NHibernate.Linq查询问题，向DateTime添加秒

Question

I am receiving the following exception while using NHibernate.Linq and Entity Framework 6.0.

NHibernate.QueryException: Cannot use subqueries on a criteria without a projection.

The issue is specifically coming from:

taco.LastRun <= DbFunctions.AddSeconds(taco.LastRun, taco.PeriodSeconds)

When I remove that section of code, the results come back perfect.

var results = (
    from taco in Session.Linq<Taco>()
    where
        taco.IsActive && !taco.IsProcessing &&
        ((taco.StartCrunching == null) || (taco.StartCrunching <= currentDateTime)) &&
        ((taco.Cycles == null) || (taco.CycleCount < taco.Cycles)) &&
        (taco.LastRun == null || (taco.LastRun <= DbFunctions.AddSeconds(taco.LastRun, taco.PeriodSeconds))) &&
        ((taco.EndCrunching == null))
    select taco).ToList();

Answer 1

I think it's because you're updating information inside a select query. This update will itself be a query of some kind(probably an UPDATE SQL statement).

Try updating the information first then doing your select query;

looking at what you're trying to do though doesn't make much sense, as

taco.LastRun <= taco.LastRun + taco.PeriodSeconds

will always be true.(Provided taco.PeriodSeconds > 0 ). But I think I know what you're trying to do:

var results = (
from taco in Session.Linq<Taco>()
where
    taco.IsActive && !taco.IsProcessing &&
    ((taco.StartCrunching == null) || (taco.StartCrunching <= currentDateTime)) &&
    ((taco.Cycles == null) || (taco.CycleCount < taco.Cycles)) &&
    (taco.LastRun == null || (taco.LastRun <= currentDateTime.AddSeconds(taco.PeriodSeconds)))
    && ((taco.EndCrunching == null))
select taco).ToList();

you're trying to check if the LastRun was less than the current time + PeriodSeconds ? The above will do that.

Also it should be noted that you don't need to use both Entity Framework and NHibernate. They're both ORM's and so they both do very similar things.