Need help with $slice MongoDB

vinaybond has asked for the wisdom of the Perl Monks concerning the following question:

Here is my sample json.

{
    "_id" : ObjectId("52dfd2750cf2169251fe8d3c"),
    "closed_on" : ISODate("2014-01-30T18:30:00Z"),
    "companies" : [
        {
            "_id" : ObjectId("52dfd2750cf2169251fe8d3f"),
            "comp_name" : "Test1",
        },
        {
            "_id" : ObjectId("52dfd7950cf2169251fe8d47"),
            "comp_name" : "Test2",
        }
    ],
    "contacts" : [
        {
            "_id" : ObjectId("52dfd2750cf2169251fe8d3e"),
            "fname" : "Solve",
            "lname" : "Scottt",
            "email" : "email1@gmail.com",
            "company" : "Test111",
        },
        {
            "_id" : ObjectId("52dfd7950cf2169251fe8d46"),
            "fname" : "signe",
            "lname" : "towne",
            "email" : "email2@gmail.com",
            "company" : "Test222",
        }
    ],
    "crt_by" : "creator@gmail.com",
    "currency" : "USD",
    "type" : "None",
}




I need: 
crt_by
conatacts.fname ( from the first record of the contacts array)
conatacts.company  ( from the first record of the contacts array)


I tried using $slice like this.
my $output = $collection->find({} },{ crt_by => 1,  'contacts' => {'$s
+lice' => 1} });

and when I am printing the the record it shows me some array for conta
+cts. 

while (my $doc = $output->next) {
                $output.= "\t- ".$doc->{'crt_by'}." Contact".$doc->{'c
+ontacts.fname'}."\n";
        }
}

print "$ouput\n";
[download]

What is the right command to do so. -Vinay

Comment on Need help with $slice MongoDB Download Code

Replies are listed 'Best First'.
Re: Need help with $slice MongoDB by Mr. Muskrat (Canon) on Jan 28, 2014 at 19:40 UTC
I don't use MongoDB much and you didn't provide a working script to start with so I can't really provide an answer. I can however point you to a snippet of code that I found that might help. I did a Google search for "perl mongodb slice" without the quotes and the fifth result was Example of using $slice and fields() in the MongoDB Perl driver 0.45.	[reply]
Re^2: Need help with $slice MongoDB by vinaybond (Novice) on Feb 04, 2014 at 07:35 UTC
Hi, Thanks for the reference. I have been through the link. Here is the code using which I am retrieving the records. It give me crt_by, name, and all the field from first array. Instead of Dumper I am using YAMP and parsing each row to get the data. `my $some_users = $collection->find({},{ crt_by => 1, name => 1, 'cont +acts' => {'$slice' => 1} })` [download]	[reply] [d/l]
Re^3: Need help with $slice MongoDB by Mr. Muskrat (Canon) on Feb 04, 2014 at 16:09 UTC
Now that I'm looking at the problem again, I don't see that usage of find in the MongoDB::Collection docs. Are you sure that you don't want to use find with fields (and then either a slice or limit of the resultant cursor, possibly with a sort_by as well) or find_one instead? What I have put together here is untested and should be considered pseudo code but it seems to me that one of the following would do the trick. `my $some_users = $collection->find->fields( { crt_by => 1, name => 1, + contacts => { '$slice' => 1 } } ); #my $some_users = $collection->find->limit( 1 )->fields( { crt_by => 1 +, name => 1, contacts => 1 } ); #my $some_users = $collection->find_one( {}, { crt_by => 1, name => 1 +, contacts => 1 } );` [download]	[reply] [d/l]
Re: Need help with $slice MongoDB by simmisam (Novice) on Jan 30, 2014 at 03:21 UTC
Check the below code. I used the JSON module, but it gave me error on decoding the string provided by you. Instead of ID value ObjectId("52dfd2750cf2169251fe8d3c"), it's "ObjectId(52dfd2750cf2169251fe8d3c)" that worked with JSON module. I don't know whether you have mentioned the correct json string or not. use JSON qw(decode_json); my $jsonString = '{ "_id" : "ObjectId(52dfd2750cf2169251fe8d3c)", "closed_on": "ISODate(2014-01-30T18:30:00Z)", "companies": [ { "_id": "ObjectId(52dfd2750cf2169251fe8d3f)", "comp_name": "Test1" }, { "_id": "ObjectId(52dfd7950cf2169251fe8d47)", "comp_name": "Test2" } ], "contacts" : [ { "_id": "ObjectId(52dfd2750cf2169251fe8d3e)", "fname": "Solve", "lname": "Scottt", "email": "email1@gmail.com", "company": "Test111" }, { "_id": "ObjectId(52dfd7950cf2169251fe8d46)", "fname": "signe", "lname": "towne", "email": "email2@gmail.com", "company": "Test222" } ], "crt_by": "creator@gmail.com", "currency": "USD", "type": "None" }'; my $decodedJSON = decode_json($jsonString); print "crts_by = $decodedJSON->{'crt_by'}\n"; print "Contact 1 => fname = $decodedJSON->{'contacts'}[0]{'fname'}, co +mpany = $decodedJSON->{'contacts'}[0]{'company'}\n"; [download]	[reply] [d/l]