C# 将where/order by子句添加到IQueryable
我具有从数据库查询一组记录的功能:C# 将where/order by子句添加到IQueryable,c#,linq,C#,Linq,我具有从数据库查询一组记录的功能: public IQueryable<PointTransactionViewModel> GetPointTransactions(int UserID) { return ( from PointTransaction p in entities.PointTransaction join Act
public IQueryable<PointTransactionViewModel> GetPointTransactions(int UserID)
{
return
(
from PointTransaction p in entities.PointTransaction
join ActivityLog a in entities.ActivityLog
on p.TransactionID equals a.TransactionID
where p.UserID == UserID
select new PointTransactionViewModel
{
ID = p.TransactionID,
Balance = p.Balance,
Points = p.Amount,
RelatedActivityID = a.ID,
When = p.When,
Sender = p.SenderUserInfo.CompleteName
}
);
}
没有错误消息,只是where子句似乎被忽略了(它还返回PointsEnned不是50的所有数据)您的
条目是一个IQueryable变量,所以这就足够了,您可以在获取数据之前添加任意数量的子句(如ToList()
之前)。
它不会运行,只会创建表达式树,直到您获取数据
var query = context.Where(x=>x.id == test);
query = query.Where(anotherCondition1);
query = query.Where(anotherCondition2);
...
var result = query.ToList();
等于
var result = context.Where(x=>x.id == test).Where(anotherCondition1)
.Where(anotherCondition2)....ToList()
请参见您确实需要创建一个新对象。IQueryable是不变的。别担心,这是你应该做的。这就是查询在内部形成的方式。所有像“Where”这样的扩展方法实际上并没有改变对象。他们只是返回一个新的
您声称有效的代码不应该有效。该方法甚至没有类型。正如其他人所指出的,您不需要新对象。但是,OrderByDescending
的语法错误,需要指定键选择器
var entries = GetPointTransaction(1);
return entries.Where(x => x.When >= start && w.When <= end).OrderbyDescending(x => x.When);
var entries=GetPointTransaction(1);
返回条目。其中(x=>x.When>=start&w.When x.When);
我的意思是您可以编写以下示例:
opportunites = from opp in oppDC.Opportunities
join org in oppDC.Organizations on opp.OrganizationID equals org.OrgnizationID
select new
{
opp.OpportunityID,
opp.Title,
opp.PostedBy,
opp.Address1,
opp.CreatedDate,
org.OrganizationName
};
if(condition)
{
opportunites = opportunites.Where(opp => opp.Title.StartsWith(title));
}
//------Other Condition you need
if(!String.IsNullOrEmpty(title))
{
opportunites = opportunites.Where(.....);
}
if(!String.IsNullOrEmpty(name))
{
opportunites = opportunites.Where(.....);
}
它起作用了。这是一个通用方法,您必须指定类型。我设法让它工作,但我无法使用var来存储IQueryable对象。我已经更新了问题中的代码。谢谢@Extrakun,我无法测试您当前的代码,但错误消息是什么?在编译还是运行时?或者发生了什么?没有错误消息,只是忽略了where子句和orderby子句。@Extrakun,可能是您没有编译它,或者您没有将结果复制到输出文件夹中,这似乎是不可能的。
var query = context.Where(x=>x.id == test);
query = query.Where(anotherCondition1);
query = query.Where(anotherCondition2);
...
var result = query.ToList();
var result = context.Where(x=>x.id == test).Where(anotherCondition1)
.Where(anotherCondition2)....ToList()
var entries = GetPointTransaction(1);
return entries.Where(x => x.When >= start && w.When <= end).OrderbyDescending(x => x.When);
opportunites = from opp in oppDC.Opportunities
join org in oppDC.Organizations on opp.OrganizationID equals org.OrgnizationID
select new
{
opp.OpportunityID,
opp.Title,
opp.PostedBy,
opp.Address1,
opp.CreatedDate,
org.OrganizationName
};
if(condition)
{
opportunites = opportunites.Where(opp => opp.Title.StartsWith(title));
}
//------Other Condition you need
if(!String.IsNullOrEmpty(title))
{
opportunites = opportunites.Where(.....);
}
if(!String.IsNullOrEmpty(name))
{
opportunites = opportunites.Where(.....);
}