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  • Vertical circular motion : time(x/y) versus velocity equation

    - by adeeti
    Hi, I wanted to simulate the following through animation : A ball starts with a certain velocity at the bottom most point of a vertical circular loop and keeps rolling in it until its velocity permits. For this, I wanted to find velocity/x/y vs. time equation. For e.g. if the ball had mass : 5Kg, radius of the circular loop = 10m, and initial velocity of the ball is 200 m/s, what will its velocity and (x,y) position be after 5 seconds? thanks.

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  • Best way to handle Many-to-Many relationships in PHP MySQL

    - by Jayrox
    I am looking for the best way to handle a database of many-to-many relationships in PHP and MySQL. Right now I have 2 tables: Users (id, user_name, first_name, last_name) Connections (id_1, id_2) In the User table id is auto incremented on add and user_name is unique, but can be changed. Unfortunately, I don't have control over the user_name and its ability to be changed, but I must account for it. The Connections table is obviously, user1 and user2's id. The connection table needs to account for these possible relations: user1 --> user2 (user 1 friends with user 2 but not user2 friends with user1) user2 --> user1 (user 2 friends with user 1 but not user1 friends with user2) user1 <--> user2 (user 1 and user 2 mutually friends) user1 <-!-> user2 (user 1 and user 2 not friends) That part is not the problem, The problem I am having with is keeping these relations unique when and if they change in batches. Possible solution 1: delete all of user 1's relations and readd them with the updated list. I think this might be too slow for my needs. Solution 2? Anyone else encounter this problem? How should I best handle this? update: distinguishing relationships: i handle relationships like this: user1, user2 user1, user3 user2, user1 in that example the following is true: user1 follows user2 and user3 user2 only follows user1 but doesn't follow user3 user3 doesn't follow either user1 or user2

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  • Managing inverse relationships without CoreData

    - by Nathaniel Martin
    This is a question for Objective-J/Cappuccino, but I added the cocoa tag since the frameworks are so similar. One of the downsides of Cappuccino is that CoreData hasn't been ported over yet, so you have to make all your model objects manually. In CoreData, your inverse relationships get managed automatically for you... if you add an object to a to-many relationship in another object, you can traverse the graph in both directions. Without CoreData, is there any clean way to setup those inverse relationships automatically? For a more concrete example, let's take the typical Department and Employees example. To use rails terminology, a Department object has-many Employees, and an Employee belongs-to a Department. So our Department model has an NSMutableSet (or CPMutableSet ) "employees" that contains a set of Employees, and our Employee model has a variable "department" that points back to the Department model that owns it. Is there an easy way to make it so that, when I add a new Employee model into the set, the inverse relationship (employee.department) automatically gets set? Or the reverse: If I set the department model of an employee, then it automatically gets added to that department's employee set? Right know I'm making an object, "ValidatedModel" that all my models subclass, which adds a few methods that setup the inverse relationships, using KVO. But I'm afraid that I'm doing a lot of pointless work, and that there's already an easier way to do this. Can someone put my concerns to rest?

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  • NHibernate with string primary key and relationships

    - by John_
    I've have just been stumped with this problem for an hour and I annoyingly found the problem eventually. THE CIRCUMSTANCES I have a table which users a string as a primary key, this table has various many to one and many to many relationships all off this primary key. When searching for multiple items from the table all relationships were brought back. However whenever I tried to get the object by the primary key (string) it was not bringing back any relationships, they were always set to 0. THE PARTIAL SOLUTION So I looked into my logs to see what the SQL was doing and that was returning the correct results. So I tried various things in all sorts of random ways and eventually worked out it was. The case of the string being passed into the get method was not EXACTLY the same case as it was in the database, so when it tried to match up the relationship items with the main entity it was finding nothing (Or at least NHIbernate wasn't because as I stated above the SQL was actually returning the correct results) THE REAL SOLUTION Has anyone else come across this? If so how do you tell NHibernate to ignore case when matching SQL results to the entity? It is silly because it worked perfectly well before now all of a sudden it has started to pay attention to the case of the string.

