实体框架核心可为空的外键 [英] Entity Framework Core nullable foreign key

问题描述

我在获取外键值可能为空的实体列表时遇到了麻烦.

I am having trouble getting a list of entities where a foreign key value could be null.

模型:

public class Company
{
    [Key]
    [Required]
    public int Id { get; set; }
    [Display(Name = "Company Name")]
    public string CompanyName { get; set; }
    [Display(Name = "Main Phone")]
    public string LandPhone { get; set; }
    [Display(Name = "Fax")]
    public string FaxPhone { get; set; }
}

public class Contact
{
    [Key]
    [Required]
    public int Id { get; set; }
    [Display(Name ="First Name")]
    public string FirstName { get; set; }
    [Display(Name = "Last Name")]
    public string LastName { get; set; }
    [EmailAddress]
    public string Email { get; set; }
    [Display(Name = "Mobile Phone")]
    public string MobilePhone { get; set; }
    [Display(Name = "Office Phone")]
    public string LandPhone { get; set; }
    [Display(Name = "Fax")]
    public string FaxPhone { get; set; }
    public string Title { get; set; }
    public int CompanyId { get; set; }
    [ForeignKey("CompanyId")]
    public Company Company { get; set; }
}

当我尝试获取所有Contacts的列表时，其中一个在我的数据库中具有CompanyId的空值时，它将跳过它返回的列表中的Contact.例如，查询var contacts = _context.Contacts.Include(c => c.Company).ToList();仅从下表中返回Josh Stone:

When I try and get the list of all Contacts and one of them has a null value for CompanyId in my database, it will skip that Contact in the list it returns. For example, the query var contacts = _context.Contacts.Include(c => c.Company).ToList(); only returns Josh Stone from the following table:

联系人表

我正在使用Entity Framework Core 1.0.0.任何帮助将由衷的感谢.

I am using Entity Framework Core 1.0.0. Any help would be sincerely appreciated.

推荐答案

假设它确实返回了mary，您希望她的CompanyId是什么?我会怀疑为null(还可能是什么?)，在这种情况下，您的模型是错误的， public int CompanyId { get; set; } 应该 public int? CompanyId { get; set; }

Supposing that it did actually return mary, what would you expect her CompanyId to be? I would suspect null (what else could it be?), in which case your model is wrong and public int CompanyId { get; set; } should be public int? CompanyId { get; set; }

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