要么以可翻译的形式重写查询，要么显式切换到客户端评估……通过插入对 'AsEnumerable 的调用

Question

I am developing a net 5 api and am trying to implement Iqueryable while querying the db. I understand the fundamental difference between IQueryable and IEnumerable. Everything works ok until I try to implement search functionality, then I get the aforementioned message in Postman: Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync. Here is my code, any help is appreciated, feel free to point me to every mistake in my code:

Services :

 public async Task<IEnumerable<TransactionsForUserVM>> 
 ShowTransactionsForSpecificUser2(QueryParameters queryParameters,
     string email)
    {
        IQueryable<TransactionsForUserVM> transactions =
                          (from t in _context.StockTransactions
                           join u in _context.Users.Where(u => u.Email == email)                          
                           on t.Email equals u.Email 
                           join s in _context.Stocks
                           on t.StockId equals s.Id
                           select new TransactionsForUserVM 
                           {
                                Id = t.Id,
                                StockId = s.Id,
                                Stock = s.Symbol,
                                Quantity = t.Quantity,
                                Purchase = t.Purchase,
                                Price = t.Price,
                                Resolved = t.Resolved,
                                Date = t.Date,
                                Email = email
                                
                         }).AsQueryable().OrderBy(s => s.Date);         

        if (queryParameters.HasQuery())
        {
                transactions = transactions
                .Where(t => t.Stock.ToLowerInvariant().Contains(queryParameters.Query.ToLowerInvariant()));
        }                                    
           return await transactions.ToListAsync();    
    }

Controller:

[HttpGet]
public async Task<ActionResult<IEnumerable<TransactionsForUserVM>>> 
GetTransactionsForSpecificUser5(
    [FromQuery]QueryParameters queryParameters)
{
     var email = HttpContext.User.RetrieveEmailFromPrincipal();
     var list = await _transactionService.ShowTransactionsForSpecificUser2(queryParameters, 
     email);
    return Ok(list);
}

Answer 1

Change this

.Where(t => t.Stock.ToLowerInvariant().Contains(queryParameters.Query.ToLowerInvariant()));

To this:

.Where(t => t.Stock.Contains(queryParameters.Query));

EF Core doesn't know how to translate ToLowerInvariant into an SQL command, so it's throwing an error so you can choose to remove the operation or perform a client side evaluation (drag all the rows out the DB and then get c# to do the filter). Any time you see the "could not be translated" error it's a "you used some C# thing that has no supported mapping in SQL" indicator that you need to redesign some aspect of the C# (make it less complex)

You can find a list of supported operations (what the C# is and what efcore can translate it to) here . If you're not using SQLS, there are links to other DBs here . You might need to approach third party documentation sites if eg you're using something like postgres