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• "Subforms" associated with tree view in VB

  - by knomdeguerre

  I am using VB Express 2008 to demonstrate my ideas for an improved UI for an existing product for my colleagues at work. The current UI has a certain page with ten tabs, allowing the user to define up to ten "things". The available choices for each of the ten "things" are all the same. On each of the ten tabs, there is a checkbox to enable that definition. Generally, a user will never use more than 5 or 6 unique definitions, the rest will remain disabled. So far, my prototype has a tree view control with one branch to contain this list of definitions, Add and Delete buttons. My idea is: there is one sub-branch to start with (corresponding to the first tab in the current UI); if the user wants addtional definitions, they click Add and other branches are added to the tree view, up to maximum of ten. I think I should be able to create a "class" that has a sub-UI (like a sub-form in Access) along with behavior code, that can be instantiated with each press of the Add button; each instantiation's settings can be set independently and is displayed in the main UI form )in a panel or frame) when selected in the tree view. For example, suppose the user Adds to make a total of three definitions: the tree view now has three sub-branches, each of which presents the same sub-UI with settings that can be set specific to the selected sub-branch. I'm sure it's possible but not sure how to do it. I know a comprehensive "answer" might be complicated and long, but I may just need some quick hints to get underway - don't be shy! Thanks in advance!

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• Can I get the amount of time for which a key is pressed on a keyboard

  - by Adi

  Dear all, I am working on a project in which I have to develop bio-passwords based on user's keystroke style. Suppose a user types a password for 20 times, his keystrokes are recorded, like holdtime : time for which a particular key is pressed. digraph time : time it takes to press a different key. suppose a user types a password " COMPUTER". I need to know the time for which every key is pressed. something like : holdtime for the above password is C-- 200ms O-- 130ms M-- 150ms P-- 175ms U-- 320ms T-- 230ms E-- 120ms R-- 300ms The rational behind this is , every user will have a different holdtime. Say a old person is typing the password, he will take more time then a student. And it will be unique to a particular person. To do this project, I need to record the time for each key pressed. I would greatly appreciate if anyone can guide me in how to get these times. Editing from here.. Language is not important, but I would prefer it in C. I am more interested in getting the dataset.

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• django simple approach to multi-field search

  - by Scott Willman

  I have a simple address book app that I want to make searchable. The model would look something like: class Address(models.Model): address1 = models.CharField("Address Line 1", max_length=128) address2 = models.CharField("Address Line 2", max_length=128) city = models.CharField("City", max_length=128) state = models.CharField("State", max_length=24) zipCode = models.CharField("Zip Code", max_length=24) def __unicode__(self): return "%s %s, %s, %s, %s" % (self.address1, self.address2, self.city, self.state, self.zipCode) class Entry(models.Model): name = models.CharField("Official School Name", max_length=128) createdBy = models.ForeignKey(User) address = models.ForeignKey(Address, unique=True) def __unicode__(self): return "%s - %s, %s" % (self.name, self.address.city, self.address.state) I want the searching to be fairly loose, like: Bank of America Los Angeles 91345. It seems like I want a field that contains all of those elements into one that I can search, but that also seems redundant. I was hoping I could add a method to the Entry model like this: def _getSearchText(self): return "%s %s %s" % (self.name, self.address, self.mascot) searchText = property(_getSearchText) ...and search that as a field, but I suppose that's wishful thinking... How should I approach this using basic Django and SqLite (this is a learning exercise). Thank you!!

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• Can't seem to get .Union to work (merging 2 array's together, exclude duplicates)

  - by D. Veloper

  I want to combine two array's, excluding duplicates. I am using a custom class: public class ArcContact : IEquatable<ArcContact> { public String Text; public Boolean Equals(ArcContact other) { if (Object.ReferenceEquals(other, null)) return false; if (Object.ReferenceEquals(this, other)) return true; return Text.Equals(other.Text); } public override Int32 GetHashCode() { return Text == null ? 0 : Text.GetHashCode(); } } I implemented and the needed IEquatable interface as mentioned in this msdn section. I only want to check the Text property of the ArcContact class and make sure an Array of ArcContact have an unique Text. Here I pasted the code that I use, as you can see I have method with two parameters, array's to combine and below that the code I got from the previous mentioned msdn section. internal static class ArcBizz { internal static ArcContact[] MergeDuplicateContacts(ArcContact[] contacts1, ArcContact[] contacts2) { return (ArcContact[])contacts1.Union(contacts2); } internal static IEnumerable<T> Union<T>(this IEnumerable<T> a, IEnumerable<T> b); } What am I doing wrong?

