Мултисортинг на IQueryable използвайки име на колона за низ в рамките на общ разширителен метод? - c #, рамка на предприятието, linq, отражение

Трябва да сортирам събирането с няколко колони. Имам списък от обекти, където всеки обект съдържа колонаName и sortDir (Asc или Desc). И така, как мога да го направя? Опитах се да го направя чрез размисъл, но аз имам грешката:

Message: `LINQ to Entities does not recognize the method "Int32 Parse(System.String)" method, and this method cannot be translated into a store expression.`
StackTrace: `   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.DefaultTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.EqualsTranslator.TypedTranslate(ExpressionConverter parent, BinaryExpression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input, DbExpressionBinding& binding)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.Convert()
at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__6()
at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__5()
at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()
at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
at System.Linq.SystemCore_EnumerableDebugView`1.get_Items()`

Четох някои статии това и това, но техните решения не ми помагат. Може би някой има някакви идеи за мен?

Код:

public static IQueryable<T> SortByParams<T>(IQueryable<T> collection, List<SortBy> sorting)
{
bool firstOrder = true;
IOrderedQueryable<T> sortedRes = null;
foreach (SortBy sort in sorting)
{
try
{
if (firstOrder)
{
if (sort.sortDir.ToLower() == "desc")
{
sortedRes = collection.OrderByDescending(obj => obj.GetType().GetProperty(sort.columnName).GetValue(obj, null));
}
else
{
sortedRes = collection.OrderBy(obj => obj.GetType().GetProperty(sort.columnName).GetValue(obj, null));
}
firstOrder = false;
}
else
{
if (sort.sortDir.ToLower() == "desc")
{
sortedRes = sortedRes.ThenByDescending(obj => obj.GetType().GetProperty(sort.columnName).GetValue(obj, null));
}
else
{
sortedRes = sortedRes.ThenBy(obj => obj.GetType().GetProperty(sort.columnName).GetValue(obj, null));
}
}
}
catch (Exception) { }
collection = sortedRes;
}
return collection;
}

Отговори:

Изрази като това

obj => obj.GetType().GetProperty(sort.columnName).GetValue(obj, null)

може да бъде приложим в LINQ To Objects контекст, но определено не е в LINQ към Entities.

Като цяло не можете да използвате размисъл (и многодруги методи) в израза на LINQ към Entities, защото те не могат да бъдат преведени на SQL (или доставчикът на заявки не разпознава и обработва тях, следователно NotSupportedException).

Вместо да отразявате, трябва да изградите израза, като използвате System.Linq.Expressions.

Така например:

public static IQueryable<T> SortByParams<T>(this IQueryable<T> source, List<SortBy> sorting)
{
var queryExpr = source.Expression;
string methodAsc = "OrderBy";
string methodDesc = "OrderByDescending";
foreach (var item in sorting)
{
var selectorParam = Expression.Parameter(typeof(T), "e");
var selector = Expression.Lambda(Expression.PropertyOrField(selectorParam, item.columnName), selectorParam);
var method = string.Equals(item.sortDir, "desc", StringComparison.OrdinalIgnoreCase) ? methodDesc : methodAsc;
queryExpr = Expression.Call(typeof(Queryable), method,
new Type[] { selectorParam.Type, selector.Body.Type },
queryExpr, Expression.Quote(selector));
methodAsc = "ThenBy";
methodDesc = "ThenByDescending";
}
return source.Provider.CreateQuery<T>(queryExpr);
}