The monk Djishin was tasked with creating a web page for
querying the system’s inventory table of rice bags. Glumly
contemplating the dull day’s work that lay before him, the
monk had a sudden inspiration:
I must produce a presentation-layer object to hold the
parameters from the search form, he thought, as well as a
service-layer object to represent each row returned by the
search. Yet these both would have the same attributes as the
RiceBag object we currently use for creating new table rows.
Can I not simply reuse that database-layer object for these
other two purposes?
With growing excitement, he thought: If a database object
were suitably annotated, I could develop a framework which
would acquire the form input, validate it, convert it to
SQL, query the table, and present the search results to the
user in tabular format... all requiring the most minimal
effort on the part of the framework’s consumer!
The monk thus spent the next few days happily coding the
framework, with the RiceBag search page as its
proof-of-concept.
At the end of the week Djishin proudly showed the fruits of
his labor to master Banzen. The master studied the new
framework, nodded, and ordered Djishin to convert seven
existing search pages in the application to use it, starting
with the Warrior page.
After the monk ran off to comply, a nun who had been
standing nearby approached Banzen.
“Master,” asked the nun, “The Warrior object has but a
single Status value. If the user’s query is represented by a
single Warrior, how could we ask for Warriors whose Status
is either Missing, Retired, or Dead?”
“We could not,” said Banzen.
“Furthermore,” continued the nun, “The Warrior object
contains only information stored in the Warrior table. How
could we find Warriors by the types of Weapons they use, or
by the Regiments they have served in, since these require
joining to child tables?”
“We could not,” said Banzen.
The master took a small dark nugget from the jar he kept on
his desk, giving it to the puzzled nun. “There once was a
monk who tired of rice. One day he stumbled upon the art of
making kuro sato—black sugar candy. For years he nibbled
piece after piece throughout the day, gradually becoming
flabby and pale and void of tooth. What was his master’s
error?”
“Failing to forbid the candy,” said the nun.
Banzen shook his head and pushed the heavy jar across the
desk.
“Finish that by tomorrow evening,” commanded Banzen. “Then
you will understand Djishin’s correction.”