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• [MySQL] Efficiently store last X records per item

  - by Saif Bechan

  I want to store the last X records in an MySQL database in an efficient way. So when the 4th record is stored the first should be deleted. The way I do this not is first run a query getting the items. Than check what I should do then insert/delete. There has to be a better way to do this. Any suggestions? Edit I think I should add that the records stored do not have a unique number. They have a mixed par. For example article_id and user_id. Then I want to make a table with the last X items for user_x. Just selecting the article from the table grouped by user and sorted by time is not an option for me. The table where I do the sort and group on has millions of records and gets hit a lot for no reason. So making a table in between with the last X records is way more effient. PS. I am not using this for articles and users.

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• SQL query to translate a list of numbers matched against several ranges, to a list of values

  - by Claes Mogren

  I need to convert a list of numbers that fall within certain ranges into a list of values, ordered by a priority column. The table has the following values: | YEAR | R_MIN | R_MAX | VAL | PRIO | ------------------------------------ 2010 18000 90100 52 6 2010 240000 240099 82 3 2010 250000 259999 50 5 2010 260000 260010 92 1 2010 330000 330010 73 4 2010 330011 370020 50 5 2010 380000 380050 84 2 The ranges will be different for different years. The ranges within one year will never overlap. The input will be a year and a list of numbers that might fall within one these ranges. The list of input number will be small, 1 to 10 numbers. Example of input numbers: (20000, 240004, 375000, 255000) With that input I would like to get a list ordered by the priority column, or a single value: 82 50 52 The only value I'm interested in here is 82, so UNIQUE and MAX_RESULTS=1 would do. It can easily be done with one query per number, and then sorting it in the Java code, but I would prefer to do it in a single SQL query. What SQL query, to be run in an Oracle database, would give me the desired result?

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• Using entity framework to connect to multiple similar tables in .net MVC.

  - by Dite

  A relative newcomer to .net MVC2 and the entity framework, I am working on a project which requires a single web application, (C# .net 4), to connect to multiple different databases depending on the route of access, (ie subdomain). No problem with this in principle and all the logic is written to transform the subdomain into an entity connection and pass this through to the Entity Model. The problem comes with the fact that the different database whilst being largely similar in structure contain 3 or 4 unique tables bespoke to that instance. To my mind there are two ways to solve this issue, neither of which i am sure will be possible. 1/ Use a separate entity model for each database. -Attempts down this route have through up conflicts where table/sp names are the same across differnt db's, or implicit conversion errors when I try and put the different models in different namespaces. or 2/ Overwrite the classes which refer to the changeable database objects based on the value of a base controller property. -I have found nothing to suggest i can even do this. My question is if either of theser routes can ever work in principle or if i should just give up on the EF and connect to the dtabases directlky using ADO. Perhaps there is another way to solve this problem i haven't thought of? Thanks for any help...

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• Have to click twice to submit the form

  - by phil

  Intended function: require user to select an option from the drop down menu. After user clicks submit button, validate if an option is selected. Display error message and not submit the form if user fails to select. Otherwise submit the form. Problem: After select an option, button has to be clicked twice to submit the form. I have no clue at all.. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <script src="jquery-1.4.2.min.js" type="text/javascript"></script> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <style> p{display: none;} </style> </head> <script> $(function(){ // language as an array var language=['Arabic','Cantonese','Chinese','English','French','German','Greek','Hebrew','Hindi','Italian','Japanese','Korean','Malay','Polish','Portuguese','Russian','Spanish','Thai','Turkish','Urdu','Vietnamese']; $('#muyu').append('<option value=0>Select</option>'); //loop through array for (i in language) //js unique statement for iterate array { $('#muyu').append($('<option>',{id:'muyu'+i,val:language[i], html:language[i]})) } $('form').submit(function(){ alert('I am being called!'); // check if submit event is triggered if ( $('#muyu').val()==0 ) {$('#muyu_error').show(); } else {$('#muyu_error').hide(); return true;} return false; }) }) </script> <form method="post" action="match.php"> I am fluent in <select name='muyu' id='muyu'></select> <p id='muyu_error'>Tell us your native language</p> <input type="submit" value="Go"> </form>

