MongoDB - The mongo Shell, Data Types in the mongo Shell
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- 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:
- 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 } } )
- 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
标签:return int des lang operation simple epo follow gis
本文系统来源:http://www.cnblogs.com/huey/p/6120385.html
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