Using Perl with Caché
Using the Perl Binding
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This chapter provides concrete examples of Perl code that uses the Caché Perl binding. The following subjects are discussed:

Many of the examples presented here are taken from the sample programs in <cachesys>/dev/perl/samples/ (see Default Caché Installation Directory in the Caché Installation Guide for the location of <cachesys> on your system). The argument processing and error trapping statements (try/catch) have been removed to simplify the code. See Sample Programs for details about loading and running the complete sample programs.
Perl Binding Basics
A Caché Perl binding application can be quite simple. Here is a complete sample program:
   use Intersys::PERLBIND;
   eval {
   # Connect to the Cache' database
      $url = "localhost[1972]:Samples";
      $user = "_SYSTEM";
      $password = "SYS";
      $conn = Intersys::PERLBIND::Connection->new($url,$user,$password,0);
      $database = Intersys::PERLBIND::Database->new($conn);
   
   # Create and use a Cache' object
      $person = $database->create_new("Sample.Person", undef);
      $person->set("Name","Doe, Joe A");
      print "Name: ",$person->get("Name"), "\n";
   };
This code imports the Intersys::PERLBIND module, and then performs the following actions:
The following sections discuss these basic actions in more detail.
Connecting to the Caché Database
The basic procedure for creating a connection to a namespace in a Cache database is as follows:
Using Caché Database Methods
The Intersys::PERLBIND::Database class allows you to run Caché class methods and connect to Caché objects on the server. Here are the basic operations that can be performed with the Database class methods:
Using Caché Object Methods
The Intersys::PERLBIND::Object class provides access to Caché objects. Here are the basic operations that can be performed with the Object class methods:
Using Tied Variables
It is possible to tie an object returned by the Perl binding to a hash, and then access the properties of the object through the hash. For example:
   $object = $database->openid("Sample.Person", "1", -1, 0);
   $person = tie %person,"Intersys::PERLBIND::ObjectHash",( _object => $object)
   $name = $person{"Name"};
# The following line is equivalent to $person->set("Name","Tregar, Sam");
   $person{"Name"} = "Tregar, Sam"; 
Instead of getting the the name of person through $person->get("Name"), you can use the tie to get it through the hash, $person{"Name"}.
You can use the return value from the tie to run methods or you can use the "tied" built-in of Perl to run methods, for example:
   $ans = $person->Addition(12,17);
   print "ans=$ans\n";
   
   $ans = tied(%person)->Addition(12,17);
   print "ans=$ans\n";
In both cases, the value 29 is returned.
You can also use the tie to iterate through a list of properties:
   while (($property, $value ) = each(%person)) {
      print "propety=$property value=$value\n";
   }
Here is a complete example:
   $database = Intersys::PERLBIND::Database->new($conn);
   $personobj = $database->openid("Sample.Person", "1", -1, 0);
   
   $person = tie %person,
      "Intersys::PERLBIND::ObjectHash",( _object => $personobj);
   while (($propname, $value) = each(%person)) {
      print "property $propname = $value\n";
   }
This example produces the following output, displaying each property and its value:
   property Age = 61
   property DOB = 1942-01-18
   property SSN = 295-62-8728
   property Home = Intersys::PERLBIND::Object=SCALAR(0x1831ee4)
   property Name = Adler, Mortimer
   property Office = Intersys::PERLBIND::Object=SCALAR(0x183eed0)
   property Spouse = 
   property FavoriteColors = Intersys::PERLBIND::Object=SCALAR(0x1831e3c) 
Using Collections and Lists
Caché %Collection objects are handled like any other Perl binding object. Caché %List variables are mapped to Perl array references. The following sections demonstrate how to use both of these items.
%Collection Objects
Collections are manipulated through object methods of the Caché %Collection class. The following example shows how you might manipulate a Caché %ListOfDataTypes collection:
# Create a %ListOfDataTypes object and add a list of colors
   $newcolors = $database->run_class_method("%ListOfDataTypes","%New",undef);
   @color_list = qw(red blue green);
   for $color (@color_list) {
      $newcolors->Insert($color);
      print " added >$color<\n";
   };

# Add the list to a Sample.Person object
   $person = $database->openid("Sample.Person",$id,-1,0);
   $person->set("FavoriteColors",$newcolors);

# Get the list back from $person and print it out.
   $colors = $person->get("FavoriteColors");
   print "Number of colors: ",$colors->get("Size"), "\n";
   do {
      $color = $colors->GetNext($i);
      print " New Color #$i = $color\n" if defined($i);
   } until (!defined($i));
   
