数据类型

Date¶

The mongo shell provides various options to return the date, either as a string or as an object:

• Date() method which returns the current date as a string.
• Date() constructor which returns an ISODate object when used with the new operator.
• ISODate() constructor which returns an ISODate object when used with or without the new operator.

Consider the following examples:

• 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:

    Wed Dec 19 2012 01:03:25 GMT-0500 (EST)
    

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

    typeof myDateString
    

    The operation returns string.

• To get the date as an ISODate object, instantiate a new instance using the Date() constructor with the new operator, as in the following example:

  var myDateObject = new Date();
  

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

    myDateObject
    

    The result is the value of myDateObject:

    ISODate("2012-12-19T06:01:17.171Z")
    

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

    typeof myDateObject
    

    The operation returns object.

• To get the date as an ISODate object, instantiate a new instance using the ISODate() constructor without the new operator, as in the following example:

  var myDateObject2 = 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:

    myDateObject2
    

    The result is the value of myDateObject2:

    ISODate("2012-12-19T06:15:33.035Z")
    

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

    typeof myDateObject2
    

    The operation returns object.

ObjectId¶

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

new ObjectId

NumberLong¶

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

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

NumberLong("2090845886852")

The following examples use the NumberLong() class 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 increment the 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 }