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  • Tables as relations in ER diagrams

    - by Richard Mar.
    Assume I have the following tables (**bold** - primary key, *italics* - foreign key): patient(**patient_id**, name) disease(**disease_id**, name) patient_disease(**p_d_id**, *patient_id*, *disease,_id* ) I want to draw the ER diagram for this. My idea is to make two entities, one for patient and one for disease, then make a n-to-n relation between them, with p_d_id as its attribute. Is that how it's supposed to be?

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  • Modeling a Generic Relationship (expressed in C#) in a Database

    - by StevenH
    This is most likely one for all you sexy DBAs out there: How would I effieciently model a relational database whereby I have a field in an "Event" table which defines a "SportType"? This "SportsType" field can hold a link to different sports tables E.g. "FootballEvent", "RubgyEvent", "CricketEvent" and "F1 Event". Each of these Sports tables have different fields specific to that sport. My goal is to be able to genericly add sports types in the future as required, yet hold sport specific event data (fields) as part of my Event Entity. Is it possible to use an ORM such as NHibernate / Entity framework / DataObjects.NET which would reflect such a relationship? I have thrown together a quick C# example to express my intent at a higher level: public class Event<T> where T : new() { public T Fields { get; set; } public Event() { EventType = new T(); } } public class FootballEvent { public Team CompetitorA { get; set; } public Team CompetitorB { get; set; } } public class TennisEvent { public Player CompetitorA { get; set; } public Player CompetitorB { get; set; } } public class F1RacingEvent { public List<Player> Drivers { get; set; } public List<Team> Teams { get; set; } } public class Team { public IEnumerable<Player> Squad { get; set; } } public class Player { public string Name { get; set; } public DateTime DOB { get; set;} }

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  • How extensible should code actually be?

    - by griegs
    I've just started a new job and one of the things my new boss talked to me about was code longevity. I've always coded to make my code infinently extensible and adaptable. I figured that if someone was going to change my code in the future then it should be easy to do. But I never really had a clear idea on how far into the future that should be. So my new boss told me not to bother coding for anything more that 3 years into the future and his reasoning was that technology changes, programs expire etc. At first I was kinda taken aback and thought he was a whack job but the longer I think about it the more I'm warming to the concept. Does anyone else have an opinion on how far into the future you should code to?

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  • In symfony/doctrine's schema.yml, where should I put onDelete: CASCADE for a many-to-many relationsh

    - by nselikoff
    I have a many-to-many relationship defined in my Symfony (using doctrine) project between Orders and Upgrades (an Order can be associated with zero or more Upgrades, and an Upgrade can apply to zero or more Orders). # schema.yml Order: columns: order_id: {...} relations: Upgrades: class: Upgrade local: order_id foreign: upgrade_id refClass: OrderUpgrade Upgrade: columns: upgrade_id: {...} relations: Orders: class: Order local: upgrade_id foreign: order_id refClass: OrderUpgrade OrderUpgrade: columns: order_id: {...} upgrade_id: {...} I want to set up delete cascade behavior so that if I delete an Order or an Upgrade, all of the related OrderUpgrades are deleted. Where do I put onDelete: CASCADE? Usually I would put it at the end of the relations section, but that would seem to imply in this case that deleting Orders would cascade to delete Upgrades. Is Symfony + Doctrine smart enough to know what I'm wanting if I put onDelete: CASCADE in the above relations sections of schema.yml?

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  • Is there any reason for an object pool to not be treated as a singleton?

    - by Chris Charabaruk
    I don't necessarily mean implemented using the singleton pattern, but rather, only having and using one instance of a pool. I don't like the idea of having just one pool (or one per pooled type). However, I can't really come up with any concrete situations where there's an advantage to multiple pools for mutable types, at least not any where a single pool can function just as well. What advantages are there to having multiple pools over a singleton pool?

