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• What are the responsibilities of the data layer?

  - by alimac83

  I'm working on a project where I had to add a data layer to my application. I've always thought that the data layer is purely responsible for CRUD functions ie. shouldn't really contain any logic but should simply retrieve data for the business layer to manipulate. However I'm a little confused with my project because I'm not sure whether I've structured my app correctly for this scenario. Basically I'm trying to retrieve a list of products from the database that fall within a certain pricing threshold. At the moment I have a function in my data layer that basically returns all products where price min threshold and price < max threshold. But it got me thinking that maybe this is incorrect. Should the data layer simply return a list of ALL products and then the business logic do the filtering? I'm pretty confused over whether the data layer should simply provide methods that allow the business layer to get raw data or whether it should be responsible for getting filtered data too? If anyone has an article or something explaining this in detail it'd be very helpful. Thanks

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• What VS Projecttype for Model and Database?

  - by Tim

  Hello folks, i've just started a new asp.net project which could increase fastly(a small erp-system for our company). So i thought it would be a good idea to split at least the model from the view/controller(the asp.net project). Because it could be that i need to access some classes and the database from a windows app in future, i dicided to put the Model into its own Project. What Visual Studio 2005 Professional Projecttype is most suitable for this requirement and why? SqlServerProject (DB is MS Sql Server 2005 EP) Class Library Web Service Application Database project no separate Project/other(keep in mind VS 2005 has no ASP.NET MVC-Project) Thanks

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• Database Modelling - Conceptually different entities but with near identical fields

  - by Andrew Shepherd

  Suppose you have two sets of conceptual entities: MarketPriceDataSet which has multiple ForwardPriceEntries PoolPriceForecastDataSet which has multiple PoolPriceForecastEntry Both different child objects have near identical fields: ForwardPriceEntry has MarketPriceDataSetId (foreign key to parent table) StartDate EndDate SimulationItemId ForwardPrice PoolPriceForecastEntry has PoolPriceForecastDataSetId (foreign key to parent table) StartDate EndDate SimulationItemId ForecastPoolPrice If I modelled them as separate tables, the only difference would be the foreign key, and the name of the price field. There has been a debate as to whether the two near identical tables should be merged into one. Options I've thought of to model this is: Just keep them as two independent, separate tables Have both sets in the one table with an additional "type" field, and a parent_id equalling a foreign key to either parent table. This would sacrifice referential integrity checks. Have both sets in the one table with an additional "type" field, and create a complicated sequence of joining tables to maintain referential integrity. What do you think I should do, and why?

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• Singleton Pattern combine with a Decorator

  - by Mike

  Attached is a classic Decorator pattern. My question is how would you modify the below code so that you can wrap zero or one of each topping on to the Pizza Right now I can have a Pepporini - Sausage -- Pepporini -- Pizza class driving the total cost up to $10, charging twice for Pepporini. I don't think I want to use the Chain of Responsibility pattern as order does not matter and not all toppings are used? Thank you namespace PizzaDecorator { public interface IPizza { double CalculateCost(); } public class Pizza: IPizza { public Pizza() { } public double CalculateCost() { return 8.00; } } public abstract class Topping : IPizza { protected IPizza _pizzaItem; public Topping(IPizza pizzaItem) { this._pizzaItem = pizzaItem; } public abstract double CalculateCost(); } public class Pepporini : Topping { public Pepporini(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 0.50; } } public class Sausage : Topping { public Sausage(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 1.00; } } public class Onions : Topping { public Onions(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + .25; } } }

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• Interface vs Abstract Class (general OO)

  - by Kave

  Hi, I have had recently two telephone interviews where I've been asked about the differences between an Interface and an Abstract class. I have explained every aspect of them I could think of, but it seems they are waiting for me to mention something specific, and I dont know what it is. From my experience I think the following is true, if i am missing a major point please let me know: Interface: Every single Method declared in an Interface will have to be implemented in the subclass. Only Events, Delegates, Properties (C#) and Methods can exist in a Interface. A class can implement multiple Interfaces. Abstract Class Only Abstract methods have to be implemented by the subclass. An Abstract class can have normal methods with implementations. Abstract class can also have class variables beside Events, Delegates, Properties and Methods. A class can only implement one abstract class only due non-existence of Multi-inheritance in C#. 1) After all that the interviewer came up with the question What if you had an Abstract class with only abstract methods, how would that be different from an interface? I didnt know the answer but I think its the inheritance as mentioned above right? 2) An another interviewer asked me what if you had a Public variable inside the interface, how would that be different than in Abstract Class? I insisted you can't have a public variable inside an interface. I didn't know what he wanted to hear but he wasn't satisfied either. Many Thanks for clarification, Kave See Also: When to use an interface instead of an abstract class and vice versa Interfaces vs. Abstract Classes How do you decide between using an Abstract Class and an Interface?

