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  • Is the set of data always normalized in one form or the other in Databases

    - by manugupt1
    Suppose I have a set of data, given the data and the relation schemas can I assume that the set of data is normalized in one form or the other. In my opinion raw data given, has to be normalized into some form. However a discussion with a friend has led to ask me this question here. To expound more on the question, I would say given a set of functional dependencies for a relation or table, is it guaranteed that the table would atleast be in 1NF if not others

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  • Solid Principle examples anywhere?

    - by user231465
    We all write code with some patterns even when we dont realise it. I am trying to really understand some of the solid principles and how you apply this principles in the real world. I am struggling with the "D" my understanding on Dependency Inversion I sometimes confuse with Dependency Injection is that as long as you keep things depending on abstraction (IE:interfaces) you are done. Has anybody got a small c# sample that explains it? thanks

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  • How can I make a family of singletons?

    - by Jay
    I want to create a set of classes that share a lot of common behavior. Of course in OOP when you think that you automatically think "abstract class with subclasses". But among the things I want these classes to do is to each have a static list of instances of the class. The list should function as sort of a singleton within the class. I mean each of the sub-classes has a singleton, not that they share one. "Singleton" to that subclass, not a true singleton. But if it's a static, how can I inherit it? Of course code like this won't work: public abstract A { static List<A> myList; public static List getList() { if (myList==null) myList=new ArrayList<A>(10); return myList; } public static A getSomethingFromList() { List listInstance=getList(); ... do stuff with list ... } public int getSomethingFromA() { ... regular code acting against current instance ... } } public class A1 extends A { ... } public class A2 extends A { ... } A1 somethingfromA1List=(A1) A1.getSomethingFromList(); A2 somethingfromA2List=(A2) A2.getSomethingFromList(); The contents of the list for each subclass would be different, but all the code to work on the lists would be the same. The problem with the above code is that I'd only have one list for all the subclasses, and I want one for each. Yes, I could replicate the code to declare the static list in each of the subclasses, but then I'd also have to replicate all the code that adds to the lists and searches the list, etc, which rather defeats the purpose of subclassing. Any ideas on how to do this without replicating code?

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  • How can I handle dynamic calculated attributes in a model in Django?

    - by bullfish
    In Django I calculate the breadcrumb (a list of fathers) for an geographical object. Since it is not going to change very often, I am thinking of pre calculating it once the object is saved or initialized. 1.) What would be better? Which solution would have a better performance? To calculate it at _init_ or to calculate it when the object is saved (the object takes about 500-2000 characters in the DB)? 2.) I tried to overwrite the _init_ or save() methods but I don't know how to use attributes of the just saved object. Accessing *args, **kwargs did not work. How can I access them? Do I have to save, access the father and then save again? 3.) If I decide to save the breadcrumb. Whats the best way to do it? I used http://www.djangosnippets.org/snippets/1694/ and have crumb = PickledObjectField(). Thats the method to calculate the attribute crumb() def _breadcrumb(self): breadcrumb = [ ] x = self while True: x = x.father try: if hasattr(x, 'country'): breadcrumb.append(x.country) elif hasattr(x, 'region'): breadcrumb.append(x.region) elif hasattr(x, 'city'): breadcrumb.append(x.city) else: break except: break breadcrumb.reverse() return breadcrumb Thats my save-Method: def save(self,*args, **kwargs): # how can I access the father ob the object? father = self.father # does obviously not work father = kwargs['father'] # does not work either # the breadcrumb gets calculated here self.crumb = self._breadcrumb(father) super(GeoObject, self).save(*args,**kwargs) Please help me out. I am working on this for days now. Thank you.

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  • How to check if two records have a self-referencing relation?

    - by Machine
    Consider the following schema with users and their collegues (friends): Users User: columns: user_id: name: user_id as userId type: integer(8) unsigned: 1 primary: true autoincrement: true first_name: name: first_name as firstName type: string(45) notnull: true last_name: name: last_name as lastName type: string(45) notnull: true email: type: string(45) notnull: true unique: true relations: Collegues: class: User local: invitor foreign: invitee refClass: CollegueStatus equal: true onDelete: CASCADE onUpdate: CASCADE Join table: CollegueStatus: columns: invitor: type: integer(8) unsigned: 1 primary: true invitee: type: integer(8) unsigned: 1 primary: true status: type: enum(8) values: [pending, accepted, denied] default: pending notnull: true Now, let's say I two records, one for the user making a HTTP request (the logged in user), and one record for a user he wants to send a message to. I want to check if these users are collegues. Questions: Does Doctrine have any pre-build functionality to check if two records with with self-relations are related? If not, how would you write a method to check this? Where would you put said method? (In the User-class, UserTable-class etc) I could probably do something like this: public function (User $user1, User $user2) { // Ensure we load collegues if $user1 was fetched with DQL that // doesn't load this relation $collegues = $user1->get('Collegues'); $areCollegues = false; foreach($collegues as $collegue) { if($collegue['userId'] === $user2['userId']) { $areCollegues = true; break; } } return $areCollegues; } But this looks a neither efficient nor pretty. I just feel that it should be solved already for self-referencing relations to be nice to use.

