Question

如何编写将此查询转换为lamda表达式？

from lst in from employee in dbe.employees
            join ordermaster in dbe.ordermasters 
                              on employee.emp_id 
                              equals ordermaster.emp_id
            select new
            {
              emp_name = employee.emp_name,
              emp_id = ordermaster.emp_id,
              order_date = ordermaster.Order_date
            }
where EntityFunctions.DiffMonths(lst.order_date, dt) == 3
select lst;

Answer 1

如果要选择列表，则可以使用：

var x = UtAccuralLstForComp.Where（x => x.VendorName == Name）.ToList（）;

这将返回对象列表。

如果要选择一个值，则可以使用：

var x = UtAccuralLstForComp.Where（x => x.VendorName ==名称）.Select（x => x.VendorNumber）;

这将仅返回一个值。

Answer 2

首先，欢迎来到！

我猜您正在使用LINQ-to-Entities，并鼓励您保留当前使用的语法。当涉及到加入时，我个人认为它更具可读性。但是如果您要将表达式转换为lambda，则应该等效：

// models just for testing...
var employees = new List<Employee>()
{
    new Employee()
    {
        emp_id = 1,
        emp_name = "Name 1"
    },
    new Employee()
    {
        emp_id = 2,
        emp_name = "Name 1"
    },
    new Employee()
    {
        emp_id = 3,
        emp_name = "Name 1"
    }
};
var ordermasters = new List<OrderMaster>()
{
    new OrderMaster()
    {
        emp_name = "Name 1",
        emp_id = 1,
        Order_date = DateTime.Now
    },
    new OrderMaster()
    {
        emp_name = "Name 3",
        emp_id = 3,
        Order_date = DateTime.Now.AddDays(1)
    }
};

var result = employees.Join(ordermasters, // Replace employees and ordermasters with your tables.
        e => e.emp_id,
        o => o.emp_id,
        (empl, ord) => new { Employees = empl, OrderMasters = ord })
    .Where(arg => EntityFunctions.DiffMonths(arg.OrderMasters.Order_date, dt) == 3)
   .Select(arg => new
   {
       emp_name = arg.Employees.emp_name,
       emp_id = arg.OrderMasters.emp_id,
       order_date = arg.OrderMasters.Order_date
   });

就LINQ而言，它应该返回相同的结果。如果将其转换为相同的SQL，则完全不同。

如何将此查询转换为lamda表达式

2 个答案: