Question

I have been wrangling with this for a while, but I just can’t find a solid example to work from so I’m turning hopefully to the experts. Appreciation in advance for any help.

I have a working SQL query that I need to convert to Linq. Initially, I had a simple linq query driving an MSChart (line chart) that showed the daily ranking of an item in a list. Unfortunately, MSChart doesn’t drop days with null values off the chart, but just connects them to the next day with a non-null value, so I have to replace the nulls with 0s.

The following query does this via a Left, Self Join against the table, where I just grab the distinct list of days (which will include all days). I know I could set up an ancillary table with a list of all days as well, but this should be just as effective in all cases. The SQL that follows works perfectly in SSMS for a specific book/List combination:

select L2.date, ISNULL(L1.ranking,0)  
from (select distinct date from ListItem where ListID = 1) L2  
Left join ListItem L1 on L2.date = L1.date and L1.BookID = 1 and L1.ListID = 1  
order by date

This returns a list of all dates and rankings, with a 0 ranking for any date that no ranking exists. Now in order to bind the chart to this, I believe converting to Linq is the best course.

I would post my attempts so far, but I fear they are woefully wrong. If any more information is necessary, please let me know.

Thanks.

-Dan

Answer 1

Something like this?

var distinctDates = 
    ListItems
        .Where(li => li.ListId == 1)
        .Select(li => li.date)
        .Distinct();

var list1 = 
    ListItems
        .Where(li => li.BookID == 1 && li.ListID == 1);

var results = 
    distinctDates
        .Join(
            list1,
            d => d,
            li1 => li1.date,
            (d, li1) => new{ date = d, ranking = li1.ranking ?? 0 }
        )
        .OrderBy(x => x.date);

(Made a few changes since 1st rev.)