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• How to leverage Spring Integration in a real-world JMS distributed architecture?

  - by ngeek

  For the following scenario I am looking for your advices and tips on best practices: In a distributed (mainly Java-based) system with: many (different) client applications (web-app, command-line tools, REST API) a central JMS message broker (currently in favor of using ActiveMQ) multiple stand-alone processing nodes (running on multiple remote machines, computing expensive operations of different types as specified by the JMS message payload) How would one best apply the JMS support provided by the Spring Integration framework to decouple the clients from the worker nodes? When reading through the reference documentation and some very first experiments it looks like the configuration of an JMS inbound adapter inherently require to use a subscriber, which in a decoupled scenario does not exist. Small side note: communication should happen via JMS text messages (using a JSON data structure for future extensibility).

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• correct approach to store in database

  - by John

  I'm developing an online website (using Django and Mysql). I have a Tests table and User table. I have 50 tests within the table and each user completes them at their own pace. How do I store the status of the tests in my DB? One idea that came to my mind is to create an additional column in User table. That column containing testid's separated by comma or any other delimiter. userid | username | testscompleted 1 john 1, 5, 34 2 tom 1, 10, 23, 25 Another idea was to create a seperate table to store userid and testid. So, I'll have only 2 columns but thousands of rows (no of tests * no of users) and they will always continue to increase. userid | testid 1 1 1 5 2 1 1 34 2 10

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• Generalized plugable caching pattern?

  - by BCS

  Given that it's one of the hard things in computer science, does anyone know of a way to set up a plugable caching strategy? What I'm thinking of would allow me to write a program with minimal thought as to what needs to be cached (e.i. use some sort of boiler-plate, low/no cost pattern that compiles away to nothing anywhere I might want caching) and then when things are further along and I know where I need caching I can add it in without making invasive code changes. As an idea to the kind of solution I'm looking for; I'm working with the D programing language (but halfway sane C++ would be fine) and I like template.

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• Is there a way to restrict access to a public method to only a specific class in C#?

  - by Anon

  I have a class A with a public method in C#. I want to allow access to this method to only class B. Is this possible? UPDATE: This is what i'd like to do: public class Category { public int NumberOfInactiveProducts {get;} public IList<Product> Products {get;set;} public void ProcessInactiveProduct() { // do things... NumberOfInactiveProducts++; } } public class Product { public bool Inactive {get;} public Category Category {get;set;} public void SetInactive() { this.Inactive= true; Category.ProcessInactiveProduct(); } } I'd like other programmers to do: var prod = Repository.Get<Product>(id); prod.SetInactive(); I'd like to make sure they don't call ProcessInactiveProduct manually: var prod = Repository.Get<Product>(id); prod.SetInactive(); prod.Category.ProcessInactiveProduct(); I want to allow access of Category.ProcessInactiveProduct to only class Product. Other classes shouldn't be able to call Category.ProcessInactiveProduct.

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• Oracle - Is there any effects of not having a primary key on a table ?

  - by Sathya

  We use sequence numbers for primary keys on the tables. There are some tables where we dont really use the primary key for any querying purpose. But, we have Indexes on other columns. These are non-unique indexes. The queries use these non-primary key columns in the WHERE conditions. So, I dont really see any benefit of having a primary key on such tables. My experience with SQL 2000 was that, it used to replicate tables which had some primary key. Otherwise it would not. I am using Oracle 10gR2. I would like to know if there are any such side-effects of having tables that dont have primary key.

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• Rails Full Engine using a Full Engine

  - by SirLenz0rlot

  I've got this full rails engine Foo with functionality X. I want to make another engine, engine Bar, that is pretty much the same, but override funcitonality x with y. (it basically does the same, but a few controller actions and views are differently implemented). (I might split this later in several mountable engines, but for now, this will be the setup: project Baz, using engine Bar, which uses engine Foo) I would like to know if there are any pitfalls. It doesn't seem like a pattern that is often used? Anybody else using this 'some sort of engine inheritance'?

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• Linq to sql Repository pattern , Some doubts

  - by MindlessProgrammer

  I am using repository pattern with linq to sql, I am using a repository class per table. I want to know , am i doing at good/standard way, ContactRepository Contact GetByID() Contact GetAll() COntactTagRepository List<ContactTag> Get(long contactID) List<ContactTag> GetAll() List<ContactTagDetail> GetAllDetails() class ContactTagDetail { public Contact Contact {get;set;} public ContactTag COntactTag {get;set;} } When i need a contact i call method in contactrepository, same for contacttag but when i need contact and tags together i call GetDetais() in ContactTag repository its not returning the COntactTag entity generated by the orm insted its returning ContactTagDetail entity conatining both COntact and COntactTag generated by the orm, i know i can simple call GetAll in COntactTag repository and can access Contact.ContactTag but as its linq to sql it will there is no option to Deferred Load in query level, so whenever i need a entity with a related entity i create a projection class Another doubt is where i really need to right the method i can do it in both contact & ContactTag repostitory like In contact repository GetALlWithTags() or something but i am doing it in in COntactTag repository Whats your suggestions ?

