C# LINQ to SQL - 一对多关系

Question

我在 LINQ 中创建此查询时遇到问题：

USE Northwind
GO

SELECT emp.FirstName, emp.LastName, tr.TerritoryDescription, reg.RegionDescription
FROM Employees emp
INNER JOIN EmployeeTerritories empt ON empt.EmployeeID = emp.EmployeeID
INNER JOIN Territories tr ON tr.TerritoryID = empt.TerritoryID
INNER JOIN Region reg ON reg.RegionID = tr.RegionID

这是我目前的创作：

var query = await context
                .Employees
                .Select(x => new
                {
                    x.FirstName,
                    x.LastName,
                    TerritoryId = x.EmployeeTerritories. //cannot access properties
                })
                .ToListAsync();

但我无法轻松访问 EmployeeTerritories 属性，因为它不是 1:1 关系。我接受这个问题的线索和完整的解决方案。

编辑

这就是我目前拥有的：

            var query = await context
            .Employees
            .Select(x => new
            {
                x.FirstName,
                x.LastName,
                TerritoryDescription = x.EmployeeTerritories
                    .Select(et => et.Territory.TerritoryDescription)
                    .ToList(),
                RegionDesicription = x.EmployeeTerritories
                    .Select(et => et.Territory.Region.RegionDescription)
                    .ToList()
            })
            .ToListAsync();

有什么办法可以优化吗？ RegionDescription 现在是一个包含一个元素的 list，但我不知道如何更好地做到这一点。

Answer 1

尝试这样的事情（假设你有对应关系）：

var query = await context
            .Employees
            .Select(x => new
            {
                x.Employee.FirstName,
                x.Employee.LastName,
                TerritoryDescription = x.EmployeeTerritories
                    .Select(et => et.Territory.TerritoryDescription)
                    .ToList(),
            })
            .ToListAsync();

UPD

要在您的特定情况下展平，您可以使用 @dhrumil shah 发布的解决方案（它更通用）或尝试类似的方法，如果您在上下文中设置了 EmployeeTerritories :

var query = await context
            .EmployeeTerritories
            .Select(et => new
                    {
                        et.Employee.FirstName,
                        et.Employee.LastName,
                        et.Territory.TerritoryDescription,
                        et.Territory.Region.RegionDescription
                    })
            .ToListAsync();

Answer 2

(from emp in context.Employees 

 join empt in context.EmployeeTerritories 
 on emp.EmployeeID equals empt.EmployeeID
 
 join tr in context.EmployeeTerritories 
 on empt.TerritoryID equals tr.EmployeeID 
 
 join reg in context.Region 
 on reg.RegionID equals tr.RegionID 
 
 select new { 
 emp.FirstName, 
 emp.LastName, 
 tr.TerritoryDescription, 
 reg.RegionDescription
 }).ToList();

C# LINQ to SQL - 一对多关系

C# LINQ to SQL - one to many relationship

c#

entity-framework

linq

linq-to-sql

entity-framework-core