On Thu, Jan 24, 2013 at 10:31 AM, Frank Chang <frankchan...@gmail.com> wrote:
> Could anyone suggest which C++ data structure to use to cache a sqlite
> query result? Thank you for your help
Because of the strong typing benefits of C++, it makes little sense
(to me) to store the result in a container of a different type. A
vector of strings would work to store anything, but that would require
lots of conversion. A struct containing only data members would be a
better fit to avoid conversion. But a class with members is the way
to go. Let the class take care of getting the values, converting
them, let the object update its own data on the database. Objects
contain data and offer services, objects have a lifetime.
class Human {
int age;
string name;
public:
...
bool TryToRob( int amount );
};
class
Imagine the following "pseudo C++ code":
void CancelCourse(string School, int Course)
{
StudentList s = PeopleList(STUDENT).Filter(SCHOOLNAME,
School).Filter(COURSEID, Course);
for_each(s.begin(), s.end(), inform_student_of_course_cancelation );
TeacherList t = PeopleList(TEACHER).Filter...;
if ( t.size() != 1 )
throw course_has_invalid_number_of_teachers;
t[0]->RemoveFromCourse(Course);
t[0]->AdjustSchedule();
if ( t[0]->Courses.size() == 0 )
t[0]->SendOnVacation();
}
In this code, the fact we're using a database and make queries has
been succesfully abstracted. The way a teacher's schedule is handled
is probably different from how a student's is. Also, the teacher gets
paid while the student pays, only students can cheat, but both can be
absent. The data that holds this information can be stored in one
single table if it makes sense, but they are two different objects in
C++.
It depends on the context, but a query that joins two table (ie
persons attributes and a person address for instance) could be viewed
as a derived object (it is still a person, but now it has an address
also and supports shipping).
In C++ it is probably best to work as close to the problem domain
you're dealing with (teachers, courses, students) rather than remain
at the lower-level where queries are made in certain ways to emulate
the higher level tasks.
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