Question

I have an array of Ids, in order, using these ids I then issue a linq query, however I want the results of the linq query to come back in the same order that the Ids in the array are in.

Example:

int[] ids = new [] {10, 9, 8, 7};

var query = from row in context.Table where ids.Contains(row.Id) select row;

How could I ensure that the obtained items are in the same order as those in the array?

Answer 1

You can order the rows by the index of their Id in ids:

var query = from row in context.Table
            where ids.Contains(row.Id)
            orderby Array.IndexOf(ids, row.Id)
            select row;

---

I’m not sure if the LINQ-to-SQL provider supports this; you may need to perform the ordering using LINQ-to-Objects:

var query = from row in context.Table
            where ids.Contains(row.Id)
            select row;

var orderedQuery = from row in query.AsEnumerable()
                   orderby Array.IndexOf(ids, row.Id)
                   select row;

or

var orderedQuery = context.Table
                          .Where(row => ids.Contains(row.Id))
                          .AsEnumerable()
                          .OrderBy(row => Array.IndexOf(ids, row.Id));