# Remove and replace the second element
   $colors->RemoveAt(2) if $colors->get("Size") > 0;
   $colors->InsertAt("purple",2);
   
# Show the changes to the collection
   print("Modified 'FavoriteColors' list:\n");
   do {
      $color = $colors->GetNext($i);
      print " Element #$i = $color\n" if defined($i);
   } until (!defined($i));
%List Variables
The Perl binding maps Caché %List variables to Perl array references.
Caution:
While a Perl array has no size limit, Caché %List variables are limited to approximately 32KB. The actual limit depends on the data type and the exact amount of header data required for each element. Be sure to use appropriate error checking (as demonstrated in the following examples) if your %List data is likely to approach this limit.
The examples in this section assume the following Caché class:
   Class Sample.List Extends %Persistent
   {
   Property CurrentList As %List;
   
   Method InitList() As %List { 
      q $LB(1,"hello",3.14) }
   
   Method TestList(NewList As %List) As %Integer {
      set $ZTRAP="ErrTestList"
      set ItemCount = $LISTLENGTH(NewList)
      if (ItemCount = 0) {set ItemCount = -1}
      q ItemCount
   ErrTestList
      set $ZERROR = ""
      set $ZTRAP = ""
      q 0 }
   }
The TestList() method is used to test if a Perl array is a valid Caché list. If the list is too large,the method traps an error and returns 0 (Perl false). If the list is valid, it returns the number of elements. If a valid list has 0 elements, it returns -1.
Example 1: Caché to Perl
The following code creates a Sample.List object, gets a predefined Caché list from the InitList() method, transforms it into a Perl array, and displays information about the array:
   $listobj = $database->create_new("Sample.List",undef);
   $arrayref = $listobj->InitList();
   @array = @$arrayref;
   
   print "Initial List from Cache:\n";
   print "array address = $arrayref\n";
   print "array contents = @array\n";
   print "There are ",scalar(@array)," elements in the list:\n";
   for ($i=0;$i<scalar(@array);$i++) {
      print " element ",$i+1," = [$array[$i]]\n";
   }
This code produces the following output:
   Initial List from Cache:
   array address = ARRAY(0x18d3d04)
   array contents = Cache to Perl: hello! 1 3.14
   There are 4 elements in the list:
      element 1 = [Cache to Perl: hello!]
      element 2 = [1]
      element 3 = []
      element 4 = [3.14]
In element 3, the null list element in Caché corresponds to value of undef in the Perl array.
Example 2: Perl to Caché and Back Again
The following code passes a list in both directions. It creates a small Perl array, stores it in the Caché object's CurrentList property, then gets it back from the property and converts it back to a Perl array.
   @oldarray = (1, undef, 2.78,"Just a small list.");
   $listobj->set("CurrentList",\@oldarray);
   $arrayref = $listobj->get("CurrentList");
   @newarray = @$arrayref;

   print "\n\nThis list is from property CurrentList:\n";
   print "There are ",scalar(@newarray)," elements in the list:\n";
   for ($i=0;$i<scalar(@newarray);$i++) {
      print " element ",$i+1," = [$newarray[$i-1]]\n";
   }
   print "\nThe old and new arrays ";
   if ("@oldarray" eq "@newarray")
       {print "match:\n"}
   else
      {print "DON'T match:\n"};
   print "   old:>@oldarray<\n",
         "   new:>@newarray<\n";
This code produces the following output:
   This list is from property CurrentList:
   There are 4 elements in the list:
     element 1 = [Just a small list.]
     element 2 = [1]
     element 3 = []
     element 4 = [2.78]
   
   The old and new arrays match:
      old:>1  2.78 Just a small list.<
      new:>1  2.78 Just a small list.<
Example 3: Testing List Capacity
It is important to make sure that a Cache %List variable can contain the entire Perl array. The following code creates a Perl array that is too large, and attempts to store it in the CurrentList property.
# Create a large array and print array information.
   $longitem = "1022 character element".(1234567890 x 100);
   @array =("This array is too long.");
   $cache_list_size = length($array[0]);
   for ($i=0;$i<33;$i++) {
        push(@array,$longitem);
        $cache_list_size += length($longitem);
   };
   print "\n\nNow for a HUGE list:\n";
   print "Total bytes required by Cache' list: more than $cache_list_size\n";
   print "There are ",scalar(@array)," elements in the ingoing list.\n\n";

