G'day Alan
Getting some data in
The student objects would be made in a AllStudents : TStudents and
TStudents.Create would create
StudentList.TList that would point to every student so, to get every student
in, I'd go
Student1 := AllStudents.AddStudent('Bob'); //AllStudents returns the pointer to
the student created
with the name 'Bob" and added to the AllStudents.StudentList TList.
Then I can create a course object
NextCourse := TCourse.Create('Programming for beginners'); // this constructor
would also create
Enrolees : TList, an empty list at this stage
And Add Student1 to that course
NextCourse.AddStudent(Student1); //Adds the pointer Student1 to the enrolees
list
Destruction: I'd destroy the courses first and it's destructor goes
destructor TCourse.Destroy;
begin
Enrolees.Free; //you mustn't free the individual TStudent objects here
inherited Destroy;
end;
After the courses are all gone, I'd destroy the TStudents which iterates
through StudentList,
casting each item as a TStudent and freeing each TStudent before the TList
itself is freed.
Bit rushed but that that's how I'd see it.
Wayne
Borland's Delphi Discussion List <[email protected]> on Thursday, 27 April 2006
at 4:15 a.m. +0000
wrote:
>
>Hi Kevin --
>
>Thanks for (yet another) response--I appreciate your help. Unfortunately, I
>have to plead ignorance and say I don't really understand what you were
>trying to teach me. I'm not actually making the application below, I've just
>been using it as an example in my efforts to learn about OOP. So, to
>simplify things, suppose we had (a) a class TStudent whose only attribute
>was the student's name, and (b) a class TCourse, with two attributes to
>start--one for the course's name, and one to hold a list of enrolling
>students. We'll ignore all the other factors for now.
>
>I guess I don't understand how any of the methods associated with the
>courseList would work. First, I'm thinking that courseList is going to be an
>object on its own, e.g., a TList. Is it correct to assume, then, that the
>constructor for TCourse would need to instantiate a TList variable
>courseList, and every instance of TCourse would need to be freed with a
>destructor that frees the courseList TList? (We don't know ahead of time how
>many TCourse objects there will be in any given session that need to be
>freed!)
>
>Second, to fill a courseList variable, wouldn't all the TStudent instances
>need to be instantiated ahead of time? Would every TStudent in the school
>need to be created at application startup? (How can you fill a TList with
>instances of classes that don't exist yet?)
>
>Perhaps if I start to understand these more basic points, then your helpful
>message will become clearer to me -- I'm saving it :-)
>
>Thanks again. This list is really helpful. -- Alan C.
>
>
>>
>>If you want a list of students associated with each course, you can
>>construct it at run time
>>by running through all students one by one to see if they have a coursename
>>corresponding to the course you
>>are concerned with;
>>If you construct a Student->Course structure and a Course->Student
>>structure, it will be hard to keep both
>>alligned: it is best to construct one only and derive a reverse
>>relationship
>>list only as needed from it;
>>
>>You need two 'course' object structures todefine the variables required:
>>tCourseAvailable and tCourseAssigned;
>>the tCourseAssigned object only need a variable that indicates which
>>tCourseAvailable instance it 'points' to (either an index number or a
>>string
>>name: you could include the student name, though this is already implicit
>>in
>>the Tstudent object that 'owns' the assigned course instance):
>>the tCourseAssigned object is already part of a tstudent object so no
>>association is necessary
>>(you need a studentname variable as part of the tstudent object: any
>>tcourse
>>objects are implicitly associated with this student name!!)
>>
>>I think you need an objectlist of all courses available
>>which will have the parameters that you want to associate with each student
>>();
>>You could create a 'Faculty_list' object which contains a
>>'courses_available_list' object, which contains a
>>list of tCourseAvailable objects:
>>
>>You can pass the coursename value to the student object which will add a
>>courseobject for that student, and which by definition is associated with
>>that particular student (if you have multiple students, you can create a
>>studentobjectlist component which contains lists of student objects, each
>>having its own internal list of assigned courses)
>>
>>College>FacultyList->Faculty->CoursesAvailableList->CourseAvailable
>>
>>StudentList->Student->CourseAssignedList->CourseAssigned
>>
>>Are you using a database to store the data: if so you can use a dataset
>>from
>>the database to read in data to your Student object
>>and to save new or altered student data;
>>You can read in data using the usual Master-Detail relationships from the
>>relevant database tables, the structure of which would resemble the object
>>stuctures that we have already defined in OO terms;
>>The types of structures that I am currently developing are very similar,
>>except they also have methods for writing and reading the data to an
>>associated database (Object Oriented Database): its a bit advanced if you
>>are only learning, and database programming knowledge is required (SQL
>>language etc.);
>>
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