Class Design RSS

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  TonyC

  Member

  140 Points

  32 Posts

  Class Design

  Aug 04, 2003 09:55 PM|LINK

  I'm working on a web app that keeps track of some user/event information and in the course of roughing out classes I find that I am duplicating alot of the same fields. For example, states and countries. My states and countries are made up of the following fields: ID, Name, Shortname. So what makes more sense?

  public class Person
  {
  	private int id;
  	private string firstname;
  	private string middlename;
  	private string lastname;
  	private string city;
  	private int stateID;
  	private string state;
  	private string stateShortname;
  	private int countryID;
  	private string country;
  	private string countryShortname;
  
  
  	public int ID
  	{
  		get {};
  		set {};
  	}
  
  
  	public string Firstname
  	{
  		get {};
  		set {};
  	}
  
  
  	public string Middlename
  	{
  		get {};
  		set {};
  	}
  
  
  	public string Lastname
  	{
  		get {};
  		set {};
  	}
  
  
  	public string City
  	{
  		get {};
  		set {};
  	}
  
  
  	public int StateID
  	{
  		get {};
  		set {};
  	}
  
  
  	public string State
  	{
  		get {};
  		set {};
  	}
  
  
  	public string StateShortname
  	{
  		get {};
  		set {};
  	}
  
  
  	public int CountryID
  	{
  		get {};
  		set {};
  	}
  
  
  	public string Country
  	{
  		get {};
  		set {};
  	}
  
  
  	public string CountryShortname
  	{
  		get {};
  		set {};
  	}
  }

  OR should I try to do something more object oriented like this:

  public class Person
  {
  	private int id;
  	private Name name;
  	private string city;
  	private State state;
  	private Country country;
  	
  	public int ID
  	{
  		get {};
  		set {};
  	}
  
  	public Name Name
  	{
  		get {};
  		set {};
  	}
  	
  	public string City
  	{
  		get {};
  		set {};
  	}
  
  	public State State
  	{
  		get {};
  		set {};
  	}
  
  	public Country Country
  	{
  		get {};
  		set {};
  	}
  }
  
  public class Name
  {
  	private string first;
  	private string middle;
  	private string last;
  
  	public string First
  	{
  		get {};
  		set {};
  	}
  
  	public string Middle
  	{
  		get {};
  		set {};
  	}
  
  	public string Last
  	{
  		get {};
  		set {};
  	}	
  }
  
  public class State
  {
  	private int id;
  	private string name;
  	private string shortname;
  
  	public int ID
  	{
  		get {};
  		set {};
  	}
  
  	public string Name
  	{
  		get {};
  		set {};
  	}
  
  	public string Shortname
  	{
  		get {};
  		set {};
  	}
  }
  
  public class Country
  {
  	private int id;
  	private string name;
  	private string shortname;
  
  	public int ID
  	{
  		get {};
  		set {};
  	}
  
  	public string Name
  	{
  		get {};
  		set {};
  	}
  
  	public string Shortname
  	{
  		get {};
  		set {};
  	}
  }
  

  I guess I am just looking for suggestions and/or a reality check on this. I feel like I might be over-engineering this, but it does make the code read much better using the intellisense.
• • Reply
  

  Phuoc

  Participant

  1150 Points

  230 Posts

  Re: Class Design

  Aug 05, 2003 02:28 AM|LINK

  Hi TonyC, 1. I do not know if there is an equivalent relationship between Datbase design and Class design. However database designwise, I see 3 tables - see point 2 - Classwise, I see we have a 'Composite' pattern for your classes. I see 3 classes - see point 3 - 2. Database design

  --Person table
  id (personid)
  firstname
  middle name
  lastname
  stateid   (Referential Integrity with State table)
  
  
  
  
  --State table
  stateid
  statename
  stateshortname
  countryid (Referential Integrity with Country table)
  
  
  --Country table
  countryid
  country
  countryShortname

  3. Class design

  --Person class
  id (personid)   	int
  firstname		string
  middle name	string
  lastname		string
  State 		object of State class
  
  
  --State class
  stateid		int
  statename		string
  stateshortname	string
  Country 		object of Country class
  
  --Country class
  countryid		int
  country		string
  countryShortname	string
  

  Where there is a will, there is a way.
  
  
  and where there is a team, there is more than one way.
• • Reply
  

  TonyC

  Member

  140 Points

  32 Posts

  Re: Class Design

  Aug 05, 2003 02:04 PM|LINK

  Hey Phuoc, What you have is very close to what I have currently in the database. One slight difference though. If someone is from a country that does not have state/province, the Person.State field becomes optional. So would you still organize it the same way or do something like this:

  --Person class
  id (personid)    int
  firstname string
  middle name string
  lastname string
  State  object of State class
  Country object of Country class
  
  
  --State class
  stateid int
  statename string
  stateshortname string
  Country  object of Country class
  
  
  --Country class
  countryid int
  country string
  countryShortname string

• • Reply
  

  Phuoc

  Participant

  1150 Points

  230 Posts

  Re: Class Design

  Aug 05, 2003 03:22 PM|LINK

  Hi TonyC, 1. ::One slight difference though What you have is very close to what I have currently in the database. One slight difference though. If someone is from a country that does not have state/province, -Yes. This is business requirement for some foreign countries that I did not see from your requirement. No problem. That's was the reason I did not include Country object into the Person class. So the Person table --Person table id (personid) firstname middle name lastname stateid (Referential Integrity with State table) countryid (Referential Integrity with Country table) -Then "how do you enforce the referential integrity for optional state?" this is the key point here because state can have NULL value or a value matching the state table. How do you enforce RI for NULL value unless you have one null value in your state table? which implies there must be one NULL value in the Country table by the reason of RI between Country and State tables. -In the case for a person with a state and country, then that person will have 2 values for those 2 columns and the state table will also have a country value as well. 2. This point 2 depends on the point 1's outcome. However, I've a question: :: --Person class id (personid) int firstname string middle name string lastname string State object of State class Country object of Country class The fact we have Country object would handle point 1 (business rule). But then the programming implication is we have to check if state object is not optional (not null/nothing) then we have to ignore country object else ignore state and use country object. Is this what you have in mind? 3. We'll have a comprehensive look again based upon your answer for point 1 and 2.
  Where there is a will, there is a way.
  
