LinqToEntities code for Query needing one entity returned foreach root node?
Question
I think I have got myself into a muddle with this one. My database looks like:
Locations [root]
Inspections [level1]
InspectionItems [level2]
InspectionReadings [level3]
Areas [level1]
Inspections [level2]
InspectionItems [level3]
InspectionReadings [level4]
each table is linked by Guid to the previous table and the Inspections table has nullable AreaID so that it can be a direct child of Locations.
What I need is
for each Location
{take all InspectionReadings entities
where location == location
sort date descending
return the top Entity details}
add the Location details and the InspectionReading details into a new table
return new table
the result should be a datagrid with a list of locations and their latest inspection reading date. each location should only appear once.
What I have managed is (this is in my DomainService.cs)
public IQueryable<LocationStatusList> GetLocationStatus()
{
var status = (from a in ObjectContext.Locations
from b in ObjectContext.InspectionReadings
orderby b.DateTaken descending, a.Name
select new LocationStatusList()
{
ID = b.ID,
LocationName = a.Name,
LastInspectionDate = b.DateTaken ?? DateTime.MinValue, // the data is nullable so it needs a value to return in that case
StatusNumber = b.Status ?? -1 // the data is nullable so it needs a value to return in that case
});
return status;
}
which returns the entire InspectionItems entities with their relevant location and although I've tried I can't find a way of doing what I need.
I would like to do all the code for this in the DomainService class but the only way I can think at the moment is to give the query each location name as a parameter from a viewmodel, return a single entity and create a new list and add each single entity.
Surely this can all be done in a LINQ query?
La solution
Final version, if I get it right:
var status = (from a in ObjectContext.Locations
select new {Location = a, LastReading = a.Inspections.SelectMany(i=>i.InspectionReadings).OrderBy(r=>r.PostDate).FirstOrDefault()};
Autres conseils
Ok try this:
var result = from l in Locations
from i in l.Inspestions
from ii in i.InspestionItems
from ir in ii.InspectionReadings
group ir by l into g
select new {Location = g.Key, LastReading = g.OrderBy(r=>r.DateTaken).LastOrDefault() };
Last or default for the reason that default sort order is ascending and you need most recent(last).
Thank you @Val, the code I now have is :
public IQueryable<LocationStatusList> GetLocationStatus()
{
var status = (from a in ObjectContext.Locations
select new LocationStatusList
{
ID=a.ID,
Name=a.Name,
LastInspectionDate= (from b in ObjectContext.Inspections
from c in ObjectContext.InspectionReadings
where c.InspectionItemID==b.ID && b.LocationID==a.ID
orderby c.DateTaken descending
select c.DateTaken).FirstOrDefault()??DateTime.MinValue,
StatusNumber = (from b in ObjectContext.Inspections
from c in ObjectContext.InspectionReadings
where c.InspectionItemID==b.ID && b.LocationID==a.ID
orderby c.DateTaken descending
select c.Status).FirstOrDefault()??-1,
});
return status;
}
which gives precisely what I need. Thank you!