.NET ICollection Class Basics

Question

All, I have an application that needs to attach and detach multiple SQL databases regularly. I want to create a class that holds all of these databases as a collection that can be iterated over. To do this I am inheriting from ICollection, but there is some thinkg I am not understanding:

class SqlDataBases : ICollection<SqlDb>
{
    private List<SqlDb> dbColl;

    public SqlDataBases()
    {
        dbColl = new List<SqlDb>();
    }

    // Add an index to the collection.
    public SqlDb this[int _nIndex]
    {
        get { return (SqlDb)dbColl[_nIndex]; }
        set { dbColl[_nIndex] = value; }
    }

    // et al.
}

public class DbEnumerator : IEnumerator<SqlDb>
{
    // ...
}

class SqlDb
{
    private string strMdfFullPath;
    private string strLdfFullPath;
    private bool bIsAttached;

    public SqlDb(string _strMdfFullPath, string _strLdfFullPath, bool _bIsAttached)
    {
        this.strMdfFullPath = _strMdfFullPath;
        this.strLdfFullPath = _strLdfFullPath;
        this.bIsAttached = _bIsAttached;
    }
}

My question is "why inherit from ICollection at all, when you have to add methods such as 'Add', 'Contains' etc. yourself? Or do you have to do this yourself as suggested in MSDN? I have been reading "C# in a Nutshell" and this question is something that stands out unaddressed in this great book.

I apologise, I know I am missing something here...

My thought is the same; why don't you just use a `List` where needed? It has the features you try to implement as far as I can see. — Fredrik Mörk, Mar 01 '12 at 12:10
@Killercam, One comment below suggests using a Dictionary<>. Unless you want to "Find" your connection by name over and over, a Dictionary<> would be better because you can specify a key like the database name. — Chris Gessler, Mar 01 '12 at 12:33

score 3 · Accepted Answer · answered Mar 01 '12 at 12:10

My question is "why inherit from ICollection at all, when you have to add methods such as 'Add', 'Contains' etc. yourself?

ICollection<T> is an interface - it just specifies the members that you have to implement. If you want to derive from something which already has an implementation, look at Collection<T>. You would implement the interface yourself if you wanted to create your own collection data structure with its own special characteristics - I doubt that you want to do that.

To be honest, it's not clear why you want your own class here at all - why not just use List<SqlDb> in the client code directly?

Thanks Jon, that has sorted out my stupidity. And you are right, I only need a `List` here - but I have not created my own collection class before and fancied doing it, but it is foolish. Thanks for your time. — MoonKnight, Mar 01 '12 at 12:17

score 3 · Answer 2 · answered Mar 01 '12 at 12:14

3

Have you thought about using List<SqlDb> directly?

It's not obvious to me what you hope to gain by the SqlDataBases class.

If you can't use List<SqlDb> directly, think about inheriting from List<SqlDb> rather than ICollection<SqlDb>.

answered Mar 01 '12 at 12:14

Antony Perkov

931
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1

I'd put it into dictionary though... but the reasons for this are yet unknown – b0rg Mar 01 '12 at 12:20

score 2 · Answer 3 · answered Mar 01 '12 at 12:11

2

Interfaces are only skeletons. They aren't containing any logic, they are containing only the signatures of all method, property etc.

Interfaces

answered Mar 01 '12 at 12:11

Peter Kiss

9,309
2
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score 2 · Answer 4 · answered Mar 01 '12 at 12:22

The reason to inherit from ICollection<> is to create your own custom collection type. Then, anywhere a method has an input variable of ICollection<>, because you inherited from ICollection<>, your new custom collection type can be passed in.

In your case, you could simply use List<> until you find a need to create a custom collection.

score 1 · Answer 5 · answered Mar 01 '12 at 12:22

1

Answering "why inherit from ICollection at all, when you have to add methods such as 'Add'":

you don't need to inherit ICollection if you don't need/want to have Add/Next etc.

answered Mar 01 '12 at 12:22

b0rg

1,879
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.NET ICollection Class Basics

5 Answers5