c# - 为什么 IQueryOver 有 2 个类型参数？

Question

为什么 IQueryOver 有 2 个类型参数:

QueryOver<TRoot,TSubType> is an API for retrieving entities by composing
NHibernate.Criterion.Expression objects expressed using Lambda expression
syntax.

Answer 1

答案是:支持流畅的语法，并且始终可以访问root设置。

不太流利

所以我们可以使用这个定义:

IQueryOver<Contact,Contact> rootQuery = session  // here we have Contact query
    .QueryOver<Contact>();                          
IQueryOver<Contact, Employee> emplQueryOver = rootQuery
    .JoinQueryOver<Employee>(c => c.Parnter);       // here we work with its Parnter
IQueryOver<Contact, Employee> creatorQueryOver = emplQueryOver
    .JoinQueryOver<Employee>(e => e.Creator);       // here we have creator of Parnter

有了这个，我们就可以进行一些过滤:

emplQueryOver.Where(...
creatorQueryOver.Where(...

然后返回根查询并设置

rootQuery.OrderBy(c => c.ID).Desc
    .ThenBy(c => c.LastName)
      .Asc
    .SelectList(...
    .Take(50);

流利

但是因为接口(interface)IQueryOver<TRoot, TSubType> beeing 一路向下返回，我们可以在没有中间变量的情况下做到这一点...我们可以在一次流畅的运行中完成

var list = session  // here we have Contact query
    .QueryOver<Contact>()
       .Where(... //filter contact
    // Join Parnter
    .JoinQueryOver<Employee>(c => c.Parnter)
        .Where(... //filter Partner
    // Join More
    .JoinQueryOver<Employee>(e => e.Creator)

    // While still having the Root in the scope we can do
    .SelectList(list => list....
    .OrderBy(c => c.ID)
      .Desc
    .ThenBy(c => c.Code)
      .Asc
    .Take(50)
    .Skip(50)
    .List<Contact>(); // the Root