Jul 5, 2015

Query Document - MongoDB

THE FIND() METHOD
To query data document from collection MongoDB, We need to use MongoDB's find() method.

Syntax
Basic syntax of find() method is as follows


>db.COLLECTION_NAME.find()


When we used find() method then all the documents will display in a non structured way.

THE PRETTY() METHOD
Here we will use the pretty() method to display the results in a formatted way.

Syntax:


>db.TestCol.find().pretty()


Example


>db.TestCol.find().pretty()
{
   "_id": ObjectId(7df78ad8902c),
   "title": "MongoDB Overview",
   "description": "MongoDB is no sql database",
   "by": "MongoBD query",
   "url": "http://www.codefari.com",
   "tags": ["mongodb", "database", "NoSQL"],
   "likes": "100"
}
> 


Apart from find() method there is findOne() method, that reruns only one document.

RDBMS Where Clause Equivalents in MongoDB
To query data document on the basis of some condition, we are using following operations

Operation
Syntax
Example
RDBMS Equivalent
Equality
{<key>:<value>}
db.TestCol.find({"by":"MongoBD query"}).pretty()
where by = 'MongoBD query'

Less Than
{<key>:{$lt:<value>}}
db.TestCol.find({"likes":{$lt:50}}).pretty()
where likes <= 50
Less Than Equals
{<key>:{$lte:<value>}}
db.TestCol.find({"likes":{$lte:50}}).pretty()
where likes <= 50
Greater Than
{<key>:{$gt:<value>}}
db.TestCol.find({"likes":{$gt:50}}).pretty()
where likes > 50

Greater Than Equals
{<key>:{$gte:<value>}}
db.TestCol.find({"likes":{$gte:50}}).pretty()
where likes > 50

Not Equals
{<key>:{$ne:<value>}}
db.TestCol.find({"likes":{$ne:50}}).pretty()
where likes != 50

                                               
AND IN Mongo DB

Syntax:
We are using find() method and we want to pass multiple keys by separating the by ',' then MongoDB collection treats it AND condition. Basic syntax of AND is shown below:


>db.TestCol.find({key1:value1, key2:value2}).pretty()



EXAMPLE
Example is given below and it will show all the (dilipsingh) which is written by 'codefari' and whose title is 'MongoDB Overview'


>db.TestCol.find({"by":"MongoBD query","title": "MongoDB Overview"}).pretty()
{
   "_id": ObjectId(7df78ad8902c),
   "title": "MongoDB Overview",
   "description": "MongoDB is no sql database",
   "by": "MongoBD query",
   "url": "http://www.codefari.com",
   "tags": ["mongodb", "database", "NoSQL"],
   "likes": "100"
}
> 


Example is given above which is  equivalent where clause will be ' where by='codefari' AND title='MongoDB Overview' '. We can pass any numeric of key, value pairs in find clause.
OR IN MongoDB

Syntax:
OR in MongoDB methods we need to use $ or keyword because to query data documents based on the OR condition. Basic syntax of OR is shown below:


>db.TestCol.find(
   {
      $or: [
                     {key1: value1}, {key2:value2}
      ]
   }
).pretty()



EXAMPLE
Example is given below will show all the (dilipsingh) written by 'codefari' or whose title is 'MongoDB Overview'

>db.TestCol.find({$or:[{"by":"MongoBD query"},{"title": "MongoDB Overview"}]}).pretty()
{
   "_id": ObjectId(7df78ad8902c),
   "title": "MongoDB Overview",
   "description": "MongoDB is no sql database",
   "by": "MongoBD query",
   "url": "http://www.codefari.com",
   "tags": ["mongodb", "database", "NoSQL"],
   "likes": "100"
}
> 



USING AND OR OR TOGETHER

EXAMPLE
The example given below is showing the documents which have likes greater than 100 and whose title is either 'MongoDB Overview' or by is "dilipsingh". Equivalent sql where clause is 'where likes>10 AND (by='codefari) OR title = 'MongoDB Overview')'

>db.TestCol.find({"likes": {$gt:10}, $or: [{"by": "MongoBD query"},{"title": "MongoDB Overview"}]}).pretty()
{
   "_id": ObjectId(7df78ad8902c),
   "title": "MongoDB Overview",
   "description": "MongoDB is no sql database",
   "by": "MongoBD query",
   "url": "http://www.codefari.com",
   "tags": ["mongodb", "database", "NoSQL"],
   "likes": "100"
}