实现员工与部门之间的外键关系表。我得到的DepartmentName值为零。我正在使用.NET-6 Razor页面

Question

表

我用外键关系创建了这样的表。

create table Departments
(
    Id int primary key identity,
    Name varchar(100)
)

create table Employees
(
    Id int primary key identity,
    Name nvarchar(max),
    Salary decimal,
    DepartmentId int foreign key references Departments(Id)
)

模型

我建立了员工和部门的关系模型

public class Employees
{
        public int Id { get; set; }     
        public string Name { get; set; }
        public decimal Salary { get; set; }
        public int DepartmentId { get; set; }   

        public virtual Departments Department { get; set; }
}

public class Departments
{
        public int Id { get; set; }
        public string Name { get; set; }

        public virtual List<Employees> Employees { get; set; }    
}

ViewModel

这是显示员工和部门数据的视图模型。在这里，我还想向DepartmentName展示

public class EmployeesVM
{
        public int Id { get; set; }
        public string Name { get; set; }
        public decimal Salary { get; set; }
        public int DepartmentId { get; set; }

        public string DepartmentName { get;set; }
}

Auto类

namespace EmployeeDetails.Helpers
{
    public class AutoMapperHelper:Profile
    {
        public AutoMapperHelper()
        {
            CreateMap<Employees, EmployeesVM>()
                .ForMember(dest => dest.DepartmentName, opt => { opt.MapFrom(src => src.Department.Name); });
        }
    }
}

Index.cshtml.cs

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;

namespace EmployeeDetails.Pages
{
    public class IndexModel : PageModel
    {
        private readonly ILogger<IndexModel> _logger;
        private readonly ApplicationContext _context;
        private readonly IMapper _mapper;
        public IndexModel(ILogger<IndexModel> logger,ApplicationContext context,IMapper mapper)
        {
            _logger = logger;
            _context = context;
            _mapper = mapper;
        }
        [BindProperty]
        public List<EmployeesVM> EmployeesVM { get; set; }
        public void OnGet()
        {
           var result = _context.Employees.ToList();
            EmployeesVM = _mapper.Map<List<EmployeesVM>>(result);
        }
    }
}

您可以在图像'DepartmentName‘中看到null：

​

Answer 1

通过模型中的导航属性，有3种不同的加载相关实体方法。在您的情况下，似乎没有启用懒惰加载 (就我个人而言，我不太喜欢它)，所以您需要使用显式加载或使用急装

var result = _context.Employees
    .Include(e => e.Department)
    .ToList();
EmployeesVM = _mapper.Map<List<EmployeesVM>>(result);

UPD

另外，您可能希望使用AutoMapper的has 可查询扩展来防止通过ProjectTo<>方法过度获取句柄关系，该方法将告诉AutoMapper的映射引擎向IQueryable发出select子句，该子句将通知实体框架它只需要查询某些字段。

请注意，ProjectTo在支持映射(请参阅文档的这一部分)方面有很多限制。