如何繪製1：在實體框架1（可選）映射

Question

我有一個類，如：

public class Employee 
{ 
    [Column("employee_id")] 
    public int EmployeId {get;set;} 
} 


public class Location 
{ 
    [Column("employee_location_id")] 
    public int Id {get;set;} 

    [Column("employee_id")] 
    public int EmployeeId {get;set;} 
} 

Employee類，我添加了一個虛擬財產：

public virtual Location Location {get;set;} 

我試圖添加一個可選屬性（延遲加載），因此員工可能擁有或1個位置。

我得到一個錯誤時，目前現在的MVC應用程序加載：

System.Data.SqlClient.SqlException: Invalid column name 'Location_Id'. 

Answer 1

您是否嘗試過明確指定FK /導航性能？

public int LocationId { get; set; } 
[ForeignKey("LocationId")] 
public virtual Location Location { get; set; } 

Navigation Property not loading when only the ID of the related object is populated

Answer 2

這是很難知道，如果你正在做的代碼的第一或數據庫/模型第一。我會給出一個有效的代碼優先答案（第一！）。對於一對多和多對多的關係，你可以用註釋，屬性等來完成。但對於1-1我認爲你也需要流利的API。

這也在"How do I code an optional one-to-one relationship in EF 4.1 code first with lazy loading and the same primary key on both tables?"回答。我相信，流暢的API要求比這個答案要短。

例如

public class ExampleContext : DbContext 
{ 
    public ExampleContext() 
     : base("Name=ExampleContext") { 
     Configuration.LazyLoadingEnabled = true; 
     Configuration.ProxyCreationEnabled = true; 
    } 

    public DbSet<Employee> Employees { get; set; } 
    public DbSet<Location> Locations { get; set; } 

    protected override void OnModelCreating(DbModelBuilder modelBuilder) 
    { 
     modelBuilder.Entity<Employee>() 
       .HasOptional(m => m.Location) 
       .WithRequired(); 
    } 
} 

public class Employee 
{ 
    [Key] 
    [Column("employee_id")] 
    public int EmployeeId { get; set; } 

    public virtual Location Location { get; set; } 
} 

public class Location 
{ 
    [Key] 
    [Column("employee_id")] 
    public int EmployeeId { get; set; } 
} 

編輯注[關鍵]屬性沒有這個樣本來創建遷移工作需要，他們只是很好的傳達意圖。這是一個很好的參考，在更詳細地談論使用Shared Primary Key Associations

// Migration class as follows was generated by code-first migrations (add-migration OneToOne) and then updated the database by update-database 
public partial class OneToOne : DbMigration 
{ 
    public override void Up() 
    { 
     CreateTable(
      "dbo.Employees", 
      c => new 
       { 
        employee_id = c.Int(nullable: false, identity: true), 
       }) 
      .PrimaryKey(t => t.employee_id); 

     CreateTable(
      "dbo.Locations", 
      c => new 
       { 
        employee_id = c.Int(nullable: false), 
       }) 
      .PrimaryKey(t => t.employee_id) 
      .ForeignKey("dbo.Employees", t => t.employee_id) 
      .Index(t => t.employee_id); 

    } 

    public override void Down() 
    { 
     DropIndex("dbo.Locations", new[] { "employee_id" }); 
     DropForeignKey("dbo.Locations", "employee_id", "dbo.Employees"); 
     DropTable("dbo.Locations"); 
     DropTable("dbo.Employees"); 
    } 
} 

例子：

using (ExampleContext db = new ExampleContext()) 
{ 
    var newEmployee = db.Employees.Add(new Employee() { /* insert properties here */ }); 
    db.SaveChanges(); 

    db.Locations.Add(new Location() { EmployeeId = newEmployee.EmployeeId /* insert properties here */ }); 
    db.SaveChanges(); 

    var employee1 = db.Employees.First(); 
    var employee1Location = employee1.Location; 
}