LINQ JOIN in .NET Core 3.1

Question

I have created a join with LINQ, and I'm wondering if there's a better way to accomplish it.

public async Task<IEnumerable<Prices>> GetTicketsPrices(db501Context _context,string Provider)
{
    int ProviderKey = 0;
    switch (Provider)
    {
        case "A":
           ProviderKey = 1;
            break;

        case "B":
            ProviderKey = 2;
            break;

        default:
            ProviderKey = 0;
            break;
    }


    var voucherPrices = await _context.VoucherPrices.Select(r => r).ToListAsync();
    var Providers = await _context.VoucherProviders.Select(p => p).ToListAsync();
    var voucherTypes = await _context.VoucherTypes.Select(t => t).ToListAsync();
    var passengerType = await _context.VouchersPassengerTypes.Select(pt => pt).ToListAsync();

    var newQueryObjectResult = from price in voucherPrices
                               join provider in Providers on price.Provider equals provider.Id
                               join type in voucherTypes on price.Type equals type.Id
                               join passenger in passengerType on price.PassengerType equals passenger.Id
                               where provider.Id == ProviderKey
                               select new Prices { Provider = provider.Name, PassengerType = passenger.Description,Type = type.Description,Price = price.Price};

    return newQueryObjectResult;
}

Currently, I'm getting data from the context four times. Each model's list result is assigned to a different variable.

Is this the best way of doing that? Can I use the context only one time in order to retrieve all the data besides using a stored procedure?

Answer 1

You could try something like this instead:

var prices = await (
    from price in _context.VoucherPrices
    where provider.Id == ProviderKey
    select new Prices
    {
        Provider = price.Provider.Name,
        PassengerType = price.PassengerType.Description,
        Type = price.Type.Description,
        Price = price.Price
    }
).ToListAsync();

This is just using the navigation properties instead of manual joins. You would just need to be careful that there were records tied to the foreign keys (or do null checks instead), like:

Provider = price.Provider != default ? price.Provider.Name : default,
PassengerType = price.PassengerType != default ? price.PassengerType.Description : default,
Type = price.Type != default ? price.Type.Description : default