Entity Framework Core

Description

Each record in table A can be associated with at most one record in table B, and vice-versa.

Implementation

Typically achieved by having a foreign key in one table that references the primary key of the other, and a unique constraint on that foreign key.

Example

• User and UserProfile
• Order and OrderDetails (if details are distinct and singular)

Code Snippet:

public class User {
public int Id { get; set; }
public UserProfile Profile { get; set; }
}

public class UserProfile {
public int Id { get; set; }
public int UserId { get; set; } // Foreign Key
public User User { get; set; } // Navigation Property
}

Description

One record in table A can be associated with many records in table B, but each record in table B can only be associated with one record in table A.

Implementation

The "many" side of the relationship holds the foreign key to the "one" side.

Example

• Blog and Posts (A blog has many posts)
• Customer and Orders (A customer can have many orders)

Code Snippet:

public class Blog {
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Post> Posts { get; set; } // Navigation Property
}

public class Post {
public int Id { get; set; }
public string Title { get; set; }
public int BlogId { get; set; } // Foreign Key
public Blog Blog { get; set; } // Navigation Property
}

Description

Records in table A can be associated with many records in table B, and vice-versa.

Implementation

Requires a third "junction" or "linking" table that contains foreign keys referencing the primary keys of both tables involved in the relationship.

Example

• Student and Course (A student enrolls in many courses, a course has many students)
• Post and Tag (A post can have many tags, a tag can be applied to many posts)

Code Snippet:

public class Student {
public int Id { get; set; }
public string Name { get; set; }
public ICollection<StudentCourse> StudentCourses { get; set; }
}

public class Course {
public int Id { get; set; }
public string Title { get; set; }
public ICollection<StudentCourse> StudentCourses { get; set; }
}

public class StudentCourse {
public int StudentId { get; set; } // FK to Student
public Student Student { get; set; }
public int CourseId { get; set; } // FK to Course
public Course Course { get; set; }
}