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  • Why would it be a bad idea to have database connection open between client requests?

    - by AspOnMyNet
    1) Book I’m reading argues that connections shouldn’t be opened between client requests, since they are a finite resource. I realize that max pool size can quickly be reached and thus any further attempts to open a connection will be queued until connection becomes available and for that reason it would be imperative that we release connection as soon as possible. But assuming all request will open connection to the same DB, then I’m not sure how having a connection open between two client requests would be any less efficient than having each request first acquiring a connection from connection pool and later returning that object to connection pool? 2) Book also recommends that when database code is encapsulated in a dedicated data access class, then method M opening a database connection should also close that connection. a) I assume one reason why M should also close it, is because if method M opening the connection doesn’t also close it, but instead this connection object is used inside several methods, then it’s more likely that a programmer will forget to close it. b) Are there any other reasons why a method opening the connection should also close it? thanx

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  • Database solutions for storing/searching EXIF data

    - by webdestroya
    I have thousands of photos on my site (each with a numeric PhotoID) and I have EXIF data (photos can have different EXIF tags as well). I want to be able to store the data effectively and search it. Some photos have more EXIF data than others, some have the same, so on.. Basically, I want to be able to query say 'Select all photos that have a GPS location' or 'All photos with a specific camera' I can't use MySQL (tried it, it doesn't work). I thought about Cassandra, but I don't think it lets me query on fields. I looked at SimpleDB, but I would rather: not pay for the system, and I want to be able to run more advanced queries on the data. Also, I use PHP and Linux, so it would be awesome if it could interface nicely to PHP. Any ideas?

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  • Is there a recommended way to use the Observer pattern in MVP using GWT?

    - by Tomislav Nakic-Alfirevic
    I am thinking about implementing a user interface according to the MVP pattern using GWT, but have doubts about how to proceed. These are (some of) my goals: - the presenter knows nothing about the UI technology (i.e. uses nothing from com.google.*) - the view knows nothing about the model or the presenter - the model knows nothing of the view or the presenter (...obviously) I would place an interface between the view and the presenter and use the Observer pattern to decouple the two: the view generates events and the presenter gets notified. What confuses me is that java.util.Observer and java.util.Observable are not supported in GWT. This suggests that what I'm doing is not the recommended way to do it, as far as GWT is concerned, which leads me to my questions: what is the recommended way to implement MVP using GWT, specifically with the above goals in mind? How would you do it?

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  • [NEWVERSION]algorithm || method to write prog[UNSOLVED] [closed]

    - by fatai
    I am one of the computer science student. Everyone solve problem with a different or same method, ( but actually I dont know whether they use method or I dont know whether there are such common method to approach problem.) if there are common method, What is it ? If there are different method, which method are you using ? All teacher give us problem which in simple form sometimes, but they donot introduce any approach or method(s) so that we cannot make a decision to choose the method then apply that one to problem , afterward find solution then write code.No help from teacher , push us to find method to solve homework. Ex: my friend is using no method , he says "I start to construct algorithm while I try to write prog." I have found one method when I failed the course, More accurately, my method: When I counter problem in language , I will get more paper and then ; first, input/ output step ; my prog will take this / these there argument(s) and return namely X , ex : in c, input length is not known and at same type , so I must use pointer desired output is in form of package , so use structure second, execution part ; in that step , I am writing all step which are goes to final output ex : in python ; 1.) [ + , [- , 4 , [ * , 1 , 2 ]], 5] 2.) [ + , [- , 4 , 2 ],5 ] 3.) [ + , 2 , 5] 4.) 7 ==> return 7 third, I will write test code ex : in c++ input : append 3 4 5 6 vector_x remove 0 1 desired output vector_x holds : 5 6 now, my other question is ; What is/are other method(s) which have/has been; used to construct class :::: for c++ , python, java used to communicate classes / computers used for solving embedded system problem ::::: for c by other user? Some programmer uses generalized method without considering prog-language(java , perl .. ), what is this method ? Why I wonder , because I learn if you dont costruct algorithm on paper, you may achieve your goal. Like no money no lunch , I can say no algorithm no prog therefore , feel free when you write your own method , a way which is introduced by someone else but you are using and you find it is so efficient

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  • Dynamically specify the type in C#

