c# - 在类中创建关联而不在数据库中创建额外的列

Question

我有三个班级：大学，学院和学科以及它们之间的关系：

public class University
    {
        public University()
        {
            Faculties = new List<Faculty>();    
        }

        public int Id { get; set; }
        public string Name { get; set; }
        public string Location { get; set; } 
        [Association(ThisKey = "Id", OtherKey = nameof(Faculty.UniversityId), CanBeNull = true, Relationship = Relationship.OneToMany, IsBackReference = true)]
        public ICollection<Faculty> Faculties { get; set; }

    }

public class Faculty
    {
        public int Id { get; set; }
        public string Code { get; set; }
        public string FacultyName { get; set; }
        public string Direction { get; set; }
        public int Grant { get; set; }
        public int Contract { get; set; }
        public int? UniversityId { get; set; }

        [Association(ThisKey = "UniversityId", OtherKey = "Id", CanBeNull = true, Relationship = Relationship.ManyToOne, BackReferenceName = "Faculties")]
        public University University { get; set; }

        [Association(ThisKey = "Id", OtherKey = "FacultyId", CanBeNull = true, Relationship = Relationship.OneToOne, IsBackReference = true)]
        public Subject Subject { get; set; }

    }

public class Subject
    {

        [Column(Name = "Id")]
        public int SubjectId { get; set; }
        public string FirstSubject { get; set; }
        public string SecondSubject { get; set; }
        public string ThirdSubject { get; set; }

        public int? FacultyId { get; set; }
        [Association(ThisKey = "FacultyId", OtherKey = "Id", CanBeNull = false, Relationship = Relationship.ManyToOne, BackReferenceName = "Subjects")]
        public Faculty Faculty { get; set; }
    }

我像这样加载大学：

public IQueryable<University> Universities => context.University.LoadWith(x => x.Faculties);

我想在大学和学科之间创建关联，以便调用它：

public IQueryable<University> Universities => context.University.LoadWith(x => x.Faculties).LoadWith(m=>m.Subjects);

我尝试在大学课堂上这样做：

public static Expression<Func<University, IDataContext, IQueryable<Subject>>> Expression()
        {
            return (u, db) => db.GetTable<Subject>().
            Where(x => u.Faculties.
            Any(m => m.Id == x.FacultyId));
        }

        [Association(QueryExpressionMethod = nameof(Expression))]
        public ICollection<Subject> Subjects { get; set; }

但我发现了一个例外：

'x.FacultyId' 无法转换为 SQL。