public class ValidateMetadata<T> : Module, IModule

This example will ensure "Title" exists. (It will also perform a type check, but since "object" matches anything, the type check will always succeed.)

ValidateMeta<object>("Title")

This example will ensure that if "Date" exists, it can convert to a valid DateTime.

ValidateMeta<DateTime>("Date")
   .IsOptional()

This example will ensure "Age" (1) exists, (2) can convert to an integer, (3) and is greater than 0 and less than 121. If it fails any assertion, the provided error message will be output. (In this case, those two assertions could be rolled into one, but then they would share an error message. Separate assertions allow more specific error messages.) Assertions will be checked in order. Any assertion can assume all previous assertions have passed. Error messages will be appended with the document Source and Id properties to assist in identifying invalid documents.

ValidateMeta<int>("Age")
   .WithAssertion(a => a > 0, "You have to be born.")
   .WithAssertion(a => a <= 120, "You are way, way too old.")

This module performs tests on metadata. It can ensure metadata exists, that it can be converted to the correct type, and that is passes arbitrary tests (delegates) to ensure validity. Metadata can be specified as optional, in which case, typing and assertion testing will only be run if the metadata exists. If any check fails, this module throws an exception with a descriptive error message then halts further execution.