    - by Lirik
    I'm creating a custom DataSet and I'm under some constrains: I want the user to specify the type of the data which they want to store. I want to reduce type-casting because I think it will be VERY expensive. I will use the data VERY frequently in my application. I don't know what type of data will be stored in the DataSet, so my initial idea was to make it a List of objects, but I suspect that the frequent use of the data and the need to type-cast will be very expensive. The basic idea is this: class DataSet : IDataSet { private Dictionary<string, List<Object>> _data; /// <summary> /// Constructs the data set given the user-specified labels. /// </summary> /// <param name="labels"> /// The labels of each column in the data set. /// </param> public DataSet(List<string> labels) { _data = new Dictionary<string, List<object>>(); foreach (string label in labels) { _data.Add(label, new List<object>()); } } #region IDataSet Members public List<string> DataLabels { get { return _data.Keys.ToList(); } } public int Count { get { _data[_data.Keys[0]].Count; } } public List<object> GetValues(string label) { return _data[label]; } public object GetValue(string label, int index) { return _data[label][index]; } public void InsertValue(string label, object value) { _data[label].Insert(0, value); } public void AddValue(string label, object value) { _data[label].Add(value); } #endregion } A concrete example where the DataSet will be used is to store data obtained from a CSV file where the first column contains the labels. When the data is being loaded from the CSV file I'd like to specify the type rather than casting to object. The data could contain columns such as dates, numbers, strings, etc. Here is what it could look like: "Date","Song","Rating","AvgRating","User" "02/03/2010","Code Monkey",4.6,4.1,"joe" "05/27/2009","Code Monkey",1.2,4.5,"jill" The data will be used in a Machine Learning/Artificial Intelligence algorithm, so it is essential that I make the reading of data very fast. I want to eliminate type-casting as much as possible, since I can't afford to cast from 'object' to whatever data type is needed on every read. I've seen applications that allow the user to pick the specific data type for each item in the csv file, so I'm trying to make a similar solution where a different type can be specified for each column. I want to create a generic solution so I don't have to return a List<object> but a List<DateTime> (if it's a DateTime column) or List<double> (if it's a column of doubles). Is there any way that this can be achieved? Perhaps my approach is wrong, is there a better approach to this problem?

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  • C++ classes with members referencing each other

    - by Saad Imran.
    I'm trying to write 2 classes with members that reference each other. I'm not sure if I'm doing something wrong or it's just not possible. Can anyone help me out here... Source.cpp #include "Headers.h" using namespace std; void main() { Network* network = new Network(); system("pause"); return; } Headers.h #ifndef Headers_h #define Headers_h #include <iostream> #include <vector> #include "Network.h" #include "Router.h" #endif Network.h #include "Headers.h" class Network { protected: vector<Router> Routers; }; Router.h #include "Headers.h" class Router { protected: Network* network; public: }; The errors I'm getting are: error C2143: syntax error : missing ';' before '<' error C2238: unexpected token(s) preceding ';' error C4430: missing type specifier - int assumed. I'm pretty sure I'm not missing any semicolons or stuff like that. The program works find if I take out one of the members. I tried finding similar questions and the solution was to use pointers, but that's what I'm doing and it does't seem to be working!

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  • IE8 displays white page when adding Javascript

    - by Chris
    I recently created a website and added some jQuery into it. However doing this makes IE8 display a white page. Whenever I remove the Javascript IE8 renders the site fine. I have tested locally as well as on the internet, the problem still persists. This is my code to include my .js files: <script type="text/javascript" src="jQuery/jQuery.js" /> <script type="text/javascript" src="jQuery/effects.js" />

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  • Can the Singleton be replaced by Factory?

    - by lostiniceland
    Hello Everyone There are already quite some posts about the Singleton-Pattern around, but I would like to start another one on this topic since I would like to know if the Factory-Pattern would be the right approach to remove this "anti-pattern". In the past I used the singleton quite a lot, also did my fellow collegues since it is so easy to use. For example, the Eclipse IDE or better its workbench-model makes heavy usage of singletons as well. It was due to some posts about E4 (the next big Eclipse version) that made me start to rethink the singleton. The bottom line was that due to this singletons the dependecies in Eclipse 3.x are tightly coupled. Lets assume I want to get rid of all singletons completely and instead use factories. My thoughts were as follows: hide complexity less coupling I have control over how many instances are created (just store the reference I a private field of the factory) mock the factory for testing (with Dependency Injection) when it is behind an interface In some cases the factories can make more than one singleton obsolete (depending on business logic/component composition) Does this make sense? If not, please give good reasons for why you think so. An alternative solution is also appreciated. Thanks Marc

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  • Python: Recursively access dict via attributes as well as index access?

    - by Luke Stanley
    I'd like to be able to do something like this: from dotDict import dotdictify life = {'bigBang': {'stars': {'planets': [] } } } dotdictify(life) #this would be the regular way: life['bigBang']['stars']['planets'] = {'earth': {'singleCellLife': {} }} #But how can we make this work? life.bigBang.stars.planets.earth = {'singleCellLife': {} } #Also creating new child objects if none exist, using the following syntax life.bigBang.stars.planets.earth.multiCellLife = {'reptiles':{},'mammals':{}} My motivations are to improve the succinctness of the code, and if possible use similar syntax to Javascript for accessing JSON objects for efficient cross platform development.(I also use Py2JS and similar.)

