Interpolating a string stored in a database

Question

We would like to maintain the emails that are sent from our ASP.NET Web Application in a database. The idea was that the format of emails are stored in a database.

The problem is that emails should include order specific information, e.g.:

Thank you for your order John Smith,

your order 1234 has been received

What I'm trying to achieve is that I have used string verbatims in the database column values where it would be stored like this:

Thank you for your order {o.customer},

your order {o.id} has been received

I'm curious as to whether it is possible to do string interpolation where the values are already in the string that is formatted. If I try to use String.Format(dbEmailString) it throws me exception:

An exception of type 'System.FormatException' occurred in mscorlib.dll but was not handled in user code

Additional information: Input string was not in a correct format.

Answer 1

String interpolation is a compile time feature. You can do what you want using the regular String.Format:

var formattedEmail = String.Format("Thank you for your order {0}, your order {1} has been received", o.customer, o.id);

If you've got a requirement to replace out various different placeholders with the values, perhaps you need to be looking for a more dynamic templating system, a very basic one could be done with String.Replace.

The bottom line is you can't reference variables in your code directly from stored strings in this fashion - you'll need to process the string in some way at runtime.