Entity Framework Configuring Relationships with the Fluent API

相关链接：Configuring Relationships with the Fluent API

Configuring a Required-to-Optional Relationship (One-to-Zero-or-One 1…0,1)

以下示例，表示1…0,1的关系。OfficeAssignment表有一个属性InstructorID，它是一个主键也是一个外键。

HasKey方法用于配置主键。

// Configure the primary key for the OfficeAssignment
modelBuilder.Entity<OfficeAssignment>()
    .HasKey(t => t.InstructorID); 

// Map one-to-zero or one relationship
modelBuilder.Entity<OfficeAssignment>()
    .HasRequired(t => t.Instructor)
    .WithOptional(t => t.OfficeAssignment);

Configuring a Relationship Where Both Ends Are Required (One-to-One)

// Configure the primary key for the OfficeAssignment
modelBuilder.Entity<OfficeAssignment>()
    .HasKey(t => t.InstructorID); 

modelBuilder.Entity<Instructor>()
    .HasRequired(t => t.OfficeAssignment)
    .WithRequiredPrincipal(t => t.Instructor);

Configuring a Many-to-Many Relationship

modelBuilder.Entity<Course>()
    .HasMany(t => t.Instructors)
    .WithMany(t => t.Courses)

modelBuilder.Entity<Course>()
    .HasMany(t => t.Instructors)
    .WithMany(t => t.Courses)
    .Map(m =>
    {
        m.ToTable("CourseInstructor");
        m.MapLeftKey("CourseID");
        m.MapRightKey("InstructorID");
    });

Configuring a Relationship with One Navigation Property

// Configure the primary Key for the OfficeAssignment
modelBuilder.Entity<OfficeAssignment>()
    .HasKey(t => t.InstructorID); 

modelBuilder.Entity<Instructor>()
    .HasRequired(t => t.OfficeAssignment)
    .WithRequiredPrincipal();

Enabling Cascade Delete

modelBuilder.Entity<Course>()
    .HasRequired(t => t.Department)
    .WithMany(t => t.Courses)
    .HasForeignKey(d => d.DepartmentID)
    .WillCascadeOnDelete(false);

Configuring a Composite Foreign Key

// Composite primary key
modelBuilder.Entity<Department>()
.HasKey(d => new { d.DepartmentID, d.Name }); 

// Composite foreign key
modelBuilder.Entity<Course>()
    .HasRequired(c => c.Department)
    .WithMany(d => d.Courses)
    .HasForeignKey(d => new { d.DepartmentID, d.DepartmentName });

Renaming a Foreign Key That Is Not Defined in the Model

modelBuilder.Entity<Course>()
    .HasRequired(c => c.Department)
    .WithMany(t => t.Courses)
    .Map(m => m.MapKey("ChangedDepartmentID"));

Configuring a Foreign Key Name That Does Not Follow the Code First Convention

modelBuilder.Entity<Course>()
         .HasRequired(c => c.Department)
         .WithMany(d => d.Courses)
         .HasForeignKey(c => c.SomeDepartmentID);

Model Used in Samples

using System.Data.Entity;
using System.Data.Entity.ModelConfiguration.Conventions;
// add a reference to System.ComponentModel.DataAnnotations DLL
using System.ComponentModel.DataAnnotations;
using System.Collections.Generic;
using System; 

public class SchoolEntities : DbContext
{
    public DbSet<Course> Courses { get; set; }
    public DbSet<Department> Departments { get; set; }
    public DbSet<Instructor> Instructors { get; set; }
    public DbSet<OfficeAssignment> OfficeAssignments { get; set; } 

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        // Configure Code First to ignore PluralizingTableName convention
        // If you keep this convention then the generated tables will have pluralized names.
        modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
    }
} 

public class Department
{
    public Department()
    {
        this.Courses = new HashSet<Course>();
    }
    // Primary key
    public int DepartmentID { get; set; }
    public string Name { get; set; }
    public decimal Budget { get; set; }
    public System.DateTime StartDate { get; set; }
    public int? Administrator { get; set; } 

    // Navigation property
    public virtual ICollection<Course> Courses { get; private set; }
} 

public class Course
{
    public Course()
    {
        this.Instructors = new HashSet<Instructor>();
    }
    // Primary key
    public int CourseID { get; set; } 

    public string Title { get; set; }
    public int Credits { get; set; } 

    // Foreign key
    public int DepartmentID { get; set; } 

    // Navigation properties
    public virtual Department Department { get; set; }
    public virtual ICollection<Instructor> Instructors { get; private set; }
} 

public partial class OnlineCourse : Course
{
    public string URL { get; set; }
} 

public partial class OnsiteCourse : Course
{
    public OnsiteCourse()
    {
        Details = new Details();
    } 

    public Details Details { get; set; }
} 

public class Details
{
    public System.DateTime Time { get; set; }
    public string Location { get; set; }
    public string Days { get; set; }
} 

public class Instructor
{
    public Instructor()
    {
        this.Courses = new List<Course>();
    } 

    // Primary key
    public int InstructorID { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }
    public System.DateTime HireDate { get; set; } 

    // Navigation properties
    public virtual ICollection<Course> Courses { get; private set; }
} 

public class OfficeAssignment
{
    // Specifying InstructorID as a primary
    [Key()]
    public Int32 InstructorID { get; set; } 

    public string Location { get; set; } 

    // When the Entity Framework sees Timestamp attribute
    // it configures ConcurrencyCheck and DatabaseGeneratedPattern=Computed.
    [Timestamp]
    public Byte[] Timestamp { get; set; } 

    // Navigation property
    public virtual Instructor Instructor { get; set; }
}