Question

我是nHibernate的新手。我有以下SQL内连接查询，

SELECT e.name, 
       d.deptname 
FROM   demo_employee AS e 
       INNER JOIN demo_department AS d 
               ON e.departmentid = d.deptid

使用以下sql查询的Query Over的linq表达式是什么。

我已经编写了以下查询，但它在以下地方“c.Department.DeptId”给我错误。

 var Query =
    Session.QueryOver<Employee>()
        .JoinQueryOver<Department>(c => c.Department.DeptId)
            .Where(k => k.Name == k.DeptId);

Answer 1

这是QueryOver版本。

我们正在使用别名，即： null 引用Employee employee = null的声明，用于对所有属性进行完全类型的访问。 NHibernate Expression解析器稍后将根据映射将它们转换为字符串（列名）。

我们也可以获得对QueryOver的FROM部分的引用。查询代表Employee，加入的查询代表部门（depQuery），我们可以直接过滤。

最后，我们可以使用List（）来获取（SELECT）所有映射的属性，或者进行一些投影：.Select()或.SelectList()。通过投影，我们应该与一些DTO合作。

// aliasing, see the Projections of the SELECT clause
Employee employee = null;
Department department = null;

// the Employee query, with alias
var query = session.QueryOver<Employee>(() => employee);

// this way we can have reference to department query, if needed
var depQuery = query.JoinQueryOver<Department>(() => employee.Department, () => department);

// WHERE
// filtering the Employee
query.Where(e => e.Name == "Undefined");

// the department filtering
depQuery.Where(d => d.DeptName == "Management");


// paging, if needed
query.Skip(100);
query.Take(10);

1）选择所有属性

var list = query.List<Employee>();

var employeeName = list.ElementAt(0).Name;
var departmentName = list.ElementAt(0).Department.DeptName;

2）投影

// The DTO class to be projected into
public class MyDTO
{
    public virtual string EmployeeName { get; set; }
    public virtual string DepartmentName { get; set; }
}


// Select with projection of just two columns
MyDTO dto = null;

// SELECT
// projection, explicit property/column to be selected only
query.SelectList(l => l
    // the full power of aliasing
    .Select(() => employee.Name).WithAlias(() => dto.EmployeeName)
    .Select(() => department.DeptName).WithAlias(() => dto.DepartmentName)
    );

var list = query
    .TransformUsing(Transformers.AliasToBean<MyDTO>())
    .List<MyDTO>();

什么是以下SQL的Linq查询

1 个答案: