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• what patern is layerd architechture in asp.net ?

  - by haansi

  Hi, I am a asp.net developer and don't know much about patterns and architecture. I will very thankful if you can please guide me here. In my web applications I use 4 layers. Web site project (having web forms + code behind cs files, user controls + code behind cs files, master pages + code behind cs files) CustomTypesLayer a class library (having custom types, enumerations, DTOs, constructers, get, set and validations) BusinessLogicLayer a class library (having all business logic, rules and all calls to DAL functions) DataAccessLayer a class library( having just classes communicating to database.) -My user interface just calls BusinessLogicLayer. BusinessLogicLayer do proecessign in it self and for data it calls DataAccessLayer funtions. -Web forms do not calls directly DAL. -CustomTypesLayer is shared by all layers. Please guide me is this approach a pattern ? I though it may be MVC or MVP but pages have there code behind files as well which are confusing me. If it is no patren is it near to some patren ? pleaes guide thanks

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• Could this be considered a well-written PHP5 class?

  - by Ben Dauphinee

  I have been learning OOP principals on my own for a while, and taken a few cracks at writing classes. What I really need to know now is if I am actually using what I have learned correctly, or if I could improve as far as OOP is concerned. I have chopped a massive portion of code out of a class that I have been working on for a while now, and pasted it here. To all you skilled and knowledgeable programmers here I ask: Am I doing it wrong? class acl extends genericAPI{ // -- Copied from genericAPI class protected final function sanityCheck($what, $check, $vars){ switch($check){ case 'set': if(isset($vars[$what])){return(1);}else{return(0);} break; } } // --------------------------------- protected $db = null; protected $dataQuery = null; public function __construct(Zend_Db_Adapter_Abstract $db, $config = array()){ $this->db = $db; if(!empty($config)){$this->config = $config;} } protected function _buildQuery($selectType = null, $vars = array()){ // Removed switches for simplicity sake $this->dataQuery = $this->db->select( )->from( $this->config['table_users'], array('tf' => '(CASE WHEN count(*) > 0 THEN 1 ELSE 0 END)') )->where( $this->config['uidcol'] . ' = ?', $vars['uid'] ); } protected function _sanityRun_acl($sanitycheck, &$vars){ switch($sanitycheck){ case 'uid_set': if(!$this->sanityCheck('uid', 'set', $vars)){ throw new Exception(ERR_ACL_NOUID); } $vars['uid'] = settype($vars['uid'], 'integer'); break; } } private function user($action = null, $vars = array()){ switch($action){ case 'exists': $this->_sanityRun_acl('uid_set', $vars); $this->_buildQuery('user_exists_idcheck', $vars); return($this->db->fetchOne($this->dataQuery->__toString())); break; } } public function user_exists($uid){ return($this->user('exists', array('uid' => $uid))); } } $return = $acl_test->user_exists(1);

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• "Abstract static" method - how?

  - by polyglot

  There are already several SO questions on why there is not abstract static method/field as such, but I'm wondering about how one would go about implementing the following psuedo-code: class Animal { abstract static int getNumberOfLegs(); // not possible } class Chicken inherits Animal { static int getNumberOfLegs() { return 2; } class Dog inherits Animal { static int getNumberOfLegs() { return 4; } Here is the problem: Assuming that I want make sure that every class that inherits Animal to contain getNumberOfLegs() method (i.e. almost like an interface, except I do want the abstract class to implement several methods that are common to all child classes, hence pure interface does not work here). getNumberOfLegs() obviously should be a static method (assuming that in a perfect world we dont' have crippled chicken and dogs so getNumberOfLegs is not instance-dependent). Without an "abstract static" method/field, one can either leave the method out from Animal class, then there is the risk that some child class do not have that method. Or one can make getNumberOfLegs an instance method, but then one would have to instantiate a class to find out how many legs that animal has - even though it is not necessary. How do one usually go about implementing this situation?