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  • Placement of defensive structures in a game

    - by Martin
    I am working on an AI bot for the game Defcon. The game has cities, with varying populations, and defensive structures with limited range. I'm trying to work out a good algorithm for placing defence towers. Cities with higher populations are more important to defend Losing a defence tower is a blow, so towers should be placed reasonably close together Towers and cities can only be placed on land So, with these three rules, we see that the best kind of placement is towers being placed in a ring around the largest population areas (although I don't want an algorithm just to blindly place a ring around the highest area of population, sometime there might be 2 sets of cities far apart, in which case the algorithm should make 2 circles, each one half my total towers). I'm wondering what kind of algorithms might be used for determining placement of towers?

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  • c# multi threaded file processing

    - by user177883
    There is a folder that contains 1000 of small text files. I aim to parse and process all of them while more files are being populated in to the folder. My intention is to multithread this operation as the single threaded prototype took 6 minutes to process 1000 files. I like to have reader and writer thread(s) as following : while the reader thread(s) are reading the files, I d like to have writer thread(s) to process them. Once the reader is started reading a file, I d like to mark it as being processed, such as by renaming it, once it s read, rename it to completed. How to approach such multithreaded application ? Is it better to use a distributed hash table or a queue? Which data structure to use that would avoid locks? Would you have a better approach to this scheme that you like to share?

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  • StockTrader RI > Controllers, Presenters, WTF?

    - by SandRock
    I am currently learning how to make advanced usage of WPF via the Prism (Composite WPF) project. I watch many videos and examples and the demo application StockTraderRI makes me ask this question: What is the exact role of each of the following part? SomethingService: Ok, this is something to manage data SomethingView: Ok, this is what's displayed SomethingPresentationModel: Ok, this contains data and commands for the view to bind to (equivalent to a ViewModel). SomethingPresenter: I don't really understand it's usage SomethingController: Don't understand too I saw that a Presenter and a Controller are not necessary but I would like to understand why they are here. Can someone tell me their role and when to use them?

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  • What division operator symbol would you pick?

    - by Mackenzie
    I am currently designing and implementing a small programming language as an extra-credit project in a class I'm taking. My problem is that the language has three numeric types: Long, Double, and Fraction. Fractions can be written in the language as proper or improper fractions (e.g. "2 1/3" or "1/2"). This fact leads to problems such as "2/3.5" (Long/Double) and "2/3"(Long/Long) not being handled correctly by the lexer.The best solution that I see is to change the division operator. So far, I think "\" is the best solution since "//" starts comments. Would you pick "\", if you were designing the language? Would you pick something else? If so, what? Note: changing the way fractions are written is not possible. Thanks in advance for your help,

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  • In a PHP project, how do you organize and access your helper objects?

    - by Pekka
    How do you organize and manage your helper objects like the database engine, user notification, error handling and so on in a PHP based, object oriented project? Say I have a large PHP CMS. The CMS is organized in various classes. A few examples: the database object user management an API to create/modify/delete items a messaging object to display messages to the end user a context handler that takes you to the right page a navigation bar class that shows buttons a logging object possibly, custom error handling etc. I am dealing with the eternal question, how to best make these objects accessible to each part of the system that needs it. my first apporach, many years ago was to have a $application global that contained initialized instances of these classes. global $application; $application->messageHandler->addMessage("Item successfully inserted"); I then changed over to the Singleton pattern and a factory function: $mh =&factory("messageHandler"); $mh->addMessage("Item successfully inserted"); but I'm not happy with that either. Unit tests and encapsulation become more and more important to me, and in my understanding the logic behind globals/singletons destroys the basic idea of OOP. Then there is of course the possibility of giving each object a number of pointers to the helper objects it needs, probably the very cleanest, resource-saving and testing-friendly way but I have doubts about the maintainability of this in the long run. Most PHP frameworks I have looked into use either the singleton pattern, or functions that access the initialized objects. Both fine approaches, but as I said I'm happy with neither. I would like to broaden my horizon on what is possible here and what others have done. I am looking for examples, additional ideas and pointers towards resources that discuss this from a long-term, real-world perspective. Also, I'm interested to hear about specialized, niche or plain weird approaches to the issue. Bounty I am following the popular vote in awarding the bounty, the answer which is probably also going to give me the most. Thank you for all your answers!

