Skip to main content

Create Collection in MongoDB


db.createCollection(name, options) is used by MongoDB to create collection.
Where name is name of collection to be created and Options is a document which is use to specify
 Name parameter is string type; here we put the name of collection.
Options parameter is document which Specify options about memory size and indexing etc. Options parameter is optional, so you need to specify only name of the collection. Following is the list of options you can use:


Field

Type

Description

capped
Boolean
 Capped collection is a fixed size collection that automatically overwrites its oldest entries when it reaches its maximum size. If you specify true, you need to specify size parameter also.

 autoIndexID
Boolean
If true, automatically create index on _id field.s Default

size
number
If capped is true it’s specify a maximum size in bytes for a capped collection, and then you need to specify this field also.

max
number
This allows the maximum number of documents allowed in the capped collection.


While inserting the document, MongoDB first checks size field of capped collection, then it checks max field.
Example:
Following I am trying to write basic syntax for createCollection() method.

>use test
switched to db test
>db.createCollection("mongocollection")
{ "ok" : 1 }

You can check the created collection by using the command show collections

>show collections
mongocollection
system.indexes

Following example shows the syntax of createCollection() method with few important options:

>db.createCollection("mongocollection ", { capped : true, autoIndexID : true, size : 6142800, max : 10000 } )
{ "ok" : 1 }

In mongodb you don't need to create collection. MongoDB creates collection automatically, when you insert some document.

>db.Codefari.insert({"name" : "Codefari"})
>show collections
mongocollection
system.indexes
codefari

Popular posts from this blog

What is difference between UNION and UNION ALL in SQL Server

We use UNION and UNION ALL operator to combine multiple results set into one result set.
UNION operator is used to combining multiple results set into one result set but removes any duplicate rows. Basically, UNION is used to performing a DISTINCT operation across all columns in the result set. UNION operator has the extra overhead of removing duplicate rows and sorting result.
UNION ALL operator use to combine multiple results set into one result set but it does not remove any duplicate result. Actually, this does not remove duplicate rows so it is faster than the UNION operator. If you want to combine multiple results and without duplicate records then use UNION otherwise UNION ALL is better.
Following some rules for using UNION/UNION ALL operator
1.The number of the column should be the same in the query's when you want to combine them. 2.The column should be of the same data type. 3.ORDER BY clause can be applied to the overall result set not within each result set.
4.Column name of …

Merge and Merge join transformation in SSIS

MERGE TRANSFORMATION
Using Merge Transformation we can combine two sorted data-set into single data-set basically Merge Transformation used to combines rows from two sorted data flows into one sorted data flow. Following tasks you may perform using Merge Transformation: 1.Suppose we have a scenario like, we need to merge data from a database table and excel means we want to merge data from two different data sources. For such type of scenario, you can use Merge Transformation. 2.If we want to merge data from two same structured tables but exists two different servers. 3.Sometimes we get an error due to data in a row, after correcting errors in the data we can re-merge rows easily. See below explanations may help you to understand Merge Transformation: I do evaluate here, you already know about the data source, data conversion, data flow, task flow, control flow etc. Note:Before Merge transformation, we need to sort the data using Sort Transformation. After sorting data add data path to Merge…

Add day to ISODate in MongoDB

We can use $add operator to add days in ISODate in mongodb, $add is the Arithmetic Aggregation Operator which adds number and date in mongodb.
Syntax:

{ $add: [ <expression1>, <expression2>, ... ] }

Note:  If one of the argument is date $add operator treats to other arguments as milliseconds to add to the date.
Example: Suppose we have a Test collection as below.

{"Title" : "Add day to ISODate in MongoBD","CreatedDate" : ISODate("2016-07-07T08:00:00.000Z")}

Query to add 2 days in CreatedDate

db.Test.aggregate([      { $project: { Title: 1, AddedDate: { $add: [ "$CreatedDate", 2*24*60*60000 ] } } }    ])

Result:

{ "_id" : ObjectId("579a1567ac1b3f3732483de0"), "Title" : "Add day to ISODate in MongoBD", "AddedDate" : ISODate("2016-07-09T08:00:00.000Z") }

Note: As mentioned in above note we have to convert days in millisecond because $add operator treat to other arg…