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• ASP.NET MVC - Wrong redirecting, how to debug?

  - by Xorty

  I am stuck with redirecting problem in ASP.NET MVC project. I have mapped tables via LINQtoSQL and each has unique ID as primary key. I am implementing functionallity of 'CREATE'. Basically, after new value is added into SQL table (which means I pressed Save button), I want to be redirected to Details of this freshly added item. Here's little code how I am doing it : [AcceptVerbs(HttpVerbs.Post), Authorize] public ActionResult Create(Item item) { .... return RedirectToAction("Details", new { id = item.ItemID }); Trouble is, I am never redirected to Details view (I have Details.aspx view for items). When I check CallHierarchy in Visual Studio (2010 pro) the hierarchy is indeed little strange, like this : RedirectToAction(string,object) Calls To 'RedirectToAction' Create Calls To Create (no results) Calls From Create (methods of created instance. From there I'll get back to 'RedirectToAction' and to 'Calls to Create' and 'Calls From Create' etc. etc. - loop Edit Calls From 'RedirectToAction' Not supported I am looking for some tools or more specifically 'know how' (since VS probably has some tools) to debug this kind of situations. PS: rooting is default :"{controller}/{action}/{id}", Thanks

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• Moving from NHibernate to FluentNHibernate: assembly error (related to versions)?

  - by goober

  Not sure where to start, but I had gotten the most recent version of NHibernate, successfully mapped the most simple of business objects, etc. When trying to move to FluentNHibernate and do the same thing, I got this error message on build: "System.IO.FileLoadException: Could not load file or assembly 'NHibernate, Version=2.1.0.4000, Culture=neutral, PublicKeyToken=aa95f207798dfdb4' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference." Background: I'm new to Hibernate, NHibernate, and FluentNHibernate -- but not to .NET, C#, etc. Database I have a database table called Category: (PK) CategoryID (type: int), unique, auto-incrementing UserID (type: uniqueidentifier) -- given the value of the user Guid in ASP.NET database Title (type: varchar(50) -- the title of the category Components involved: I have a SessionProviderClass which creates the mapping to the database I have a Category class which has all the virtual methods for FluentNHibernate to override I have a CategoryMap : ClassMap class, which does the fluent mappings for the entity I have a CategoryRepository class that contains the method to add & save the category I have the TestCatAdd.aspx file which uses the CategoryRepository class. Would be happy to post code for any of those, but I'm not sure that it's necessary, as I think the issue is that somewhere there's a version conflict between what FluentNHibernate references and the NHibernate I have installed from before. Thanks in advance for any help you can give!

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• XML jquery shortcuts

  - by Llamabomber

  I am writing a bit of code that appends my site nav with and extra ul that gives a description about where that link takes you. I need to use our CMS's built in Nav structure so appending via jQuery was the best solution, and XML makes the data easier to manage. My question is this: is there a more efficient way to write out the js? What I have so far is this: $(document).ready(function() { $.ajax({ type: "GET", url: "/js/sitenav.xml", dataType: "xml", success: function parseXml(xml) { // WORK $(xml).find("CaseStudies").each(function() { $("li#case_studies").append('<ul><li>' + $(this).find("NavImage").text() + $(this).find("NavHeader").text() + $(this).find("NavDescription").text() + $(this).find("NavLink").text() + "</li></ul>"); }); }; }); }); and the xml structure resembles this: <SiteNav> <Work> <CaseStudies> <NavImage></NavImage> <NavHeader></NavHeader> <NavDescription></NavDescription> <NavLink></NavLink> </CaseStudies> </Work> </SiteNav> I'm happy with my xml structure, but is there a more compact/efficient method of writing out the code for the jqeury? Every li in the nav has a unique id as well in case that helps...

