Configure One-to-One (Configure a One-to-One relationship) [Code-First series], codefirst One-to-One

Configure One-to-One (Configure a One-to-One relationship) [Code-First series], codefirst One-to-One

Now, I want to learn how to configure a one-to-one relationship. As we all know, the one-to-one relationship is the primary key in one table. In another table, both the primary key and the foreign key are [in fact one-to-zero or one-to-one ].

Note: The one-to-one relationship is technically impossible in ms SQL Server. It is mainly a one-to-zero or one-to-one relationship.

For more information about entity relationships, see MSDN. ----- >>> Entity Relationship.

1. Use the data Annotation Feature to configure a one-to-one (one-to-zero) relationship.

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace EF5{   public class Student    {       public int StudentID { get; set; }       public string StudentName { get; set; }       public virtual StudentAddress StudentAddress { get; set; }    }}

Using System; using System. collections. generic; using System. componentModel. dataAnnotations; using System. componentModel. dataAnnotations. schema; using System. linq; using System. text; namespace EF5 {public class StudentAddress {// the parameters in the ForeignKey attribute fill in the navigation attribute. [Key, ForeignKey ("Student")] public int StudentID {get; set;} public string Address1 {get; set;} public string Address2 {get; set ;} public string City {get; set;} public int Zipcode {get; set;} public string State {get; set;} public string Country {get; set ;} public virtual Student {get; set ;}}}

using System;using System.Collections.Generic;using System.Data.Entity;using System.Linq;using System.Text;using System.Threading.Tasks;namespace EF5{   public class DbContextClass:DbContext    {       public DbContextClass() : base("ConnectionString")        {           Database.SetInitializer(new DropCreateDatabaseIfModelChanges<DbContextClass>());       }       public DbSet<Student> Students { get; set; }       public DbSet<StudentAddress> StudentAddresses { get; set; }           }}

 

Database:

Note that in the above Code, Student entity does not do anything. Then, the Code-First default convention uses StudentID as the table's primary key, and then in the StudentAddress entity, I have specifically specified the Key and ForeignKey features to mark StudentId as both a primary Key and a foreign Key. In the ForeignKey feature, I specified the Student object parameter, so it forms a one-to-one relationship.

Of course, we can use the Fluent API to configure a one-to-one relationship:

Use the Fluent APi to configure the one-to-one (one-to-zero) relationship

Using System; using System. collections. generic; using System. data. entity; using System. linq; using System. text; using System. threading. tasks; namespace EF5 {public class DbContextClass: DbContext {public DbContextClass (): base ("ConnectionString") {Database. setInitializer (new DropCreateDatabaseIfModelChanges <DbContextClass> ();} public DbSet <Student> Students {get; set;} public DbSet <StudentAddress> StudentAddresses {get; set ;} protected override void OnModelCreating (DbModelBuilder modelBuilder) {// configure the table's primary key modelBuilder. entity <StudentAddress> (). hasKey (s => s. studentID); // configure the table's foreign key modelBuilder. entity <StudentAddress> (). hasRequired (s => s. student ). witexceptional (p => p. studentAddress); base. onModelCreating (modelBuilder );}}}

Please note: the following code is incorrectly written and reversed !!!

Using System; using System. collections. generic; using System. data. entity; using System. linq; using System. text; using System. threading. tasks; namespace EF5 {public class DbContextClass: DbContext {public DbContextClass (): base ("ConnectionString") {Database. setInitializer (new DropCreateDatabaseIfModelChanges <DbContextClass> ();} public DbSet <Student> Students {get; set;} public DbSet <StudentAddress> StudentAddresses {get; set ;} protected override void OnModelCreating (DbModelBuilder modelBuilder) {// configure the table's primary key modelBuilder. entity <StudentAddress> (). hasKey (s => s. studentID); // configure the table's foreign key // modelBuilder. entity <StudentAddress> (). hasRequired (s => s. student ). witexceptional (p => p. studentAddress); modelBuilder. entity <StudentAddress> (). hasOptional (s => s. student ). withRequired (p => p. studentAddress); base. onModelCreating (modelBuilder );}}}

The database is as follows:

 

The following section describes how to configure a one-to-many relationship.

 

 

Attached series directory:

• What is Code First?
• Simple Code First example
• Code-First Convention
• DB Initialization (Database Initialization)
• Inheritance Strategy (Inheritance Policy)
• Configure Domain Classes (configuration Domain class)
• DataAnnotations (Data annotation)
• Fluent API
• Configure One-to-One (Configure a One-to-One relationship)
• Configure One-to-multiple (Configure One-to-multiple relationships)
• Configure allow-to-Configure (Configure Many-to-Many relationships)
• Move deployments (data migration)
• DB Initialization Strategy (Database Initialization Policy)