CODEWITHSUNDEEP
c#entity-frameworklinq
doorman
doorman

Reputation: 16949

Select latest item in list except when property has a certain value

I need to get the latest status for each product in a list. Except if the status is "Success" it should be returned instead of the latest status. I have the following query to get the latest item but not sure how to conditionally select items that have the Success status. E.g. in the table below ProductId 1 should return the SUCCESS row but not the CANCEL row which is the latest one. Any ideas how to solve this in a single linq query?

var query = list
    .GroupBy(g => g.ProductId)
    .Select(g => g.OrderByDescending(s => s.Created)
                                          .FirstOrDefault())
    .Select(s => new ProductDto
    {
         ProductId = s.ProductId,
         Created = s.Created,
         Status = s.Status
    });

ProductId         Created                         Status
1                 2021-08-19 00:34:30             PREPARING
1                 2021-08-19 00:35:30             VALIDATE
1                 2021-08-19 00:36:30             SUCCESS
1                 2021-08-19 00:37:30             CANCELLED
2                 2021-08-19 00:36:30             PREPARING
2                 2021-08-19 00:38:30             VALIDATE

Upvotes: 0

Views: 52

Answers (1)

Charlieface
Charlieface

Reputation: 71308

You can sort first by whether it's a SUCCESS row:

.Select(g => g.OrderBy(s => s.Status == "SUCCESS" ? 0 : 1)
              .ThenByDescending(s => s.Created)
              .FirstOrDefault())

This causes all SUCCESS rows to come first, sorted by date, then the other rows, also sorted by date.

The intermediate sort (before FirstOrDefault) is effectively:

ProductId         Created                         Status
1                 2021-08-19 00:36:30             SUCCESS
1                 2021-08-19 00:37:30             CANCELLED
1                 2021-08-19 00:35:30             VALIDATE
1                 2021-08-19 00:34:30             PREPARING
2                 2021-08-19 00:38:30             VALIDATE
2                 2021-08-19 00:36:30             PREPARING

Upvotes: 1

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