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• Omit Properties from WebControl Serialization

  - by Laramie

  I have to serialize several objects inheriting from WebControl for database storage. These include several unecessary (to me) properties that I would prefer to omit from serialization. For example BackColor, BorderColor, etc. Here is an example of an XML serialization of one of my controls inheriting from WebControl. <Control xsi:type="SerializePanel"> <ID>grCont</ID> <Controls /> <BackColor /> <BorderColor /> <BorderWidth /> <CssClass>grActVid bwText</CssClass> <ForeColor /> <Height /> <Width /> ... </Control> I have been trying to create a common base class for my controls that inherits from WebControl and uses the "xxxSpecified" trick to selectively choose not to serialize certain properties. For example to ignore an empty BorderColor property, I'd expect [XmlIgnore] public bool BorderColorSpecified() { return !base.BorderColor.IsEmpty; } to work, but it's never called during serialization. I've also tried it in the class to be serialized as well as the base class. Since the classes themselves might change, I'd prefer not to have to create a custom serializer. Any ideas?

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• Entity Framework Validation & usage

  - by kmsellers

  I'm aware there is an AssociationChanged event, however, this event fires after the association is made. There is no AssociationChanging event. So, if I want to throw an exception for some validation reason, how do I do this and get back to my original value? Also, I would like to default values for my entity based on information from other entities but do this only when I know the entitiy is instanced for insertion into the database. How do I tell the difference between that and the object getting instanced because it is about to be populated based on existing data? Am I supposed to know? Is that considiered business logic that should be outside of my entity business logic? If that's the case, then should I be designing controller classes to wrap all these entities? My concern is that if I deliver back an entity, I want the client to get access to the properties, but I want to retain tight control over validations on how they are set, defaulted, etc. Every example I've seen references context, which is outside of my enity partial class validation, right? BTW, I looked at the EFPocoAdapter and for the life of me cannot determine how to populate lists of from within my POCO class... anyone know how I get to the context from a EFPoco Class?

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• Speed comparison - Template specialization vs. Virtual Function vs. If-Statement

  - by Person

  Just to get it out of the way... Premature optimization is the root of all evil Make use of OOP etc. I understand. Just looking for some advice regarding the speed of certain operations that I can store in my grey matter for future reference. Say you have an Animation class. An animation can be looped (plays over and over) or not looped (plays once), it may have unique frame times or not, etc. Let's say there are 3 of these "either or" attributes. Note that any method of the Animation class will at most check for one of these (i.e. this isn't a case of a giant branch of if-elseif). Here are some options. 1) Give it boolean members for the attributes given above, and use an if statement to check against them when playing the animation to perform the appropriate action. Problem: Conditional checked every single time the animation is played. 2) Make a base animation class, and derive other animations classes such as LoopedAnimation and AnimationUniqueFrames, etc. Problem: Vtable check upon every call to play the animation given that you have something like a vector<Animation>. Also, making a separate class for all of the possible combinations seems code bloaty. 3) Use template specialization, and specialize those functions that depend on those attributes. Like template<bool looped, bool uniqueFrameTimes> class Animation. Problem: The problem with this is that you couldn't just have a vector<Animation> for something's animations. Could also be bloaty. I'm wondering what kind of speed each of these options offer? I'm particularly interested in the 1st and 2nd option because the 3rd doesn't allow one to iterate through a general container of Animations. In short, what is faster - a vtable fetch or a conditional?