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  • Revisions: algorithm and data structure

    - by SODA
    Hi, I need ideas for structuring and processing data with revisions. For example, I have a database of objects (e.g. cars). Each object has a number of properties, which can be arbitrary, so there's no a set schema to describe these objects. These objects are probably saved as key-value pairs. Now I need to change property of an object. I don't want to completely rewrite it - I want to be able to go back and see history of changes to these properties, that's why I want to add new property and keep the old one (so I guess a timestamp would do the job of telling which property is the latest). At the same time I want to be able to get info about any object in a snap, with only latest versions of each of the properties. Any ideas what would be the best approach? At least please point me in the right direction. Thanks!

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  • If we make a number every millisecond, how much data would we have in a day?

    - by Roger Travis
    I'm a bit confused here... I'm being offered to get into a project, where would be an array of certain sensors, that would give off reading every millisecond ( yes, 1000 reading in a second ). Reading would be a 3 or 4 digit number, for example like 818 or 1529. This reading need to be stored in a database on a server and accessed remotely. I never worked with such big amounts of data, what do you think, how much in terms of MBs reading from one sensor for a day would be?... 4(digits)x1000x60x60x24 ... = 345600000 bits ... right ? about 42 MB per day... doesn't seem too bad, right? therefor a DB of, say, 1 GB, would hold 23 days of info from 1 sensor, correct? I understand that MySQL & PHP probably would not be able to handle it... what would you suggest, maybe some aps? azure? oracle? ... Thansk!

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  • How should I use color in my application? Single, Theme, or Chaos?

    - by CodeSlave
    How should I be using color in my application? I have over a 100 different forms (windows) in my application, and the default windows grey seems like a bad choice to me. One school of thought says pick one neutral color, and use the same one everywhere. Another school of thought says pick a set of neutral colors, and use them same ones within a group of form (e.g., shipping screens might be light green, receiving screens light orange, user administration screens light blue, etc.). The final school of thought says make every form different. We've got millions of colors, why not use them? What should I do and why?

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  • How to implement Auto_Increment per User, on the same table?

    - by Jonas
    I would like to have multiple users that share the same tables in the database, but have one auto_increment value per user. I will use an embedded database, JavaDB and as what I know it doesn't support this functionality. How can I implement it? Should I implement a trigger on inserts that lookup the users last inserted row, and then add one, or are there any better alternative? Or is it better to implement this in the application code? Or is this just a bad idea? I think this is easier to maintain than creating new tables for every user. Example: table +----+-------------+---------+------+ | ID | ID_PER_USER | USER_ID | DATA | +----+-------------+---------+------+ | 1 | 1 | 2 | 3454 | | 2 | 2 | 2 | 6567 | | 3 | 1 | 3 | 6788 | | 4 | 3 | 2 | 1133 | | 5 | 4 | 2 | 4534 | | 6 | 2 | 3 | 4366 | | 7 | 3 | 3 | 7887 | +----+-------------+---------+------+ SELECT * FROM table WHERE USER_ID = 3 +----+-------------+---------+------+ | ID | ID_PER_USER | USER_ID | DATA | +----+-------------+---------+------+ | 3 | 1 | 3 | 6788 | | 6 | 2 | 3 | 4366 | | 7 | 3 | 3 | 7887 | +----+-------------+---------+------+ SELECT * FROM table WHERE USER_ID = 2 +----+-------------+---------+------+ | ID | ID_PER_USER | USER_ID | DATA | +----+-------------+---------+------+ | 1 | 1 | 2 | 3454 | | 2 | 2 | 2 | 6567 | | 4 | 3 | 2 | 1133 | | 5 | 4 | 2 | 4534 | +----+-------------+---------+------+

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  • How to keep historic details of modification in a database (Audit trail)?

    - by mada
    I'm a J2EE developer & we are using hibernate mapping with a PostgreSQL database. We have to keep track of any changes occurs in the database, in others words all previous & current values of any field should be saved. Each field can be any type (bytea, int, char...) With a simple table it is easy but we a graph of objects things are more difficult. So we have, speaking in a UML point of view, a graph of objects to store in the database with every changes & the user. Any idea or pattern how to do that?

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  • friendship database schema

    - by Daniel Hertz
    I'm creating a db schema that involves users that can be friends, and I was wondering what the best way to model the ability for these friends to have friendships. Should it be its own table that simply has two columns that each represent a user? Thanks!

