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问题 I use Hibernate to access to a legacy DB. For some tables the parent-child reference integrity is not enforced, and the long 0 value is used instead of NULL for some "parent" columns in child tables to denote "no parent". I still want to use these relations in @ManyToOne and @OneToMany fields, but get EntityNotFound error since the 0 value does not correspond to any record in master table. What are my options? 回答1: Use the NotFound annotation: @NotFound(action = NotFoundAction.IGNORE) See

问题 I read many posts on forum about pointers, Assigned function, Free function, FreeAndNil function, etc... I already know Free function don't remove the pointer reference to an object assigned and FreeAndNil does it... All posts I read treat this subject considering Create method already was executed, or in other words, considering an object already created. My question is: Why Assigned function returns true for a uninitialized object variable ? Follow an example: procedure TForm1.FormCreate

问题 recordsList.ListOfRecords = new StudentRecordsBAL() .GetStudentsList() .Select(q => new StudentRecords() { _RollNumber = q._RollNumber, _Class = q._Class, _Name = q._Name, _Address = q._Address, _City = q._City, _State = q._State, _Subjects = q._Subject, _AttendedDays = new AttendanceBAL() .GetAttendanceListOf(q._RollNumber) .Where(date => date != null) .Select(date => new DateTime(date._Date.Year, date._Date.Month, date._Date.Day)) .Distinct() .ToList(), _AttendedSubjects =

问题 This question already has answers here : C++ standard: dereferencing NULL pointer to get a reference? [duplicate] (5 answers) Why dereferencing a null pointer is undefined behaviour? (12 answers) Closed 6 years ago . #include <iostream> int main() { int* i = 0; int x = (*i); std::cout << x; } The above program will crash when I compile and run it using Visual Studio 2010 and I know it crashes because I set the pointer to 0. What I would like to know, is accessing a null pointer in C++ defined

问题 accidentally at work I wrote the following line of code: string x = (object) null; // It was var x = (object)null and I changed from var to string instead of // object x = null; This gave me a compilation error similar to this: Can't cast source type object to target type string Why? Isn't null just a bunch of zeros pointing to "nowhere" memory address, no matter what the type is? 回答1: The question here is basically "why does the compiler not take into account the fact that it knows that the

问题 accidentally at work I wrote the following line of code: string x = (object) null; // It was var x = (object)null and I changed from var to string instead of // object x = null; This gave me a compilation error similar to this: Can't cast source type object to target type string Why? Isn't null just a bunch of zeros pointing to "nowhere" memory address, no matter what the type is? 回答1: The question here is basically "why does the compiler not take into account the fact that it knows that the

问题 I want to return a reference of an object from a vector, and the object is in an iterator object. How can I do that? I tried the following: Customer& CustomerDB::getCustomerById (const string& id) { vector<Customer>::iterator i; for (i = customerList.begin(); i != customerList.end() && !(i->getId() == id); ++i); if (i != customerList.end()) return *i; // is this correct? else return 0; // getting error here, cant return 0 as reference they say } In the code, customerList is a vector of

问题 I'm starting with this code: String startingValue = getMyValue(); String finishingValue = ""; if (startingValue != null) { finishingValue = startingValue; } else { System.out.println("Value was null"); } I want to transform it using Java 8 options to something like this: Optional<String> startingOptional = getMyOptional(); String finishingValue = startingOptional .map(value -> value) .orElse(System.out.println("value not found")); My question is: Is there a way to combine Java8 Optional

问题 This question already has answers here : Why cannot convert null to type parameter T in c#? (3 answers) Closed last month . A similar question, but without casting the T parameter. This does not work public T GetValueG<T>(string Query) { object value = DBNull.Value; // Read from Database which can return DBNull if (value is DBNull) return (T)null; else return (T)value; } Error CS0037 Cannot convert null to 'T' because it is a non-nullable value type But this works public T GetValueG<T>(string

问题 I am using flask_restplus to create a documented API. The marshal decorator controls what data actually gets rendered in your response, but I am having trouble rendering the data. I have the following code: kpis_model = api.model('kpis', { 'cpl_actual': fields.Integer(description='costo por lead total del mes actual'), 'cpl_anterior': fields.Integer(description='costo por lead total del mes anterior'), 'cpl_diferencia': fields.Integer(description='diferencia de cpl_actual y cpl_anterior') })