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• Ideas in implenting the following entry form in ASP.NET MVC 2

  - by KiD0M4N

  Hi guys, I have a very simple data entry form to implement. It looks like this: Obviously I have mocked out the actual requirements but the essence is similar. Entering a name and clicking history should bring up a pop up pointing to the url '/student/viewhistory/{name}' Name and age are required fields The sub form (in the mockup) with Class (a drop down, containing the numbers 1 - 10) and Subject (containing A - D, say) form a unique pair of values for which a score is required. So, selecting the Class and Subject, entering a score and clicking on Add should 'add' this record for the student. Then the user should be able to click Save (to persist the entry to the database) or be able to add further (class, subject, score) pairs to the entry. Any ideas how to smartly implement this? (I am coming from a DWH field... so thinking in a stateless manner is slightly foreign to me.) Any help is appreciated. I would imagine a smart use of jQuery would give a easy solution. Regards, Karan

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• Is sending a hashed password over the wire a security hole?

  - by Ubiquitous Che

  I've come across a system that is in use by a company that we are considering partnering with on a medium-sized (for us, not them) project. They have a web service that we will need to integrate with. My current understanding of proper username/password management is that the username may be stored as plaintext in the database. Every user should have a unique pseudo-random salt, which may also be stored in plaintext. The text of their password must be concatenated with the salt and then this combined string may be hashed and stored in the database in an nvarchar field. So long as passwords are submitted to the website (or web service) over plaintext, everything should be just lovely. Feel free to rip into my understanding as summarized above if I'm wrong. Anyway, back to the subject at hand. The WebService run by this potential partner doesn't accept username and password, which I had anticipated. Instead, it accepts two string fields named 'Username' and 'PasswordHash'. The 'PasswordHash' value that I have been given does indeed look like a hash, and not just a value for a mis-named password field. This is raising a red flag for me. I'm not sure why, but I feel uncomfortable sending a hashed password over the wire for some reason. Off the top of my head I can't think of a reason why this would be a bad thing... Technically, the hash is available on the database anyway. But it's making me nervous, and I'm not sure if there's a reason for this or if I'm just being paranoid.

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• How to split up levels? (cocos2d,box2d,iphone) to save CPU and memory?

  - by cocos2dbeginner

  Hi, so I'm going to create large levels. But there's a problem: There's much unseen space (it's a jump'n run like mario bros.) and this will use memory + cpu. so how could I split up my levels? I'm using Box2D+ cocos2d for iphone. Any ideas? Mayby just set the visible property to NO? But it would be still in the memory :(. But what with the box2d bodies? Destroy and recreate them would be to heavy for the FPS, because I have physics built in which should not be recreated. Should I make fix points where i want to split the level up, than if the player is 200 px away it should preload it. and if the player is 200 px away from the last part of the level I unload it. But there would be the problem with the physics, because on the start of the level it has a unique movement and later if i destroy and recreate it it would do the same. but i don't want that. other ideas?

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• "requiresuniqueemail=true" implementation in asp.net site

  - by domineer

  Hi people I got a social networking site that is running live right now.The first time I launched my site I let requiresuniqueemail=false set-up on my web.config inorder for me to create dummy accounts for testing purposes and to start up the site you know.However the site is kind of stable right now w/ almost 5k members.So I would like to set-up the requiresuniqueemail to true so that users cannot reuse their existing email address and for me to make it sure that there will be unique email ad for each site user.I know the site got like 100 users with the same email address.My question is what could be the problem I'm going to face if I do this right now(requiresuniqueemail="true") and how to do this efficiently(without errors and if possible sitewide say in the global assax)?I tested and I already got an error if I logout an account.Like say a user try to click log-out this code runs: Dim d As DateTime = DateTime.Now.AddMinutes(-1 * Membership.UserIsOnlineTimeWindow) Dim theuser As MembershipUser = Membership.GetUser() theuser.LastActivityDate = d Membership.UpdateUser(theuser) If Not Cache(Page.User.Identity.Name.ToLower() + "currentstatus") Is Nothing Then Cache.Remove(Page.User.Identity.Name.ToLower() + "currentstatus") End If Then an exception occured on updateuser() function saying System.Configuration.Provider.ProviderException: The E-mail supplied is invalid. This is just one instance I know that I encountered a problem. Hoping to hear your ideas guys.....

