我应该使用“每种类型的表”还是“每种层次的表”？

Question

If I have a database with courses and course templates, and company course templates, what is the best way to store them in a SQL database? Course will probably have some other metadata about score, time-taken, and perhaps some other info.

Table Per Hierarchy

// Classes
public class CourseTemplate { } 
public class CompanyCourseTemplate { }
public class Course { }

Table Per Type

public class CourseTemplate { }
public class CompanyCourseTemplate : CourseTemplate { }
public class Course : CompanyCourseTemplate { }  
// Also for Course what if there are Course that belong to 
// either CompanyCourseTemplate or else CourseTemplate

Hybrid Using Both - TPH

public class CourseTemplate { }
public class CompanyCourseTemplate : CourseTemplate { }

And - TPT

public class Course { } 

It seems like the querying always gets messy when you need to differentiate the types within a table. As well, if you create a table per type the database gets cluttered with similar named tables as well. I am leaning towards the hybrid since it seems to be more natural with the types.

However, let's say we are storing a reference to the templates and we are using table per type what is the best way to manage this relationship?

In the exam table I could have two foreign keys to the template tables.

public class ExamTemplate { }
public class CompanyExamTempalte { } 
public class Exam { 
public Int32 ? ExamTemplateId { get;set; }
public Int32 ? CompanyExamTemplateId { get;set; }  

The problem with this is that my code gets really ugly when I have to get an template from an exam template reference. I haven't found the best way to really take care of this problem. What is the best way to inherit from one of two templates. I am thinking that a hierarchy needs to be created where all exam instances must have a company exam template as well as a master template and the exam can hold references to both. The change would look like this.

public class Exam {
    public Int32 CompanyExamTemplateId { get;set; }  
    public CompanyExamTemplate { get; set; }
    public Int32 ExamTemplateId { get; set; }
    public ExamTemplate { get; set; }
}

NOTE the nullables are gone since the hierarchy is always required.

Answer 1

Seems like you were initially leaning toward a one-to-many parent-child table structure something like this:

tblCourseTemplate:
CourseTemplateID
CourseTemplateName
CourseTemplateIsCompanyTemplate
CourseTemplateCompanyNameIfApplies

tblCourse:
CourseID
CourseTemplateID (ie parent record)
CourseName
CourseScore
CourseDateTaken
CourseTimeTaken

But then you said that a course could have more than one "parent" record so perhaps use an intermediate table to handle a many-to-many relationship:

tblCourseTemplate:
CourseTemplateID
CourseTemplateName
CourseTemplateIsCompanyTemplate
CourseTemplateCompanyNameIfApplies

tblCourseTemplateAndCourse:
CourseTemplateAndCourseID
CourseTemplateID
CourseID

tblCourse:
CourseID
CourseName
CourseScore
CourseDateTaken
CourseTimeTaken