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• How do "and" and "or" work when combined in one statement?

  - by orokusaki

  For some reason this function confused me: def protocol(port): return port == "443" and "https://" or "http://" Can somebody explain the order of what's happening behind the scenes to make this work the way it does. I understood it as this until I tried it: Either A) def protocol(port): if port == "443": if bool("https://"): return True elif bool("http://"): return True return False Or B) def protocol(port): if port == "443": return True + "https://" else: return True + "http://" Is this some sort of special case in Python, or am I completely misunderstanding how statements work?

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• Disjunction in ActiveRecord

  - by samuil

  Is it possible to use ActiveRecord named_scopes to create one query with sql OR clauses? When I use Model.scope1.scope2 generated query is conjunction of these scopes.

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• Database schema to store AND, OR relation, association

  - by user455387

  Many thanks for your help on this. In order for an entreprise to get a call for tender it must meet certain requirements. For the first example the enterprise must have a minimal class 4, and have qualification 2 in sector 5. Minimal class is always one number. Qualification can be anything (single, or multiple using AND, OR logical operators) I have created tables in order to map each number to it's given name. Now I need to store requirements in the database. minimal class 4 Sector Qualification 5.2 minimal class 2 Sector Qualifications 3.9 and 3.10 minimal class 3 Sector Qualifications 6.1 or 6.3 minimal class 1 Sector Qualifications (3.1 and 3.2) or 5.6 class Domain < ActiveRecord::Base has_many :domain_classes has_many :domain_sectors has_many :sector_qualifications, :through => :domain_sectors end class DomainClass < ActiveRecord::Base belongs_to :domain end class DomainSector < ActiveRecord::Base belongs_to :domain has_many :sector_qualifications end class SectorQualification < ActiveRecord::Base belongs_to :domain_sector end create_table "domains", :force => true do |t| t.string "name" end create_table "domain_classes", :force => true do |t| t.integer "number" t.integer "domain_id" end create_table "domain_sectors", :force => true do |t| t.string "name" t.integer "number" t.integer "domain_id" end create_table "sector_qualifications", :force => true do |t| t.string "name" t.integer "number" t.integer "domain_sector_id" end

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• How to determine if CNF formula is satisfiable in Scheme?

  - by JJBIRAN

  Program a SCHEME function sat that takes one argument, a CNF formula represented as above. If we had evaluated (define cnf '((a (not b) c) (a (not b) (not d)) (b d))) then evaluating (sat cnf) would return #t, whereas (sat '((a) (not a))) would return (). You should have following two functions to work: (define comp (lambda (lit) ; This function takes a literal as argument and returns the complement literal as the returning value. Examples: (comp 'a) = (not a), and (comp '(not b)) = b. (define consistent (lambda (lit path) This function takes a literal and a list of literals as arguments, and returns #t whenever the complement of the first argument is not a member of the list represented by the 2nd argument; () otherwise. . Now for the sat function. The real searching involves the list of clauses (the CNF formula) and the path that has currently been developed. The sat function should merely invoke the real "workhorse" function, which will have 2 arguments, the current path and the clause list. In the initial call, the current path is of course empty. Hints on sat. (Ignore these at your own risk!) (define sat (lambda (clauselist) ; invoke satpath (define satpath (lambda (path clauselist) ; just returns #t or () ; base cases: ; if we're out of clauses, what then? ; if there are no literals to choose in the 1st clause, what then? ; ; then in general: ; if the 1st literal in the 1st clause is consistent with the ; current path, and if << returns #t, ; then return #t. ; ; if the 1st literal didn't work, then search << ; the CNF formula in which the 1st clause doesn't have that literal Don't make this too hard. My program is a few functions averaging about 2-8 lines each. SCHEME is consise and elegant! The following expressions may help you to test your programs. All but cnf4 are satisfiable. By including them along with your function definitions, the functions themselves are automatically tested and results displayed when the file is loaded. (define cnf1 '((a b c) (c d) (e)) ) (define cnf2 '((a c) (c))) (define cnf3 '((d e) (a))) (define cnf4 '( (a b) (a (not b)) ((not a) b) ((not a) (not b)) ) ) (define cnf5 '((d a) (d b c) ((not a) (not d)) (e (not d)) ((not b)) ((not d) (not e)))) (define cnf6 '((d a) (d b c) ((not a) (not d) (not c)) (e (not c)) ((not b)) ((not d) (not e)))) (write-string "(sat cnf1) ") (write (sat cnf1)) (newline) (write-string "(sat cnf2) ") (write (sat cnf2)) (newline) (write-string "(sat cnf3) ") (write (sat cnf3)) (newline) (write-string "(sat cnf4) ") (write (sat cnf4)) (newline) (write-string "(sat cnf5) ") (write (sat cnf5)) (newline)

