我写这个查询的目的是为了让用户使用分页。我使用的是 Sieve 用于分页，过滤和排序，但我有一个问题，这个查询。
我打算发送一个单一的请求到数据库，并只是返回我这个数据。
public class UserPagingDto
{
[Sieve(CanFilter = true, CanSort = true)]
public Guid Id { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public string Username { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public string DisplayName { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public bool IsActive { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public bool IsLockedEnd { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public bool ConfirmPhoneNumber { get; set; }
public UserPagingInfo UserInfos { get; set;
}
}
public class UserPagingInfo
{
[Sieve(CanFilter = true, CanSort = true)]
public int AccountFaile { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public bool ConfirmEmail { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public string PhoneNumber { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public DateTimeOffset? LockedEnd { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public string? Email { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public string Name { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public string Family { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public string RoleName { get; set; }
[Sieve(CanFilter = true, CanSort = true)]
public Guid RoleId { get; set; }
}
为了这个目的，我写了这个。
var user = Users.AsNoTracking().Select(x => new
{
Id=x.Id,
Username = x.Username,
Name = x.Name,
Family = x.Family,
DisplayName = $"{x.Name} {x.Family}",
Email = x.Email,
PhoneNumber = x.PhoneNumber,
AccountFaile = x.AccountFaile,
IsActive = x.IsActive,
IsLockedEnd = x.IsLockedEnd,
ConfirmPhoneNumber = x.ConfirmPhoneNumber,
ConfirmEmail = x.ConfirmEmail,
LockedEnd = x.LockedEnd,
Role = x.UserRoles.Role
}).Select(c => new UserPagingDto
{
Id=c.Id,
ConfirmPhoneNumber = c.ConfirmPhoneNumber,
DisplayName = c.DisplayName,
IsActive = c.IsActive,
IsLockedEnd = c.IsLockedEnd,
Username = c.Username,
UserInfos = new UserPagingInfo
{
AccountFaile = c.AccountFaile,
ConfirmEmail = c.ConfirmEmail,
Email = c.Email,
Family = c.Family,
LockedEnd = c.LockedEnd,
Name = c.Name,
PhoneNumber = c.PhoneNumber,
RoleId = c.Role.Id,
RoleName = c.Role.Name
}
});
var sieveModel = new SieveModel
{
PageSize = formQuery.PageSize,
Filters = formQuery.Filters,
Page = formQuery.Page,
Sorts = formQuery.Sorts
};
var result = sieveProcessor.Apply(sieveModel, user);
return OperationResult<GetAllPaging<UserPagingDto>>.BuildSuccessResult(new GetAllPaging<UserPagingDto>
{
Records = result,
TotalCount = await Users.CountAsync()
});
但它发送的是 两种 请求到数据库，但效果不好。我想通过发送一个请求来达到同样的结果。
我用profiler跟踪对数据库的查询。
一个查询是这个。
SELECT COUNT(*)
FROM [User] AS [u]
WHERE [u].[IsDelete] = CAST(0 AS bit)
第二个查询是这个，我打算只发送这个查询。
SELECT [u].[Id], [u].[ConfirmPhoneNumber], [u].[Name], [u].[Family], [u].[IsActive], [u].[IsLockedEnd], [u].[Username], [u].[AccountFaile], [u].[ConfirmEmail], [u].[Email], [u].[LockedEnd], [u].[PhoneNumber], [t0].[Id], [t0].[Name]
FROM [User] AS [u]
LEFT JOIN (
SELECT [u0].[Id], [u0].[IsDelete], [u0].[RoleId], [u0].[UserId]
FROM [UserRole] AS [u0]
WHERE [u0].[IsDelete] = CAST(0 AS bit)
) AS [t] ON [u].[Id] = [t].[UserId]
LEFT JOIN (
SELECT [r].[Id], [r].[Description], [r].[IsDelete], [r].[Name], [r].[SecurityStamp]
FROM [Role] AS [r]
WHERE [r].[IsDelete] = CAST(0 AS bit)
) AS [t0] ON [t].[RoleId] = [t0].[Id]
WHERE [u].[IsDelete] = CAST(0 AS bit)
ORDER BY [u].[Id]
OFFSET @__p_0 ROWS FETCH NEXT @__p_1 ROWS ONLY
你混淆了查询和集合。
这个。
var user = Users.AsNoTracking().Select(x => new
{
. . .
RoleId = c.Role.Id,
RoleName = c.Role.Name
}
});
不是一个对象的集合 它是一个查询。 如果你把查询传递给一个方法，这个方法运行的是 .Count() 然后 .ToList() 你正在运行两个不同的查询。
所以只需运行一次查询，并将结果存储在List中。
var userQuery = Users.AsNoTracking().Select(x => new
{
. . .
RoleId = c.Role.Id,
RoleName = c.Role.Name
}
});
var user = userQuery.ToList();
让我们来思考一下这个问题。你有一个表，我们假设有100 000 000条记录。在过滤和应用你的分页设置后，你的查询最终会得到一页记录，让我们假设有100条这样的项目。从项数（例子中是100项）你无法推断出总数（例子中是100 000 000）。如果我们看一下这些字段，没有一个字段给出任何关于总记录数的提示。增加一列所有记录的计数是一个非常糟糕的主意。
所以，如果我们保持理智，那么我们承认，你打算作为唯一的查询的查询将不会给你任何关于计数的信息。为了补救这种情况，你需要将该计数存储为一个新的记录。服务器变量. 如果你以这样的方式缓存了计数，那么你将能够使用该服务器变量，并随时重复使用它，而不是在每次加载时硬性计算它。然而，为了保证这个工作的顺利进行，你将需要维护这个值。