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• java question: Is it a method?

  - by Stefan

  Hello, I'm no Java guy, so I ask myself what this means: public Button(Light light) { this.light = light; } Is Button a method? I ask myself, because it takes an input parameter light. But if it was a method, why would it begin with a capital letter and has no return data type? Here comes the full example: public class Button { private Light light; public Button(Light light) { this.light = light; } public void press() { light.turnOn(); } } I know, this question is really trivial. However, I have nothing to do with Java and haven't found a description for the Button thing above. I'm just interested.

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• Database: Storing Dates as Numeric Values

  - by Chin

  I'm considering storing some date values as ints. i.e 201003150900 Excepting the fact that I lose any timezone information, is there anything else I should be concerned about with his solution? Any queries using this column would be simple 'where after or before' type lookups. i.e Where datefield is less than 201103000000 (before March next year). currently the app is using MSSQL2005. Any pointers to pitfalls appreciated.

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• Clean up upon the kill signal

  - by Begui

  How do you handle clean up when the program receives a kill signal? For instance, there is an application I connect to that wants any third party app (my app) to send a finish command. What is the best say to send that finish command when my app has been destroyed with a kill -9?

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• Accessing a Class Member from a First-Class Function

  - by dbyrne

  I have a case class which takes a list of functions: case class A(q:Double, r:Double, s:Double, l:List[(Double)=>Double]) I have over 20 functions defined. Some of these functions have their own parameters, and some of them also use the q, r, and s values from the case class. Two examples are: def f1(w:Double) = (d:Double) => math.sin(d) * w def f2(w:Double, q:Double) = (d:Double) => d * q * w The problem is that I then need to reference q, r, and s twice when instantiating the case class: A(0.5, 1.0, 2.0, List(f1(3.0), f2(4.0, 0.5))) //0.5 is referenced twice I would like to be able to instantiate the class like this: A(0.5, 1.0, 2.0, List(f1(3.0), f2(4.0))) //f2 already knows about q! What is the best technique to accomplish this? Can I define my functions in a trait that the case class extends? EDIT: The real world application has 7 members, not 3. Only a small number of the functions need access to the members. Most of the functions don't care about them.

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

  - by manugupt1

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

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• Perl classes like stuff

  - by user350571

  Hello, lovers of the camel. I'm new to perl and it's blessing stuff to imitate class like functionality made me feel strange I even had to go to the bathroom. Now, please tell me: what do you don't like, find wrong or strange with this code: sub Person { my $age = shift || 15; return { printAge => sub { print "Age -> $age\n"; }, changeAge => sub { $age = shift } } } my $p = Person(); my $p2 = Person(27); $p->{printAge}->(); $p->{changeAge}->(30); $p->{printAge}->(); $p2->{printAge}->(); I'm going to walk my dog, hope to get responses when I'm back. Thanks in advance. Cheers. Be back soon. Thanks again.

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• Populating a foreign key table with variable user input

  - by Vincent

  I'm working on a website that will be based on user contributed data, submitted using a regular HTML form. To simplify my question, let's say that there will be two fields in the form: "User Name" and "Country" (this is just an example, not the actual site). There will be two tables in the database : "countries" and "users," with "users.country_id" being a foreign key to the "countries" table (one-to-many). The initial database will be empty. Users from all over the world will submit their names and the countries they live in and eventually the "countries" table will get filled out with all of the country names in the world. Since one country can have several alternative names, input like Chile, Chili, Chilli will generate 3 different records in the countries table, but in fact there is only one country. When I search for records from Chile, Chili and Chilli will not be included. So my question is - what would be the best way to deal with a situation like this, with conditions such that the initial database is empty, no other resources are available and everything is based on user input? How can I organize it in such way that Chile, Chili and Chilli would be treated as one country, with minimum manual interference. What are the best practices when it comes to normalizing user submitted data and is there a scientific term for this? I'm sure this is a common problem. Again, I used country names just to simplify my question, it can be anything that has possible different spellings.

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• What is the best algorithm to use in creating binary trees??

  - by Hanseh

  I've been doing a research about the best algorithm to use in creating a binary tree implementation. THe top entry in my list is nested sets. Are there any other alternative or better algorithm??

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• how to get access to private members of nested class?