  
  and where there is a team, there is more than one way.
• • Reply
  

  Phuoc

  Participant

  1150 Points

  230 Posts

  Re: Class Design

  Aug 05, 2003 03:45 PM|LINK

  TonyC, Additional note for previous point 1 of previous post: -If State can have a NULL value to enforce R.I for optional state, then you must be careful during the Insert into the Person Table which implies your front-end validation must be strict and well tested because people can enter a NULL for state by mistake then NULL can be accepted since state table has a NULL. Your code would not be able to know whether the customer is having optional state or not.
  Where there is a will, there is a way.
  
  
  and where there is a team, there is more than one way.
• • Reply
  

  TonyC

  Member

  140 Points

  32 Posts

  Re: Class Design

  Aug 05, 2003 04:00 PM|LINK

  Just to kind of clean the code up a bit so we can clearly see what we are discussing (I realize our naming conventions are alittle different but bear with me).

  --- Person Table
  ID int (PK)
  Firstname varchar(50)
  Middlename varchar(50)
  Lastname varchar(50)
  State_ID int (FK for State table)
  Country_ID int (FK for Country table)
  
  
  --- State Table
  ID int (PK)
  Name varchar(50)
  Shortname varchar(5)
  Country_ID int (FK for Country table)
  
  
  --- Country Table
  ID int (PK)
  Name varchar(50)
  Shortname varchar(5)
  
  
  --- Person Class
  ID int
  Firstname string
  Middlename string
  Lastname string
  State object of State class
  Country object of Country class

  1. Currently, I just do left joins on the Person and State tables. If there is no match for the state, the sproc returns null values for state information. There is another left join for the country that works the same way. I tinkered with putting a null placeholder in the State and Country tables, but I didn't like the way that worked. Maybe I'm wrong here. 2. I'm struggling with that part too. The trick to that would probably have to be in the properties of the Person class. On a set for the State, you would copy the state in to the Person.State and copy the Person.State.Country to the Person.Country field. Or you could set the Person.State and skip a set for the Person.Country. On the get for Person.Country, you could first check if Person.State is null. If it is, then return the country field, otherwise return Person.State.Country. Does that help/make sense?
• • Reply
  

  Phuoc

  Participant

  1150 Points

  230 Posts

  Re: Class Design

  Aug 05, 2003 08:07 PM|LINK

  Tony, ::Currently, I just do left joins on the Person and State tables. If there is no match for the state, the sproc returns null values for state information 1 quick question before I proceed further: Right now, is your database already set up and used in production OR is it in design mode as we discussed now?
  Where there is a will, there is a way.
  
  
  and where there is a team, there is more than one way.
• • Reply
  

  TonyC

  Member

  140 Points

  32 Posts

  Re: Class Design

  Aug 05, 2003 08:20 PM|LINK

  It's not in production. This is just my little pet project that is more/less in design mode.
• • Reply
  

  Phuoc

  Participant

  1150 Points

  230 Posts

  Re: Class Design

  Aug 05, 2003 10:11 PM|LINK

  Tony, 1. Before we consider my question #2 and your #2 (which are about Class design). Let's have a common ground first. -My question # 1 is concerned about designing first which focused on R.I for the optional state requirement. See Posted: 08-05-2003 11:22 AM, Posted: 08-05-2003 11:45 AM -Your # 1 (Posted: 08-05-2003 12:00 PM) is about data access (SELECT) which is OK but that would not be possible at this stage since my question # 1 has not been fully answered yet. Please read that question again and let me know if we're on the same level. In addition to my question#1 on the previous 2 mentioned posts: How can you insert a row into a Person table for a optional state given there is a R.I between Person table and State table. E.g: -INSERT INTO PERSON VALUES (2, 'TONY', 'C', 'TONYLASTNAME', 'what is the value for optional state that would match the value in State table by R.I' ,1) 3. If possible, set up a sample of data/values for rows for the 3 tables that you see from your point of view.
  Where there is a will, there is a way.
  
  
  and where there is a team, there is more than one way.
• • Reply
  

  TonyC

  Member

  140 Points

  32 Posts

  Re: Class Design

  Aug 05, 2003 10:41 PM|LINK

  Phuoc #1: The answer is null. If there is no state selected, I just insert a NULL. There is no row in the State or Country table that represents a blank. Should there be? Does that answer your question?

  INSERT INTO Person (Firstname, Middlename, Lastname, State_ID, Country_ID) VALUES ('Gerry', NULL, 'MacNamara', NULL, 3)

  Phuoc #3:

  Person Table
  ID      Firstname       Middlename      Lastname        State_ID        Country_ID
  ------- --------------- --------------- --------------- --------------- ----------
  1       Tony                      C               1               1
  2       Konstantine               Pavlov                    2
  3       Gerry                     MacNamara                 3
  
  State Table
  ID      Name    Shortname       Country_ID
  ------- ------- --------------- ----------
  1       Texas   TX              1
  2       Utah    UT              1
  3       Alaska  AK              1
  
  Country Table
  ID      Name            Shortname
  ------- --------------- ---------
  1       United States   USA
  2       Russia          RUS
  3       Ireland         IRE