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• Passing Extras and screen rotation

  - by Luis A. Florit

  This kind of questions appear periodically. Sorry if this has been covered before, but I'm a newbie and couldn't find the appropriate answer. It deals with the correct implementation of communication between classes and activities. I made a gallery app. It has 3 main activities: the Main one, to search for filenames using a pattern; a Thumb one, that shows all the images that matched the pattern as thumbnails in a gridview, and a Photo activity, that opens a full sized image when you click a thumb in Thumbs. I pass to the Photo activity via an Intent the filenames (an array), and the position (an int) of the clicked thumb in the gridview. This third Photo activity has only one view on it: a TouchImageView, that I adapted for previous/next switching and zooming according to where you shortclick on the image (left, right or middle). Moreover, I added a longclick listener to Photo to show EXIF info. The thing is working, but I am not happy with the implementation... Some things are not right. One of the problems I am experiencing is that, if I click on the right of the image to see the next in the Photo activity, it switches fine (position++), but when rotating the device the original one at position appears. What is happening is that Photo is destroyed when rotating the image, and for some reason it restarts again, without obeying super.onCreate(savedInstanceState), loading again the Extras (the position only changed in Photo, not on the parent activities). I tried with startActivityForResult instead of startActivity, but failed... Of course I can do something contrived to save the position data, but there should be something "conceptual" that I am not understanding about how activities work, and I want to do this right. Can someone please explain me what I am doing wrong, which is the best method to implement what I want, and why? Thanks a lot!!!

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• In Ruby or Python can the very idea of Class be rewritten?

  - by John Berryman

  Howdy All... first time at stack overflow. I'm looking into using some of the metaprogramming features provided by Ruby or Python, but first I need to know the extent to which they will allow me to extend the language. The main thing I need to be able to do is to rewrite the concept of Class. This doesn't mean that I want to rewrite a specific class during run time, but rather I want to make my own conceptualization of what a Class is. To be a smidge more specific here, I want to make something that is like what people normally call a Class, but I want to follow an "open world" assumption. In the "closed world" of normal Classes, if I declare Poodle to be a subclass of Dog to be a subclass of Animal, then I know that Poodle is not going to also be a type of FurCoat. However, in an open world Class, then the Poodle object I've defined may or may not be and object of type FurCoat and we won't know for sure until I explain that I can wear the poodle. (Poor poodle.) This all has to do with a study I'm doing concerning OWL ontologies. Just so you know, I've tried to find information online, but due to the overloading of terms here I haven't found anything helpful. Super thanks, John

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• C++ Eclipse error class mynamespace::mynamespace

  - by user2969329

  I'm new to C++, coming from a Java and web programming background. I specified a header file, with class definition. The class and the namespace have the same name. I do not know if that causes this issue, eclipse is very unspecific. Here is the World.h file: `/* * World.h * * Created on: 5 nov. 2013 * Author: Mo */ #ifndef WORLD_H_ #define WORLD_H_ #include "../../lib/tinyxml/tinyxml.h" #include "Layer.h" namespace World { class World { private: Layer layers[]; public: World(); virtual ~World(); TiXmlElement toXML(); }; } /* namespace World */ #endif /* WORLD_H_ */` The error occurs in the class definition. The only thing eclipse shows is: class World::World I have been googling for the last day and a half, and haven't found anything similar. In other classes, World is not seen as a type: "World" does not name a type. What have I done wrong? Help would be greatly appreciated.

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• Spring MessageSource not being used during validation

  - by Jeremy

  I can't get my messages in messages.properties to be used during Spring validation of my form backing objects. app-config.xml: <bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource"> <property name="basename" value="messages" /> </bean> WEB-INF/classes/messages.properties: NotEmpty=This field should not be empty. Form Backing Object: ... @NotEmpty @Size(min=6, max=25) private String password; ... When I loop through all errors in the BindingResult and output the ObjectError's toString I get this: Field error in object 'settingsForm' on field 'password': rejected value []; codes [NotEmpty.settingsForm.password,NotEmpty.password,NotEmpty.java.lang.String,NotEmpty]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [settingsForm.password,password]; arguments []; default message [password]]; default message [may not be empty] As you can see the default message is "may not be empty" instead of my message "This field should not be empty". I do get my correct message if I inject the messageSource into a controller and output this: messageSource.getMessage("NotEmpty", new Object [] {"password"}, "default empty message", null); So why isn't the validation using my messages.properties? I'm running Spring 3.1.1. Thanks!

