11-4.在”模型定义”函数里调用另一个”模型定义”函数
问题
想要用一个”模型定义”函数去实现另一个”模型定义”函数
解决方案
假设我们已有一个公司合伙人关系连同它们的结构模型,如Figure 11-4所示:
Figure 11-4. A model representing the associate types in a company together with the reporting association
在我们的虚拟的公司里, , team members被一个team leader管理. Team leaders 被 project Managers管理. 而Supervisors管理 project managers.
如果我们想从给定的一个project manager 或supervisor返回所有他们管理的team members ,我们将需要通过 project managers 和team leaders才能获取到 team members. 为了隐藏导航透过这些层的复杂性,我们可以创建”模型定义”函数,来更简单地和直接地访问这些导航属性:
1. 在解决方案资源管理中右击.edmx 文件,打开方式 ➤ XML 编辑器.
2.把Listing 11-7 里的代码插入到概念层的<Schema> 标签下,这样就定义好了函数
Listing 11-7. Model-Defined Functions for Navigating the Associate Hierarchy
<Function Name="GetProjectManager" ReturnType="EFRecipesModel1104.ProjectManager">
<Parameter Name="teammember" Type="EFRecipesModel1104.TeamMember" />
<DefiningExpression>
treat(teammember.Manager.Manager as EFRecipesModel1104.ProjectManager)
</DefiningExpression>
</Function>
<Function Name="GetSupervisor" ReturnType="EFRecipesModel1104.Supervisor">
<Parameter Name="teammember" Type="EFRecipesModel1104.TeamMember" />
<DefiningExpression>
treat(EFRecipesModel1104.GetProjectManager(teammember).Manager as
EFRecipesModel1104.Supervisor)
</DefiningExpression>
</Function>
3.插入和查询模型的代码,如 Listing 11-8所示:
Listing 11-8. Using Both eSQL and LINQ to Query the Model
class Program
{
static void Main(string[] args)
{
RunExample();
Console.WriteLine("\nPress any key to exit...");
Console.ReadKey();
}
static void RunExample()
{
using (var context = new EFRecipesEntities1104())
{
context.Database.ExecuteSqlCommand("delete from chapter11.associate");
var john = new Supervisor { Name = "John Smith" };
var steve = new Supervisor { Name = "Steve Johnson" };
var jill = new ProjectManager
{
Name = "Jill Masterson",
Manager = john
};
var karen = new ProjectManager
{
Name = "Karen Carns",
Manager = steve
};
var bob = new TeamLead { Name = "Bob Richardson", Manager = karen };
var tom = new TeamLead { Name = "Tom Landers", Manager = jill };
var nancy = new TeamMember { Name = "Nancy Jones", Manager = tom };
var stacy = new TeamMember
{
Name = "Stacy Rutgers",
Manager = bob
};
context.Associates.Add(john);
context.Associates.Add(steve);
context.SaveChanges();
}
using (var context = new EFRecipesEntities1104())
{
Console.WriteLine("Using eSQL...");
var emps = context.Associates.OfType<TeamMember>()
//译注:这个where是下载的源码用的形式,但它怎么看也不是eSQL
.Where(q => q.Manager.Name == "Jill Masterson" || q.Manager.Name == "Steve Johnson");
//译注:这个where里书里的代码,倒像eSQL,可是找不到Where这个形式的重载,可能在某个扩展包里,有知晓,望赐教!
// .Where(@"EFRecipesModel1104.GetProjectManager(it).Name = @projectManager ||
//EFRecipesModel.GetSupervisor(it).Name == @supervisor",
// new ObjectParameter("projectManager", "Jill Masterson"),
// new ObjectParameter("supervisor", "Steve Johnson"));
Console.WriteLine("Team members that report up to either");
Console.WriteLine("Project Manager Jill Masterson ");
Console.WriteLine("or Supervisor Steve Johnson");
foreach (var emp in emps)
{
Console.WriteLine("\tAssociate: {0}", emp.Name);
}
}
using (var context = new EFRecipesEntities1104())
{
Console.WriteLine();
Console.WriteLine("Using LINQ...");
var emps = from e in context.Associates.OfType<TeamMember>()
where MyFunctions.GetProjectManager(e).Name ==
"Jill Masterson" ||
MyFunctions.GetSupervisor(e).Name == "Steve Johnson"
select e;
Console.WriteLine("Team members that report up to either");
Console.WriteLine("Project Manager Jill Masterson ");
Console.WriteLine("or Supervisor Steve Johnson");
foreach (var emp in emps)
{
Console.WriteLine("\tAssociate: {0}", emp.Name);
}
}
}
}
public class MyFunctions
{
[EdmFunction("EFRecipesModel1104", "GetProjectManager")]
public static ProjectManager GetProjectManager(TeamMember member)
{
throw new NotSupportedException("Direct calls not supported.");
}
[EdmFunction("EFRecipesModel1104", "GetSupervisor")]
public static Supervisor GetSupervisor(TeamMember member)
{
throw new NotSupportedException("Direct calls not supported.");
}
}
上述Listing 11-8 代码输出如下:
Using eSQL...
Team members that report up to either
Project Manager Jill Masterson
or Supervisor Steve Johnson
Associate: Nancy Jones
Associate: Stacy Rutgers
Using LINQ...
Team members that report up to either
Project Manager Jill Masterson
or Supervisor Steve Johnson
Associate: Nancy Jones
Associate: Stacy Rutgers
它是如何工作的?
在如Listing 11-7所示的GetSupervisor() 函数中,我们需要做给 Manager 属性做三次导航.第一次从TeamMember导航到TeamLead, 第二次从TeamLead,导航到ProjectManager,最后一次从ProjectManager导航到Supervisor. 在Listing 11-7中,我们也定义了GetProjectManager() 函数,所以我们可以用这个函数来简化GetSupervisor() 函数.
我们使用eSQL的treat()运算符把一个公司合伙人实例转化为它们正确的类型 (ProjectManager 或Supervisor). 如果不使用这个运算符,EF将引发一个异常(不能遇到将Associate 映射为ProjectManager 或Supervisor)
在Listing 11-8中, 用 GetProjectManager() 和GetSupervisor() 函数,可以使我们的代码简洁些,因为隐藏了所有通过Manager导航属性穿越对象图的细节
因为我们函数不是返回一个IQueryable<T>, 所以我们不必为LINQ查询实现运行时方法,只需要用到它们的方法存根.