我有一个 NHibernate 的 linq 查询。
var q = SessionInstance.Query<Identity>()
.Count(x => MyPerson != null && x.Person.Id == MyPerson.Id);
但检查条件Count
无效。因为如果值为MyPerson
null ,count 的预期结果是,0
但是这个查询有一个NullReferenceException
By this 消息:
Object reference not set to an instance of an object.
为什么?
堆栈跟踪是:
at lambda_method(Closure )
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitors.PartialEvaluatingExpressionTreeVisitor.EvaluateSubtree(Expression subtree)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitors.PartialEvaluatingExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitBinaryExpression(BinaryExpression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitors.PartialEvaluatingExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitBinaryExpression(BinaryExpression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitors.PartialEvaluatingExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitLambdaExpression(LambdaExpression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitors.PartialEvaluatingExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitUnaryExpression(UnaryExpression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitors.PartialEvaluatingExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitAndConvert[T](T expression, String methodName)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.<>c__DisplayClass6`1.<VisitAndConvert>b__5(T expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitList[T](ReadOnlyCollection`1 list, Func`2 visitMethod)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitAndConvert[T](ReadOnlyCollection`1 expressions, String callerName)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitMethodCallExpression(MethodCallExpression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitors.PartialEvaluatingExpressionTreeVisitor.VisitExpression(Expression expression)
at Remotion.Data.Linq.Parsing.ExpressionTreeVisitors.PartialEvaluatingExpressionTreeVisitor.EvaluateIndependentSubtrees(Expression expressionTree)
at NHibernate.Linq.NhLinqExpression..ctor(Expression expression)
at NHibernate.Linq.NhQueryProvider.PrepareQuery(Expression expression, IQuery& query, NhLinqExpression& nhQuery)
at NHibernate.Linq.NhQueryProvider.Execute(Expression expression)
at NHibernate.Linq.NhQueryProvider.Execute[TResult](Expression expression)
at System.Linq.Queryable.Count[TSource](IQueryable`1 source, Expression`1 predicate)
at RCISP.NHibernate.Repository.IdentityRepositoryNh.IsExistOriginalIdentityForThisAlias(Identity item)
at RCISP.Domain.Services.IdentityService.CreateIdentity(IRepositoryLocator locator, Person person)
at RCISP.Domain.Services.IdentityService.LoadByPersonIdentificationCode(IRepositoryLocator locator, String identificationCode, Nullable`1 autoCreate)
at RCISP.Domain.Services.EvidenceRequestService.Update[T](IRepositoryLocator locator, EvidenceRequestDto dto)
at RCISP.Domain.Services.EvidenceRequestService.UpdateEntityCommand[T,TR](IRepositoryLocator locator, EvidenceRequestDto dto)
at RCISP.Domain.Services.WeaponLicenseRequestService.<>c__DisplayClass4.<UpdateEntity>b__3(IRepositoryLocator locator)
at RCISP.NHibernate.TransManager.TransManagerNh.ExecuteCommand[TResult](Func`2 command)