MongoDB - The mongo Shell, Data Types in the mongo Shell

 shell provides various methods to return the date, either as a string or as a Date object:

• Date() method which returns the current date as a string.
• new Date() constructor which returns a Date object using the ISODate() wrapper.
• ISODate() constructor which returns a Date object using the ISODate() wrapper.

Internally, Date objects are stored as a 64 bit integer representing the number of milliseconds since the Unix epoch (Jan 1, 1970), which results in a representable date range of about 290 millions years into the past and future.

Return Date as a String

To return the date as a string, use the Date() method, as in the following example:

var myDateString = Date();

To print the value of the variable, type the variable name in the shell, as in the following:

myDateString

The result is the value of myDateString:

Thu Dec 01 2016 00:44:26 GMT+0800 (CST)

To verify the type, use the typeof operator, as in the following:

typeof myDateString

The operation returns string.

Return Date

The mongo shell wraps objects of Date type with the ISODate helper; however, the objects remain of type Date.

The following example uses both the new Date() constructor and the ISODate() constructor to return Date objects.

var myDate = new Date();
var myDateInitUsingISODateWrapper = ISODate();

You can use the new operator with the ISODate() constructor as well.

To print the value of the variable, type the variable name in the shell, as in the following:

myDate

The result is the Date value of myDate wrapped in the ISODate() helper:

ISODate("2016-11-30T16:48:47.527Z")

To verify the type, use the instanceof operator, as in the following:

myDate instanceof Date
myDateInitUsingISODateWrapper instanceof Date

The operation returns true for both.

ObjectId

The mongo shell provides the ObjectId() wrapper class around the ObjectId data type. To generate a new ObjectId, use the following operation in the mongo shell:

new ObjectId

SEE: ObjectId

NumberLong

By default, the mongo shell treats all numbers as floating-point values. The mongo shell provides theNumberLong() wrapper to handle 64-bit integers.

The NumberLong() wrapper accepts the long as a string:

NumberLong("2090845886852")

The following examples use the NumberLong() wrapper to write to the collection:

db.collection.insert( { _id: 10, calc: NumberLong("2090845886852") } )
db.collection.update( { _id: 10 }, { $set:  { calc: NumberLong("2555555000000") } } )
db.collection.update( { _id: 10 }, { $inc: { calc: NumberLong(5) } } )

Retrieve the document to verify:

db.collection.findOne( { _id: 10 } )

In the returned document, the calc field contains a NumberLong object:

{ "_id" : 10, "calc" : NumberLong("2555555000005") }

If you use the $inc to increment the value of a field that contains a NumberLong object by a float, the data type changes to a floating point value, as in the following example:

1. Use $inc to increment the calc field by 5, which the mongo shell treats as a float:

   db.collection.update( { _id: 10 }, { $inc: { calc: 5 } } )

2. Retrieve the updated document:

   db.collection.findOne( { _id: 10 } )

   In the updated document, the calc field contains a floating point value:

   { "_id" : 10, "calc" : 2555555000010 }

NumberInt

By default, the mongo shell treats all numbers as floating-point values. The mongo shell provides theNumberInt() constructor to explicitly specify 32-bit integers.

 

Check Types in the mongo Shell

To determine the type of fields, the mongo shell provides the instanceof and typeof operators.

instanceof

instanceof returns a boolean to test if a value is an instance of some type.

For example, the following operation tests whether the _id field is an instance of type ObjectId:

mydoc._id instanceof ObjectId

The operation returns true.

typeof

typeof returns the type of a field.

For example, the following operation returns the type of the _id field:

typeof mydoc._id

In this case typeof will return the more generic object type rather than ObjectId type.

 

MongoDB - The mongo Shell, Data Types in the mongo Shell

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