More querying in MongoDB

In the last post we started running queries on MongoDB. To continue on the operators, I decided to do a find on the auto generated id:

> db.fruits.find({ "_id" : ObjectId("52d49575e3a91584ad8f614e")})
{ "_id" : ObjectId("52d49575e3a91584ad8f614e"), "name" : "mango", "color" : "yel
low", "rating" : 2, "weight" : 1.03 }

There are also comparison operators available for use in queries:

> db.fruits.find( { rating: { $gt: 0 } } )
{ "_id" : ObjectId("52d305ab4e386a0b85ac249a"), "name" : "apple", "color" : "red
", "rating" : 4, "weight" : 2.3 }
{ "_id" : ObjectId("52d49575e3a91584ad8f614e"), "name" : "mango", "color" : "yel
low", "rating" : 2, "weight" : 1.03 }

Other operators are $gte,$lt and $lte. Similar to the $in operator, we can also try the $nin operator:

> db.fruits.find( { rating: { $nin: [1,2,3] } } )
{ "_id" : ObjectId("52d305ab4e386a0b85ac249a"), "name" : "apple", "color" : "red
", "rating" : 4, "weight" : 2.3 }
{ "_id" : ObjectId("52d30d464e386a0b85ac249b"), "name" : "lost", "age" : 12 }
{ "_id" : ObjectId("52d30d524e386a0b85ac249c"), "name" : "INS Viraat", "wt" : 50
00, "displacement" : 190.87 }
>

This is interesting. The records returned were those that did not match as well as those that did not have the specified attribute.
There is also the not equal operator:

> db.fruits.find( { rating: { $ne: 1 } } )
{ "_id" : ObjectId("52d305ab4e386a0b85ac249a"), "name" : "apple", "color" : "red
", "rating" : 4, "weight" : 2.3 }
{ "_id" : ObjectId("52d30d464e386a0b85ac249b"), "name" : "lost", "age" : 12 }
{ "_id" : ObjectId("52d30d524e386a0b85ac249c"), "name" : "INS Viraat", "wt" : 50
00, "displacement" : 190.87 }
{ "_id" : ObjectId("52d49575e3a91584ad8f614e"), "name" : "mango", "color" : "yel
low", "rating" : 2, "weight" : 1.03 }
>

The ne operator also returns records that do not possess the specified attribute.
We saw the and operator and the or operator in the earlier post. Next is the not operator:

> db.fruits.find( { weight: { $not: { $gt: 1.00}}})
{ "_id" : ObjectId("52d30d464e386a0b85ac249b"), "name" : "lost", "age" : 12 }
{ "_id" : ObjectId("52d30d524e386a0b85ac249c"), "name" : "INS Viraat", "wt" : 50
00, "displacement" : 190.87 }
>

This is an interesting point from the docs:

{ $not: { $gt: 1.99 } } is different from the $lte operator. { $lte: 1.99 } 
returns only the documents where --- field exists and its value is less 
than or equal to 1.99.

As we see, the records returned do not even have the weight field.
There is also a nor operator. The below query will fetch documents colors are not red nor their rating a 4.

> db.fruits.find( { $nor: [ { color: 'red' }, { rating: 4 } ]  } )
{ "_id" : ObjectId("52d30d464e386a0b85ac249b"), "name" : "lost", "age" : 12 }
{ "_id" : ObjectId("52d30d524e386a0b85ac249c"), "name" : "INS Viraat", "wt" : 50
00, "displacement" : 190.87 }
{ "_id" : ObjectId("52d49575e3a91584ad8f614e"), "name" : "mango", "color" : "yel
low", "rating" : 2, "weight" : 1.03 }
>

We specified the multiple conditions using an array.