Question

I am trying to convert a complex (and rather hacky) dynamic SQL query in to a LINQ query.

I have the following LINQ query so far:

var results = (
    from c in Customers
    from d in MonthCalendar
        join f in Facilities on c.CustomerCode equals f.CustomerCode
        join p in ProjectedCashFlows on f.FacilityId equals p.FacilityId into pj
                from p in pj.DefaultIfEmpty()                      
        where d.ExpectedYear == currentYear 
                && f.FacilityStatusId == 1
                && (p.ExpectedYear == null || d.ExpectedYear == p.ExpectedYear)
                && (p.ExpectedMonth == null || d.ExpectedMonth == p.ExpectedMonth)
                && c.PrimaryArmId == userId 
                && (p.ProjectedCashFlowStatusId == null || p.ProjectedCashFlowStatusId != 4)
        select new 
            {
                CustomerCode = c.CustomerCode,
                CustomerName = c.CustomerName,
                FacilityId = f.FacilityId,
                FacilityDescription = f.FacilityProductDescription,
                FacilityCurrency = f.FacilityCurrencyId,
                FacilityLimit = f.Limit,
                ExpectedYear = d.ExpectedYear,
                ExpectedMonth = d.ExpectedMonth,
                ExpectedAmount = p == null ? 0 : (double)p.ExpectedAmount

            }
            );

I am trying to retrieve details from a Customer table that has a one-to-many relationship with a Facilities table. I am then trying to retrieve any details located in the ProjectedCashFlows

The problem I am having is that the query should return all Customer and Facilites information regardless of whether any values exist in the ProjectedCashFlows table.

Unfortunately this query is not doing that – it is only returning Customer and Facilities information when the Facility exists in the ProjectedCashFlows table.

I have used a MonthCalender table to list out each month in the year.

The relevant table information is:

Customers

• CustomerCode
• CustomerName
• PrimaryArmId

Facilities

• CustomerCode
• FacilityId
• FacilityCurrencyId
• FaciliyLimit
• FacilityDescription

ProjectedCashFlows

• CustomerCode
• FacilityId
• ExpectedYear
• ExpectedMonth
• ExpectedAmount
• ProjectedCashFlowStatusId

MonthsCalendar

• ExpectedMonth
• ExpectedYear

As an example I have a customer that has 4 rows in the Facilities table however, 2 of these facilities do not appear in the ProjectedCashFlows table so they are not being displayed.

If an entry doesn’t exist in ProjectedCashFlows it should take the ExpectedMonth & ExpectedYear from the CalendarMonths table, return 0 for the ExpectedAmount and use the FacilityId from the Facilities table.

As you can probably work out I have just started to use LINQ.

Can anyone poke me in the right direction?

Answer 1

Your query uses p assuming it is non-null:

where d.ExpectedYear == currentYear 
      && f.FacilityStatusId == 1
      && (p.ExpectedYear == null || d.ExpectedYear == p.ExpectedYear)
      // etc

But you’ve used DefaultIfEmpty() which will logically create a sequence with a single null value when there are no ProjectedCashFlows.

So basically you need something like:

where d.ExpectedYear == currentYear 
      && f.FacilityStatusId == 1
      && (p == null ||
          ((p.ExpectedYear == null || d.ExpectedYear == p.ExpectedYear)
          // etc
          ))