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  • How to easily substitute a Base class

    - by JTom
    Hi, I have the following hierarchy of classes class classOne { virtual void abstractMethod() = 0; }; class classTwo : public classOne { }; class classThree : public classTwo { }; All classOne, classTwo and classThree are abstract classes, and I have another class that is defining the pure virtual methods class classNonAbstract : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; And right now I need it differently...I need it like class classNonAbstractOne : public classOne { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; class classNonAbstractTwo : public classTwo { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; and class classNonAbstractThree : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; But all the nonAbstract classes have the same new methods, with the same code...and I would like to avoid copying all the methods and it's code to every nonAbstract class. How could I accomplish that? Hopefully it's understandable...

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  • PHP Classes Extend

    - by John
    I have two classes that work seperate from another, but they extend the same class. Is it possible to have them work the same instance of the extended class. I'm wanting the constructor of the extended class to run only once. I know this isn't right but something like this: <?php $oApp = new app; class a extends $oApp {} class b extends $oApp {}

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  • Fowler Analysis Patterns lately?

    - by Berryl
    As much as I've always loved this one is how much I always wished there were more meaty examples of how to apply some of the concepts available. Is anyone aware of anything out there worth looking at that attempts to that? Cheers, Berryl

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  • Is it bad practice to make a setter return "this"?

    - by Ken Liu
    Is it a good or bad idea to make setters in java return "this"? public Employee setName(String name){ this.name = name; return this; } This pattern can be useful because then you can chain setters like this: list.add(new Employee().setName("Jack Sparrow").setId(1).setFoo("bacon!")); instead of this: Employee e = new Employee(); e.setName("Jack Sparrow"); ...and so on... list.add(e); ...but it sort of goes against standard convention. I suppose it might be worthwhile just because it can make that setter do something else useful. I've seen this pattern used some places (e.g. JMock, JPA), but it seems uncommon, and only generally used for very well defined APIs where this pattern is used everywhere. Update: What I've described is obviously valid, but what I am really looking for is some thoughts on whether this is generally acceptable, and if there are any pitfalls or related best practices. I know about the Builder pattern but it is a little more involved then what I am describing - as Josh Bloch describes it there is an associated static Builder class for object creation.

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  • Learning Modelling

    - by me1234
    Is there a good book which I can follow to learn modelling/doing architecture? Good samples? What would you do if you have to learn modelling from very basics? Thanks

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  • Need alternative field names for these reserved words

    - by MattSlay
    “type” and “class” are likely reserved or problematic words in C# and/or Ruby, two languages I may use to program against my new database schema in the future. So, in order to avoid potential conflicts with those languages, I’m looking for alternative names for these field names in my tables. In this case, it is from my Machines table, where I have: “class” field (values would be something like “manual” or “computerized”) and “type” field (values would be “lathe” or “mill”) I could call the fields “machineclass” and “machinetype”, but that is inconsistent with naming scheme in the rest of my schema (meaning, I do not re-use the table name in the field… For instance, I use Machine.name, not Machine.machinename) Any thought on this madness?

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  • When is it better to use a method versus a property for a class definition?

    - by ccomet
    Partially related to an earlier question of mine, I have a system in which I have to store complex data as a string. Instead of parsing these strings as all kinds of separate objects, I just created one class that contains all of those objects, and it has some parser logic that will encode all properties into strings, or decode a string to get those objects. That's all fine and good. This question is not about the parser itself, but about where I should house the logic for the parser. Is it a better choice to put it as a property, or as a method? In the case of a property, say public string DataAsString, the get accessor would house the logic to encode all of the data into a string, while the set accessor would decode the input value and set all of the data in the class instance. It seems convenient because the input/output is indeed a string. In the case of a method, one method would be Encode(), which returns the encoded string. Then, either the constructor itself would house the logic for the decoding a string and require the string argument, or I write a Decode(string str) method which is called separately. In either case, it would be using a method instead of a property. So, is there a functional difference between these paths, in terms of the actual running of the code? Or are they basically equivalent and it then boils down to a choice of personal preference or which one looks better? And in that kind of question... which would look cleaner anyway?

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  • Is Form validation and Business validation too much?