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• why my array is losing it's contents when I refresh the page?

  - by Fernando SBS

  I have created an: var checkboxFarm = new Array(); then I want to record a checkbox status in that array, as there are 11 checkboxes. Button.addEventListener("click", function() { rp_farmAtivada(index); }, false); when clicked change the variable in the array: function rp_farmAtivada(index) { checkboxFarm[index] = !checkboxFarm[index]; }; but every time I refresh the page it loses all the checkboxes status and I'm aware that all that array gets the "undefined" value. the checkboxFarm array is defined in the beginning of the script, so it should have a global scope. Am I missing something?

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• Python `if x is not None` or `if not x is None`?

  - by orokusaki

  I've always thought of the if not x is None version to be more clear, but Google's style guide implies (based on this excerpt) that they use if x is not None. Is there any minor performance difference (I'm assuming not), and is there any case where one really doesn't fit (making the other a clear winner for my convention)?* *I'm referring to any singleton, rather than just None. ...to compare singletons like None. Use is or is not.

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• C# bool as enum?

  - by fearofawhackplanet

  the following is not legal, but is there any way to do something similar? public enum DatastoreFunctionResult : bool { Error, OK }

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• Why doesn't c++ have &&= or ||= for booleans?

  - by Kache4

  Is there "very bad thing" that can happen &&= and ||= were used as syntactic sugar for bool foo = foo && bar and bool foo = foo || bar?

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• Python 3 order of testing undetermined

  - by user578598

  string='a' p=0 while (p <len(string)) & (string[p]!='c') : p +=1 print ('the end but the process already died ') while (p <1) & (string[p]!='c') : IndexError: string index out of range I want to test a condition up to the end of a string (example string length=1) why are both parts of the and executed is the condition is already false! as long as p < len(string). the second part does not even need executing. if it does a lot of performance can be lost

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• fastest method for minimum of two numbers

  - by user85030

  I was going through mit's opencourseware related to performance engineering. The quickest method (requiring least number of clock cycles) for finding the minimum of two numbers(say x and y) is stated as: min= y^((x^y) & -(x<y)) The output of the expression x < y can be 0 or 1 (assuming C is being used) which then changes to -0 or -1. I understand that xor can be used to swap two numbers. Questions: 1. How is -0 different from 0 and -1 in terms of binary? 2. How is that result used with the and operator to get the minimum? Thanks in advance.

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• Variables combined with && and ||

  - by gcc

  What do the last lines mean? a=0; b=0; c=0; a && b++; c || b--; Can you vary this question to explain with more interesting example?

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• How can I use && in if in Ruby on Rails?

  - by Angela

  I tried the following && conditional for my if statement and I get a "bad range" error: <% if (from_today(contact, call.days) == 0..7) && (show_status(contact, call) == 'no status') %> Why and how can I fix it? The only other way I could do it was to have a second nested if statement and break it apart...not pretty :(

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• Should I use C(99) booleans ? ( also c++ booleans in c++ ?)

