我在实体框架中使用每层次结构表 (TPH) 继承。现在,我希望获得一个列表(在此示例中),其中部门可以是子类型。我希望集合中的项目包含它们自己的自定义属性,而不仅仅是基本模型的属性。
我怎样才能实现这个目标?
public class Department
{
public Department()
{
DepartmentType = this.GetType.Name;
}
public int Id {get; set;}
public string DepartmentType {get; set;}
}
public class Finance : Department
{
public virtual Manager Manager {get; set;}
}
public class Sports : Department
{
public virtual Coach Coach {get; set;}
}
// This obviously crashes instantly
// How can I include Manager if type is Finance and Coach if type is Sports?
context.Departments
.Include(c => (c is Finance) ? c.Manager : null)
.Include(c => (c is Sports) ? c.Coach : null);
我什至尝试返回
IEnumerable<object>
并向每个子类型添加一个多态方法,如下所示:
public class Sports : Department
{
public Coach Coach {get; set;}
public object Export()
{
return new
{
this.Id,
this.DepartmentType,
this.Coach
}
}
}
然后做这样的事情:
context.Departments.Select(c => c.Export())
但这也行不通。
[
{ Id: 1, DepartmentType: "Finance", Manager: { Name: "John" } },
{ Id: 2, DepartmentType: "Finance", Manager: { Name: "Harold" } },
{ Id: 3, DepartmentType: "Sport", Coach: { Name: "Fred", SportType: "Soccer" } },
{ Id: 4, DepartmentType: "Finance", Manager: { Name: "Hank" } },
{ Id: 5, DepartmentType: "Sport", Coach: { Name: "Mark", SportType: "Football" } }
]
通过这种方式你可以找到财务和体育部门并包括他们的财产:
var financeDeparments = context.Departments.OfType<Finance>().Include(p => p.Manager).ToList();
var sportDepartments = context.Departments.OfType<Sports>().Include(p => p.Coach).ToList();
将所有部门放入一个可以序列化为 JSON 的列表中的一种方法是
var deparments = context.Departments.OfType<Finance>().Include(p => p.Manager)
.AsEnumerable()
.OfType<Department>()
.Union(
context.Departments.OfType<Sports>().Include(p => p.Coach)
).ToList();
说明:
OfType<Department>()
:您不能直接Union
两个列表。您必须将其中一个投射到 IEnumerable<Department>
才能将另一个投射到 Union
。但是....AsEnumerable()
:如果您只进行强制转换,EF 将断定它正在处理 Depeartment
,并且不会接受 Include
的 Manager
。通过包含 AsEnumerble
,您可以在内存中执行后续转换,而 EF 永远不会知道它。我认为这是一堆仅为了序列化而设计的代码。
一个完全不同的选项是确保在上下文处于活动状态时进行序列化,因此会触发延迟加载来填充导航属性。在这种情况下,您可以简单地序列化
Department
,然后您将在 JSON 中找到派生类型的所有属性。也许(如果实际模型比您显示的更复杂)您必须防止循环引用。Department
的数量不太大,我认为这是一个可行的选择,尽管它会生成大量延迟加载的查询。
这对我有用。 创建与
相同的结果类public class DepartmentQueryResult
{ 公开列出部门{ get; }
public DepartmentQueryResult()
{
Departments= new List<Department>();
}
public int Add(Department department)
{
if (type(department) == Finance )
Departments.Add((Finance)department);
else
Departments.Add((Sports )department);
return Departments. Count;
}
编写您的 LINQ 查询
var queryResult =new List<Department>();
DbSet.Where(specification)
.Select(p=>queryResult.Add(p))
.ToList();
您可以将queryResult序列化为JSON