# Check to see if the array will fit.
   $bool =  $listobj->TestList(\@array);
   print "TestList() reports that the array ";
   if ($bool) {print "is okay, and has $bool elements.\n";}
   else {print "will be damaged by the conversion.\n"};

# Pass the array to Cache', get it back, and display the results
   $listobj->set("CurrentList",\@array);
   $badarrayref = $listobj->get("CurrentList");
   @badarray = @$badarrayref;

   print "There are ",scalar(@badarray)," elements in the returned list:\n";
   for ($i=0;$i<scalar(@badarray);$i++) {
      $line = $badarray[$i];
      # long elements are shortened for readability.
      if (length($line)> 1000) {substr($line,10,980) = "..."};
      print "   element ",$i+1," = [$line]\n";
   }
The printout shortens undamaged sections of the long elements to make the output more readable. The following output is produced on a unicode system:
   Now for a HUGE list:
   Total bytes required by Cache' list: more than 33749
   There are 34 elements in the ingoing list.
   
   TestList() reports that the array will be damaged by the conversion.
   There are 17 elements in the returned list:
      element 1 = [This array is too long.]
      element 2 = [1022 chara...90123456789012345678901234567890]
      element 3 = [1022 chara...90123456789012345678901234567890]
      element 4 = [1022 chara...90123456789012345678901234567890]
      element 5 = [1022 chara...90123456789012345678901234567890]
      element 6 = [1022 chara...90123456789012345678901234567890]
      element 7 = [1022 chara...90123456789012345678901234567890]
      element 8 = [1022 chara...90123456789012345678901234567890]
      element 9 = [1022 chara...90123456789012345678901234567890]
      element 10 = [1022 chara...90123456789012345678901234567890]
      element 11 = [1022 chara...90123456789012345678901234567890]
      element 12 = [1022 chara...90123456789012345678901234567890]
      element 13 = [1022 chara...90123456789012345678901234567890]
      element 14 = [1022 chara...90123456789012345678901234567890]
      element 15 = [1022 chara...90123456789012345678901234567890]
      element 16 = [1022 chara...90123456789012345678901234567890]
      element 17 = [1022 chara...90123456ray is too long.ï´√ȇ1022 c]
The damaged list contains only 17 of the original 34 elements, and element 17 is corrupted.
Using Relationships
Relationships are supported through the relationship object and its methods.
The following example generates a report by using the one/many relationship between the $company object and a set of $employee objects. The relationship object $emp_relationship allows the code to access all $employee objects associated with the $company object:
   $company = $database->openid("Sample.Company", "1", -1, 0);
   $emp_relationship = $company->get("Employees");
   $index=undef;
   do {
      $employee = $emp_relationship->run_obj_method("GetNext",$index);
      # "GetNext" sets $index to the next valid index, or to undef if
      # there are no more records.
      if ($index) {
         $name = $employee->get("Name");
         $title = $employee->get("Title");
         $company = $employee->get("Company");
         $compname = $company->get("Name");
         $SSN = $employee->get("SSN");
         print "index=$index employee name=$name SSN=$SSN ",
               "title=$title companyname=$compname\n";
      };
   } while ($index);
The following code creates a new employee record, adds it to the relationship, and automatically saves the employee information when it saves $company.
   $new_employee = $database->create_new("Sample.Employee","");
   $new_employee->set("Name",$name);
   $new_employee->set("Title",$title);
   $new_employee->set("SSN",$SSN);
   $emp_relationship->run_obj_method("Insert", $new_employee);
   $company->run_obj_method("%Save"); 
Using Queries
The basic procedure for running a query is as follows:
For more information on the Intersys::PERLBIND::Query class, see Queries in the Perl Client Class Reference chapter. For information about queries in Caché, see Defining and Using Class Queries in Using Caché Objects.
Using %Binary Data
The Perl binding uses the Perl pack() and unpack() functions to convert data between a Caché %Binary and a Perl array of ords. Each byte of the Caché binary data is represented in Perl as an integer between 0 and 255.
The examples in this section assume the following Caché class:
   Class Sample.Bin Extends %Persistent
   {
      Property B As %Binary;

