OrderBy列出LINQ查询

Question

My Model contains List of Offers . offers having SpecialOffers value true should be orderd by RGU and OfferPriority . The offers having SpecialOffers value false should be ordered by InitialPrice (descending) only.

I tried the following query, it achieves the first part ie ordered by RGU and OfferPriority but this is applied on the non SpecialOffers too. What should be the query to achieve these two tasks?

List<OfferModel> providerOffers = Model.Offers
    .Where(x => x.Provider.ProviderCode.Equals(provider))
    .OrderByDescending(o => o.SpecialOffer)
    .ThenByDescending(t => t.RGU)
    .ThenBy(p => p.OfferPriority)
    .Select(x => x)
    .ToList();

EDIT SpecialOffer is a boolean property attached to each offer that determines whether an offer is Special or not

Answer 1

You should first group by this property to get two groups which you can order separately:

var offers = Model.Offers.Where(o => o.Provider.ProviderCode.Equals(provider));
var offerGroups = offers.GroupBy(o => o.SpecialOffer);
var specialGroup = offerGroups.Where(g => g.Key == true)
    .SelectMany(g => g)
    .OrderByDescending(o => o.InitialPrice);
var nonSpecialGroup = offerGroups.Where(g => g.Key == false)
    .SelectMany(g => g)
    .OrderByDescending(t => t.RGU)
    .ThenBy(p => p.OfferPriority);
var result = specialGroup.Concat(nonSpecialGroup).ToList(); 

Due to LINQ's deferred execution these queries will be executed as a single sql query.

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Disclaimer: i'm not sure if the generated sql will keep the order of the groups, normally you have to apply the ORDER BY on the outer query which is the final CONCAT , it's translated to a UNION ALL . Then the easiest would be to use Linq-To-Objects with AsEnumerable :

var result = specialGroup.AsEnumerable().Concat(nonSpecialGroup.AsEnumerable()).ToList(); 

Answer 2

You have to split your lists based on their type, you can´t order two different lists with the same statement:

var result1 = model.Offers.Where(x => x.SpecialOffer).OrderBy(x => x.InitialPrice);
var result2 = model.Offers.Except(result1).OrderBy(...);

If not all elements within your list that are not a SpecialOffer should be sorted by ProviderCode , RGU and OfferPriority you can use this for the second list:

var result2 = mode.Offers.Where(x => !x.SpecialOffer)
    .Where(x => x.Provider.ProviderCode.Equals(provider))
    .OrderByByDescending(t => t.RGU)
    .ThenBy(p => p.OfferPriority);