  - by macias

  Background: I have enclosed (parent) class E with nested class N with several instances of N in E. In the enclosed (parent) class I am doing some calculations and I am setting the values for each instance of nested class. Something like this: n1.field1 = ...; n1.field2 = ...; n1.field3 = ...; n2.field1 = ...; ... It is one big eval method (in parent class). My intention is -- since all calculations are in parent class (they cannot be done per nested instance because it would make code more complicated) -- make the setters only available to parent class and getters public. And now there is a problem: when I make the setters private, parent class cannot acces them when I make them public, everybody can change the values and C# does not have friend concept I cannot pass values in constructor because lazy evaluation mechanism is used (so the instances have to be created when referencing them -- I create all objects and the calculation is triggered on demand) I am stuck -- how to do this (limit access up to parent class, no more, no less)? I suspect I'll get answer-question first -- "but why you don't split the evaluation per each field" -- so I answer this by example: how do you calculate min and max value of a collection? In a fast way? The answer is -- in one pass. This is why I have one eval function which does calculations and sets all fields at once.

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• wrapping user controls in a transaction

  - by Hans Gruber

  I'm working on heavily dynamic and configurable CMS system. Therefore, many pages are composed of a dynamically loaded set of user controls. To enable loose coupling between containers (pages) and children (user controls), all user controls are responsible for their own persistence. Each User Control is wired up to its data/service layer dependencies via IoC. They also implement an IPersistable interface, which allows the container .aspx page to issue a Save command to its children without knowledge of the number or exact nature of these user controls. Note: what follows is only pseudo-code: public class MyUserControl : IPersistable, IValidatable { public void Save() { throw new NotImplementedException(); } public bool IsValid() { throw new NotImplementedException(); } } public partial class MyPage { public void btnSave_Click(object sender, EventArgs e) { foreach (IValidatable control in Controls) { if (!control.IsValid) { throw new Exception("error"); } } foreach (IPersistable control in Controls) { if (!control.Save) { throw new Exception("error"); } } } } I'm thinking of using declarative transactions from the System.EnterpriseService namespace to wrap the btnSave_Click in a transaction in case of an exception, but I'm not sure how this might be achieved or any pitfalls to such an approach.

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• Compiler doesn't find methods from base class

  - by Paul

  I am having a problem with my virtual methods in a derived class. Here are my (simplified) C++ classes. class Base virtual method accept( MyVisitor1* v ) { /*implementation is here*/ }; virtual method accept( MyVisitor2* v ) { /*implementation is here*/ }; virtual method accept( MyVisitor3* v ) { /*implementation is here*/ }; class DerivedClass virtual method accept( MyVisitor2* v ) { /*implementation is here*/ }; The following use causes VS 2005 to give: "error C2664: 'DerivedClass::accept' : cannot convert parameter 1 from 'Visitor1*' to 'Visitor2 *'". DerivedClass c; MyVisitor1 v1; c.accept(v1); I was expecting the compiler to find and call Base::accept(MyVisitor1) for my DerivedClass as well. Obviously this is not working, but I don't understand why. Any ideas? Thanks, Paul

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• Attributes in XML subtree that belong to the parent

  - by Bart van Heukelom

  Say I have this XML <doc:document> <objects> <circle radius="10" doc:colour="red" /> <circle radius="20" doc:colour="blue" /> </objects> </doc:document> And this is how it is parsed (pseudo code): // class DocumentParser public Document parse(Element edoc) { doc = new Document(); doc.objects = ObjectsParser.parse(edoc.getChild("objects")); for ( ...?... ) { doc.objectColours.put(object, colour); } return doc; } ObjectsParser is responsible for parsing the objects bit, but is not and should not be aware of the existence of documents. However, in Document colours are associated with objects by use of a Map. What kind of pattern would you recommend to give the colour settings back to DocumentParser.parse from ObjectsParser.parse so it can associate it with the objects they belong to in a map? The alternative would be something like this: <doc:document> <objects> <circle id="1938" radius="10" /> <circle id="6398" radius="20" /> </objects> <doc:objectViewSettings> <doc:objectViewSetting object="1938" colour="red" /> <doc:objectViewSetting object="6398" colour="blue" /> </doc:objectViewSettings> </doc:document> Ugly!

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• Small methods - Small sprocs

  - by Berlioz

  Uncle Bob recommends having small methods. Do stored procedures have an ideal size? Or can they run on for 100's and 100's of lines long? Also does anyone have anything to say about where to place business logic. If located in stored procedures, the database is being used as data processing tier. If you read Adam Machanic, his bias is toward the database, does that imply long stored procedures that only the author of the sproc understands, leaving maintainers to deal with the mess? I guess there is two inter-related questions, somehow. Thanks in advance for responding to a fuzzy question(s).

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