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  • many-to-many query

    - by kofto4ka
    Hello, guys! I have a problem and I dont know what is better solution. Okay, I have 2 tables: posts(id, title), posts_tags(post_id, tag_id). I have next task: must select posts with tags ids for example 4, 10 and 11. Not exactly, post could have any other tags at the same time. So, how I could do it more optimized? Creating temporary table in each query? Or may be some kind of stored procedure? In the future, user could ask script to select posts with any count of tags (it could be 1 tag only or 10 at the same time) and I must be sure that method that I will choose would be the best method for my problem. Sorry for my english, thx for attention.

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  • Bi-directional view model syncing with "live" collections and properties (MVVM)

    - by Schneider
    I am getting my knickers in a twist recently about View Models (VM). Just like this guy I have come to the conclusion that the collections I need to expose on my VM typically contain a different type to the collections exposed on my business objects. Hence there must be a bi-directional mapping or transformation between these two types. (Just to complicate things, on my project this data is "Live" such that as soon as you change a property it gets transmitted to other computers) I can just about cope with that concept, using a framework like Truss, although I suspect there will be a nasty surprise somewhere within. Not only must objects be transformed but a synchronization between these two collections is required. (Just to complicate things I can think of cases where the VM collection might be a subset or union of business object collections, not simply a 1:1 synchronization). I can see how to do a one-way "live" sync, using a replicating ObservableCollection or something like CLINQ. The problem then becomes: What is the best way to create/delete items? Bi-directinal sync does not seem to be on the cards - I have found no such examples, and the only class that supports anything remotely like that is the ListCollectionView. Would bi-directional sync even be a sensible way to add back into the business object collection? All the samples I have seen never seem to tackle anything this "complex". So my question is: How do you solve this? Is there some technique to update the model collections from the VM? What is the best general approach to this?

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  • Pattern/Matcher in Java?

    - by user1007059
    I have a certain text in Java, and I want to use pattern and matcher to extract something from it. This is my program: public String getItemsByType(String text, String start, String end) { String patternHolder; StringBuffer itemLines = new StringBuffer(); patternHolder = start + ".*" + end; Pattern pattern = Pattern.compile(patternHolder); Matcher matcher = pattern.matcher(text); while (matcher.find()) { itemLines.append(text.substring(matcher.start(), matcher.end()) + "\n"); } return itemLines.toString(); } This code works fully WHEN the searched text is on the same line, for instance: String text = "My name is John and I am 18 years Old"; getItemsByType(text, "My", "John"); immediately grabs the text "My name is John" out of the text. However, when my text looks like this: String text = "My name\nis John\nand I'm\n18 years\nold"; getItemsByType(text, "My", "John"); It doesn't grab anything, since "My" and "John" are on different lines. How do I solve this?

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  • Database Modeling - Either/Or in Many-to-Many

    - by EkoostikMartin
    I have an either/or type of situation in a many-to-many relationship I'm trying to model. So I have these tables: Message ---- *MessageID MessageText Employee ---- *EmployeeID EmployeeName Team ---- *TeamID TeamName MessageTarget ---- MessageID EmployeeID (nullable) TeamID (nullable) So, a Message can have either a list of Employees, or a list of Teams as a MessageTarget. Is the MessageTarget table I have above the best way to implement this relationship? What constraints can I place on the MessageTarget effectively? How should I create a primary key on MessageTarget table?

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  • Include everything, Separate with "using"

    - by Dave
    I'm developing a C++ library. It got me thinking of the ways Java and C# handle including different components of the libraries. For example, Java uses "import" to allow use of classes from other packages, while C# simply uses "using" to import entire modules. My questions is, would it be a good idea to #include everything in the library in one massive include and then just use the using directive to import specific classes and modules? Or would this just be down right crazy? EDIT: Good responses so far, here are a few mitigating factors which I feel add to this idea: 1) Internal #includes are kept as normal (short and to the point) 2) The file which includes everything is optionally supplied with the library to those who wish to use it3) You could optionally make the big include file part of the pre-compiled header

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  • What do you call functions which get and set?

    - by nickf
    The jQuery framework has a lot of functions which will either retrieve or mutate values depending on the parameters passed: $(this).html(); // get the html $(this).html('blah'); // set the html Is there a standard name for functions which behave like this?

