如何绘制1：在实体框架1（可选）映射

Question

我有一个类，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类，我添加了一个虚拟财产：

public virtual Location Location {get;set;} 

我试图添加一个可选属性（延迟加载），因此员工可能拥有或1个位置。

我得到一个错误时，目前现在的MVC应用程序加载：

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

Answer 1

您是否尝试过明确指定FK /导航性能？

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

这是很难知道，如果你正在做的代码的第一或数据库/模型第一。我会给出一个有效的代码优先答案（第一！）。对于一对多和多对多的关系，你可以用注释，属性等来完成。但对于1-1我认为你也需要流利的API。

这也在"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，流畅的API要求比这个答案要短。

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; } 
} 

编辑注[关键]属性没有这个样本来创建迁移工作需要，他们只是很好的传达意图。这是一个很好的参考，在更详细地谈论使用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; 
}