07 - MongoDB - CRUD operations - select the fields using $regex,$exists,$type

#  our database-UNIVERSITY ,  collection-NAME

insert into this two documents
> db.name.insert({"_id":"Fana","favoriteGame":["IPL","cricket"],"age":23})

> db.name.insert({"_id":"Nimishan","favoriteGame":["football","cricket"],"age":24})

> db.name.find({})

.....

{ "_id" : "Brigida Hertzog", "favoriteGame" : [  "basketball",  "tennis" ] }
{ "_id" : "Gisele Melancon", "favoriteGame" : [  "cricket",  "tennis" ] }
{ "_id" : "Tula Steadman", "favoriteGame" : [  "football",  "formula" ] }
{ "_id" : "Nimishan", "favoriteGame" : [  "football",  "cricket" ], "age" : 24 }
{ "_id" : "Fana", "favoriteGame" : [  "IPL",  "cricket" ], "age" : 23 }

#  query using $exists
> db.name.find({"age":{$exists:true}})
{ "_id" : "Nimishan", "favoriteGame" : [  "football",  "cricket" ], "age" : 24 }
{ "_id" : "Fana", "favoriteGame" : [  "IPL",  "cricket" ], "age" : 23 }

> db.name.find({"age":{$exists:false}})
{ "_id" : "Tonia Jefferis", "favoriteGame" : [  "basketball",  "tennis" ] }
{ "_id" : "Daphine Chilson", "favoriteGame" : [  "hokey",  "basketball" ] }
{ "_id" : "Tiffani Trapp", "favoriteGame" : [  "cricket",  "NFS" ] }
{ "_id" : "Pearlie Luther", "favoriteGame" : [  "formula",  "pool" ] }
{ "_id" : "Pierre Ye", "favoriteGame" : [  "pool",  "basketball" ] }

....

#  query using $type

$type selects the documents where the value of the field is the specified BSON type

Type	Number
Double	1
String	2
Object	3
find more types....

> db.name.find({"age":{$type:1}})
{ "_id" : "Nimishan", "favoriteGame" : [  "football",  "cricket" ], "age" : 24 }
{ "_id" : "Fana", "favoriteGame" : [  "IPL",  "cricket" ], "age" : 23 }
> db.name.find({"age":{$type:2}})

> db.name.find({"_id":{$type:1}})

> db.name.find({"_id":{$type:2}})
{ "_id" : "Alessandra Helton", "favoriteGame" : [  "NFS",  "football" ] }
{ "_id" : "Alta Oxner", "favoriteGame" : [  "cricket",  "pool" ] }
{ "_id" : "Bambi Geraci", "favoriteGame" : [  "IPL",  "formula" ] }
{ "_id" : "Brigida Hertzog", "favoriteGame" : [  "basketball",  "tennis" ] }
{ "_id" : "Carey Carriere", "favoriteGame" : [  "cricket",  "hokey" ] }

....

#  query using $regex

The $regex operator provides regular expression capabilities for pattern matching strings in queries
> db.name.find({"_id":{$regex:"ss"}})
{ "_id" : "Alessandra Helton", "favoriteGame" : [  "NFS",  "football" ] }

> db.name.find({"_id":{$regex:"na"}})

{ "_id" : "Daina Mclendon", "favoriteGame" : [  "hokey",  "IPL" ] }

{ "_id" : "Fana", "favoriteGame" : [  "IPL",  "cricket" ], "age" : 23 }

{ "_id" : "Gianna Kowaleski", "favoriteGame" : [  "NFS",  "formula" ] }

find first character
> db.name.find({"_id":{$regex:"^D"}})
{ "_id" : "Daina Mclendon", "favoriteGame" : [  "hokey",  "IPL" ] }
{ "_id" : "Daphine Chilson", "favoriteGame" : [  "hokey",  "basketball" ] }
{ "_id" : "Dion Spradlin", "favoriteGame" : [  "pool",  "NFS" ] }
> db.name.find({"_id":{$regex:"^Da"}})
{ "_id" : "Daina Mclendon", "favoriteGame" : [  "hokey",  "IPL" ] }
{ "_id" : "Daphine Chilson", "favoriteGame" : [  "hokey",  "basketball" ] }

find last character
> db.name.find({"_id":{$regex:"on$"}})
{ "_id" : "Alessandra Helton", "favoriteGame" : [  "NFS",  "football" ] }
{ "_id" : "Daina Mclendon", "favoriteGame" : [  "hokey",  "IPL" ] }
{ "_id" : "Daphine Chilson", "favoriteGame" : [  "hokey",  "basketball" ] }
{ "_id" : "Gisele Melancon", "favoriteGame" : [  "cricket",  "tennis" ] }
> db.name.find({"_id":{$regex:"n$"}})
{ "_id" : "Alessandra Helton", "favoriteGame" : [  "NFS",  "football" ] }
{ "_id" : "Daina Mclendon", "favoriteGame" : [  "hokey",  "IPL" ] }
{ "_id" : "Daphine Chilson", "favoriteGame" : [  "hokey",  "basketball" ] }
{ "_id" : "Dion Spradlin", "favoriteGame" : [  "pool",  "NFS" ] }
{ "_id" : "Gisele Melancon", "favoriteGame" : [  "cricket",  "tennis" ] }
{ "_id" : "Nimishan", "favoriteGame" : [  "football",  "cricket" ], "age" : 24 }
{ "_id" : "Tula Steadman", "favoriteGame" : [  "football",  "formula" ] }