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• What is an interface in C (COM) is it the same as a interface in C#

  - by numerical25

  Ok, I know what a interface is, but since I got into C and working with COM objects, it seems an interface in COM is a little different from the interface I know of. So what I am trying to do is bridge the gaps here cause since I been learning C, alot of things have been sounding very familiar to me but are not exactly what they seem. The interface I know of are like contracts. They are objects that have only method declarations, with no body. All classes that implement an interface must include the methods of the interface. The interface I hear about in COM seems to be just pointers. They can not retrieve objects directly but only can retrieve objects through the means of a method. Is this what a COM Interface is ?? If so, then why did they give them the same names if they are completely different. Also I just wanted to add that headers in C++ kind of remind me of the C# Interfaces. Not sure if their are any relations. But anyways, I am just trying to clear that up.

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• Casting pointer to object to void * in C++

  - by JB

  I've been reading StackOverflow too much and started doubting all the code I've ever written, I keep thinking "Is that undefined behavour?" even in code that has been working for ages. So my question - Is it safe and well defined behavour to cast a pointer to an object (In this case abstract interface classes) to a void* and then later on cast them back to the original class and call method using them? I'm fully aware that the code that does this is probably awful. I wouldn't even consider writing it like this now (this is old code which I don't really want to change), so I'm not looking for a discussion of better ways to do this. I already know how to write it better if I ever did this again. But if it's actually broken to rely on this in C++ then I'll have to look at changing the code, if it's merely awful code then changing it won't be a priority. I would have had no doubts about something this simple a year or two ago but as my understanding of C++ increases I actually find I have more and more worries about code being safe under the standards even if it works perfectly well. Perhaps reading too much stack overflow is a bad thing for productivity sometimes :P

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• Obfuscator for .NET assembly (Maybe just a C++ obfuscator?)

  - by Pirate for Profit

  The software company I work for is using a ton of open source LGPL/BSD/MIT C++ code that we have written wrappers around to port "helper classes" into a .NET assembly, via C++/CLI. These libraries have wrapped old cryptic APIs into easy-to-use ones based on common sense, and will be very helpful for a lot of different tasks will be included in many future client's applications, and we might even license it to other software companies in the same field. So naturally we are tasked with looking into solutions for securing the code from prying eyes. What we're trying to do is stop the casual observer from seeing what's going on. Now I have hacked some crazy shit in EverQuest and other video games in my day so I know with enough tireless effort anything can be done. But we don't want to make it easy for whomever. To the point, besides the Visual Studio compiler's optimizations, is there's a C++ obfuscator or .NET assembly obfuscator (after it's been built o.O) or something that would scramble everything up, re-arrange data structures, string constants, etc. idk? And if such a thing exists, we'd be curious to know how that would impact performance, as some sections of code are time critical (funny saying that using a managed M$ framework).

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• Installing Plugins from Cloud p2 repository in Eclipse IDE

  - by user1495036

  I have been recently reading a lot about p2 for a requirement of mine. Most of the p2 documentation online points to p2 for RCP. My requirement is for a plugin repo. I have a plugin that is used within Eclipse IDE. I dnt want to change the repo location but based on the Eclipse Version, if the user looks for Install New Software or Check for Updates it needs to download the respective plugins. My repo currently contains all the plugins for all the versions. but i need to everytime give a different URL to my user based on the Version. For e.g i am using Eclipse 3.7(Indigo). I install the plugin thru Install New Software by adding the p2 Repo URL. Now the user decides to for some requirement move to Eclipse 3.6, I want him to connect to the same p2 Repo URL and download the plugins created for Eclipse 3.6. This is definitely possible using p2 Discovery, or i could categorize the downloads using composite repository but i dnt want to do any of these. Just want to kno is there any API that i can hold on to, so that before processing the URL and finding the updates, i can check the version of Eclipse and redirect it based on the version to an internal URL. This is possible in RCP, want to kno if i can do it in Eclipse p2 UI. All the p2 UI looks to be internal classes. Any directives would be appreciated. Malai

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• Is it acceptable to wrap PHP library functions solely to change the names?