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  • Displaying User Relationships Module Blocks

    - by Bob Lerner
    I'm unable to display any of the User Relationships' auto-created blocks in any of my sidebars. I have tried enabling all modules and permissions I can think of, with no success. The block I'm most interested in is the block that would allow users to be invited to an existing relationship (e.g. Friend), but as I say this nor any of the other blocks display. Other Drupal blocks and custom blocks display just fine. The blocks do show up in the blocks listing, and I've tried different ways of configuring them. Any help, or even confirmation that someone has been able to do this with the latest stable versions of Drupal and the User Relationships module, would be appreciated. Thank you.

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  • Injecting relationships in DBIx::Class

    - by Carl
    I have a handful of DBIx::Class::Core objects that model various database tables. For some of those models (those that have a 'queue' column), I have another class inject subs (basically, to 'move' the model object along it's queue states). I'd like to also have that class inject has_many relationships ala class($name)->has_many('queue_history','MySchema::Result::QueueHistory', { 'foreign.record_id'=>'self.id' }, { where => { type => $name }} ); but I can't seem to get the relationships to register properly (keep getting "No Such Relationship" errors - however, when calling the relationship method on the sources provides back the relationship). Any clues as to what's wrong?

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  • How to return relationships in a custom un-typed dataservice provider

    - by monkey_p
    I have a custom .Net DataService and can't figure out how to return the data for relationships. The data base has 2 tables (Customer, Address). A Customer can have multiple addresses, but each address can only have on customer. I'm using Dictionary<string,object> as my data type. My question, for the following 2 urls how do i return the data. http://localhost/DataService/Customer(1)/Address http://localhost/DataService/Address(1)/Customer For the none relational queries I return a List<Dictionary<string,object>> So I imagined for the relation I should just populate the element with a either a Dictionary<string,object> for the single ones and a List<Dictionary<string,object>> for many relationships. But this just gives me a NullRefferenceException So what am I doing wrong?

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  • Intellij UML diagram does not show one to many relationships

    - by Calm Storm
    I am trying to follow http://www.jetbrains.com/idea/features/uml_class_diagram.html I have a few classes so when I do Ctrl + Alt + U I only see all classes and just Extends relationships. Please note that I have set the "Diagrams" options in my settings to show one to many etc. I do not see One to One, One to Many relationships at all ? I have used JPA OneToOne Annotations and they dont turn up at all? Pressing Ctrl Shift F12 does not do anything? Can someone please explain?

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  • Python: circular imports needed for type checking

    - by phild
    First of all: I do know that there are already many questions and answers to the topic of the circular imports. The answer is more or less: "Design your Module/Class structure properly and you will not need circular imports". That is true. I tried very hard to make a proper design for my current project, I in my opinion I was successful with this. But my specific problem is the following: I need a type check in a module that is already imported by the module containing the class to check against. But this throws an import error. Like so: foo.py: from bar import Bar class Foo(object): def __init__(self): self.__bar = Bar(self) bar.py: from foo import Foo class Bar(object): def __init__(self, arg_instance_of_foo): if not isinstance(arg_instance_of_foo, Foo): raise TypeError() Solution 1: If I modified it to check the type by a string comparison, it will work. But I dont really like this solution (string comparsion is rather expensive for a simple type check, and could get a problem when it comes to refactoring). bar_modified.py: from foo import Foo class Bar(object): def __init__(self, arg_instance_of_foo): if not arg_instance_of_foo.__class__.__name__ == "Foo": raise TypeError() Solution 2: I could also pack the two classes into one module. But my project has lots of different classes like the "Bar" example, and I want to seperate them into different module files. After my own 2 solutions are no option for me: Has anyone a nicer solution for this problem?

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  • Should I worry about circular references in Python?

    - by bodacydo
    Suppose I have code that maintains parent/children structure. In such a structure I get circular references, where child points to parent and parent points to child. Should I worry about them? I'm using Python 2.5. I am concerned that they will not be garbage collected and the application will eventually consume all memory. Thanks, Boda Cydo.

