c# - Linq 到 NHibernateMax

Question

我正在使用 Linq to NHibernate 开发 C#。

我定义了 2 组类和映射：

public class Employee
{
    public int ID { get; set; }
    public string Name { get; set; }
}

<hibernate-mapping ...>
    <class name="Example.Employee, Example">
        <id name="ID">
            <generator class="assigned" />
        </id>
        <property name="Name" length="100" not-null="true" />
  </class>
</hibernate-mapping>

public class Department
{
    public DepartmentID ID { get; set; }
    public int EmployeeID
    {
        get { return this.ID.Employee.ID; }
        set { }
    }
    public string Name { get; set; }
}

<hibernate-mapping ...>
    <class name="Example.Department, Example">
        <composite-id name="ID">
            <key-many-to-one name="Employee" column="EmployeeID" />
            <key-property name="StartDate" />
        </composite-id>
        <property name="EmployeeID" not-null="true"/>
        <property name="Name" not-null="true"/>    
    </class>
</hibernate-mapping>

并执行以下查询：

var result =
    from x in employeeQueryable
    join y in departmentQueryable on x.ID equals y.EmployeeID
    where y.ID.StartDate <= DateTime.Parse("2012/9/10")
    group y by y.EmployeeID into xy
    select xy.Max(a => a.ID.StartDate);

但此查询引发以下异常：

无法识别查询源。ItemName = a，ItemType = Example.Department，Expression = from Department a in [x]

如果employeeQueryableanddepartmentQueryable是数组类型（不是 linq to NHibernate），那么这个查询不会抛出异常。

我应该怎么办？

Answer 1

摆脱部门中的 EmployeeID 并使用

var result =
    from d in departmentQueryable 
    where d.ID.StartDate <= new DateTime(2012, 9, 10)
    group d by d.ID.Employee.Id into g
    select g.Max(d => d.ID.StartDate);