c# – EF 4.1一对多关系

我有一个非常简单的数据模型,而且我在使用EF 4.1 CF时遇到了很多困难.

我的数据模型有两个类：

public class Site {
  public int id { get; set; }
  public string name { get; set; }

  public ICollection<Building> buildings { get; set; }
}

public class Building {
  public int id { get; set; }
  public int siteId { get; set; }
  public string name { get; set; }
}

我的配置文件是这样的：

public class SiteConfiguration : EntityTypeConfiguration<Site> {

public SiteConfiguration() {
  HasMany(c => c.buildings)
    .WithRequired()
    .HasForeignKey(c => c.siteId);
  }
}

在我的MVC控制器中,我只想从一个站点中删除一个建筑物.这是我的控制器代码：

public ActionResult Delete(int id, int siteId) {
  var site = repo.GetById(siteId);
  var building = site.buildings.SingleOrDefault(c => c.id == id);
  ou.buildings.Remove(site);
  repo.Save(); 
}

我的错误信息：

The operation failed: The relationship
could not be changed because one or
more of the foreign-key properties is
non-nullable. When a change is made to
a relationship, the related
foreign-key property is set to a null
value. If the foreign-key does not
support null values, a new
relationship must be defined, the
foreign-key property must be assigned
another non-null value, or the
unrelated object must be deleted. Any
thoughts or suggestions would be
greatly appreciated.

解决方法:

试试这个：

public class Building 
{
    public int id { get; set; }
    public Site Site { get; set; }
    ...
}

public class SiteConfiguration : EntityTypeConfiguration<Site> 
{
    public SiteConfiguration() 
    {
        HasMany(c => c.buildings);
    }
}

public BuildingConfiguration : EntityTypeConfiguration<Building> 
{
    public BuildingConfiguration()
    {
        HasRequired(s=>s.Site);
    }
}

这告诉站点它可以有许多建筑物,并告诉建筑物它需要一个站点,并且不会让站点担心建立需求,反之亦然.

据我所知,你只在许多关系等中引入HasMany.WithMany / WithRequired.

标签：c,entity-framework,code-first
来源： https://codeday.me/bug/20190710/1419270.html