In Sinatra, I use params to get the key/value passed through the URL query string. I noticed I can use either a string or a symbol as the key to get the value. So if the URL is:
http://localhost:4567/x?a=1&b=2
Then:
params[:a] # => "1"
params["a"] # => "1"
params.to_s # => '{"name"=>"x", "a"=>"1", "b"=>"2"}'
params.class # => Hash
I can tell params is a Hash. But this doesn't seem to be a common behavior of a Hash.
h = {"a" => "1", "b" => "2"}
h["a"] # => "1"
h[:a] # => nil
Can someone please explain how this is achieved through Sinatra?
Always a good idea to have a read of the source. Specifically, the indifferent_params method.
# Enable string or symbol key access to the nested params hash.
def indifferent_params(params)
params = indifferent_hash.merge(params)
params.each do |key, value|
next unless value.is_a?(Hash)
params[key] = indifferent_params(value)
end
end
As the comment states, it's this method (invoked on line 704 of the same file) that allows string and symbol access to the params hash.
Related
I have a perl code like this:
use constant OPERATING_MODE_MAIN_ADMIN => 'super_admin';
use constant OPERATING_MODE_ADMIN => 'admin';
use constant OPERATING_MODE_USER => 'user';
sub system_details
{
return {
operating_modes => {
values => [OPERATING_MODE_MAIN_ADMIN, OPERATING_MODE_ADMIN, OPERATING_MODE_USER],
help => {
'super_admin' => 'The system displays the settings for super admin',
'admin' => 'The system displays settings for normal admin',
'user' => 'No settings are displayed. Only user level pages.'
}
},
log_level => {
values => [qw(FATAL ERROR WARN INFO DEBUG TRACE)],
help => "http://search.cpan.org/~mschilli/Log-Log4perl-1.49/lib/Log/Log4perl.pm#Log_Levels"
},
};
}
How will I access the "value" fields and "help" fields of each key from another subroutine? Suppose I want the values of operating_mode alone or log_level alone?
The system_details() returns a hashref, which has two keys with values being hashrefs. So you can dereference the sub's return and assign into a hash, and then extract what you need
my %sys = %{ system_details() };
my #loglevel_vals = #{ $sys{log_level}->{values} };
my $help_msg = $sys{log_level}->{help};
The #loglevel_vals array contains FATAL, ERROR etc, while $help_msg has the message string.
This makes an extra copy of a hash while one can work with a reference, as in doimen's answer
my $sys = system_details();
my #loglevel_vals = #{ $sys->{log_level}->{values} };
But as the purpose is to interrogate the data in another sub it also makes sense to work with a local copy, what is generally safer (against accidentally changing data in the caller).
There are modules that help with deciphering complex data structures, by displaying them. This helps devising ways to work with data. Often quoted is Data::Dumper, which also does more than show data. Some of the others are meant to simply display the data. A couple of nice ones are Data::Dump and Data::Printer.
my $sys = system_details;
my $log_level = $sys->{'log_level'};
my #values = #{ $log_level->{'values'} };
my $help = $log_level->{'help'};
If you need to introspect the type of structure stored in help (for example help in operating_mode is a hash, but in log_level it is a string), use the ref builtin func.
I'm using Dancer2 and the YAML session engine. I stored a complete hash in a session with the following code:
post '/login' => sub {
# ...
my $userdata = {
fname => 'John',
lname => 'Doe',
uid => 1234,
};
# ...
session userdata => $userdata;
# ...
}
The omitted code checks the login data against a database and returns that $userdata hashref.
This code creates a session file under $appdir/sessions with this content:
session file
userdata:
fname: John
lname: Doe
uid: 1234
How can I retrieve single values from this session in my app.pm file?
It works great in the template files (*.tt) and <% session.userdata.fname %> yields John, as expected.
However, I want to fetch the first name in app.pm, like so:
get '/userdetails' => sub {
my $firstname = session('userdata.fname'); # gives undef
# do sth. with $firstname
}
Is that feasable? Or do I have to
my $userdata = session('userdata'); # fetch complete hash
# do sth. with $userdata->{fname}
I tried
session('userdata.fname')
session('userdata/fname')
session('userdata:fname')
session('userdata fname')
RTFM (YAML's and Dancer2's)
but none of them worked and gave undef. The manuals and tutorials only fetch "first level values", not nested ones.
The Template Toolkit syntax is completely independent of Perl Dancer2, and you should expect any form of addressing to carry over. The origin of the data as a YAML file is also irrelevant, as the Dancer session is just a Perl hash structure
The manual doesn't make it very clear, but
session('userdata')
is the same as
session->{userdata}
So you can use
session->{userdata}{fname}
to read the subsidiary fields
(Or possibly session('username')->{fname} if you prefer, but that looks a bit icky to me!)
Note that you shouldn't use the YAML session engine in production code, as it's very slow
I have a Perl script that pulls a table from a SQL database ($row variable) and attempts to do a MongoDB update like so:
my $res = $users->update({"meeting_id" => $row[0]},
{'$set' => {
"meeting_id" => $row[0],
"case_id" => $row[1],
"case_desc" => $row[2],
"date" => $row[3],
"start_time" => $row[4],
"end_time" => $row[5],
#"mediator_LawyerID" => $row[6],
"mediator_LawyerIDs" => \#medLawIds,
"case_number" => $row[6],
"case_name" => $row[7],
"location" => $row[8],
"number_of_parties" => $row[9],
"case_manager" => $row[10],
"last_updated" => $row[11],
"meeting_result" => $row[12],
"parties" => \#partyList
}},
{'upsert' => 1}) or die "I ain't update!!!";
My client now wants ICS style calendar invites sent to their mediators. Thus, I need to know whether an update or insert happened. The documentation for MongoDB::UpdateResult implies that this is how you access such a property:
my $id = $res->upserted_id;
So I tried:
bless ($res,"MongoDB::UpdateResult");
my $id = $res->upserted_id;
After this code $id is like:
HASH(0x356f8fc)
Are these the actual IDs? If so, how do I convert to a hexadecimal string that can be cast to Mongo's ObjectId type? It should be noted I know absolutely nothing about perl; if more of the code is relevant, at request I will post any section ASAP. Its 300 lines so I didn't want to include the whole file off the bat.
