Prevent sort result of union in entity framework - entity-framework

Question

In SQL server union, result is sorted based on primary key column. I want to prevent this behavior in entity framework.
In this post, #praveen has explained how to do this in pure sql. But I want to do this in entity framework.
My code:
public virtual ActionResult Search(string keyword)
{
var products = _db.Products
.Where(x => x.IsActive)
.AsQueryable();
var productExactlyTitle = products.Where(x => x.Title == keyword);
var productStartTitle = products.Where(x => x.Title.StartsWith(keyword));
var productContainsTitle = products.Where(x => x.Title.Contains(keyword)
|| x.Title.Contains(keyword)
|| x.SubTitle.Contains(keyword)
|| x.OtherName.Contains(keyword));
var productList = productExactlyTitle.Union(productStartTitle)
.Union(productContainsTitle)
.Take(10)
.AsEnumerable()
.Select(x => new ProductItemViewModel()
{
Id = x.Id,
Title = x.Title,
Price = x.Price.ToPrice(),
Image = x.Images.FirstOrDefault(y => y.IsCoverPhoto)?.ImageUrl
});
// some code ...
}
I want to show records with below order:
First: records of productExactlyTitle
Second: records of productStartTitle
Third: records of productContainsTitle
But result is sorted with Id column! and I don't want this.
Is there a way for do this?

Answer 1

In SQL all queries without an order by explicitly set is considered unordered. (and EF queries a translated into SQL). So if you want a specific order after your union just specify it.
var result = q1.Union(q2).OrderBy(x => x.?);
For your specific case:
var p1 = productExactlyTitle.Select(x => new { Item = x, Order = 1 });
var p2 = productStartTitle.Select(x => new { Item = x, Order = 2 });
var p3 = productContainsTitle.Select(x => new { Item = x, Order = 3 });
var productList = p1.Union(p2)
.Union(p3)
.OrderBy(x => x.Order)
.Select(x => x.Item)
.Take(10);