DataPresenter: The Saga Continues

1
DataPresenter The Saga Continues

• Part 1 Using Callback Functions to Filter
  DataPresenter Objects
• Glenn Maciag
• Glenn_Maciag_at_Kaplan.com

2
Advanced Filtering the Easy Way

• Let the User Do It!

3
Jim Keenans DataPresenter Module

• Allows users to manipulate database reports.
• Sorting
• Filtering
• Writing to files
• Lets look at a sample database report.

4
Jim Keenans DataPresenter Module

• CLIENTS - JULY 26, 2001 - C O N F I D E N T I A L
  PAGE 1
• SHRED WHEN NEW LIST IS RECEIVED!!!!!!!!!!!!!!!!!!!
  !!!!!!!!!!!!!!!!!!!!!!
• NAME C. NO UNIT WARD
  ADMIT BIRTH
• HERNANDEZ SHARON 456791 SAMSON 0217
  2001-07-25 1963-08-01
• JONES TIMOTHY 803092 LAVER 0103
  2001-03-19 1969-06-29
• SMITH HAROLD 359962 TRE 0111
  2001-07-19 1973-10-02
• SMITH BETTY SUE 698389 SAMSON 0211
  1992-01-23 1949-08-12
• THOMPSON GEORGE 786792 LAVER 0104
  2001-07-26 1973-08-17
• THOMPSON JEFFREY 906786 TRE 0111
  2001-07-15 1953-02-28
• VASQUEZ JORGE 456787 LAVER 0105
  1986-01-17 1956-01-13
• VASQUEZ JOAQUIN 456789 SAMSON 0209
  1990-11-14 1970-03-25
• WATSON JUNE 456788 LAVER 0107
  1990-08-23 1970-15-23
• WELKMAN THOMAS 456790 LAVER 0110
  1980-11-14 1960-14-02
• WILSON SYLVESTER 498703 LAVER 0110
  1983-04-02 1953-06-22

5
Jim KeenansDataPresenter Module

• Every type of object has a configuration file.
  Here is the beginning of one for the
  DataPresenterCensus class.
• _at_fields qw(
• lastname
• firstname
• cno
• unit
• ward
• dateadmission
• datebirth)

6
Filtering a DataPresenter Object

• columndateofbirth
• relationbefore
• _at_choices(01/01/1970)
• dpobject-gtselect_rows( column,relation,\_at_choice
  s)

7
Filtering a DataPresenter Object

• Advantages
• Elegant, natural language interface
• Easy for user to work with
• Disadvantage
• What if a user wants to enter a regular
  expression?

8
Advanced Filtering My First Thought

• User can pass in to the new method a compiled
  regex along with its target
• dpobject-gtselect_rows_adv( lastname,qr/SMITH/,
• firstname,qr/JOHN/)
• Within the method, I could then use an eval to
  filter the data accordingly.
• But I decided I wanted something more general.

9
Filtering using Callback Functions

• A callback function is an ordinary subroutine
  whose reference is passed around.
• Srinivasan, Sriram Advanced Perl Programming
  (OReilly, 1997), p. 53

10
The new DataPresenter Method

• The user creates a subroutine and passes a
  reference to it into the method.
• Inside the new method, the subroutine is called
  to help filter the data.

11
The new DataPresenter Method (slightly revised
by Jim Keenan)

• sub select_rows_adv
• my (self, do_it) _at__
• my data self
• foreach my key (sort keys data)
• unless (reservedkey)
• unless (do_it-gt(datakey))
• delete datakey
• self data
• return self

12
Using select_rows_adv

• create data presenter object as usual
• my dp1 DataPresenterCensus-gtnew( sourcefile
  , \_at_fields, \parameters, index)
• write the sub-routine
• sub mine
• my arrayrefshift(_at__)
• my lastarrayref-gt0
• if (last/VASQUEZ/)
• return 1
• elsereturn 0

13
Using select_rows_adv

• create the reference to the sub-routine
• my subref\mine create the reference to the
  sub
• call select_rows_adv
• dp1-gtselect_rows_adv(subref)
• and if you want, print the output
• outputfile 'myfiltered.txt'
• dp1-gtprint_to_file(outputfile)

14
Advantages of select_rows_adv

• The user can get as fancy as she wants to and the
  DataPresenter code does not have to change.
• "Give me all records where the ward number is
  between 100 and 300, the last name ends with Z,
  the third letter of the first name is A, and
  client number plus ward number is greater than
  456,900."

15
Advantages of select_rows_adv

• sub mine2
• my ( lastname,firstname,cno,unit,ward,
  dateadmission,datebirth)_at_shift()
• if (wardgt100 and wardlt300 and lastname /Z/
  and firstname/..A/ and (wardcnogt456900))
  
• return 1
• else return 0
• my subref\mine2
• dp_object-gtselect_rows_adv(subref)
• dp_object-gtprint_to_file(filtered.txt)

16
Advantages of select_rows_adv

• Heres what gets printed in filtered.txt (the
  print_to_file method prints semicolon delimited
  text)
• HERNANDEZSHARON456791SAMSON02172001-07-25196
  3-08-01
• VASQUEZJOAQUIN456789SAMSON02091990-11-141970
  -03-25

17
Advantages of select_rows_adv

• The method resides in the DataPresenter package.
• Because the method uses the field information the
  object itself carries around with it, the code
  will work on all DataPresenter subclasses. The
  programmer doesnt have to add extra methods to
  subclasses he creates.

18
Disadvantages of select_rows_adv

• Select_rows_adv is not as elegant and simple as
  select_rows.
• It requires the user to write a sub-routine.
• Probably many other things I havent thought of
  yet.

19
Conclusions

• Use the easier select_rows when you can.
• When you want to filter in a way not supported by
  select_rows, use select_rows_adv.
• Callback functions can make a programmers life
  easier!

20
The End