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  • C# reference collection for storing reference types

    - by ivo s
    I like to implement a collection (something like List<T>) which would hold all my objects that I have created in the entire life span of my application as if its an array of pointers in C++. The idea is that when my process starts I can use a central factory to create all objects and then periodically validate/invalidate their state. Basically I want to make sure that my process only deals with valid instances and I don't re-fetch information I already fetched from the database. So all my objects will basically be in one place - my collection. A cool thing I can do with this is avoid database calls to get data from the database if I already got it (even if I updated it after retrieval its still up-to-date if of course some other process didn't update it but that a different concern). I don't want to be calling new Customer("James Thomas"); again if I initted James Thomas already sometime in the past. Currently I will end up with multiple copies of the same object across the appdomain - some out of sync other in sync and even though I deal with this using timestamp field on the MSSQL server I'd like to keep only one copy per customer in my appdomain (if possible process would be better). I can't use regular collections like List or ArrayList for example because I cannot pass parameters by their real local reference to the their existing Add() methods where I'm creating them using ref so that's not to good I think. So how can this be implemented/can it be implemented at all ? A 'linked list' type of class with all methods working with ref & out params is what I'm thinking now but it may get ugly pretty quickly. Is there another way to implement such collection like RefList<T>.Add(ref T obj)? So bottom line is: I don't want re-create an object if I've already created it before during the entire application life unless I decide to re-create it explicitly (maybe its out-of-date or something so I have to fetch it again from the db). Is there alternatives maybe ?

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  • Make is more OOPey - good structure?

    - by Tom
    Hi, I just want advice on whether I could improve structure around a particular class which handles all disk access functions The structure of my program is that I have a class called Disk which gets data from flatfiles and databases on a, you guessed it, hard disk drive. I have functions like LoadTextFileToStringList, WriteStringToTextFile, DeleteLineInTextFile etc which are kind of "generic methods" In the same class I also have some more specific methods such as GetXFromDisk where X might be a particular field in a database table/query. Should I separate out the generic methods from the specialised. Should I make another class which inherits the generic methods. At the moment my class is static as there is no need to have an internal state of the class. I'm not really OOPing am I? Thanks Thomas

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  • Inheritance: when implementing an interface which define a base class property why cant the class im

    - by Deepak
    Lets create some interfaces public interface ITimeEventHandler { string Open(); } public interface IJobTimeEventHandler: ITimeEventHandler { string DeleteJob(); } public interface IActivityTimeEventHandler: ITimeEventHandler { string DeleteActivity(); } public interface ITimeEvent { ITimeEventHandler Handler; } Another Interface public interface IJobTimeEvent :ITimeEvent { int JobID; } Create a class public class JobTimeEvent : IJobTimeEvent { public int JobID = 0; public IJobTimeEventHandler Handler = null; } My question is .. when implementing an interface which define a base class property why cant the class implementing interface return a derived class type object ?? For ex in class JobTimeEvent, IJobtimeEvent needs a property of type ITimeEventHandler but why IJobTimeEventHandler type is not allowed which derived from ITimeEventHandler

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  • Resources on wordpress theme-development

    - by Espenhh
    What are the best resources for Wordpress theme-development? I am currently in the phase of starting my own blog, and don't want to use one of the many free themes. I already have a theme for my website, so I want to read about best-practices. Any advice on how to get started would be very welcome :) I have now created my theme (wohoo!), and thought I should summarize the best resources I found. Lets see.. Resources: ThemeTation's three-part guide to create a wordpress-theme from scratch Nettuts.com's guide: How to Create a Wordpress Theme from Scratch (And Part 2) Didn't actually use this, it's a quite new article, but anyway - it's great. It will get a follow-up in the next few days too.. Wordpress.org's own guide on templates Definatly a must-read for everyone new to wordpress-designing.. "The loop" Essential knowledge, also a must-read Directory of all the template tags Used by wordpress to actually output blog-content.. Inspiration: Smashing Magazine's lists: first, one more, yet another one Wordpress.org's theme-directory

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  • Understanding colors

    - by Ankur Gupta
    Hello everyone, Kindly point towards theory/material to read for understanding colors and what makes a good color combinations. Mind it that I am not interested in say "Color combinations for web application" etc. More of the lines of say "Colors and humans". Material free to read is what i am looking for. Thanks

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  • Which should be created first ER Diagram OR Class Diagram?

    - by isthatacode
    The very first step i created a DFD. Then i moved on to create a Class Diagram. And while doing that i felt that i should create the ER diagram first. As there were many details which could not be captured in a Class diagram. So, my question should i create ERD first OR Class Diagrams ? your valuable inputs are appreciated guys!!! thanks for reading

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