  - by Carson Myers

  I'm going to be starting a fairly large PHP application this summer, on which I'll be the sole developer (so I don't have any coding conventions to conform to aside from my own). PHP 5.3 is a decent language IMO, despite the stupid namespace token. But one thing that has always bothered me about it is the standard library and its lack of a naming convention. So I'm curious, would it be seriously bad practice to wrap some of the most common standard library functions in my own functions/classes to make the names a little better? I suppose it could also add or modify some functionality in some cases, although at the moment I don't have any examples (I figure I will find ways to make them OO or make them work a little differently while I am working). If you saw a PHP developer do this, would you think "Man, this is one shoddy developer?" Additionally, I don't know much (or anything) about if/how PHP is optimized, and I know that usually PHP performace doesn't matter. But would doing something like this have a noticeable impact on the performance of my application?

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• Compare Properties automatically

  - by juergen d

  I want to get the names of all properties that changed for matching objects. I have these (simplified) classes: public enum PersonType { Student, Professor, Employee } class Person { public string Name { get; set; } public PersonType Type { get; set; } } class Student : Person { public string MatriculationNumber { get; set; } } class Subject { public string Name { get; set; } public int WeeklyHours { get; set; } } class Professor : Person { public List<Subject> Subjects { get; set; } } Now I want to get the objects where the Property values differ: List<Person> oldPersonList = ... List<Person> newPersonList = ... List<Difference> = GetDifferences(oldPersonList, newPersonList); public List<Difference> GetDifferences(List<Person> oldP, List<Person> newP) { //how to check the properties without casting and checking //for each type and individual property?? //can this be done with Reflection even in Lists?? } In the end I would like to have a list of Differences like this: class Difference { public List<string> ChangedProperties { get; set; } public Person NewPerson { get; set; } public Person OldPerson { get; set; } } The ChangedProperties should contain the name of the changed properties.

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• Refer to a Spark view component in code

  - by David

  I'm building a mobile AIR app using Flash Builder 4.5. The initial view in my views package is TestHomeView.mxml. I want to refer to it in one of my .as classes elsewhere in the app, and I'm not sure how to do that. Theoretically I should be able to add an "id" attribute to TestHomeView.mxml, but FB gives me an error: "id is not allowed on the root tag of a component". The root tag is s:view. The reason I need to do this is that within another class I make various calculations and then need to pass an array of values to a component in my view class. So in SomeOtherActionScriptClass.as I first assemble the array, myArray, and then in that class I want to do this: myViewComponent.viewArray = myArray; If I'm going to do that, I also need to import the view class into the .as class, which strikes me as weird. So is there a simple way to do what I want, or do I have to dispatch a custom event which contains the array, and listen for it in the view class? Thanks.

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• I have a bunch of template parameters that I want to hide from my users. How can I do this?

  - by Alex

  I have a superclass which is defined in terms of a few internal types it uses. Subclassing is performed as so: template <class InternalType1, class InternalType2> class Super { ... } class Sub : Super <interalTypeClass1, interalTypeClass2> { ... } But when I want to write a function that takes a pointer to the superclass, this happens : template <class InternalType1, class InternalType2> void function(Super<InternalType1, InternalType2>* in) { ... } The user really shouldn't know anything about the inside classes, and should really just concern himself with the use of the function. Some of these template lists become very very large, and expecting the user to pass them every time is wasteful, in my opinion. Any suggestions? EDIT: The function needs to know the internal types in use, so unless there is a way to access template types at compile time, I think there is no solution? Potential solution: Have each class do the following: #define SubTemplateArgs <SubTypeName, SubInternalType1, SubInternalType2> ?

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• Windows XP: RegSvr32 /i:[cmdline]: What exactly is "Command line" in this case?