      Method GetBinary() As %Binary {
         q "hello"}

      Method SetBinary(PerlBin As %Binary) {
         s ^foobar=PerlBin}
   }
The class uses %Binary data in a variety of ways: as a property value, a method return value, a method argument, and a global variable. The following code transfers binary data back and forth between Caché and Perl several times. The Perl application makes a change in the data each time.
The first input is a method result. The GetBinary() method returns the %Binary value "hello". The value is unpacked and the resulting array is printed out:
   $binobj = $database->openid("Sample.Bin",1,-1,0);
   $B_packed = $binobj->run_obj_method("GetBinary");
   @B_unpacked = unpack("c*",$B_packed ); # "c*" is the template for an ord
   foreach $c (@B_unpacked) {
      # "%c" turns the ord value $c into a character
      printf "[%c]",$c
   }
   print "\n";
The first line of output looks like this:
   [h][e][l][l][o]
Now the program changes the first byte to a "j" and repacks the array. The packed value is stored in Caché %Binary property B, and the altered Caché object is saved:
   $B_unpacked[0] = ord("j");
   $B_packed = pack("c*",@B_unpacked);
   $binobj->set("B",$B_packed);
   $binobj->run_obj_method("%Save");
The second input is a property value. The %Binary value "jello" is retrieved from property B and unpacked. The program changes the value again, this time by adding a new element to the end of the array:
   $B_packed = $binobj->get("B");
   @B_unpacked = unpack("c*",$B_packed ); # "c*" is the template for an ord
   push @B_unpacked, ord("!");
   foreach $c (@B_unpacked) {
      printf "[%c]",$c
   }
   print "\n";
   };
Combined with the previous line, the output now look like this:
   [h][e][l][l][o]
   [j][e][l][l][o][!]
Finally, the program packs the array again and passes it as an argument to the SetBinary() method, which stores it in Caché global variable ^foobar:
   $B_packed = pack("c*",@B_unpacked);
   $binobj->run_obj_method("SetBinary",$B_packed); 
Handling Exceptions
The Perl binding uses Perl exceptions to return errors from the C binding and elsewhere.
Here are some examples of using Perl exceptions:
   eval {
      $answer = $variant2->run_obj_method("PassLastByRefAdd17","10","goodbye");
   };
   if ($@) {
      print "Perl exception $@\n";
   }

   # Attempt to open a nonexistent id
   eval {
      $causeException = $database2->openid("NonExistent", "1", -1, 0);
   };
   if ($@) {
      print "Perl exception $@\n";
   }
Handling %Status Return Values
When a method declares a return type of %Status, the status value is not returned. Instead, an exception is thrown. For example, assume that we want to call the following Caché method that returns %Status:
   Class User.PerlStatus Extends %Persistent{
      ClassMethod MyStatus() as %Status
      {
         q $$$ERROR(-137,"bad fine structure constant")
      }
   }
The following Perl binding program calls the MyStatus() method, captures the exception, and prints the return status value:
   # TestStatus.pl: illustrate handling a bad status return from COS 

   use Intersys::PERLBIND; 
   my $user="_SYSTEM"; 
   my $password="SYS"; 
   my $url = "localhost[1972]:USER";
   eval { 
      $conn = Intersys::PERLBIND::Connection->new($url,$user,$password,0);
      $database = Intersys::PERLBIND::Database->new($conn);
      $status=$database->run_class_method("User.PerlStatus", "MyStatus");
      # exception is thrown before we get here
      print "status=$status\n"; 
   }; 

   if ($@) { 
      print "Caught exception: $@\n"; 
   } else { 
      print "\nSample finished running\n"; 
   } 
Error Reporting
When processing an argument or a return value, error messages from the C binding are specially formatted by the Perl binding layer. This information can be used by InterSystems WRC to help diagnose the problem.
Here is a sample error message:
   file=PERLBIND.xs line=71 err=-1 message=cbind_variant_set_buf()
   cpp_type=4 var.cpp_type=-1 var.obj.oref=1784835886
   class_name=%Library.RelationshipObject mtd_name=GetNext argnum=0
The error message components are:
message
meaning
file=PERLBIND.xs
file where the failure occurred.
line=71
line number in the file.
err=-1
return code from the C binding.
message= cbind_variant_set_buf()
C binding error message.
cpp_type=4
cpp type of the method argument or return type.
var.cpp_type=-1
variant cpp type.
var.obj.oref=1784835886
variant oref.
class_name= %Library.RelationshipObject
class name of the object on which the method is invoked.
mtd_name=GetNext
method name.
argnum=0
argument number. 0 is the first argument and -1 indicates a return value.
Perl Binding Constraints and Limitations
The Perl binding imposes the following limitations, which are usually related to differences in the way that Perl and Caché handle certain datatypes: