c# create an arbitrary length generic parameter string e.g. ?,?,?

Question

I know I am forgetting to remember how to do this and it is late.

I want to, in an elegant manner, build a placeholder list for a munged sql command.

Have a command with an arbitrary number of parameters, need to build ?,?,?

Did I mention that it was a wet brain fart? this is what came out:

You are welcome to make me feel like more of an idiot if you just remember me what I am forgetting. ;-)

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Ok, looks like I should be calling it a night.

Both you guys confirmed what I was doing before going off the deep end.

This is my name list,

string names = string.Join(",", _command.Parameters.Cast<SQLiteParameter>().Select(p => p.ParameterName).ToArray());

And I just replaced the p.Name with '?'

string vals = string.Join(",", _command.Parameters.Cast<object>().Select(p => "?").ToArray());

But for some reason I did not approve.

Thanks.

Answer 1

Well, this suggests itself:

string x = string.Join(",", Enumerable.Repeat("?", count).ToArray());

In .NET 4 this can be simplified slightly as string.Join has new overloads:

string x = string.Join(",", Enumerable.Repeat("?", count));

On the other hand, I'd be tempted to just do it with a loop:

StringBuilder builder = new StringBuilder();
for (int i = 0; i < count; i++)
{
    builder.Append("?,");
}
builder.Length--; // Remove trailing ,
return builder.ToString();

Either way I'd put it in a separate method, so the brevity isn't likely to matter.

Answer 2

Along the lines of @Jon's answer:

string.Join(",", _command.Parameters.Cast<object>().Select(p => "?").ToArray())