" : [
                        2500,
                        2200,
                        3500
                ],
                "friends" : {
                        "valued_friends_id" : [
                                "vinod",
                                "viki",
                                "john"
                        ],
                        "ban_friends_id" : [
                                "jalan",
                                "monoj",
                                "evan"
                        ]
                }
        }
}

Document written in command prompt

The above output shows, documents appears from the collection containing the field "community_members" in each document, because the 'true' keyword along with $exists operator have used.

MongoDB $exists operator with 'false' keyword

If we want to fetch documents from the collection "testtable" where the field "community_members" does not exists, the following mongodb command can be used :

>db.testtable.find({"extra.community_members" : { $exists : false } } ).pretty();

N.B. find() method displays the documents in a non structured format but to display the results in a formatted way, the pretty() method can be used.

Output of the command:

{
        "_id" : ObjectId("528f4f8a0fe5e6467e58ae7f"),
        "user_id" : "user5",
        "password" : "user5",
        "sex" : "Male",
        "age" : 21,
        "date_of_join" : "17/08/2011",
        "education" : "MCA",
        "profession" : "S.W. Engineer",
        "interest" : "SPORTS",
        "extra" : {
                "community_name" : [
                        "ATHELATIC",
                        "GAMES FAN GYES",
                        "FAVOURIT GAMES"
                ]
        }
}

Document written in command prompt

The above output shows, documents appears from the collection not to be containing the field "community_members" in each document, because the 'false' keyword along with $exists operator have used.



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