将 linq 查询连接到视图模型的结果

Question

在我的操作方法中，我正在运行以下返回列表的查询：

var list = db.WorkRoles.
                Join(db.WorkRolesUsersDetails,
                o => o.WorkRoleId, od => od.WorkRoleId,
                (o, od) => new
                {
                    WorkRoleId = o.WorkRoleId,
                    RoleName = o.RoleName,
                    RoleDescription = o.RoleDescription,
                    CompanyId = o.CompanyId,
                    WRUDId = od.WRUDId,
                    UserDetailsId = od.UserDetailsId,
                    FocusStart = od.FocusStart,
                    FocusEnd = od.FocusEnd
                }).ToList();

我有一个相同格式的 viemodel，如下所示：

public class RoleViewModel
{
    public RoleViewModel(int workRoleId, string roleName, string roleDescription, int companyId, int wRUDId, string userDetailsId, DateTime focusStart, DateTime focusEnd)
    {
        WorkRoleId = workRoleId;
        RoleName = roleName;
        RoleDescription = roleDescription;
        CompanyId = companyId;
        WRUDId = wRUDId;
        UserDetailsId = userDetailsId;
        FocusStart = focusStart;
        FocusEnd = focusEnd;
    }
    int WorkRoleId { get; set; }
    string RoleName  { get; set; }
    string RoleDescription { get; set; }
    int CompanyId { get; set; }
    int WRUDId { get; set; }
    string UserDetailsId { get; set; }
    DateTime FocusStart { get; set; }
    DateTime FocusEnd { get; set; }
}

将查询结果转换为视图模型列表的最佳方法是什么？

我从 stackoverflow 上的答案中尝试过的一件事是：

var list = db.WorkRoles.
                Join(db.WorkRolesUsersDetails,
                o => o.WorkRoleId, od => od.WorkRoleId,
                (o, od) => new
                {
                    WorkRoleId = o.WorkRoleId,
                    RoleName = o.RoleName,
                    RoleDescription = o.RoleDescription,
                    CompanyId = o.CompanyId,
                    WRUDId = od.WRUDId,
                    UserDetailsId = od.UserDetailsId,
                    FocusStart = od.FocusStart,
                    FocusEnd = od.FocusEnd
                }).ToList()
                .Select(item => new RoleViewModel(
                   item.WorkRoleId,
                    item.RoleName,
                    item.RoleDescription,
                    item.CompanyId,
                    item.WRUDId,
                    item.UserDetailsId,
                    item.FocusStart,
                    item.FocusEnd));

但是，遗憾的是，这让喵喵叫的不是RoleViewModels 的列表。这是调试器中值部分的副本：

{System.Linq.Enumerable.WhereSelectListIterator<<>f__AnonymousType6<int, string, string, int, int, string, System.DateTime, System.DateTime>, eksp.Models.RoleViewModel>}

Answer 1

您必须使用ToList 来获取您的项目列表。您将 query 分配给您的 list 变量。查询被延迟，这意味着它不会被执行，直到您通过调用ToList、ToArray、First 等来实际检索结果：

List<RoleViewModel> list = db.WorkRoles.
                Join(db.WorkRolesUsersDetails,
                o => o.WorkRoleId, od => od.WorkRoleId,
                (o, od) => new
                {
                    WorkRoleId = o.WorkRoleId,
                    RoleName = o.RoleName,
                    RoleDescription = o.RoleDescription,
                    CompanyId = o.CompanyId,
                    WRUDId = od.WRUDId,
                    UserDetailsId = od.UserDetailsId,
                    FocusStart = od.FocusStart,
                    FocusEnd = od.FocusEnd
                }).ToEnumerable()
                .Select(item => new RoleViewModel(
                   item.WorkRoleId,
                    item.RoleName,
                    item.RoleDescription,
                    item.CompanyId,
                    item.WRUDId,
                    item.UserDetailsId,
                    item.FocusStart,
                    item.FocusEnd)).ToList();

我能给你的最好的提示：避免使用var，并尽可能明确地指定类型。如果你这样做了，你的编译器就会给你一个错误。