Tag: regex

Count Method: MongoDB

Let’s learn to use count() method in MongoDB.

Count method outputs numeric value of the number of documents retrieved.

count-method-mongodb

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> use test
switched to db test
> db.names.find().pretty()
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "name" : "Alia" }
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }
{ "_id" : ObjectId("53be5d6804cc1cb0a7bfc3c4"), "name" : "Emli" }
{ "_id" : ObjectId("53be5d8604cc1cb0a7bfc3c5"), "name" : "Farhan" }
{ "_id" : ObjectId("53be5d9204cc1cb0a7bfc3c6"), "name" : "Gangs" }
{ "_id" : ObjectId("53be5d9904cc1cb0a7bfc3c7"), "name" : "Hum" }
{ "_id" : ObjectId("53be5e3704cc1cb0a7bfc3c8"), "name" : 25 }
> db.names.count();
9
> db.names.count({"name": {$type: 2}});
8
> db.names.count({"name": {$type: 1}});
1
> db.names.count({"name": {$regex: "e"}});
3

We have 9 documents, out of which 8 documents have string values as name and 1 document has numeric value as it’s name.

Count Method: MongoDB



YouTube Link: https://www.youtube.com/watch?v=1Cx0KT43xlw [Watch the Video In Full Screen.]



Related Read: $exists, $type, $regex operators: MongoDB

$type: 2, represents string value in BSON specification. And we have 8 documents with string value for the name field.

$type: 1, represents double value in BSON specification. And we have 1 document with numeric value for the name field.

$regex: “e”, we have 3 documents which has small letter e in the string value for name field.

Note: We can make use of count() method, when we want to show the number of friends or followers each member has. So MongoDB makes it easy by facilitating developers with count() method.

SELECT / LIST Records From Database Table: PHP & MySQL
In sql, we have SELECT count(*) FROM table_name;

$and operator: MongoDB

Lets quickly learn about using $and operator in MongoDB.

Related Read:
$exists, $type, $regex operators: MongoDB
$or (Union) Operator: MongoDB

Documents in our collection
test database, names collection.

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> db.names.find().pretty()
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "name" : "Alia" }
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }
{ "_id" : ObjectId("53be5d6804cc1cb0a7bfc3c4"), "name" : "Emli" }
{ "_id" : ObjectId("53be5d8604cc1cb0a7bfc3c5"), "name" : "Farhan" }
{ "_id" : ObjectId("53be5d9204cc1cb0a7bfc3c6"), "name" : "Gangs" }
{ "_id" : ObjectId("53be5d9904cc1cb0a7bfc3c7"), "name" : "Hum" }
{ "_id" : ObjectId("53be5e3704cc1cb0a7bfc3c8"), "name" : 25 }
{
        "_id" : ObjectId("53beaa0f6a8a31dc255d4589"),
        "name" : "Satish",
        "age" : 27
}

$and operator: MongoDB



YouTube Link: https://www.youtube.com/watch?v=Ur0Mmj7yEOI [Watch the Video In Full Screen.]



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> db.names.find({$and: [{"name": {$regex: "e"}}, {"name": {$gt: "C"}}]});
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }

As you can see, $and works/outputs results only when all the conditions in the array is met. i.e., in above command, the name must have small letter “e” in it and must be lexicographically greater than capital letter “C”.

$exists, $type, $regex operators: MongoDB

In today’s video tutorial, lets learn to use $exists, $type and $regex operators.

mongodb-exisits-type-regex

Documents in our collection
test database, names collection.

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> use test
switched to db test
> show collections
names
system.indexes
 
> db.names.find().pretty()
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "name" : "Alia" }
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }
{ "_id" : ObjectId("53be5d6804cc1cb0a7bfc3c4"), "name" : "Emli" }
{ "_id" : ObjectId("53be5d8604cc1cb0a7bfc3c5"), "name" : "Farhan" }
{ "_id" : ObjectId("53be5d9204cc1cb0a7bfc3c6"), "name" : "Gangs" }
{ "_id" : ObjectId("53be5d9904cc1cb0a7bfc3c7"), "name" : "Hum" }
{ "_id" : ObjectId("53be5e3704cc1cb0a7bfc3c8"), "name" : 25 }
 
> db.names.insert({"name": "Satish", "age": 27});
WriteResult({ "nInserted" : 1 })
 
 
> db.names.find().pretty()
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "name" : "Alia" }
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }
{ "_id" : ObjectId("53be5d6804cc1cb0a7bfc3c4"), "name" : "Emli" }
{ "_id" : ObjectId("53be5d8604cc1cb0a7bfc3c5"), "name" : "Farhan" }
{ "_id" : ObjectId("53be5d9204cc1cb0a7bfc3c6"), "name" : "Gangs" }
{ "_id" : ObjectId("53be5d9904cc1cb0a7bfc3c7"), "name" : "Hum" }
{ "_id" : ObjectId("53be5e3704cc1cb0a7bfc3c8"), "name" : 25 }
{
        "_id" : ObjectId("53beaa0f6a8a31dc255d4589"),
        "name" : "Satish",
        "age" : 27
}

Observe the documents – it has some names which are in alphabetical order. Last document has an extra field called age. And another odd entry is a document with name as 25.

