Question

I’m not really sure what tags should be on this sort of question so feel free to give me some suggestions if you think some others are more suited.

I have a dynamic object with an unknown number or properties on it, it’s from a sort of dynamic self describing data model that lets the user build the data model at runtime. However because all of the fields holding relevant information to the user are in dynamic properties, it’s difficult to determine what should be the human readable identifier, so it’s left up to the administrator. (Don’t think it matters but this is an ASP.NET MVC3 Application). To help during debugging I had started decorating some classes with DebuggerDisplayAttribute to make it easier to debug. This allow me to do things like

[DebuggerDisplay(@"\{Description = {Description}}")]
public class Group

to get a better picture of what a specific instance of an object is. And this sort of setup would be perfect but I can’t seem to find the implementation of this flexibility. This is especially useful on my dynamic objects because the string value of the DebuggerDisplayAttribute is resolved by the .NET framework and I have implementations of TryGetMember on my base object class to handle the dynamic aspect. But this only makes it easier for development. So I’ve added a field on what part of my object is still strongly typed and called it Title, and I’d like to let the administer set the implementation using their own format, so to speak. So for example they might build out a very simplistic rental tracking system to show rentals and they might specify a format string along the lines of

"{MovieTitle} (Due: {DueDate})"

I would like that when they save the record to add some logic to first update the Title property by resolving the format string to substitute each place holder with the value of the appropriate property on the dynamic object. So this might resolve to a title of
“Inception (Due: May 21, 2011)”, or a more realistic scenario of a format string of

"{LastName}, {FirstName}"

I don’t want the user to have to update the title of a record when they change the first name field or the last name field. I fully realize this will likely use reflection but I’m hoping some one out there can give me some pointers or even a working example to handle complex format strings that could be a mix if literal text and placeholders.

I’ve not had much luck looking for an implementation on the net that will do what I want since I’m not really sure what keywords would give me the most relevant search results?

Answer 1

You need two things:

1) A syntax for formatting strings

You have already described a syntax where variables are surrounded by bracers, and if you want to use that you need to build a parser that can parse that. Perhaps you also want to add ways to specify say a date or a number format.

2) Rules for resolving variables

If there is a single context object you can use reflection and match variable names to properties but if your object model is more complex you can add conventions for searching say a hierarchy of objects.

If you are planning to base your model objects on dynamic chances are that you will find the Clay library on CodePlex interesting.