Linq generic Expression in query on "element" or on IQueryable (multiple use)
- by Bogdan Maxim
Hi,
I have the following expression
public static Expression<Func<T, bool>> JoinByDateCheck<T>(T entity, DateTime dateToCheck) where T : IDateInterval
{
return (entityToJoin) =>
entityToJoin.FromDate.Date <= dateToCheck.Date && (entityToJoin.ToDate == null || entityToJoin.ToDate.Value.Date >= dateToCheck.Date);
}
IDateInterval interface is defined like this:
interface IDateInterval
{
DateTime FromDate {get;}
DateTime? ToDate {get;}
}
and i need to apply it in a few ways:
(1) Query on Linq2Sql Table:
var q1 = from e in intervalTable where FunctionThatCallsJoinByDateCheck(e, constantDateTime) select e;
or something like this:
intervalTable.Where(FunctionThatCallsJoinByDateCheck(e, constantDateTime))
(2) I need to use it in some table joins (as linq2sql doesn't provide comparative join):
var q2 = from e1 in t1 join e2 in t2 on e1.FK == e2.PK where OtherFunctionThatCallsJoinByDateCheck(e2, e1.FromDate)
or
var q2 = from e1 in t1 from e2 in t2 where e1.FK == e2.PK && OtherFunctionThatCallsJoinByDateCheck(e2, e1.FromDate)
(3) I need to use it in some queries like this:
var q3 = from e in intervalTable.FilterFunctionThatCallsJoinByDateCheck(constantDate);
Dynamic linq is not something that I can use, so I have to stick to plain linq.
Thank you
Clarification:
Initially I had just the last method (FilterFunctionThatCallsJoinByDateCheck(this IQueryable<IDateInterval> entities, DateTime dateConstant) ) that contained the code from the expression.
The problem is that I get a SQL Translate exception if I write the code in a method and call it like that.
All I want is to extend the use of this function to the where clause (see the second query in point 2)
