Perl get array element from mongodb - mongodb

Question

I wanted to fetch array element and store in Perl variable. If I put 0 in replace of ? in $cur->{Type}[?]->{_id} I'm able to get only one array element but I want all. below is my collection
{
"_id" : ObjectId("5b7fdb050cc3c23478005741"),
"DBName" : "sample",
"DBServerURL" : "mongodb://localhost:27017/",
"Type" : [
{
"_id" : ObjectId("5b801dc963f8c81df83891bd")
},
{
"_id" : ObjectId("5b801dc963f8c81df83891be")
},
{
"_id" : ObjectId("5b801dc963f8c81df83891bf")
},
{
"_id" : ObjectId("5b801dc963f8c81df83891c0")
}
]
}
I'm trying to get ObjectId from all fields
$cursor = $CustColl->find(
{DBName => "sample",DBServerURL => "mongodb://localhost:27017/"},{'_id' => 1, 'Type.$._id' => 1, 'DBServerURL' => 1, 'DBName' => 1}
);
while(my $cur = $cursor->next){
my $cid = "$cur->{_id}" ;
my $jid = "$cur->{Type}[?]->{_id}" ;
my $url = "$cur->{DBServerURL}" ;
my $name = "$cur->{DBName}" ;
print "$cid : $jid : $url : $name\n" ;
}
I wanted an output like below:
5b7fdb050cc3c23478005741 : 5b801dc963f8c81df83891bd : mongodb://localhost:27017/ sample
5b7fdb050cc3c23478005741 : 5b801dc963f8c81df83891be : mongodb://localhost:27017/ sample
5b7fdb050cc3c23478005741 : 5b801dc963f8c81df83891bf : mongodb://localhost:27017/ sample
5b7fdb050cc3c23478005741 : 5b801dc963f8c81df83891c0 : mongodb://localhost:27017/ sample

Answer 1

You are almost there. First, I fixed up your data to make it JSON but that's not a big deal:
my $json = q([{
"_id" : "5b7fdb050cc3c23478005741",
"DBName" : "sample",
"DBServerURL" : "mongodb://localhost:27017/",
"Type" : [
{
"_id" : "5b801dc963f8c81df83891bd"
},
{
"_id" : "5b801dc963f8c81df83891be"
},
{
"_id" : "5b801dc963f8c81df83891bf"
},
{
"_id" : "5b801dc963f8c81df83891c0"
}
]
} ]);
use JSON::XS;
my $perl = decode_json( $json );
That's a JSON array so you can go through it one element at a time. In Perl that shows up as an array reference Using the postfix dereference introduced in v5.20 makes this palatable (but not so hard without it):
while(my $cur = shift $perl->#*){ # or #$perl
my $cid = $cur->{_id} ;
my $url = $cur->{DBServerURL} ;
my $name = $cur->{DBName} ;
foreach my $hash ( $cur->{Type}->#* ) { # or #{ $cur->{Type} }
my $jid = $hash->{_id};
print "$cid : $jid : $url : $name\n" ;
}
}
The trick is that the $jid stuff is in another array and you want to go through those individually. There's a foreach inside the while to do that. It runs once for each of those and outputs the lines.