can't get data from mongodb using perl (get undefined value)

Question

I am trying to get data from mongodb using perl, but I get undefined value for variable $people

my $client = MongoDB::MongoClient->new(host => 
'mongodb://xxx.xxx.xxx.xxx',port=>27017, username => 'xxxx', 
password => 'xxxx');
my $db = $client->get_database("xxx");
my $collection = $db->get_collection("xxx");
my $people = $collection->find_one({"transactionid" => $id});
while (my $p = $people->next) {
    print Dumper $p;
}

and I want to get this data :

{
    "_id" : ObjectId("5c453500e2fb4adc98e9fa84"),
    "transactionid" : NumberLong(45282),
    "transactionbillerid" : NumberLong(43137),
    "requesttime" : ISODate("2019-01-21T02:57:04.923Z"),
    "requestmessage" : "xxxxxxxx",
    "responsetime" : ISODate("2019-01-21T02:57:05.236Z"),
    "responsemessage" : "xxx"
}

any suggestions, is there something wrong with my code ?

Most likely, $id does not have the value you think it has, or there is no element in your collection with the transactionid you're looking for, — Corion
– Corion, Commented Jan 27, 2019 at 14:32
I get $id value from param.. my $id = $query->param('trx_id'); and there is element in my collection with transactionid I'm looking for :D — Yudistira Sugandi
– Yudistira Sugandi, Commented Jan 27, 2019 at 14:35
Does the query work with $id set to a hardcoded value? Try my $id = '1234'; (or whatever the value is) to see if it works. Also, ->find_one does not return an iterator but the document itself. — Corion
– Corion, Commented Jan 27, 2019 at 14:55

Dave Cross · Accepted Answer · 2019-01-27 16:13:01Z

1

I think you're misunderstanding the value returned by find_one(). There's a big clue in the name, but find_one() returns a single record, not an iterator.

Obviously, I don't have access to your data, so I can't confirm this, but I expect you'll get what you want by running this code:

my $client = MongoDB::MongoClient->new(
  host     => 'mongodb://xxx.xxx.xxx.xxx',
  port     => 27017,
  username => 'xxxx', 
  password => 'xxxx',
);

my $db = $client->get_database("xxx");
my $collection = $db->get_collection("xxx");

my $person = $collection->find_one({"transactionid" => $id});
print Dumper $person;

answered Jan 27, 2019 at 16:13

Dave Cross

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7 Comments

Yudistira Sugandi Over a year ago

I got this response $VAR1 = undef; .-. actually I use this for cgi-perl..

Hannibal Over a year ago

@YudistiraSugandi check your query. In the code you provided there's no a value assignment to $id.. is it a typo error? BTW the answer of @davecross is correct.

Yudistira Sugandi Over a year ago

I got it from my $id = $query->param('trx_id'); , and I don't know why I got undef value...

Yudistira Sugandi Over a year ago

and I got new error like this

MongoDB::DecodingError: Invalid UTF-8 detected while decoding BSON at /usr/lib/x86_64-linux-gnu/perl5/5.24/MongoDB/BSON.pm

Hannibal Over a year ago

$query->param smells of a query string parameter got using the CGI module. Well.. I guess the problem is in the input data at HTTP layer, so focus your debug on that direction. Check the data received by your web request handler, and why the trx_id parameter is empty.

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