Prevent sort result of union in entity framework after select and distinct - entity-framework

Question

Before I asked Prevent sort result of union in entity framework
I got my answer but now I have new problem with this issue. I have this code:
var productExactlyTitle = products.Where(x => x.Title == keyword);
var productStartWithPhrase = products.Where(x => x.Title.StartsWith(keyword));
var productStartWithWord = products.Where(x => x.Title.StartsWith(keyword + " "));
var productContainsWord = products.Where(x => x.Title.Contains(" " + keyword + " "));
var productContainsPhrase = products.Where(x => x.Title.Contains(keyword)
|| x.Title.Contains(keyword)
|| x.SubTitle.Contains(keyword)
|| x.OtherName.Contains(keyword));
var splitWords = keyword.Split(' ');
var productSplitWordSearch = splitWords.Aggregate(products, (current, word) => current.Where(x => x.Title.Contains(word.Trim())));
var p1 = productExactlyTitle.Select(x => new { Item = x, Order = 1 });
var p2 = productStartWithWord.Select(x => new { Item = x, Order = 2 });
var p3 = productStartWithPhrase.Select(x => new { Item = x, Order = 3 });
var p4 = productContainsWord.Select(x => new { Item = x, Order = 4 });
var p5 = productContainsPhrase.Select(x => new { Item = x, Order = 5 });
var p6 = productSplitWordSearch.Select(x => new { Item = x, Order = 6 });
var productList = p1
.Union(p2)
.Union(p3)
.Union(p4)
.Union(p5)
.Union(p6)
.OrderBy(x => x.Order)
.Take(21)
.AsEnumerable()
.Select(x => new ProductItemViewModel()
{
Id = x.Item.Id,
Title = x.Item.Title,
Price = DiscountController.ApplyDiscountToPrice(x.Item).ToPrice(),
Image = x.Item.Images.FirstOrDefault(y => y.IsCoverPhoto)?.ImageUrl
});
Result of above code have duplicate records and I have to use select and distinct to remove duplicate records. so I change my code like this:
var productList = p1
.Union(p2)
.Union(p3)
.Union(p4)
.Union(p5)
.Union(p6)
.OrderBy(x => x.Order)
.Select(x => x.Item)
.Distinct()
.Take(21)
.AsEnumerable()
.Select(x => new ProductItemViewModel()
{
Id = x.Id,
Title = x.Title,
Price = DiscountController.ApplyDiscountToPrice(x).ToPrice(),
Image = x.Images.FirstOrDefault(y => y.IsCoverPhoto)?.ImageUrl
});
But after that my result is sorted with Id column again.
How can I solved this?

Answer 1

First, since adding Order field to each query makes the record unique, using Union (which is supposed to remove duplicates) doesn't make sense, so simply use Concat instead.
Second, to remove duplicates and not lose the Order field needed for later ordering, you need to group by Item and take the minimum Order for each group. The rest is the same as in the original solution.
var productList = p1
.Concat(p2)
.Concat(p3)
.Concat(p4)
.Concat(p5)
.Concat(p6)
.GroupBy(e => e.Item)
.Select(g => new { Item = g.Key, Order = g.Min(e => e.Order) })
.OrderBy(e => e.Order)
.Select(e => e.Item)
.Take(21)
.AsEnumerable()
...