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• Django extending user model and displaying form

  - by MichalKlich

  Hello, I am writing website and i`d like to implement profile managment. Basic thing would be to edit some of user details by themself, like first and last name etc. Now, i had to extend User model to add my own stuff, and email address. I am having troubles with displaying form. Example will describe better what i would like achieve. This is mine extended user model. class UserExtended(models.Model): user = models.ForeignKey(User, unique=True) kod_pocztowy = models.CharField(max_length=6,blank=True) email = models.EmailField() This is how my form looks like. class UserCreationFormExtended(UserCreationForm): def __init__(self, *args, **kwargs): super(UserCreationFormExtended, self).__init__(*args, **kwargs) self.fields['email'].required = True self.fields['first_name'].required = False self.fields['last_name'].required = False class Meta: model = User fields = ('username', 'first_name', 'last_name', 'email') It works fine when registering, as i need allow users to put username and email but when it goes to editing profile it displays too many fields. I would not like them to be able to edit username and email. How could i disable fields in form? Thanks for help.

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• Symfony2 entity field type alternatives to "property" or "__toString()"?

  - by Polmonino

  Using Symfony2 entity field type one should specify property option: $builder->add('customers', 'entity', array( 'multiple' => true, 'class' => 'AcmeHelloBundle:Customer', 'property' => 'first', )); But sometimes this is not sufficient: think about two customers with the same name, so display the email (unique) would be mandatory. Another possibility is to implement __toString() into the model: class Customer { public $first, $last, $email; public function __toString() { return sprintf('%s %s (%s)', $this->first, $this->last, $this->email); } } The disadvances of the latter is that you are forced to display the entity the same way in all your forms. Is there any other way to make this more flexible? I mean something like a callback function: $builder->add('customers', 'entity', array( 'multiple' => true, 'class' => 'AcmeHelloBundle:Customer', 'property' => function($data) { return sprintf('%s %s (%s)', $data->first, $data->last, $data->email); }, ));

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• Django: Determining if a user has voted or not

  - by TheLizardKing

  I have a long list of links that I spit out using the below code, total votes, submitted by, the usual stuff but I am not 100% on how to determine if the currently logged in user has voted on a link or not. I know how to do this from within my view but do I need to alter my below view code or can I make use of the way templates work to determine it? I have read http://stackoverflow.com/questions/1528583/django-vote-up-down-method but I don't quite understand what's going on ( and don't need any ofjavascriptery). Models (snippet): class Link(models.Model): category = models.ForeignKey(Category, blank=False, default=1) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add=True) modified = models.DateTimeField(auto_now=True) url = models.URLField(max_length=1024, unique=True, verify_exists=True) name = models.CharField(max_length=512) def __unicode__(self): return u'%s (%s)' % (self.name, self.url) class Vote(models.Model): link = models.ForeignKey(Link) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add=True) def __unicode__(self): return u'%s vote for %s' % (self.user, self.link) Views (snippet): def hot(request): links = Link.objects.select_related().annotate(votes=Count('vote')).order_by('-created') for link in links: delta_in_hours = (int(datetime.now().strftime("%s")) - int(link.created.strftime("%s"))) / 3600 link.popularity = ((link.votes - 1) / (delta_in_hours + 2)**1.5) if request.user.is_authenticated(): try: link.voted = Vote.objects.get(link=link, user=request.user) except Vote.DoesNotExist: link.voted = None links = sorted(links, key=lambda x: x.popularity, reverse=True) links = paginate(request, links, 15) return direct_to_template( request, template = 'links/link_list.html', extra_context = { 'links': links, }) The above view actually accomplishes what I need but in what I believe to be a horribly inefficient way. This causes the dreaded n+1 queries, as it stands that's 33 queries for a page containing just 29 links while originally I got away with just 4 queries. I would really prefer to do this using Django's ORM or at least .extra(). Any advice?

