Re: A question on database access classes - a little long, sorry

libei71@xxxxxxxxx wrote:
But when the query condition became complex, I realized I should
have an interpreter pattern (combine with composition pattern) to
specify the search condition. Then I added an abstract class
'Filter' and some classes such as 'FilterDirectorEqualsTo with
constructor paramters (directorId)', 'FilterAnd (filter a, filter
b)' extend this abstract class. Then I only had to specify filter and
then retrieve records:


Filter f1 = new FilterDirectorIdEqualsTo(10);
Filter f2 = new FilterApprovedBy("TeamLeader");
Filter f3 = new FilterAnd(f1,f2);
List l = Reports.getReportsInfo(f3);

Filter f4 = new FilterLeaderIdEqualsTo(22);
Filter f5 = new new FilterAnd(f4,f3); // f3 could be reused
l = Project.getProjectsInfo(f5);
// they are used to generate the search condition after the 'WHERE'
in sql,so //they are tightly bound with database details

This design looks rather stupid. What is the point of having the Filter
class (with a bunch of ugly methods)? Do you imply that the user of
this class would be able to construct ad-hock query via these methods
calls? Can't he construct a dynamic query by just concatenating strings?

.

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