11. MongoDB - CRUD operations - Part_I_Querying , Coursor {count()}

dba@HP:~$ mongo university
MongoDB shell version: 2.4.9
connecting to: university
> show collections
info
name
result
system.indexes
> 
#  count()
Counts the number of documents in a collection. Returns a document that contains this count and as well as the command status

/* count all document */

> db.name.find().count()

31

> db.name.count()

31

> db.name.find({}).count()

31

> db.name.count({})

31

/* count the document  '_id' value start with first letter 'A'  */   

> db.name.find({_id:{$regex:"^A"}}).count()

2

> db.name.count({_id:{$regex:"^A"}})

2

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

{ "_id" : "Alessandra Helton", "favoriteGame" : [  "NFS",  "football" ] }

{ "_id" : "Alta Oxner", "favoriteGame" : [  "cricket",  "pool" ] }

/* find the all document */   

> db.name.find({})

{ "_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" ] }

{ "_id" : "Kelvin Spurling", "favoriteGame" : [  "NFS",  "football" ] }

{ "_id" : "Erminia Kubala", "favoriteGame" : [  "IPL",  "pool" ] }

{ "_id" : "Petra Clarke", "favoriteGame" : [  "pool",  "tennis" ] }

{ "_id" : "Bambi Geraci", "favoriteGame" : [  "IPL",  "formula" ] }

{ "_id" : "Jene Goding", "favoriteGame" : [  "football",  "cricket" ] }

{ "_id" : "Dion Spradlin", "favoriteGame" : [  "pool",  "NFS" ] }

{ "_id" : "Enola Robert", "favoriteGame" : [  "formula",  "IPL" ] }

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

{ "_id" : "Lazaro Izzi", "favoriteGame" : [  "basketball",  "IPL" ] }

{ "_id" : "Sebastian Kuo", "favoriteGame" : [  "NFS",  "football" ] }

{ "_id" : "Jeanine Pigott", "favoriteGame" : [  "cricket",  "formula" ] }

{ "_id" : "Gene Smits", "favoriteGame" : [  "formula",  "pool" ] }

{ "_id" : "Janett Olivera", "favoriteGame" : [  "football",  "basketball" ] }

{ "_id" : "Alta Oxner", "favoriteGame" : [  "cricket",  "pool" ] }

{ "_id" : "Alessandra Helton", "favoriteGame" : [  "NFS",  "football" ] }

Type "it" for more

/* count the document  '_id' value start with first letter 'A' and 'favoriteGame' equal 'NFS' */  

 > db.name.find({_id:{$regex:"^A"},"favoriteGame":"NFS"})

{ "_id" : "Alessandra Helton", "favoriteGame" : [  "NFS",  "football" ] }

> db.name.find({_id:{$regex:"^A"},"favoriteGame":"NFS"}).count()

1

> db.name.count({_id:{$regex:"^A"},"favoriteGame":"NFS"})

1

/* count the all document */  

> db.result.find().count()

60

> db.result..count()

60

/* count the document  'score' value graterthan equal '90'*/  

> db.result.find({score:{$gte:90}}).count()

3

> db.result.count({score:{$gte:90}})

3 

> db.result.find({score:{$gte:90}})

{ "_id" : ObjectId("538de41d2110740e7c9a5374"), "student" : 1, "exam type" : "Essay", "score" : 92 }

{ "_id" : ObjectId("538de41d2110740e7c9a5387"), "student" : 7, "exam type" : "Quiz", "score" : 92 }

{ "_id" : ObjectId("538de41d2110740e7c9a5390"), "student" : 10, "exam type" : "Quiz", "score" : 93 }

> db.result.find({score:{$gte:90}},{_id:false})

{ "student" : 1, "exam type" : "Essay", "score" : 92 }

{ "student" : 7, "exam type" : "Quiz", "score" : 92 }

{ "student" : 10, "exam type" : "Quiz", "score" : 93 }

/* count the document  'score' value graterthan equal '92' and 'exam type' equal 'Essay'*/  

> db.result.find({score:{$gte:90},"exam type":"Essay"},{_id:false}).count()

1

> db.result.count({score:{$gte:90},"exam type":"Essay"},{_id:false})

1                                                                                                                                               

> db.result.find({score:{$gte:90},"exam type":"Essay"},{_id:false})

{ "student" : 1, "exam type" : "Essay", "score" : 92 }

> db.result.find({score:{$gte:90},"exam type":"Essay"},{_id:false,student:true})

{ "student" : 1 }

> db.result.find({score:{$gte:90},"exam type":"Essay"},{_id:false,student:false})

{ "exam type" : "Essay", "score" : 92 }