C# 我可以创建一个用于Linq的助手函数吗?
我有一个助手函数:C# 我可以创建一个用于Linq的助手函数吗?,c#,linq,C#,Linq,我有一个助手函数: namespace PublicationSystem.Tools { public class Format { public static string FullName(string salutation, string first, string middle, string last, string suffix = "")
namespace PublicationSystem.Tools
{
public class Format
{
public static string FullName(string salutation,
string first,
string middle,
string last,
string suffix = "")
{
var fullName = new StringBuilder();
if (!string.IsNullOrEmpty(salutation)) fullName.Append(salutation + " ");
fullName.Append(first + " ");
if (!string.IsNullOrEmpty(middle)) fullName.Append(middle.Trim() + " ");
fullName.Append(last);
if (!string.IsNullOrEmpty(suffix)) fullName.Append(" " + suffix);
return fullName.ToString().Trim();
}
}
}
我希望在Linq查询中使用它,如下所示:
SessionUser = (
from pi in db.ProfileIdentifier
join p in db.Profile on pi.ProfileId equals p.ProfileId
where
pi.ProfileIdentifierTypeId == (int)ProfileIdentifierTypes.email &&
pi.ProfileIdentifierValue == email &&
pi.IsActive
select new LoginViewModel
{
ProfileId = p.ProfileId,
SessionId = sessionTokenId,
FullName = Format.FullName(p.Salutation,p.FirstName,p.MiddleName,p.LastName),
Email = email,
Permissions = (
from ra in db.RoleAssignment
join rp in db.RolePermission on ra.RoleId equals rp.RoleId
join perm in db.Permission on rp.PermissionId equals perm.PermissionId
where ra.AssigneeId == p.ProfileId &&
rp.IsActive
select new ProfilePermission
{
RoleId = ra.RoleId,
AssignedToId = ra.AssignedToId,
PermissionId = perm.PermissionId,
PermissionName = perm.PermissionName,
PermissionGroupId = perm.PermissionGroupId
}).ToList()
}).FirstOrDefault();
有什么方法可以做到这一点吗?是的,但是当查询数据源(例如SQL Server)时,该提供程序将不知道如何处理您的函数 您可以在查询中使用,使该查询的其余部分在客户端而不是数据库中进行计算。调用.AsEnumerable()后,可以使用自己的函数,如Format.FullName() 请注意,您应该避免在数据库中完成筛选之前调用.AsEnumerable(),因为调用之后的所有数据都会从数据库传输到客户端程序。不知道如何将方法的内容
全名(…)
解析为sql
您可以执行查询,返回匿名对象,例如:
var tempUser = (
from pi in db.ProfileIdentifier
join p in db.Profile on pi.ProfileId equals p.ProfileId
where
pi.ProfileIdentifierTypeId == (int)ProfileIdentifierTypes.email &&
pi.ProfileIdentifierValue == email &&
pi.IsActive
select new
{
p.ProfileId,
SessionId = sessionTokenId,
p.Salutation,
p.FirstName,
p.MiddleName,
p.LastName,
Email = email
}).FirstOrDefault();
if (tempUser != null)
{
SessionUser = new LoginViewModel
{
ProfileId = tempUser.ProfileId,
SessionId = tempUser.SessionId,
FullName = Format.FullName(tempUser.Salutation, tempUser.FirstName, tempUser.MiddleName, tempUser.LastName),
Email = tempUser.Email
};
}
之后,您可以使用函数FullName(..)
