Override a public property from a derived class

Question

In an old project we are using a third party assembly with a class that has a property with some hardcoded information:

public string ConnectionString
{
    get
    {
        string[] fullDbName = new string[5];
        fullDbName[0] = "Data Source=";
        fullDbName[1] = this.dbServer;
        fullDbName[2] = ";Initial Catalog=";
        fullDbName[3] = this.FullDbName;
        fullDbName[4] = ";Integrated Security=SSPI;Pooling=false";
        return string.Concat(fullDbName);
    }
}

I need to be able to construct the connection string my self. So I have tried to make a derived class that hides the original property, but it does not seem to work:

public class SqlServerRestorerExstension : SQLServerRestorer
{
    public SqlServerRestorerExstension(string dbServer, string dbName, string dbFilePath, string dbDataFileName, string dbLogFileName, bool detachOnFixtureTearDown, string connectionstring) : base(dbServer, dbName, dbFilePath, dbDataFileName, dbLogFileName, detachOnFixtureTearDown)
    {
        ConnectionString = connectionstring;
    }

    public string ConnectionString { get; private set; }
}

Is it possible do achive this in any way when I don't have acces to the third party code?

Answer 1

As others have pointed out you can use the new keyword to hide the base member property. Note however that this doesn't magically turn the ConnectionString property into a polymorphic function, i.e. if you have something like this:

public class A 
{
    public string CString { get { return "a"; } }
}

public class B : A
{
    public new string CString { get { return "b"; }}
}

and you do this:

A a = new B();

Console.WriteLine(a.CString);

Then you will still see an "a" printed to the console. In fact the new keyword just stops the compiler from issuing a warning regarding the hiding of the member of the base class. It doesn't change the behavior of the code at runtime.

You can try to use a Decorator pattern and wrap the SQLServerRestorer, but if that doesn't work either, you are out of luck I am afraid.

Answer 2

You will need to indicate that you want to 'replace' this property, using new:

public new string ConnectionString
{
   get { return "My custom connection string"; }
}

Obviously you can extend that to implement your own set, even if just to utilise auto-implemented accessors. Documentation on 'versioning' with new can be found here, but specifically:

Using the new keyword tells the compiler that your definition hides the definition contained in the base class. This is the default behavior.