Using Extension Methods

Purpose Summary

This page explains how to use extension methods within LINQ Reporting Engine templates.

LINQ Reporting Engine enables you to use the following built‑in extension methods in template expressions:

• Extension methods mimicking the ones for IEnumerable<T> (see “Appendix A. Enumeration Extension Methods” for more information)
• Extension methods for iteration variables (see “Using Extension Methods of Iteration Variables” for more information)

Note – Extension methods, other than the built‑in ones, can be used only in the form of plain static methods in template expressions.

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FAQ

1. Q: How can I call a custom static method as an extension method in a LINQ Reporting Engine template?
   A: Custom extension methods cannot be called with extension-method syntax; call them as plain static methods. Make the class and the method public, add the class to the known types (engine.KnownTypes.Add(typeof(MyUtilities))), and call the method with the class name, e.g., <<[MyUtilities.FormatDate(order.Date)]>>.

2. Q: Which built‑in extension methods are available for iteration variables?
   A: Iteration variables have the IndexOf() and NumberOf() methods (see “Using Extension Methods of Iteration Variables”), e.g., <<[item.NumberOf()]>>. Enumeration extension methods such as Where are applied to sequences, e.g., <<foreach [p in Products.Where(p => p.Price > 100)]>>.

3. Q: Can I use full LINQ query operators like Select or OrderBy inside a template expression?
   A: Yes, in method syntax: Select, OrderBy, and the other methods listed in “Appendix A. Enumeration Extension Methods” can be used, e.g., Persons.OrderBy(p => p.Age). LINQ query syntax (from … select …) is not supported.

4. Q: Why do I receive a “Method not found” error when using an extension method in a template?
   A: Custom methods must be public and static, their class must be added to ReportingEngine.KnownTypes, and they must be called as static methods (MyUtilities.Method(value)), not with extension-method syntax (value.Method()). Otherwise the engine cannot resolve the member and throws an exception.

5. Q: Can I return a custom object type from an extension method used in a template?
   A: Yes. An expression tag outputs the result’s ToString() value, so a custom object is rendered with its ToString() implementation. You can also access the object’s public members in the template, e.g., <<[MyUtilities.GetPoint().X]>>.