    - by Robert Cabri
    I've got this question about form validation and business validation. I see a lot of frameworks that use some sort of form validation library. You submit some values and the library validates the values from the form. If not ok it will show some errors on you screen. If all goes to plan the values will be set into domain objects. Here the values will be or, better said, should validated (again). Most likely the same validation in the validation library. I know 2 PHP frameworks having this kind of construction Zend/Kohana. When I look at programming and some principles like Don't Repeat Yourself (DRY) and single responsibility principle (SRP) this isn't a good way. As you can see it validates twice. Why not create domain objects that do the actual validation. Example: Form with username and email form is submitted. Values of the username field and the email field will be populated in 2 different Domain objects: Username and Email class Username {} class Email {} These objects validate their data and if not valid throw an exception. Do you agree? What do you think about this aproach? Is there a better way to implement validations? I'm confused about a lot of frameworks/developers handling this stuff. Are they all wrong or am I missing a point? Edit: I know there should also be client side kind of validation. This is a different ballgame in my Opinion. If You have some comments on this and a way to deal with this kind of stuff, please provide.

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  • Cpp some basic problems

    - by DevAno1
    Hello. My task was as follows : Create class Person with char*name and int age. Implement contructor using dynamic allocation of memory for variables, destructor, function init and friend function show. Then transform this class to header and cpp file and implement in other program. Ok so I've almost finished my Person class, but I get error after destructor. First question is how to write this properly ? #include <iostream> using namespace std; class Person { char* name; int age; public: int * take_age(); Person(){ int size=0; cout << "Give length of char*" << endl; cin >> size; name = new char[size]; age = 0; } ~Person(){ cout << "Destroying resources" << endl; delete *[] name; delete * take_age(); } friend void(Person &p); int * Person::take_age(){ return age; } void init(char* n, int a) { name = n; age = a; } void show(Person &p){ cout << "Name: " << p.name << "," << "age: " << p.age << endl; } }; int main(void) { Person *p = new Person; p->init("Mary", 25); p.show(); system("PAUSE"); return 0; } And now with header/implementation part : - do I need to introduce constructor in header/implementation files ? If yes - how? - my show() function is a friendly function. Should I take it into account somehow ? I already failed to return this task on my exam, but still I'd like to know how to implement it.

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  • How to reference a specific object in an array of objects using jTemplates

    - by Travis
    I am using the excellent jTemplates plugin to generate content. Given a data object like this... var data = { name: 'datatable', table: [ {id: 1, name: 'Anne'}, {id: 2, name: 'Amelie'}, {id: 3, name: 'Polly'}, {id: 4, name: 'Alice'}, {id: 5, name: 'Martha'} ] }; ..I'm wondering if it is possible to directly specify an object in an array of objects using $T. (I'm hoping there is something like $T.table:3 available) Currently the only way I can think of to access a specific object in an array is to do something like this... {#foreach $T.table as record} {#if $T.record$iteration == 3} This is record 3! Name: {$T.record.name} {#/if} {#/for} However that seems clumsy... Any suggestions? Thanks

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  • 3 tier application pattern suggestion

    - by Maxim Gershkovich
    I have attempted to make my first 3 tier application. In the process I have run into one problem I am yet to find an optimal solution for. Basically all my objects use an IFillable interface which forces the implementation of a sub as follows Public Sub Fill(ByVal Datareader As Data.IDataReader) Implements IFillable.Fill This sub then expects the Ids from the datareader will be identical to the properties of the object as such. Me.m_StockID = Datareader.GetGuid(Datareader.GetOrdinal("StockID")) In the end I end up with a datalayer that looks something like this. Public Shared Function GetStockByID(ByVal ConnectionString As String, ByVal StockID As Guid) As Stock Dim res As New Stock Using sqlConn As New SqlConnection(ConnectionString) sqlConn.Open() res.Fill(StockDataLayer.GetStockByIDQuery(sqlConn, StockID)) End Using Return res End Function Mostly this pattern seems to make sense. However my problem is, lets say I want to implement a property for Stock called StockBarcodeList. Under the above mentioned pattern any way I implement this property I will need to pass a connectionstring to it which obviously breaks my attempt at layer separation. Does anyone have any suggestions on how I might be able to solve this problem or am I going about this the completely wrong way? Does anyone have any suggestions on how I might improve my implementation? Please note however I am deliberately trying to avoid using the dataset in any form.

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  • In Ruby, can the coerce() method know what operator it is that requires the help to coerce?