转换结果,例如:
var tempUser = (
from pi in db.ProfileIdentifier
join p in db.Profile on pi.ProfileId equals p.ProfileId
where
pi.ProfileIdentifierTypeId == (int)ProfileIdentifierTypes.email &&
pi.ProfileIdentifierValue == email &&
pi.IsActive
select new
{
p.ProfileId,
SessionId = sessionTokenId,
p.Salutation,
p.FirstName,
p.MiddleName,
p.LastName,
Email = email
}).FirstOrDefault();
if (tempUser != null)
{
SessionUser = new LoginViewModel
{
ProfileId = tempUser.ProfileId,
SessionId = tempUser.SessionId,
FullName = Format.FullName(tempUser.Salutation, tempUser.FirstName, tempUser.MiddleName, tempUser.LastName),
Email = tempUser.Email
};
}
这是最简单的转换:
SessionUser = (
from pi in db.ProfileIdentifier
join p in db.Profile on pi.ProfileId equals p.ProfileId
where
pi.ProfileIdentifierTypeId == (int)ProfileIdentifierTypes.email &&
pi.ProfileIdentifierValue == email &&
pi.IsActive
select p)
.ToList()
.Select(p=>new LoginViewModel
{
ProfileId = p.ProfileId,
SessionId = sessionTokenId,
FullName = Format.FullName(p.Salutation,p.FirstName,p.MiddleName,p.LastName),
Email = email
}).FirstOrDefault();
这将更有效率:
SessionUser = (
from pi in db.ProfileIdentifier
join p in db.Profile on pi.ProfileId equals p.ProfileId
where
pi.ProfileIdentifierTypeId == (int)ProfileIdentifierTypes.email &&
pi.ProfileIdentifierValue == email &&
pi.IsActive
select p)
.Take(1)
.ToList()
.Select(p=>new LoginViewModel
{
ProfileId = p.ProfileId,
SessionId = sessionTokenId,
FullName = Format.FullName(p.Salutation,p.FirstName,p.MiddleName,p.LastName),
Email = email
}).FirstOrDefault();
SessionUser = (
from pi in db.ProfileIdentifier
join p in db.Profile on pi.ProfileId equals p.ProfileId
where
pi.ProfileIdentifierTypeId == (int)ProfileIdentifierTypes.email &&
pi.ProfileIdentifierValue == email &&
pi.IsActive
select new
{
p.ProfileId,
p.Salutation,
p.FirstName,
p.MiddleName,
p.LastName
})
.Take(1)
.ToList()
.Select(p=>new LoginViewModel
{
ProfileId = p.ProfileId,
SessionId = sessionTokenId,
FullName = Format.FullName(p.Salutation,p.FirstName,p.MiddleName,p.LastName),
Email = email
}).FirstOrDefault();
更有效的是:
SessionUser = (
from pi in db.ProfileIdentifier
join p in db.Profile on pi.ProfileId equals p.ProfileId
where
pi.ProfileIdentifierTypeId == (int)ProfileIdentifierTypes.email &&
pi.ProfileIdentifierValue == email &&
pi.IsActive
select p)
.Take(1)
.ToList()
.Select(p=>new LoginViewModel
{
ProfileId = p.ProfileId,
SessionId = sessionTokenId,
FullName = Format.FullName(p.Salutation,p.FirstName,p.MiddleName,p.LastName),
Email = email
}).FirstOrDefault();
SessionUser = (
from pi in db.ProfileIdentifier
join p in db.Profile on pi.ProfileId equals p.ProfileId
where
pi.ProfileIdentifierTypeId == (int)ProfileIdentifierTypes.email &&
pi.ProfileIdentifierValue == email &&
pi.IsActive
select new
{
p.ProfileId,
p.Salutation,
p.FirstName,
p.MiddleName,
p.LastName
})
.Take(1)
.ToList()
.Select(p=>new LoginViewModel
{
ProfileId = p.ProfileId,
SessionId = sessionTokenId,
FullName = Format.FullName(p.Salutation,p.FirstName,p.MiddleName,p.LastName),
Email = email
}).FirstOrDefault();
看起来不错。但是,我在linq语句中添加了一些代码。我正在做第二个/子查询。我想知道我是否还能这样做?在这里使用
ToList
是一个非常糟糕的主意。您至少应该使用可计算的aseneumerable
,即使这样也不是最好的。@MKenyonII是的,您仍然可以这样做。只需确保执行.Take(1),将从数据库返回的行数限制为仅1行。将您的权限放在第一个选择中,这样它就可以访问数据库,并在第二个选择中添加Permissions=p.Permissions
。请按照Servy的建议将.ToList()更改为.AsEnumerable(),尽管在我的系统中,两者之间的差异约为2/10000秒+/-1/10000秒。我不认为这是一个非常糟糕的主意,但最好使用