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  • JCarousel wrap set to 'circular' bug

    - by Scott
    I'm trying to set up a JCarousel instance witht the wrap set to circular, however, I noticed an issue where I "inspect element" in Chrome, duplicate elements are added to the html when the slides repeat (it can be viewed on the official example page). http://sorgalla.com/projects/jcarousel/examples/static_circular.html I know this is an open bug on GitHub. I'm just wondering if anyone has found a temporary workaround. Thanks in advance, - Scott

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  • Why do i get a circular reference exception when calling to_json on an ActiveRecord::Relation

    - by midas06
    In Rails 3 (beta 3 on 1.8.7), when calling to_json on a relation i get a circular reference exception. Converting that relation to an array first, and THEN calling to_json works. Code That fails: Model.where().to_json (Where model is any model in your Rails 3 app) Code that works: Model.where().to_a.to_json This can be reproed on the console. Has anyone else run in to this? Is this expected?

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  • circular shift c

    - by simion
    I am doing some past papers and noticed a question where i have to shift the int one place to the right and return it i no in java i can just return n 1; is this possible in c? or is there a typically more compelx way of doing it :D. The method we were given is as follows // Return n after a right circular 1-bit shift unsigned int right_circular_shift_1(unsigned int n) {

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  • mysql circular dependency in foreign key constraints

    - by Flavius
    Given the schema: What I need is having every user_identities.belongs_to reference an users.id. At the same time, every users has a primary_identity as shown in the picture. However when I try to add this reference with ON DELETE NO ACTION ON UPDATE NO ACTION, MySQL says #1452 - Cannot add or update a child row: a foreign key constraint fails (yap.#sql-a3b_1bf, CONSTRAINT #sql-a3b_1bf_ibfk_1 FOREIGN KEY (belongs_to) REFERENCES users (id) ON DELETE NO ACTION ON UPDATE NO ACTION) I suspect this is due to the circular dependency, but how could I solve it (and maintain referential integrity)?

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  • Circular shift operations in C++

    - by Elroy
    Left and right shift operators (<< and ) are already available in C++. However, I couldn't find out how I could perform circular shift or rotate operations. How can operations like "Rotate Left" and "Rotate Right" be performed? Rotating right twice here Initial --> 1000 0011 0100 0010 should result in: Final --> 1010 0000 1101 0000 An example would be helpful.

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  • Circular increment: Which is "better"?

    - by Helper Method
    When you have a circular buffer represented as an array, and you need the index to wraparound (i.e., when you reach the highest possible index and increment it), is it "better" to: return (i++ == buffer.length) ? 0: i; Or return i++ % buffer.length; Has using the modulo operator any drawbacks? Is it less readable than the first solution?

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  • How to avoid circular reference when excel cell update

    - by Nimo
    Hi, I'm writing a set of functions in c++ which can be called by excel. However, these functions are asynchronous, therefore no immediate return values available. Once a result is available I used a callback function through VBA which update the result to the relevant cell which called the functions. But, here I'm having circular function calling problem, because when I update the cell. excel automatically call the original function once again. Please help me to get around this problem Thank You

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  • Trouble with Rails has_many relationships

    - by Tchock
    I'm writing an app where a user can both create their own pages for people to post on, and follow posts on pages that users have created. Here is what my model relationships look like at the moment... class User < ActiveRecord::Base has_many :pages has_many :posts has_many :followings has_many :pages, :through => :followings, :source => :user class Page < ActiveRecord::Base has_many :posts belongs_to :user has_many :followings has_many :users, :through => :followings class Following < ActiveRecord::Base belongs_to :user belongs_to :page class Post < ActiveRecord::Base belongs_to :page belongs_to :user The trouble happens when I try to work my way down through the relationships in order to create a homepage of pages (and corresponding posts) a given user is following (similar to the way Twitter's user homepage works when you login - a page that provides you a consolidated view of all the latest posts from the pages you are following)... I get a "method not found" error when I try to call followings.pages. Ideally, I'd like to be able to call User.pages in a way that gets me the pages a user is following, rather than the pages they have created. I'm a programming and Rails newb, so any help would be much appreciated! I tried to search through as much of this site as possible before posting this question (along with numerous Google searches), but nothing seemed as specific as my problem...

