How to check whether a base class object or derived object?

Question

I have a BankAccount class. FixedBankAccount and SavingsBankAccount are derived from it.
I need to throw an exception if the recieved object is not a derived object. I have the following code.

IEnumerable<DBML_Project.BankAccount> accounts = AccountRepository.GetAllAccountsForUser(userId);
foreach (DBML_Project.BankAccount acc in accounts)
{
    string typeResult = Convert.ToString(acc.GetType());
    string baseValue = Convert.ToString(typeof(DBML_Project.BankAccount));

    if (String.Equals(typeResult, baseValue))
    {
        throw new Exception("Not correct derived type");
    }
}

namespace DBML_Project
{

public  partial class BankAccount
{
    // Define the domain behaviors
    public virtual void Freeze()
    {
        // Do nothing
    }
}

public class FixedBankAccount : BankAccount
{
    public override void Freeze()
    {
        this.Status = "FrozenFA";
    }
}

public class SavingsBankAccount : BankAccount
{
    public override void Freeze()
    {
        this.Status = "FrozenSB";
    }
}

} // namespace DBML_Project

Is there any better code than this?

Its ok, just change to if(acc.getType() == typeof(DBML_Project.BankAccount)) — A G, Jul 03 '12 at 06:53
It's not clear what you want to do. The compiler won't let you, or anyone else, add an obejct to `accounts` that is not derived from `BankAccount`, so you do not need to check that. — O. R. Mapper, Jul 03 '12 at 06:53
@AseemGautam: That will return `false` if `acc` is of a derived type. — O. R. Mapper, Jul 03 '12 at 06:54
The answer of @bhuvin is correct from the design point of view, you should not have to check for the types at first place. — Asif Mushtaq, Jul 03 '12 at 06:56
I cannot make base class abstract. Some other clients need to instantiate the base class — LCJ, Jul 03 '12 at 06:59

score 12 · Answer 1 · edited Nov 04 '16 at 07:40

12

You should be using Type.IsAssignableFrom

if (acc.GetType().IsAssignableFrom(typeof(BankAccount)))
    // base class
else
    // derived

edited Nov 04 '16 at 07:40

Bitterblue

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answered Jul 03 '12 at 06:53

V4Vendetta

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score 5 · Answer 2 · answered Jul 03 '12 at 06:53

5

Declare BankAccount class as Abstract.

answered Jul 03 '12 at 06:53

bhuvin

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How does this help with the question? – O. R. Mapper Jul 03 '12 at 06:55
2

It will constrain the caller of the method to only pass the derived types and there will not need for the check at all. – Asif Mushtaq Jul 03 '12 at 06:57
1

Ooh, now I get what he's actually asking for ... from reading the question, it seemed like he wanted to check the type compatibility on his own. – O. R. Mapper Jul 03 '12 at 06:58
I cannot make base class abstract. Some other clients need to instantiate the base class – LCJ Jul 03 '12 at 06:59
From design point of view there should be no need to create BankAccount instance, – Asif Mushtaq Jul 03 '12 at 07:01
1

@Lijo - Dude the design in that case needs a scan. Coz designwise that shoudn't be the case. – bhuvin Jul 03 '12 at 07:02

score 3 · Accepted Answer · answered Jul 03 '12 at 08:46

3

I would define an interface (something like IAccettableBankAccount, but you know your domain, so you should be able to find a better name) and have FixedBankAccount and SavingsBankAccount implement it. Then your test would simply be:

if (!acc is IAccettableBankAccount)
{
     throw new Exception("Not correct derived type");
}

answered Jul 03 '12 at 08:46

Francesco Baruchelli

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Thanks for the idea. Is it better than my current implementation? – LCJ Jul 03 '12 at 08:54
1

It depends. For sure it gives you more control, i.e. in your implementation every subclass of BankAccount (even future classes) will always be OK, with the interface you could have classes which are derived from BankAccount, but can throw your exception. – Francesco Baruchelli Jul 03 '12 at 08:58

score 2 · Answer 4 · answered Jul 03 '12 at 06:54

2

Use Type.IsSubclassOf Method. For more info check this

foreach (DBML_Project.BankAccount acc in accounts)
{
    if (!acc.GetType().IsSubclassOf(typeof(DBML_Project.BankAccount))
    {
        throw new Exception("Not correct derived type");
    }
}

answered Jul 03 '12 at 06:54

AksharRoop

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score 0 · Answer 5 · answered Jul 03 '12 at 06:53

You can just check the types directly:

    var accounts = AccountRepository.GetAllAccountsForUser(userId);
    if (accounts.Any(acc => acc.GetType() == typeof(DBML_Project.BankAccount))) {
        throw new Exception("Not correct derived type");
    }

Declaring the class as abstract might help, too, but i don't know if that's an option in your case.

How to check whether a base class object or derived object?

5 Answers5