self-reference

问题 This question already has answers here : What do ellipsis […] mean in a list? (6 answers) Closed 4 years ago . Suppose I ran the program x=[] x.append(x) print(x) I get [[...]] as the output. But what does it mean? Is the list storing pointers and then pointing to itself? Or is it copying itself never quite completely? How is this list stored in memory? Amendment: I'm trying to get my head around how python accomplishes this self reference. If I wanted to design a way of storing lists that

问题 I am creating a linked list with self referential class in C++ and I want to have a static pointer of the type Item (Item is the class name) named "startPointer" so that when i call my static member function "free" , it can free up the memory by using Item::startPointer but i am getting an error(shown after code). Pls Help, class Item { public: std::string name; int row,column; int fileType; Item *ptr; static Item *startPointer; void setNextPointer(Item* ptr) { ptr=ptr; } Item *getNextPointer

问题 Every so often I am making a simple interface more complicated by adding a self-referencing ("reflexive") type parameter constraint to it. For example, I might turn this: interface ICloneable { ICloneable Clone(); } class Sheep : ICloneable { ICloneable Clone() { … } } //^^^^^^^^^^ Sheep dolly = new Sheep().Clone() as Sheep; //^^^^^^^^ into: interface ICloneable<TImpl> where TImpl : ICloneable<TImpl> { TImpl Clone(); } class Sheep : ICloneable<Sheep> { Sheep Clone() { … } } //^^^^^ Sheep

问题 This isn't a difficult question, but I can't wrap my head around it when dealing with MVC architecture (passing arguments between the VIEW, MODEL, and CONTROLLER). Error in question: Exception in Tkinter callback Traceback (most recent call last): File "C:\Python33\lib\tkinter__init__.py", line 1482, in call return self.func(*args) File "C:\Users\Mike\Desktop\code\Assignment 6\glue.py", line 37, in buttonPressed self.model.convertTempF2C(view.fahrenheitEntrySpace.get) NameError: global name

问题 I'm having real trouble pulling out a set of records that are self-referentially related to a user in order to show these on a user's 'show' page. Here's the idea: Users ( current_user ) rate the compatibility between two other users ( user_a and user_b ). They can rate compatibility either positively or negatively: rating two users "compatible" creates a positive_connection between user_a and user_b, and rating them "incompatible" creates a negative_connection . So there are models for

问题 I have a self-referencing table 'comments' where comments.replyToId REFERENCES comments.ID. My question is, how do I query a database with a self-referencing table to get a result that is properly ordered so that I can represent the result as a tree in PHP? I've tried select * from comments as comments_1 left join comments as comments_2 on comments_1.id = comments_2.replyToId I'm trying to use the result of this in php 回答1: You're not going to get a recursive result out of MySQL directly.

问题 Disclaimer: I'm finding it hard to summarise the problem in the title of the question, so if you have better suggestions, please let me know in the comments. Let's take the following simplified TypeScript class: class Model { save():Model { // save the current instance and return it } } The Model class has a save() method that returns an instance of itself: a Model . We can extend Model like so: class SomeModel extends Model { // inherits the save() method } So, SomeModel will inherit save()

问题 i need to query a self referencing relationship for unit prerequisites. i know that you need to use two Joins, do i SELECT my column and then join it to itself ? SELECT u.unit_code, u.name + ' is a prerequisite of ' + u.name AS unit_prerequisite FROM units AS u so far that is what i have, not sure where my joins have to be made? not even sure if that first part is correct. 回答1: You do this by joining the table to itself on the self-referencing column: SELECT u.unit_code, u1.name + ' is a

问题 I want to implement versioning on my entity Stuff . Each entity has an optional reference to the next version (the latest version will be null) and an optional reference to the previous version (the first version will be null). I am using entity framework 6, code first. I tried with the following model and modelbuilder statement (and many variations). public class Stuff { public int StuffId { get; set; } [ForeignKey("NextVersion")] public int? NextVersionId { get; set; } [InverseProperty(

问题 I use angular-bootstrap-nav-tree I have Array that i get from self-reference table Like this: var obj = [ {id:1,label:"Animal"}, {id:2,label:"Vigitable"}, {id:3,label:"Cats",parent:1}, {id:4,label:"black cat",parent:3}, {id:5,label:"orange",parent:2}, ]; I want to convert it to be nested like this: var convrted = [ {id:1,label:"Animal",children[ {id:3,label:"Cats",parent:1,children[{id:4,label:"black cat",parent:3}]} ]}, {id:2,label:"Vigitable",children[ {id:5,label:"orange",parent:2} ]} ]; I