Question

我有一个包含两个表的数据库：用户（idUser，firstName，lastName）和 文档（idDoc，title，expirationDate，UserDoc）其中UserDoc是 idUser

的外键

此外，我的C＃代码中有两个类：

 public class DocumentUI
{
    public string Title { get; set; }
    public string Description { get; set; }
    public DateTime ExpirationDate { get; set; }
    public int UserDoc { get; set; }
    public UserUI User { get; set; }
}

和

 public class UserUI
{
    public int IdUser { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

}

我需要转换以下查询：

select a.*, (select u.lastName from Users as u where u.idUser = a.UserDoc),(select u.firstName from Users as u where u.idUser = a.UserDoc)

来自Documents的

其中getdate（）＆lt; = a.expirationDate

我试过，这是它的结果：

            var documents = (from d in DocumentDAO.GetDocument()
                             join k in UserDAO.GetUsers()
                             on d.UserDoc equals k.IdUser
                             where (DateTime.Now <= d.ExpirationDate)
                             select new DocumentUI
                             {
                                 Title = d.Title,
                                 Description = d.Description,
                                 DateOfAdd = d.DateOfAdd,
                                 ExpirationDate = d.ExpirationDate,
                                 UserDoc = d.UserDoc,
                                 User = new UserUI { FirstName = k.FirstName, LastName = k.LastName}

                             }).ToList();

但在调试器中我注意到它没有看到任何文件（我检查并且有一个应该返回）

我也试过这种方式：

            var documents = (from d in DocumentDAO.GetDocument()
                             from k in UserDAO.GetUsers().Where(k =>k.IdUser == d.UserDoc
                             where (DateTime.Now <= d.ExpirationDate)
                             select new DocumentUI
                             {
                                 Title = d.Title,
                                 Description = d.Description,
                                 DateOfAdd = d.DateOfAdd,
                                 ExpirationDate = d.ExpirationDate,
                                 UserDoc = d.UserDoc,
                                 User = new UserUI { FirstName = k.FirstName, LastName = k.LastName}

                             }).ToList();

但它给了我相同的结果

第三种方式：

            var documents = (from d in DocumentDAO.GetDocument()
                             from k in UserDAO.GetUsers()
                             where ((DateTime.Now <= d.ExpirationDate) && (k.IdUser == d.UserDoc))
                             select new DocumentUI
                             {
                                 Title = d.Title,
                                 Description = d.Description,
                                 DateOfAdd = d.DateOfAdd,
                                 ExpirationDate = d.ExpirationDate,
                                 UserDoc = d.UserDoc,
                                 User = new UserUI { FirstName = k.FirstName, LastName = k.LastName}

                             }).ToList();

但仍然没有，但是如果我删除（k.IdUser == d.UserDoc）它会向我展示这个包含所有用户的文档

更新用你的意见和想法我写了这个：

 var now = DateTime.Now;
        var documents = DocumentDAO.GetDocument()
                    .Where(d => d.ExpirationDate > now)
                    .Select(d => new DocumentUI
             {
                 Title = d.Title,
                 Description = d.Description,
                 DateOfAdd = d.DateOfAdd,
                 ExpirationDate = d.ExpirationDate,
                 UserDoc = d.UserDoc,
                 User = new UserUI {
                     FirstName =UserDAO.GetUsers().First().FirstName,
                     LastName = UserDAO.GetUsers().First().LastName
                           }
             }).ToList();

但我仍然不检查UserDoc是否等于IdUser。我应该在哪里添加这个？

Answer 1

所以你应该有类似的东西：

var result = DocumentDAO.Where(d => d.expirationDate >= DateTime.Now).Select(d =>
                     new {
                       Document = d,
                       User = UserDAO.FirstOrDefault(u => u.idUser = d.UserDoc),
                       FirstName = User.firstName,
                       LastName = User.lastName,  
                     });

如果您使用 EF 作为 ORM 框架并在实体之间配置了正确的关系，那么您应该在User中拥有Document属性。在这种情况下，它会更容易：

var result = context.Documents.Where(d => d.expirationDate >= DateTime.Now).Select(d =>
                         new {
                           Document = d,
                           FirstName = d.User.firstName,
                           LastName = d.User.lastName,  
                         });

Answer 2

vat now = DateTime.Now;
var result = DocumentDAO.GetDocument()
                        .Where(d => d.ExpirationDate > now)
                        .Select(d => new {
                                           doc = d,
                                           firstname = d.User.FirstName,
                                           lastname = d.User.LastName
                                       });

<强>更新

要返回DocumentUI列表，请将Select()语句替换为以下

.Select(d => new DocumentUI
                 {
                     Title = d.Title,
                     Description = d.Description,
                     DateOfAdd = d.DateOfAdd,
                     ExpirationDate = d.ExpirationDate,
                     UserDoc = d.UserDoc,
                     User = new UserUI { 
                                   FirstName = d.User.FirstName, 
                                   LastName = d.user.LastName
                               }
                 }).ToList();

将SQL查询转换为LINQ＃2

2 个答案: