Linq left outer join not returning results

Question

I'm trying to perform a left outer join on two tables based on the model on the picture

I'm using the following linq query:

var query = from u in Context.Set<CpcUnidadProceso>()
            join p in Context.Set<CpcParadasPrevistasUnidad>()
                on u.IdCpcUnidadesProceso equals p.IdCpcUnidadesProceso
                into g
            from result in g.DefaultIfEmpty()
            where u.RefineriaArea.IdTipoArea == filters.IdTipoArea &&
            (result.FechaParada >= filters.Fecha || result == null) && (result.FechaArranque <= filters.Fecha || result == null)
            select
                new CpcPrevisionParadasUnidadesDto
                {
                    IdCpcUnidadesProceso = u.IdCpcUnidadesProceso,
                    CodigoUnidadProceso = u.CodUnidadProceso,
                    DescripcionUnidadProceso = u.Nombre,
                    IdCpcPrevisionParadasUnidadesDto = result == null ? 0 : result.IdCpcParadasPrevistasUnidades,
                    FechaParada = result == null ? null : result.FechaParada,
                    FechaArranque = result == null ? null : result.FechaArranque,
                    Observaciones = result == null ? null : result.Observaciones
                };

But the results are not as expected, it's not returning results when there is a record with FechaParada and/or FechaArranque not null. What am I doing wrong here?

Answer 1

I suspect the problem to be caused by the following where condition:

(result.FechaParada >= filters.Fecha || result == null) && (result.FechaArranque <= filters.Fecha || result == null)

First off, it might not be essential for SQL queries, but it's always a good practice to first check the null condition, so the above can be reduced to

(result == null || (result.FechaParada >= filters.Fecha && result.FechaArranque <= filters.Fecha))

Even better, the filtering on the right side of the left outer join should be performed before the join (for left side or inner join it really doesn't matter):

from u in Context.Set<CpcUnidadProceso>()
join p in Context.Set<CpcParadasPrevistasUnidad>()
    .Where(x => x.FechaParada >= filters.Fecha && x.FechaArranque <= filters.Fecha)
on u.IdCpcUnidadesProceso equals p.IdCpcUnidadesProceso
into g
from result in g.DefaultIfEmpty()
where u.RefineriaArea.IdTipoArea == filters.IdTipoArea
// ...

In all the cases, you have to check if you really have a data satisfying the FechaParada >= filters.Fecha && FechaArranque <= filters.Fecha condition.