覆盖 ToString() 方法

Question

I need to redefine the toString () method, to contemplate a specific situation.

When you want to connect to Oracle, you do it with the Oracle.Data.Access .dll, I am having problems with version 12 of the client, when trying to get the value of an output parameter and converting it to string you get the word "null" , on the other hand, with version 10 of the client, when doing the same, "" is obtained.

Example:

string  _value = "";

OracleConnection cone = new OracleConnection(this.conectionString);
OracleCommand cmd = new OracleCommand("schema.PKG.sp_null_test", cone);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("po_mensaje", OracleDbType.Varchar2,300);
cmd.Parameters["po_mensaje"].Direction = ParameterDirection.Output;

try
{
   cone.Open();
   cmd.ExecuteNonQuery();
   _value = cmd.Parameters["po_mensaje"].Value.ToString();
    //This returns "" if the parameter is not loaded from the database in 
    //version 10 and "null" in 12
}
catch (OracleException ex)
{
   throw ex;
}

I tried this:

public override string ToString()
{
   return base.Equals("null") ? "" : base.ToString();
}

But ToString() still returns the "null" word when the result of oracleParameter.Value is converted to string .

Can I make ToString() return "" instead of "null" , when this happens?

Answer 1

It must be like this

public override string ToString()
{
  return base.Equals(DbNull.Value) ? "" : base.ToString();
}

Answer 2

I don't think you are override the ToString() method from the cmd.Parameters["po_mensaje"].Value . When looking at this code I believe you are just overriding the ToString() method from your current class.

To override such a function you need to extend the Value -class and override the method there. I believe this would be too much at this point.

The easier one would be to create a new method where you use the cmd.Parameters["po_mensaje"].Value as a parameter.

So basically something like this:

public string GetValueFromParameter(var Value)
{
    if(Value == null)
        return ""; 
    else
        return Value.ToString(); 
}

Then you can call it like this:

try
{
   cone.Open();
   cmd.ExecuteNonQuery();
   _value = GetValueFromParameter(cmd.Parameters["po_mensaje"].Value);
    //This returns "" if the parameter is not loaded from the database in 
    //version 10 and "null" in 12
}
catch (OracleException ex)
{
   throw ex;
}

Couldn't test the function, cause I have no running oracle server. But you should get the idea.