  - by Roman A. Taycher

  I haven't done much c programming but when I do when I need a false I put 0 when I want true I put 1, (ex. while(1)), in other cases I use things like "while(ptr)" or "if(x)". Should I try using C99 booleans, should I recommend them to others if I'm helping people new to programming learn c basics(thinking of cs 1?? students)? I'm pretty sure the Visual Studio compiler supports c99 bools, but do a lot of projects (open source and c apps in industry) compile for c89? If I don't use C bools should I at least do something like #define TRUE 1 #define FALSE 0? Also what about c++ Booleans (for c++)?

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• MYSQL question - AND or OR?

  - by U22199

  Which is a better way to select ans and quest from the table? SELECT * FROM tablename WHERE option='ans' OR option='quest'"; OR SELECT * FROM tablename WHERE option='ans' AND option='quest'"; Thanks so much!

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• Are booleans as method arguments unacceptable?

  - by koschi

  A colleague of mine states that booleans as method arguments are not acceptable. They shall be replaced by enumerations. At first I did not see any benefit, but he gave me an example. What's easier to understand? file.writeData( data, true ); Or enum WriteMode { Append, Overwrite }; file.writeData( data, Append ); Now I got it! ;-) This is definitely an example where an enumeration as second parameter makes the code much more readable. So, what's your opinion on this topic?

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• How to name a method that both performs a task and returns a boolean as a status?

  - by Limbo Exile

  If there is a method bool DoStuff() { try { // doing stuff... return true; } catch (Exception ex) { return false; } } should it rather be called IsStuffDone()? Both names could be misinterpreted by the user: If the name is DoStuff() why does it return a boolean? If the name is IsStuffDone() it is not clear whether the method performs a task or only checks its result. Is there a convention for this case? Or an alternative approach, as this one is considered flawed? For example in languages that have output parameters, like C#, a boolean status variable could be passed to the method as one and the method's return type would be void.

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• Is it wrong to use a boolean parameter to determine behavior?

  - by Ray

  I have seen a practice from time to time that "feels" wrong, but I can't quite articulate what is wrong about it. Or maybe it's just my prejudice. Here goes: A developer defines a method with a boolean as one of its parameters, and that method calls another, and so on, and eventually that boolean is used, solely to determine whether or not to take a certain action. This might be used, for example, to allow the action only if the user has certain rights, or perhaps if we are (or aren't) in test mode or batch mode or live mode, or perhaps only when the system is in a certain state. Well there is always another way to do it, whether by querying when it is time to take the action (rather than passing the parameter), or by having multiple versions of the method, or multiple implementations of the class, etc. My question isn't so much how to improve this, but rather whether or not it really is wrong (as I suspect), and if it is, what is wrong about it.

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• Java: private static boolean a,b,c,d <--each has the same prefix?

  - by HH

  Are they equivalent? private static boolean readAllFiles = false,readAllDirs = false; private static boolean readAllFiles = false; private static boolean readAllDirs = false; CASE TRUE: Have they still the same prefix with different values? private static boolean readAllFiles = false,readAllDirs = true;

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• How to filter rows in JTable based on boolean valued columns?

  - by vinny

  Im trying to filter rows based on a column say c1 that contains boolean values. I want to show only rows that have 'true' in c1. I looked up the examples in http://java.sun.com/docs/books/tutorial/uiswing/components/table.html#sorting. The example uses a regex filter. Is there any way I can use boolean values to filter rows? Following is the code Im using (borrowed from the example) private void filter(boolean show) { RowFilter<TableModel, Object> filter = null; TableModel model = jTb.getModel(); boolean value = (Boolean) model.getValueAt(0,1); //If current expression doesn't parse, don't update. try { // I need to used 'value' to filter instead of filterText. filter =RowFilter.regexFilter(filterText, 0); } catch (java.util.regex.PatternSyntaxException e) { return; } sorter.setRowFilter(filter); } thank you.