    - by Jian Lin
    In Ruby, it seems that a lot of coerce() help can be done by def coerce(something) [self, something] end that's is, when 3 + rational is needed, Fixnum 3 doesn't know how to handle adding a Rational, so it asks Rational#coerce for help by calling rational.coerce(3), and this coerce instance method will tell the caller: # I know how to handle rational + something, so I will return you the following: [self, something] # so that now you can invoke + on me, and I will deal with Fixnum to get an answer So what if most operators can use this method, but not when it is (a - b) != (b - a) situation? Can coerce() know which operator it is, and just handle those special cases, while just using the simple [self, something] to handle all the other cases where (a op b) == (b op a) ? (op is the operator).

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  • Help required in adding new methods, properties into existing classes dynamically

    - by Bepenfriends
    Hi All, I am not sure whether it is possible to achieve this kind of implementation in Dot Net. Below are the information Currently we are on an application which is done in COM+, ASP, XSL, XML technologies. It is a multi tier architecture application in which COM+ acts as the BAL. The execution steps for any CRUD operation will be defined using a seperate UI which uses XML to store the information. BAL reads the XML and understands the execution steps which are defined and executes corresponding methods in DLL. Much like EDM we have our custom model (using XML) which determines which property of object is searchable, retrievable etc. Based on this information BAL constructs queries and calls procedures to get the data. In the current application both BAL and DAL are heavily customizable without doing any code change. the results will be transmitted to presentation layer in XML format which constructs the UI based on the data recieved. Now I am creating a migration project which deals with employee information. It is also going to follow the N Tier architecture in which the presentation layer communicates with BAL which connects to DAL to return the Data. Here is the problem, In our existing version we are handling every information as XML in its native form (no converstion of object etc), but in the migration project, Team is really interested in utilizing the OOP model of development where every information which is sent from BAL need to be converted to objects of its respective types (example employeeCollection, Address Collection etc). If we have the static number of data returned from BAL we can have a class which contains those nodes as properties and we can access the same. But in our case the data returned from our BAL need to be customized. How can we handle the customization in presentation layer which is converting the result to an Object. Below is an example of the XML returned <employees> <employee> <firstName>Employee 1 First Name</firstName> <lastName>Employee 1 Last Name</lastName> <addresses> <address> <addressType>1</addressType> <StreetName>Street name1</StreetName> <RegionName>Region name</RegionName> <address> <address> <addressType>2</addressType> <StreetName>Street name2</StreetName> <RegionName>Region name</RegionName> <address> <address> <addressType>3</addressType> <StreetName>Street name3</StreetName> <RegionName>Region name</RegionName> <address> <addresses> </employee> <employee> <firstName>Employee 2 First Name</firstName> <lastName>Employee 2 Last Name</lastName> <addresses> <address> <addressType>1</addressType> <StreetName>Street name1</StreetName> <RegionName>Region name</RegionName> <address> <address> <addressType>2</addressType> <StreetName>Street name2</StreetName> <RegionName>Region name</RegionName> <address> <addresses> </employee> </employees> If these are the only columns then i can write a class which is like public class Address{ public int AddressType {get;set;}; public string StreetName {get;set;}; public string RegionName {get;set;}; } public class Employee{ public string FirstName {get; set;} public string LastName {get; set;} public string AddressCollection {get; set;} } public class EmployeeCollection : List<Employee>{ public bool Add (Employee Data){ .... } } public class AddressCollection : List<Address>{ public bool Add (Address Data){ .... } } This class will be provided to customers and consultants as DLLs. We will not provide the source code for the same. Now when the consultants or customers does customization(example adding country to address and adding passport information object with employee object) they must be able to access those properties in these classes, but without source code they will not be able to do those modifications.which makes the application useless. Is there is any way to acomplish this in DotNet. I thought of using Anonymous classes but, the problem with Anonymous classes are we can not have methods in it. I am not sure how can i fit the collection objects (which will be inturn an anonymous class) Not sure about datagrid / user control binding etc. I also thought of using CODEDom to create classes runtime but not sure about the meory, performance issues. also the classes must be created only once and must use the same till there is another change. Kindly help me out in this problem. Any kind of help meterial/ cryptic code/ links will be helpful.

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