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• Building a system that allows users to see a video only once

  - by Bart van Heukelom

  My client wants to distribute a video to some people, specifically car dealers, but he doesn't want the video to end up on Youtube or something like that. Therefore he wants the recipients of the video to be able to see it only once. My idea to implement this is: Generate a unique key per viewer Send each viewer a link to a page with a Flash based video player, with their key in the URL Have Flash get the video from the server. On the server the key is checked and the file sent (using php's readfile or something equivalent). Then the key is invalidated. I was thinking this wouldn't take more than a day to build. I know that if you want somebody to be able to play something, you implicitly give them the power to record it as well, but the client just wants me to make it as hard as possible. Do you think this is secure enough for the intended audience? Anything else I can do to add some security without exceeding the development time of 1 day? I'm also interested in ready made solutions, if they exist.

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• MySQL: SELECT highest column value when WHERE finds similar entries

  - by Ike

  My question is comparable to this one, but not quite the same. I have a database with a huge amount of books, with different editions of some of the same book titles. I'm looking for an SQL statement giving me the highest edition number of each of the titles I'm selecting with a WHERE clause (to find specific book series). Here's what the table looks like: |id|title |edition|year| |--|-------------------------|-------|----| |01|Serie One Title One |1 |2007| |02|Serie One Title One |2 |2008| |03|Serie One Title One |3 |2009| |04|Serie One Title Two |1 |2001| |05|Serie One Title Three |1 |2008| |06|Serie One Title Three |2 |2009| |07|Serie One Title Three |3 |2010| |08|Serie One Title Three |4 |2011| |--|-------------------------|-------|----| The result I'm looking for is this: |id|title |edition|year| |--|-------------------------|-------|----| |03|Serie One Title One |3 |2009| |04|Serie One Title Two |1 |2001| |08|Serie One Title Three |4 |2011| |--|-------------------------|-------|----| The closest I got was using this statement: select id, title, max(edition), max(year) from books where title like "serie one%" group by name; but it returns the highest edition and year and includes the first id it finds: |--|-----------------------|-------|----| |01|Serie One Title One |3 |2009| |04|Serie One Title Two |1 |2001| |05|Serie One Title Three |4 |2011| |--|-----------------------|-------|----| This fancy join also comes close, but doesn't give the right result: select b.id, b.title, b.edition, b.year from books b inner join (select name, max(edition) as maxedition from books group by title) g on b.edition = g.maxedition where b.title like "serie one%" group by title; Using this I'm getting unique titles, but mostly old editions.

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• Is this an acceptable use of "ASCII arithmetic"?

  - by jmgant

  I've got a string value of the form 10123X123456 where 10 is the year, 123 is the day number within the year, and the rest is unique system-generated stuff. Under certain circumstances, I need to add 400 to the day number, so that the number above, for example, would become 10523X123456. My first idea was to substring those three characters, convert them to an integer, add 400 to it, convert them back to a string and then call replace on the original string. That works. But then it occurred to me that the only character I actually need to change is the third one, and that the original value would always be 0-3, so there would never be any "carrying" problems. It further occurred to me that the ASCII code points for the numbers are consecutive, so adding the number 4 to the character "0", for example, would result in "4", and so forth. So that's what I ended up doing. My question is, is there any reason that won't always work? I generally avoid "ASCII arithmetic" on the grounds that it's not cross-platform or internationalization friendly. But it seems reasonable to assume that the code points for numbers will always be sequential, i.e., "4" will always be 1 more than "3". Anybody see any problem with this reasoning? Here's the code. string input = "10123X123456"; input[2] += 4; //Output should be 10523X123456

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• Combining two-part SQL query into one query