$exists take 2 values, true or false

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> db.names.find({"age": {$exists: true}});
{ "_id" : ObjectId("53beaa0f6a8a31dc255d4589"), "name" : "Satish", "age" : 27 }
 
> db.names.find({"age": {$exists: false}});
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "name" : "Alia" }
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }
{ "_id" : ObjectId("53be5d6804cc1cb0a7bfc3c4"), "name" : "Emli" }
{ "_id" : ObjectId("53be5d8604cc1cb0a7bfc3c5"), "name" : "Farhan" }
{ "_id" : ObjectId("53be5d9204cc1cb0a7bfc3c6"), "name" : "Gangs" }
{ "_id" : ObjectId("53be5d9904cc1cb0a7bfc3c7"), "name" : "Hum" }
{ "_id" : ObjectId("53be5e3704cc1cb0a7bfc3c8"), "name" : 25 }

If $exists is true, it retrieves documents which has the specified field. If $exists is false, then it retrieves all the documents which do not have the specified field.

$exists, $type, $regex operators: MongoDB



YouTube Link: https://www.youtube.com/watch?v=kAU4egwsBYo [Watch the Video In Full Screen.]



$type take numeric value(BSON specification)

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> db.names.find({"name": {$type: 1}});
{ "_id" : ObjectId("53be5e3704cc1cb0a7bfc3c8"), "name" : 25 }
 
> db.names.find({"name": {$type: 2}});
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "name" : "Alia" }
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }
{ "_id" : ObjectId("53be5d6804cc1cb0a7bfc3c4"), "name" : "Emli" }
{ "_id" : ObjectId("53be5d8604cc1cb0a7bfc3c5"), "name" : "Farhan" }
{ "_id" : ObjectId("53be5d9204cc1cb0a7bfc3c6"), "name" : "Gangs" }
{ "_id" : ObjectId("53be5d9904cc1cb0a7bfc3c7"), "name" : "Hum" }
{ "_id" : ObjectId("53beaa0f6a8a31dc255d4589"), "name" : "Satish", "age" : 27 }
TypeNumber
Double1
String2
Object3
Array4
Binary data5
Undefined6
Object id7
Boolean8
Date9
Null10
Regular Expression11
JavaScript13
Symbol14
JavaScript (with scope)15
32-bit integer16
Timestamp17
64-bit integer18
Min key255
Max key127

$regex (similar to perl regular expression)

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> db.names.find({"name": {$regex: "e"}});
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }
 
> db.names.find({"name": {$regex: "^E"}});
{ "_id" : ObjectId("53be5d6804cc1cb0a7bfc3c4"), "name" : "Emli" }
 
> db.names.find({"name": {$regex: "h$"}});
{ "_id" : ObjectId("53beaa0f6a8a31dc255d4589"), "name" : "Satish", "age" : 27 }
 
> db.names.find({"name": {$regex: "^[A-Z]"}});
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "name" : "Alia" }
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }
{ "_id" : ObjectId("53be5d6804cc1cb0a7bfc3c4"), "name" : "Emli" }
{ "_id" : ObjectId("53be5d8604cc1cb0a7bfc3c5"), "name" : "Farhan" }
{ "_id" : ObjectId("53be5d9204cc1cb0a7bfc3c6"), "name" : "Gangs" }
{ "_id" : ObjectId("53be5d9904cc1cb0a7bfc3c7"), "name" : "Hum" }
{ "_id" : ObjectId("53beaa0f6a8a31dc255d4589"), "name" : "Satish", "age" : 27 }
 
> db.names.find({"name": {$regex: "^[A-E]"}});
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "name" : "Alia" }
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d5904cc1cb0a7bfc3c2"), "name" : "Chameli" }
{ "_id" : ObjectId("53be5d6104cc1cb0a7bfc3c3"), "name" : "Dev D" }
{ "_id" : ObjectId("53be5d6804cc1cb0a7bfc3c4"), "name" : "Emli" }

$regex: “e” retrieves all the documents in which small letter “e” is present.
$regex: “^E” retrieves all the documents which has it’s name beginning letter as “E”.
$regex: “h$” retrieves all the documents which has it’s name ending letter as “h”.
$regex: “^[A-Z]” retrieves all the documents which has it’s name starting with characters “A” to “Z”.
$regex: “^[A-E]” retrieves all the documents which has it’s name starting with characters “A” to “E”.

Note: There is more to regular expression, this video is just an introduction. We’ll cover more about regular expressions in a separate video of it’s own.