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  • How to implement Gradient Opacity (Mask) using html css javascript

    - by brz dot net
    I have to show 25% right screen in such way that the text looks appeared from right. For this I need to set opacity from 0 to 100 at 25% right side screen means rightmost opacity would be 0 and at 75% the opacity would be 100. For this, I took a Div and set opacity but It looks bad because of border. I need to gray out text. It looks a block. Let me know how I can implement cross browser compatible gradient opacity mask for right screen text. What is the best way to do this?

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  • Primary key/foreign Key naming convention

    - by Jeremy
    In our dev group we have a raging debate regarding the naming convention for Primary and Foreign Keys. There's basically two schools of thought in our group: 1) Primary Table (Employee) Primary Key is called ID Foreign table (Event) Foreign key is called EmployeeID 2) Primary Table (Employee) Primary Key is called EmployeeID Foreign table (Event) Foreign key is called EmployeeID I prefer not to duplicate the name of the table in any of the columns (So I prefer option 1 above). Conceptually, it is consisted with a lot of the recommended practices in other languages, where you don't use the name of the object in its property names. I think that naming the foreign key EmployeeID (or Employee_ID might be better) tells the reader that it is the ID column of the Employee Table. Some others prefer option 2 where you name the primary key prefixed with the table name so that the column name is the same throughout the database. I see that point, but you now can not visually distinguish a primary key from a foreign key. Also, I think it's redundant to have the table name in the column name, because if you think of the table as an entity and a column as a property or attribute of that entity, you think of it as the ID attribute of the Employee, not the EmployeeID attribute of an employee. I don't go an ask my coworker what his PersonAge or PersonGender is. I ask him what his Age is. So like I said, it's a raging debate and we go on and on and on about it. I'm interested to get some new perspective.

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  • multiple classes with same methods - best pattern

    - by Tony
    I have a few classes in my current project where validation of Email/Website addresses is necessary. The methods to do that are all the same. I wondered what's the best way to implement this, so I don't need to have these methods copy pasted everywhere? The classes themselves are not necessarily related, they only have those validation methods in common.

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  • How big is too big (for NTFS)

    - by BCS
    I have a program and as it's done now, it has a data directory with something like 10-30K files in it and it's starting to cause problems. Should I expect that to cause problems and my only solution to tweak my file structure or does that indicate other problems?

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  • MySQL forgot about automatically creating an index for a foreign key?

    - by bobo
    After running the following SQL statements, you will see that, MySQL has automatically created the non-unique index question_tag_tag_id_tag_id on the tag_id column for me after the first ALTER TABLE statement has run. But after the second ALTER TABLE statement has run, I think MySQL should also automatically create another non-unique index question_tag_question_id_question_id on the question_id column for me. But as you can see from the SHOW INDEXES statement output, it's not there. Why does MySQL forget about the second ALTER TABLE statement? By the way, since I have already created a unique index question_id_tag_id_idx used by both question_id and tag_id columns. Is creating a separate index for each of them redundant? mysql> DROP DATABASE mydatabase; Query OK, 1 row affected (0.00 sec) mysql> CREATE DATABASE mydatabase; Query OK, 1 row affected (0.00 sec) mysql> USE mydatabase; Database changed mysql> CREATE TABLE question (id BIGINT AUTO_INCREMENT, html TEXT, PRIMARY KEY(id)) ENGINE = INNODB; Query OK, 0 rows affected (0.05 sec) mysql> CREATE TABLE tag (id BIGINT AUTO_INCREMENT, name VARCHAR(10) NOT NULL, UNIQUE INDEX name_idx (name), PRIMARY KEY(id)) ENGINE = INNODB; Query OK, 0 rows affected (0.05 sec) mysql> CREATE TABLE question_tag (question_id BIGINT, tag_id BIGINT, UNIQUE INDEX question_id_tag_id_idx (question_id, tag_id), PRIMARY KEY(question_id, tag_id)) ENGINE = INNODB; Query OK, 0 rows affected (0.00 sec) mysql> ALTER TABLE question_tag ADD CONSTRAINT question_tag_tag_id_tag_id FOREIGN KEY (tag_id) REFERENCES tag(id); Query OK, 0 rows affected (0.10 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> ALTER TABLE question_tag ADD CONSTRAINT question_tag_question_id_question_id FOREIGN KEY (question_id) REFERENCES question(id); Query OK, 0 rows affected (0.13 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> SHOW INDEXES FROM question_tag; +--------------+------------+----------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +--------------+------------+----------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | question_tag | 0 | PRIMARY | 1 | question_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 0 | PRIMARY | 2 | tag_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 0 | question_id_tag_id_idx | 1 | question_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 0 | question_id_tag_id_idx | 2 | tag_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 1 | question_tag_tag_id_tag_id | 1 | tag_id | A | 0 | NULL | NULL | | BTREE | | +--------------+------------+----------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 5 rows in set (0.01 sec) mysql>

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