Relationship between entities (EF basics article 7), entity ef

Relationship between entities (EF basics article 7), entity ef

The relationship between EF entities is divided:

1. One-to-one;

2. one-to-many;

3. Many to many;

 

One-to-one relationship:

Between Student and StudentAddress:

public partial class Student    {        public int StudentID { get; set; }        public string StudentName { get; set; }        public Nullable<int> StandardID { get; set; }        public string RowVersion { get; set; }            public virtual Standard Standard { get; set; }        public virtual StudentAddress StudentAddress { get; set; }    }

 public partial class StudentAddress    {        public int StudentID { get; set; }        public string Address1 { get; set; }        public string Address2 { get; set; }        public string City { get; set; }        public string State { get; set; }            public virtual Student Student { get; set; }    }

One-to-multiple relationship:

There are many of the above. Here is an example: Teacher and Standard.

 public partial class Standard    {        public Standard()        {            this.Students = new HashSet<Student>();            this.Teachers = new HashSet<Teacher>();        }            public int StandardID { get; set; }        public string StandardName { get; set; }        public string Description { get; set; }            public virtual ICollection<Student> Students { get; set; }        public virtual ICollection<Teacher> Teachers { get; set; }    }

 public partial class Teacher    {        public Teacher()        {            this.Courses = new HashSet<Course>();        }            public int TeacherID { get; set; }        public string TeacherName { get; set; }        public Nullable<int> StandardID { get; set; }        public string TeacherType { get; set; }            public virtual ICollection<Course> Courses { get; set; }        public virtual Standard Standard { get; set; }    }

Many-to-many relationship:

Between Student and Course:

 public partial class Student    {        public Student()        {            this.Course = new HashSet<Course>();        }            public int StudentID { get; set; }        public string StudentName { get; set; }        public Nullable<int> StandardID { get; set; }        public string RowVersion { get; set; }            public virtual Standard Standard { get; set; }        public virtual StudentAddress StudentAddress { get; set; }        public virtual ICollection<Course> Course { get; set; }    }

 public partial class Course    {        public Course()        {            this.Student = new HashSet<Student>();        }            public int CourseID { get; set; }        public string CourseName { get; set; }        public string Location { get; set; }        public Nullable<int> TeacherID { get; set; }            public virtual Teacher Teacher { get; set; }        public virtual ICollection<Student> Student { get; set; }    }

Note: EF supports many-to-many relationships. It is only a join table (StudentCourse here) that does not contain tables of columns other than Student and Course primary keys. If the associated table contains other columns, such as the date of deletion (Datedelete), you must perform the operation manually to implement multi-to-many relationships;

We use the XML view to open the object data model. In SSDL, we can see the StudentCourse EntitySet entity set. CSDL does not include the StudentCourse entity set, it is mapped to the navigation properties of Student and Course, and it can be seen in MSL (C-S Mapping) in the <AssociationSetMapping> node

 

So, the many-to-many relationship is in the C-S ing section of the Entity Data Model, so when you add a Course to the Student table or add a Student to the Course table, when you save the data, the primary keys of the students or courses you inserted will be added to the StudentCourse table. Therefore, this ing not only facilitates the association between the two entities, in addition, it manages addition, deletion, query, and modification operations;