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• Defining a dd/mm/yyyy field within an abstract table model

  - by Simon Andi

  I have defined an abstract table model but one of the columns should house date values as dd/mm/yyyy format not sure how to do this. I have a external global file and have hard coded the dates as dd/mm/yyyy. How can I define this column within my abstract table model so that to only allow only dates having dd/mm/yyyy format. public class OptraderGlobalParameters { public static boolean DEBUG = true; //Set DEBUG = true for Debugging /*=========================*/ /*Table Array For Dividends*/ /*=========================*/ public static String[] columnNames = {"Date", "Dividend", "Actual", "Yield (%)" }; public static Object[][] data = { {"dd/mm/yyyy", new Double(5), new Boolean(false), new Boolean(false)}, {"dd/mm/yyyy", new Double(5), new Boolean(false), new Boolean(false)}, {"dd/mm/yyyy", new Double(5), new Boolean(false), new Boolean(false)}, {"dd/mm/yyyy", new Double(5), new Boolean(false), new Boolean(false)}, {"dd/mm/yyyy", new Double(5), new Boolean(false), new Boolean(false)}, }; }

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• PathTooLongException after migrating from ASP.NET MVC 1 to ASP.NET MVC 2

  - by admax

  I had updated my app from MVC 1 to MVC 2. After that some pages throws PathTooLongException: [PathTooLongException: The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters, and the directory name must be less than 248 characters.] System.IO.Path.SafeSetStackPointerValue(Char* buffer, Int32 index, Char value) +7493057 System.IO.Path.NormalizePathFast(String path, Boolean fullCheck) +387 System.IO.Path.NormalizePath(String path, Boolean fullCheck) +36 System.IO.Path.GetFullPathInternal(String path) +21 System.Security.Util.StringExpressionSet.CanonicalizePath(String path, Boolean needFullPath) +73 System.Security.Util.StringExpressionSet.CreateListFromExpressions(String[] str, Boolean needFullPath) +278 System.Security.Permissions.FileIOPermission.AddPathList(FileIOPermissionAccess access, AccessControlActions control, String[] pathListOrig, Boolean checkForDuplicates, Boolean needFullPath, Boolean copyPathList) +87 System.Security.Permissions.FileIOPermission..ctor(FileIOPermissionAccess access, String path) +65 System.Web.InternalSecurityPermissions.PathDiscovery(String path) +29 System.Web.HttpRequest.MapPath(VirtualPath virtualPath, VirtualPath baseVirtualDir, Boolean allowCrossAppMapping) +146 System.Web.HttpRequest.MapPath(VirtualPath virtualPath) +37 System.Web.HttpServerUtility.Execute(IHttpHandler handler, TextWriter writer, Boolean preserveForm, Boolean setPreviousPage) +43 System.Web.HttpServerUtility.Execute(IHttpHandler handler, TextWriter writer, Boolean preserveForm) +28 System.Web.HttpServerUtilityWrapper.Execute(IHttpHandler handler, TextWriter writer, Boolean preserveForm) +22 System.Web.Mvc.ViewPage.RenderView(ViewContext viewContext) +284 System.Web.Mvc.WebFormView.RenderViewPage(ViewContext context, ViewPage page) +82 System.Web.Mvc.WebFormView.Render(ViewContext viewContext, TextWriter writer) +85 System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +267 System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult) +10 System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +320 System.Web.Mvc.Controller.ExecuteCore() +104 System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +36 System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +7 System.Web.Mvc.<c_DisplayClass8.b_4() +34 System.Web.Mvc.Async.<c_DisplayClass1.b_0() +21 System.Web.Mvc.Async.<c__DisplayClass81.<BeginSynchronous>b__7(IAsyncResult _) +12 System.Web.Mvc.Async.WrappedAsyncResult1.End() +53 System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +30 System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +7 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8678910 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155 I know the issue with 260-character-url-lenght in ASP.NET, but my app works fine before update to ASP.NET MVC 2.0!

