Asp.Net C# Object Related Ques

Question

I am new to Asp .net C#. i have question about objects and inheritance. if i have parent class (Base-Table) that have 2 child classes (Credit-Card-Table , Bank-Account-Table) i have fun. in another class that take an object from the base-table class. my problem is i want to know if the Base-table is Credit-card or Bank-account ?!

class BaseTable
{
    string date;
    public string Date
    {
        get { return date; }
        set { date = value; }
    }

    string description;
    public string Description
    {
        get { return description; }
        set { description = value; }
    }

}



class CreditCardTable:BaseTable
{
    string Amount;
    public string amount
    {
        get { return Amount; }
        set { Amount = value; }
    }

    string Type;
    public string type
    {
        get { return Type; }
        set { Type = value; }
    }

}



class BankAccountTable:BaseTable
{
    string Refr;

    public string Ref
    {
        get { return Refr; }
        set { Refr = value; }
    }
    string debit;

    public string Debit
    {
        get { return debit; }
        set { debit = value; }
    }

    string credit;

    public string Credit
    {
        get { return credit; }
        set { credit = value; }
    }

}

More often than not something like this is an indication of an error in the design. Maybe BaseTable should be abstract? Maybe the other code needs a child instance and not a base instance? What specific reason do you have to need to know the type of the instance? — David
– David, Commented Jun 26, 2013 at 11:16
Why do you need to know what type your BaseTable is? Usually this means you've gone wrong in your design. The usual way of approaching this would be to make a virtual/abstract method in BaseTable that is overridden in the derived classes to implement the type-specific behaviour. That way, anything using a BaseTable reference can call the virtual method and get different behaviour depending on the actual type of the BaseTable reference. — spender
– spender, Commented Jun 26, 2013 at 11:17
its a code to create a pdf there is 2 types of pdfs credit card pdf and bank account pdf so in the business i want to check if the obj is credit card or bank account so i can choose which one to create — user2401745
– user2401745, Commented Jun 26, 2013 at 11:29

Marc Gravell · Accepted Answer · 2013-06-26 11:16:08Z

2

3 options:

use is, as or GetType() to explicitly check the type of an instance you have been given, to test it against some known types
```
if(obj is CreditCardTable) {...} else ...
```
add a virtual or abstract method to the base-type, and use that instead of ever having to worry about which it is (since it will automatically invoke the most derived override)
```
obj.SomeMethod();
```
add a discriminator - perhaps a virtual enum property to the BaseTable which all derived types return a different value from, and switch on that discriminator:
```
switch(obj.Type) { ... }
```

answered Jun 26, 2013 at 11:16

Marc Gravell

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2 Comments

spender Over a year ago

Number two!!!!! Switching on type (effectively options 1&3) suggests a design problem to me.

Marc Gravell Over a year ago

@spender depends on the scenario; that would be my preference too, but in some cases separation-of-concerns means that the type itself shouldn't know this "whatever"; for example, if the entity is a POCO, and the "whatever" is "an ORM persisting it", then I would accept the ORM using .GetType() and comparing that to the expected types; it isn't the job of the POCO to persist. Likewise with a serializer; so "number one" definitely has some utility

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