EDIT: I should mention before anyone suggests this that using update_one instead of update returns the exact same result.
HASH(0x356f8fc) is a Perl Hash reference. It's basically some kind of (internal) memory address of some data.
The easiest way to get the contents is Data::Dumper:
use Data::Dumper
[...]
my $result = $res->upserted_id;
print Dumper($result);
HASH(0x356f8fc) is just the human readable representation of the real pointer. You must dump it in the same process and can't pass it from one to another.
You'll probably end up with something like
`my $id = $result->{_id};`
See the PerlRef manpage for details.
See also the MongoDB documentation about write concern.
PS: Also remember that you could use your own IDs for MongoDB. You don't need to work with the generated ones.
I'm trying to write a simple data manipulation language in Perl (read-only, it's meant to transform SQL-inspired queries into filters and properties to use with vSphere Perl API: http://pubs.vmware.com/vsphere-60/topic/com.vmware.perlsdk.pg.doc/viperl_advancedtopics.5.1.html_)
I currently have something similar to lexer output if I understand it properly - a list of tokens like this (Data::Dumper prints array of hashes):
$VAR1 = {
'word' => 'SHOW',
'part' => 'verb',
'position' => 0
};
$VAR2 = {
'part' => 'bareword',
'word' => 'name,',
'position' => 1
};
$VAR3 = {
'word' => 'cpu,',
'part' => 'bareword',
'position' => 2
};
$VAR4 = {
'word' => 'ram',
'part' => 'bareword',
'position' => 3
};
Now what I'd like to do is to build a syntax tree. The documentation I've seen so far is mostly on using modules and generating grammars from BNF, but at the moment I can't wrap my head around it.
I'd like to tinker with relatively simple procedural code, probably recursive, to make some ugly implementation myself.
What I'm currently thinking about is building a string of $token->{'part'}s like this:
my $parts = 'verb bareword bareword ... terminator';
and then running a big and ugly regular expression against it, (ab)using Perl's capability to embed code into regular expressions: http://perldoc.perl.org/perlretut.html#A-bit-of-magic:-executing-Perl-code-in-a-regular-expression:
$parts =~ /
^verb(?{ do_something_smart })\s # Statement always starts with a verb
(bareword\s(?{ do_something_smart }))+ # Followed by one or more barewords
| # Or
# Other rules duct taped here
/x;
Whatever I've found so far requires solid knowledge of CS and/or linguistics, and I'm failing to even understand it.
What should I do about lexer output to start understanding and tinker with proper parsing? Something like 'build a set of temporary hashes representing smaller part of statement' or 'remove substrings until the string is empty and then validate what you get'.
I'm aware of the Dragon Book and SICP, but I'd like something lighter at this time.
Thanks!
As mentioned in a couple of comments above, but here again as a real answer:
You might like Parser::MGC. (Disclaimer: I'm the author of Parser::MGC)
Start by taking your existing (regexp?) definitions of various kinds of token, and turn them into "token_..." methods by using the generic_token method.
From here, you can start to build up methods to parse larger and larger structures of your grammar, by using the structure-building methods.
As for actually building an AST - it's possibly simplest to start with to simply emit HASH references with keys containing named parts of your structure. It's hard to tell a grammatical structure from your example given in the question, but you might for instance have a concept of a "command" that is a "verb" followed by some "nouns". You might parse that using:
sub parse_command
{
my $self = shift;
my $verb = $self->token_verb;
my $nouns = $self->sequence_of( sub { $self->token_noun } );
# $nouns here will be an ARRAYref
return { type => "command", verb => $verb, nouns => $nouns };
}
It's usually around this point in writing a parser that I decide I want some actual typed objects instead of mere hash references. One easy way to do this is via another of my modules, Struct::Dumb:
use Struct::Dumb qw( -named_constructors );
struct Command => [qw( verb nouns )];
...
return Command( verb => $verb, nouns => $nouns );
I am not sure if this question is a duplicate or not but I cannot find any example of how one would do this. Is there any way we can query jenkins for the list of jobs. I have tried using the Jenkins::API that cpan provides but $jenkins->current_status()->jobs() returns a list of hash values. I am not sure if i am supposed to somehow translate these to readable jobs in english. Any tips??
Have a look at http://metacpan.org/pod/Jenkins::API.
$jenkins->current_status() does indeed return hash values. Each job hash contains keys 'color','name', and 'url'. But they are nested in a list at several levels. I found Data::Dumper helpful in seeing the full structure.
current_status
Returns the current status of the server as returned by the API. This is a hash containing a fairly comprehensive list of what's going on.
$jenkins->current_status();
# {
# 'assignedLabels' => [
# {}
# ],
# 'description' => undef,
# 'jobs' => [
# {
# 'color' => 'blue',
# 'name' => 'Jenkins-API',
# 'url' => 'http://jenkins:8080/job/Jenkins-API/'
# },
# ...
# ]
Example:
use Jenkins::API;
$jenkins = Jenkins::API->new({ base_url => 'http://localhost:8080' });
#statuses = $jenkins->current_status();
for ($i = 0;$i <= $#{$statuses[0]{'jobs'}};$i++) {
print $statuses[0]{'jobs'}[$i]{'name'},"\n";
}