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  • SQL Server 2005 database design - many-to-many relationships with hierarchy

    - by Remnant
    Note I have completely re-written my original post to better explain the issue I am trying to understand. I have tried to generalise the problem as much as possible. Also, my thanks to the original people who responded. Hopefully this post makes things a little clearer. Context In short, I am struggling to understand the best way to design a small scale database to handle (what I perceive to be) multiple many-to-many relationships. Imagine the following scenario for a company organisational structure: Textile Division Marketing Division | | ---------------------- ---------------------- | | | | HR Dept Finance Dept HR Dept Finance Dept | | | | ---------- ---------- ---------- --------- | | | | | | | | Payroll Hiring Audit Tax Payroll Hiring Audit Accounts | | | | | | | | Emps Emps Emps Emps Emps Emps Emps Emps NB: Emps denotes a list of employess that work in that area When I first started with this issue I made four separate tables: Divisions - Textile, Marketing (PK = DivisionID) Departments - HR, Finance (PK = DeptID) Functions - Payroll, Hiring, Audit, Tax, Accounts (PK = FunctionID) Employees - List of all Employees (PK = EmployeeID) The problem as I see it is that there are multiple many-to-many relationships i.e. many departments have many divisions and many functions have many departments. Question Giving the database structure above, suppose I wanted to do the following: Get all employees who work in the Payroll function of the Marketing Division To do this I need to be able to differentiate between the two Payroll departments but I am not sure how this can be done? I understand that I could build a 'Link / Junction' table between Departments and Functions so that I can retrieve which Functions are in which Departments. However, I would still need to differentiate the Division they belong to. Research Effort As you can see I am an abecedarian when it comes to database deisgn. I have spent the last two days resaerching this issue, traversing nested set models, adjacency models, reading that this issue is known not to be NP complete etc. I am sure there is a simple solution?

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  • Understanding many to many relationships and Entity Framework

    - by Anders Svensson
    I'm trying to understand the Entity Framework, and I have a table "Users" and a table "Pages". These are related in a many-to-many relationship with a junction table "UserPages". First of all I'd like to know if I'm designing this relationship correctly using many-to-many: One user can visit multiple pages, and each page can be visited by multiple users..., so am I right in using many2many? Secondly, and more importantly, as I have understood m2m relationships, the User and Page tables should not repeat information. I.e. there should be only one record for each user and each page. But then in the entity framework, how am I able to add new visits to the same page for the same user? That is, I was thinking I could simply use the Count() method on the IEnumerable returned by a LINQ query to get the number of times a user has visited a certain page. But I see no way of doing that. In Linq to Sql I could access the junction table and add records there to reflect added visits to a certain page by a certain user, as many times as necessary. But in the EF I can't access the junction table. I can only go from User to a Pages collection and vice versa. I'm sure I'm misunderstanding relationships or something, but I just can't figure out how to model this. I could always have a Count column in the Page table, but as far as I have understood you're not supposed to design database tables like that, those values should be collected by queries... Please help me understand what I'm doing wrong...

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  • Still Confused About Identifying vs. Non-Identifying Relationships

    - by Jason
    So, I've been reading up on identifying vs. non-identifying relationships in my database design, and a number of the answers on SO seem contradicting to me. Here are the two questions I am looking at: What's the Difference Between Identifying and Non-Identifying Relationships Trouble Deciding on Identifying or Non-Identifying Relationship Looking at the top answers from each question, I appear to get two different ideas of what an identifying relationship is. The first question's response says that an identifying relationship "describes a situation in which the existence of a row in the child table depends on a row in the parent table." An example of this that is given is, "An author can write many books (1-to-n relationship), but a book cannot exist without an author." That makes sense to me. However, when I read the response to question two, I get confused as it says, "if a child identifies its parent, it is an identifying relationship." The answer then goes on to give examples such as SSN (is identifying of a Person), but an address is not (because many people can live at an address). To me, this sounds more like a case of the decision between primary key and non-primary key. My own gut feeling (and additional research on other sites) points to the first question and its response being correct. However, I wanted to verify before I continued forward as I don't want to learn something wrong as I am working to understand database design. Thanks in advance.

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