  - by Kim

  I am trying to register a dll using regsvr32 in a cmd window. I do this on an administrator account, but I need this dll to be registered for all the users. Turns out regsvr32 does not do that, it only registers for your current user. Well, when you use it this way anyways: "regsvr32 /i "C:\MyDll.dll"" What happens; The entry is added to Local_User, and Classes in the registry, but not Local_Machine. The msdn article on regsvr32 says it also takes a [cmdline] when using the /i option. But the article fails to specify what I can put in place of [cmdline]. Google is refusing to help me as well, so I'm a bit stuck on this. I realize this is not exactly on the topic of programming, but this is something programmers might know, so... Has anyone run into this before? Perhaps someone knows how this [cmdline] tag works? Are there any other ways to add this dll to all users? (Apart from editing the registry manually that is.) Any insight would be greatly appreciated!

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• ReflectionTypeLoadException when I try to run Enable-Migrations with Entity Framework 5.0

  - by Eric Anastas

  I'm trying to use Entity Framework for the first time on one of my projects. I'm using the code first workflow to automatically create my database. Intitaly setting up the database worked fine. Now I'm trying to migrate changes in my classes into the database. The tutorial I'm reading says I need to run "Enable-Migrations" in the package manager console. Yet when I do this I get the following error PM> Enable-Migrations System.Reflection.ReflectionTypeLoadException: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information. at System.Reflection.RuntimeModule.GetTypes(RuntimeModule module) at System.Reflection.RuntimeModule.GetTypes() at System.Reflection.Assembly.GetTypes() at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.FindType[TBase](String typeName, Func`2 filter, Func`2 noType, Func`3 multipleTypes, Func`3 noTypeWithName, Func`3 multipleTypesWithName) at System.Data.Entity.Migrations.Design.ToolingFacade.GetContextTypeRunner.RunCore() at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.Run() Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information. What am I doing wrong? How do I retrieve the loader exceptions property? Also NuGet says I have EF 5.0, but Version property of the EntityFramework item in my project references says 4.4.0.0. I'm not sure if this is related.

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• Oddities in Linq-to-SQL generated code related to property change/changing events

  - by Lasse V. Karlsen

  I'm working on creating my own Linq-to-Sql generated classes in order to learn the concepts behind it all. I have some questions, if anyone knows the answer to one or more of these I'd be much obliged. The code below, and thus the questions, are from looking at code generated by creating a .DBML file in the Visual Studio 2010 designer, and inspecting the .Designer.cs file afterwards. 1. Why is INotifyPropertyChanging not passing the property name The event raising method is defined like this: protected virtual void SendPropertyChanging() Why isn't the name of the property that is changing passed to the event here? It is defined to be part of the EventArgs descendant that is passed to the event handler, but the method only passes an empty such value to it. 2. Why are the EntitySet<X> attach/detach methods not raising property changed? For an EntitySet<X> reference, the following two methods are generated: private void attach_EmailAddress1s(EmailAddress1 entity) { this.SendPropertyChanging(); entity.Person1 = this; } private void detach_EmailAddress1s(EmailAddress1 entity) { this.SendPropertyChanging(); entity.Person1 = null; } Why isn't SendPropertyChanged also called here? I'm sure I have more questions later, but for now these will suffice :)

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• importing symbols from python package into caller's namespace

  - by Paul C

  I have a little internal DSL written in a single Python file that has grown to a point where I would like to split the contents across a number of different directories + files. The new directory structure currently looks like this: dsl/ __init__.py types/ __init__.py type1.py type2.py and each type file contains a class (e.g. Type1). My problem is that I would like to keep the implementation of code that uses this DSL as simple as possible, something like: import dsl x = Type1() ... This means that all of the important symbols should be available directly in the user's namespace. I have tried updating the top-level __init__.py file to import the relevant symbols: from types.type1 import Type1 from types.type2 import Type2 ... print globals() the output shows that the symbols are imported correctly, but they still aren't present in the caller's code (the code that's doing the import dsl). I think that the problem is that the symbols are actually being imported to the 'dsl' namespace. How can I change this so that the classes are also directly available in the caller's namespace?

