Showing posts with label read. Show all posts
Showing posts with label read. Show all posts

Friday, 4 January 2019

How to Query on MongoDB by _id - INTERMEDIATE II


What if we have to query on MongoDB collections based on the "_id" field, Can we really query on "_id" field ? If so, what is the syntax ? Let's try this out -

Let's first fetch a document's id -

$ db.user.find_one()

{'_id': ObjectId('5c16e863817810ed3fc5e5f9'),
 'Fname': 'atul',
 'Lname': 'Singh',
 'Grade': 12.0,
 'College': 'SGM',
 'Job': 'Student',
 'Address': 'Young St.'}



Now, we will pick the object id and use this to fetch the same document from collection

$ db.user.find_one({'_id':'5c16e863817810ed3fc5e5f9'}) #this will return nothing

$ db.user.find_one({'_id':ObjectId('5c16e863817810ed3fc5e5f9')})
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
 in 
----> 1 db.user.find_one({'_id':ObjectId('5c16e863817810ed3fc5e5f9')})

NameError: name 'ObjectId' is not defined


We have received this error because ObjectId is not the same as its string representation, it must be converted to ObjectId from a string before it is passed to find command.

$ from bson.objectid import ObjectId
$ db.user.find_one({'_id':ObjectId('5c16e863817810ed3fc5e5f9')})

{'_id': ObjectId('5c16e863817810ed3fc5e5f9'),
 'Fname': 'atul',
 'Lname': 'Singh',
 'Grade': 12.0,
 'College': 'SGM',
 'Job': 'Student',
 'Address': 'Young St.'}



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Monday, 21 November 2016

Reading DSParam - datastage parameter file



I am sharing a utility which can help you to read DSParam file which holds all the environmental datastage parameters.

Utility to view contents of DSParams file. Useful when trying to see what all the customer has set at the project level.



Usage:
$ cat DSParams | ./DSParamReader.pl | more
or
$ cat DSParams | ./DSParamReader.pl > outputfile


Instructions:
1. copy script text below to a file (DSParamReader.pl) on a UNIX system
2. Set execute permissions on this file. chmod 777 envvar.pl
3. Usually perl is in /usr/bin/perl but you might have to adjust this path if neccessary. (hint "which perl" should tell you which one to use)
4. cat the DSParams file from the project you are concerned with and redirect the output to this script. You may have to put the Fully Qualified Path for this file.
5. capture the output to screen or file. File may be useful to have the customer send the info to you in email.








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