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• Why doesn't my Unity DependencyResolver work on shared hosting but works locally?

  - by frennky

  I'm trying to deploy ASP.NET MVC 3 application wich uses Unity as a IoC container. Application works fine on local server, but when deployed it throws an exception: No parameterless constructor defined for this object. And this is thrown for a controller that should get some repository injected by my Unity DependencyResolver. I've installed Unity with NuGet so it should be referenced directly, and I've checked that it gets copied to bin folder. Edit: Here's the stack trace: [MissingMethodException: No parameterless constructor defined for this object.] System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck) +0 System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache) +98 System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean skipCheckThis, Boolean fillCache) +241 System.Activator.CreateInstance(Type type, Boolean nonPublic) +69 System.Web.Mvc.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType) +67 [InvalidOperationException: An error occurred when trying to create a controller of type 'nBlog.Controllers.HomeController'. Make sure that the controller has a parameterless public constructor.] System.Web.Mvc.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType) +182 System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +80 System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) +74 System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +196 System.Web.Mvc.<>c__DisplayClass6.<BeginProcessRequest>b__2() +49 System.Web.Mvc.<>c__DisplayClassb`1.<ProcessInApplicationTrust>b__a() +13 System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f) +7 System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +22 System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Func`1 func) +124 System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +98 System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) +50 System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) +16 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8841400 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +18 Anyone have an idea what might be the problem?

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• ASP.NEt MVC 2 application error on IIS7 works fine on local machine

  - by aspCoolguy

  My ASP.NET MVC2 application is developed using 1. VS 2010 2. Linq To SQL for Models Here is Call controller code: namespace CallTrackMVC.Controllers { public class CallController : Controller { private CallTrackRepository repository; public CallController():this(new CallTrackRepository()) { } public CallController(CallTrackRepository newRepository) { repository = newRepository; } } } Error on IIS7 when browsing the Call Create page is NullReferenceException: Object reference not set to an instance of an object.] CallTrackMVC.Models.ExecOfficeDataContext..ctor() in C:\ClearCase\rartadi_view\STS_Dev_TEST\CallTrackMVC\Models\ExecOffice.designer.cs:71 CallTrackMVC.Controllers.CallController..ctor() in C:\ClearCase\rartadi_view\STS_Dev_TEST\CallTrackMVC\Controllers\CallController.cs:16 [TargetInvocationException: Exception has been thrown by the target of an invocation.] System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck) +0 System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache) +117 System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean skipCheckThis, Boolean fillCache) +247 System.Activator.CreateInstance(Type type, Boolean nonPublic) +106 System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +102 [InvalidOperationException: **An error occurred when trying to create a controller of type 'CallTrackMVC.Controllers.CallController'. Make sure that the controller has a parameterless public constructor.**] System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +541 System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) +85 System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +165 System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +80 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +389 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +371 Code in Global.asax is protected void Application_Start() { AreaRegistration.RegisterAllAreas(); RegisterRoutes(RouteTable.Routes); } Any suggestion would be a great help.

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• How do I insert the null value in a Boolean attribute when using Hibernate?

  - by Pedro Morte Rolo

  I have a class with a Boolean attribute. When I instantiate and persist this class, the Boolean attribute is stored with the "false" value instead of the expectable "null". How can I set a Boolean attribute to "Null"?

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• Why is it bad to use boolean flags in databases? And what should be used instead?

  - by David Chanin

  I've been reading through some of guides on database optimization and best practices and a lot of them suggest not using boolean flags at all in the DB schema (ex http://forge.mysql.com/wiki/Top10SQLPerformanceTips). However, they never provide any reason as to why this is bad. Is it a peformance issue? is it hard to index or query properly? Furthermore, if boolean flags are bad, what should you use to store boolean values in a database? Is it better to store boolean flags as an integer and use a bitmask? This seems like it would be less readable.

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