不支持NHibernate指定的方法

Question

我使用S＃arpLite開發了webapp來構建查詢以從許多表中獲取列表。 使用NHibernate版本3.3.1.4000

我在運行時收到來自應用的錯誤消息，例如

`NHibernate System.NotSupportedException Specified method is not supported. {Name = "PolymorphicQuerySourceDetector" FullName = "NHibernate.Hql.Ast.ANTLR.PolymorphicQuerySourceDetector"}

   at NHibernate.Hql.Ast.ANTLR.PolymorphicQuerySourceDetector.GetClassName(IASTNode querySource)
   at NHibernate.Hql.Ast.ANTLR.PolymorphicQuerySourceDetector.Process(IASTNode tree)
   at NHibernate.Hql.Ast.ANTLR.AstPolymorphicProcessor.Process()
   at NHibernate.Hql.Ast.ANTLR.AstPolymorphicProcessor.Process(IASTNode ast, ISessionFactoryImplementor factory)
   at NHibernate.Hql.Ast.ANTLR.ASTQueryTranslatorFactory.CreateQueryTranslators(IASTNode ast, String queryIdentifier, String collectionRole, Boolean shallow, IDictionary`2 filters, ISessionFactoryImplementor factory)
   at NHibernate.Hql.Ast.ANTLR.ASTQueryTranslatorFactory.CreateQueryTranslators(String queryIdentifier, IQueryExpression queryExpression, String collectionRole, Boolean shallow, IDictionary`2 filters, ISessionFactoryImplementor factory)
   at NHibernate.Engine.Query.HQLExpressionQueryPlan.CreateTranslators(String expressionStr, IQueryExpression queryExpression, String collectionRole, Boolean shallow, IDictionary`2 enabledFilters, ISessionFactoryImplementor factory)
   at NHibernate.Engine.Query.HQLExpressionQueryPlan..ctor(String expressionStr, IQueryExpression queryExpression, String collectionRole, Boolean shallow, IDictionary`2 enabledFilters, ISessionFactoryImplementor factory)
   at NHibernate.Engine.Query.HQLExpressionQueryPlan..ctor(String expressionStr, IQueryExpression queryExpression, Boolean shallow, IDictionary`2 enabledFilters, ISessionFactoryImplementor factory)
   at NHibernate.Engine.Query.QueryPlanCache.GetHQLQueryPlan(IQueryExpression queryExpression, Boolean shallow, IDictionary`2 enabledFilters)
   at NHibernate.Impl.AbstractSessionImpl.GetHQLQueryPlan(IQueryExpression queryExpression, Boolean shallow)
   at NHibernate.Impl.AbstractSessionImpl.CreateQuery(IQueryExpression queryExpression)
   at NHibernate.Linq.DefaultQueryProvider.PrepareQuery(Expression expression, IQuery& query, NhLinqExpression& nhQuery)
   at NHibernate.Linq.DefaultQueryProvider.Execute(Expression expression)
   at NHibernate.Linq.DefaultQueryProvider.Execute[TResult](Expression expression)
   at Remotion.Linq.QueryableBase`1.GetEnumerator()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at EzLife.Tasks.EmployeeCudTasks.GetEmployees(List`1 listSkill, List`1 listDepartment, List`1 listAssignment, String searchTerm, String jobtitle, String tier, String competency, Nullable`1 startDate, Nullable`1 endDate, Int32 effort, Nullable`1 active, Int32 currentPage, Int32 pageSize, Int32 sortId, Int32 sortName, Int32 sortTitle, Int32 sortTier, Int32 sortJoinedDate, Int32 sortDepartment) in d:\Projects\EzLife\_source\Ezlife\app\EzLife.Tasks\EmployeeCudTasks.cs:line 206`

這是我的代碼

`public static IQueryable GetEmployeesQ(this IQueryable employees, IQueryable employeeTitles, int currentPage,int pageSize)
        {
           var query = from employee in employees
                        join employeeTitle in employeeTitles
                        on employee.Id equals employeeTitle.Employee.Id
                        select new EmployeeDto()
                        {
                            Id = employee.Id,
                            CustomCode = employee.CustomCode,
                            FirstName = employee.FirstName,
                            LastName = employee.LastName,
                            MiddleName = employee.MiddleName,
                            FullName = string.Empty,
                            JoinedDate = employee.JoinedDate,
                        };
            return query;
        }


public static IQueryable GetEmployeeTitlesQ(this IQueryable employeeTitles)
        {
            return from et1 in employeeTitles
                   join et2 in
                       (
                           from et in employeeTitles
                           orderby et.Employee.Id, et.StartDate
                           group et by et.Employee.Id into etmax
                           select new { Id = etmax.Max(et => et.Id) }
                           ) on et1.Id equals et2.Id
                   select et1;
}`



I call GetEmployeeTitlesQ in GetEmployeesQ as :

'
public IList GetEmployees(int currentPage = 1, int pageSize = 20)
        {

        IList<EmployeeDto> employees = new List<EmployeeDto>();

        IQueryable<EmployeeTitle> employeeTitles = employeeTitleRep.GetAll().GetEmployeeTitlesQ();

        IQueryable<EmployeeDto> employeeDto = employeeRep.GetAll().GetEmployeesQ(
            employeeTitles
            , jobTitles
            , currentPage
            , pageSize);

        try
        {
            employees = employeeDto.ToList();
        }
        catch (Exception ex) {
            var mess = ex.Message.ToString();
        }

        return employees;
    }

'我想Max（）函數有問題，但我不為什么。 有什么辦法可以解決它？

Answer 1

NHibernate無法將每個LINQ查詢轉換為SQL。 對我來說，只需重新排列where和join語句的順序就足夠了。

Answer 2

我建議您對代碼進行以下更改，這有助於我克服同樣的異常：

public static IQueryable GetEmployeeTitlesQ(this IQueryable employeeTitles)
{
    var employeeTitlesEnumerable = employeeTitles.ToArray();
    return from et1 in employeeTitlesEnumerable 
           join et2 in (
               from et in employeeTitlesEnumerable 
               orderby et.Employee.Id, et.StartDate
               group et by et.Employee.Id into etmax
               select new { Id = etmax.Max(et => et.Id) }
           ) on et1.Id equals et2.Id
           select et1;
}

我在可查詢對象上添加了對.ToArray()的調用。 我對FluentNHibernate的經驗是，有時返回的IQueryable試圖將整個LINQ表達式轉換為SQL。 當查詢涉及無法用SQL表示的對象時，將拋出您看到的錯誤。 因此，我的猜測很簡單，那就是Max調用沒有被NHibernate正確翻譯。

使用.ToArray() （或者如果您更喜歡.ToList() ），將NHibernate可查詢的對象轉換為IEnumerable的實例，然后由.NET框架完全處理該實例。 這意味着應用於IEnumerable LINQ表達式將不再轉換為SQL。

上面的副作用是，您將無法對數據庫執行整個選擇作為SQL查詢。

最重要的是（至少對我來說），您應該仔細地對NHibernate層中所有與數據庫相關的操作進行排序，並且在完成查詢后，將其轉換為可枚舉，以防止業務邏輯調用潛在的進一步LINQ操作干擾該操作。 IQueryable的內部細節。