EF Core的条件选择

Question

I've trying to make a conditional select using EF Core, but i think i'm a litle bit confusing about how to do this. I have two tables in my MySql Schema: Products and Offers . I want to select all products and merge with the offers, overriding the product with your current promotional value. I've try to use include , join and all sort of things, but i think the problem is my logic. Here is my current EF core select, without 'merge' with the offers.

List<ProductViewModel> viewModel = await _context.product
  .Where(p => p.establishment_id == EstablishmentId)
  .Select(p => new ProductViewModel()
  {
    Id = p.id,
    Name = p.name,
    Description = p.description,
    Rating = p.rating,
    Price = p.price,
    Photos = p.product_photo
     .Where(pho => pho.product_id == p.id)
     .Select(pho => new ProductPhotoViewModel()
     {
       Path = pho.path
     }).ToList(),
     Category = _context.category
     .Join(_context.product_has_category, c => c.id, phc => phc.category_id, (c, phc) => new {c, phc})
     .Where(c => c.phc.product_id == p.id)
     .Select(c => new CategoryViewModel()
     {
       Id = c.phc.category.id,
       Name = c.phc.category.name
     }).SingleOrDefault()
  }).ToListAsync();

All help are useful! Many thanks!

Answer 1

Use the ternary conditional operator ?: along with a not equals condition != to add a conditional to your select statement.

.Select(p => new ProductViewModel()
{
    Id = p.id,
    Name = p.name,
    Description = p.description,
    Rating = p.rating,
    Price = p.offer != null ? p.offer.sale_price : p.price
});