FOREIGN KEY constraint May cause cycles or multiple paths - entity-framework-core

Question

I have read tons of articles seemingly similar to my issue, but just haven't been able to arrive at my ideal solution.
My specific error says:
Introducing FOREIGN KEY constraint 'FK_Scores_Tees_TeeId' on table 'Scores' may cause cycles or multiple cascade paths.
So, the table in question here, looks like this:
{
[Key]
public Guid ScoreId { get; set; }
public int Strokes { get; set; }
public Guid PersonId { get; set; }
public Guid CourseId { get; set; }
public Guid TeeId { get; set; }
[ForeignKey("PersonId")]
public virtual Person Person { get; set; }
[ForeignKey("CourseId")]
public virtual Course Course { get; set; }
[ForeignKey("TeeId")]
public virtual Tee Tee { get; set; }
}
Now, this table references Tees table, shown here:
public class Tee
{
[Key]
public Guid TeeId { get; set; }
public string Name { get; set; }
public int Par { get; set; }
public int Yards { get; set; }
public float Rating { get; set; }
public int Slope { get; set; }
public Guid CourseId { get; set; }
[ForeignKey("CourseId")]
public virtual Course Course { get; set; }
}
I read about making the TeeId nullable in the Scores table. I did that and was able to build run my migration successfully... however I do need this field to be required. If that id is empty/null then I don't have enough information about that particular Score record.

Answer 1

Both Tee and Score have a required reference to Course. When you delete a referenced Course, EF will want to delete the associated Tee and Score. When Tee is deleted, EF will again want to delete the associated Score. This is the "multiple cascade path" problem.
This error brings to light a problem with the design; the two references to Course can be different values which makes no sense in the context used (the score is for one course while referencing a "tee" from another course?). You should refactor your design.
Tees in golf are usually a small subset of value by either color (blue, white, gold, red) or name (ladies', back/champions', seniors, etc). One way to resolve your design issue is to normalize these name and/or color values in a Tee table, then have a CourseTee table that defines the properties of the Course's tees. This would be done by using a compound key either as primary key or candidate key (called alternate key in EF) composed of FK's to Course and Tee. This entity is where you would then define the properties of the course's tees:
public class CourseTee
{
[Key]
public Guid CourseId { get; set; }
public Course Course { get; set; ]
[Key]
public Guid TeeId { get; set; }
public Tee Tee { get; set; }
public int Par { get; set; }
// additional course-tee specific properties
...
}
public class Score // as a golfer, change this to `Round`
{
[Key]
public Guid ScoreId { get; set; } // RoundId :D
public Person Player { get; set; }
public CourseTee CourseTee { get; set; }
public int Strokes { get; set; }
...
}
public class Tee
{
public Guid TeeId { get; set; }
public string Color { get; set }
public string Name { get; set; }
}
Now Course is only defined once in a Score's object graph. To get the Course for a given Score is simply an extra hop: score.CourseTee.Course