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• Grails one-to-many mapping with joinTable

  - by intargc

  I have two domain-classes. One is a "Partner" the other is a "Customer". A customer can be a part of a Partner and a Partner can have 1 or more Customers: class Customer { Integer id String name static hasOne = [partner:Partner] static mapping = { partner joinTable:[name:'PartnerMap',column:'partner_id',key:'customer_id'] } } class Partner { Integer id static hasMany = [customers:Customer] static mapping = { customers joinTable:[name:'PartnerMap',column:'customer_id',key:'partner_id'] } } However, whenever I try to see if a customer is a part of a partner, like this: def customers = Customer.list() customers.each { if (it.partner) { println "Partner!" } } I get the following error: org.springframework.dao.InvalidDataAccessResourceUsageException: could not execute query; SQL [select this_.customer_id as customer1_162_0_, this_.company as company162_0_, this_.display_name as display3_162_0_, this_.parent_customer_id as parent4_162_0_, this_.partner_id as partner5_162_0_, this_.server_id as server6_162_0_, this_.status as status162_0_, this_.vertical_market as vertical8_162_0_ from Customer this_]; nested exception is org.hibernate.exception.SQLGrammarException: could not execute query It looks as if Grails is thinking partner_id is a part of the Customer query, and it's not... It is in the PartnerMap table, which is supposed to find the customer_id, then get the Partner from the corresponding partner_id. Anyone have any clue what I'm doing wrong? Edit: I forgot to mention I'm doing this with legacy database tables. So I have a Partner, Customer and PartnerMap table. PartnerMap has simply a customer_id and partner_id field.

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• Linq - reuse expression on child property

  - by user175528

  Not sure if what I am trying is possible or not, but I'd like to reuse a linq expression on an objects parent property. With the given classes: class Parent { int Id { get; set; } IList<Child> Children { get; set; } string Name { get; set; } } class Child{ int Id { get; set; } Parent Dad { get; set; } string Name { get; set; } } If i then have a helper Expression<Func<Parent,bool> ParentQuery() { Expression<Func<Parent,bool> q = p => p.Name=="foo"; } I then want to use this when querying data out for a child, along the lines of: using(var context=new Entities.Context) { var data=context.Child.Where(c => c.Name=="bar" && c.Dad.Where(ParentQuery)); } I know I can do that on child collections: using(var context=new Entities.Context) { var data=context.Parent.Where(p => p.Name=="foo" && p.Childen.Where(childQuery)); } but cant see any way to do this on a property that isnt a collection. This is just a simplified example, actually the ParentQuery will be more complex and I want to avoid having this repeated in multiple places as rather than just having 2 layers I'll have closer to 5 or 6, but all of them will need to reference the parent query to ensure security.

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• C++ variable to const expression

  - by user1344784

  template <typename Real> class A{ }; template <typename Real> class B{ }; //... a few dozen more similar template classes class Computer{ public slots: void setFrom(int from){ from_ = from; } void setTo(int to){ to_ = to; } private: template <int F, int T> void compute(){ using boost::fusion::vector; using boost::fusion::at_c; vector<A<float>, B<float>, ...> v; at_c<from_>(v).operator()(at_c<to_>(v)); //error; needs to be const-expression. }; This question isn't about Qt, but there is a line of Qt code in my example. The setFrom() and setTo() are functions that are called based on user selection via the GUI widget. The root of my problem is that 'from' and 'to' are variables. In my compute member function I need to pick a type (A, B, etc.) based on the values of 'from' and 'to'. The only way I know how to do what I need to do is to use switch statements, but that's extremely tedious in my case and I would like to avoid. Is there anyway to convert the error line to a constant-expression?

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