  - by user332523

  Hello, I have a SQL query that I'm currently solving by doing two queries. I am wondering if there is a way to do it in a single query that makes it more efficient. Consider two tables: Transaction_Entries table and Transactions, each one defined below: Transactions - id - reference_number (varchar) Transaction_Entries - id - account_id - transaction_id (references Transactions table) Notes: There are multiple transaction entries per transaction. Some transactions are related, and will have the same reference_number string. To get all transaction entries for Account X, then I would do SELECT E.*, T.reference_number FROM Transaction_Entries E JOIN Transactions T ON (E.transaction_id=T.id) where E.account_id = X The next part is the hard part. I want to find all related transactions, regardless of the account id. First I make a list of all the unique reference numbers I found in the previous result set. Then for each one, I can query all the transactions that have that reference number. Assume that I hold all the rows from the previous query in PreviousResultSet UniqueReferenceNumbers = GetUniqueReferenceNumbers(PreviousResultSet) // in Java foreach R in UniqueReferenceNumbers // in Java SELECT * FROM Transaction_Entries where transaction_id IN (SELECT * FROM Transactions WHERE reference_number=R Any suggestions how I can put this into a single efficient query?

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• In mysql, is "explain ..." always safe?

  - by tye

  If I allow a group of users to submit "explain $whatever" to mysql (via Perl's DBI using DBD::mysql), is there anything that a user could put into $whatever that would make any database changes, leak non-trivial information, or even cause significant database load? If so, how? I know that via "explain $whatever" one can figure out what tables / columns exist (you have to guess names, though) and roughly how many records are in a table or how many records have a particular value for an indexed field. I don't expect one to be able to get any information about the contents of unindexed fields. DBD::mysql should not allow multiple statements so I don't expect it to be possible to run any query (just explain one query). Even subqueries should not be executed, just explained. But I'm not a mysql expert and there are surely features of mysql that I'm not even aware of. In trying to come up with a query plan, might the optimizer actual execute an expression in order to come up with the value that an indexed field is going to be compared against? explain select * from atable where class = somefunction(...) where atable.class is indexed and not unique and class='unused' would find no records but class='common' would find a million records. Might 'explain' evaluate somefunction(...)? And then could somefunction(...) be written such that it modifies data?

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• Protecting critical sections based on a condition in C#

  - by NAADEV

  Hello, I'm dealing with a courious scenario. I'm using EntityFramework to save (insert/update) into a SQL database in a multithreaded environment. The problem is i need to access database to see whether a register with a particular key has been already created in order to set a field value (executing) or it's new to set a different value (pending). Those registers are identified by a unique guid. I've solved this problem by setting a lock since i do know entity will not be present in any other process, in other words, i will not have same guid in different processes and it seems to be working fine. It looks something like that: static readonly object LockableObject = new object(); static void SaveElement(Entity e) { lock(LockableObject) { Entity e2 = Repository.FindByKey(e); if (e2 != null) { Repository.Insert(e2); } else { Repository.Update(e2); } } } But this implies when i have a huge ammount of requests to be saved, they will be queued. I wonder if there is something like that (please, take it just as an idea): static void SaveElement(Entity e) { (using ThisWouldBeAClassToProtectBasedOnACondition protector = new ThisWouldBeAClassToProtectBasedOnACondition(e => e.UniqueId) { Entity e2 = Repository.FindByKey(e); if (e2 != null) { Repository.Insert(e2); } else { Repository.Update(e2); } } } The idea would be having a kind of protection that protected based on a condition so each entity e would have its own lock based on e.UniqueId property. Any idea?

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• Does Microsoft Access use the PK fields for anything?

  - by chrismay

  Ok this is going to sound strange, but I have inherited an app that is an Access front end with a SQL Server backend. I am in the process of writing a new front end for it, but... we need to continue using the access front end for a while even after we deploy my new front end for reasons I won't go into. So both the existing Access app and my new app will need to be able to access and work with the data. The problem is the database design is a nightmare. For example some simple parent-child table relationships have like 4 and 5 part composite primary keys. I would REALLY like to remove these PKs and replace them with unique constraints or whatever, and add a new column to each of these tables called ID that is just an identity. If I change the PK and FKs on these tables to more managable fields, will the Access app have problems? What I mean is, does access use the meta data from the tables (PK and FK info) in such a way that it would break the app to change these?

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