Querying validation results

A strongly-typed validator returns an instance of IQueryableValidationResult<T>. This interface implements IEnumerable<ValidationRuleResult> and so it is possible to query it using Linq.

The validation framework also adds a few methods to make querying even easier. All of the following methods work a lot like .Where() in Linq; each returns a filtered collection of results, without modifying the original result object.

ForMember narrows the results by member

The ForMember method is used to filter/narrow a collection of results to only those which relate to a member, or descendent values derived from that member's value. In essence this allows narrowing of the results by traversing the object graph which is being validated.

ForMatchingMemberItem narrows the results by a collection item

The ForMatchingMemberItem method is similar to ForMember (above) except that it works with collections. As well as an expression identifying the collection property, you also specify the item (from the original validated object) which you wish to narrow-by.

WithoutSuccesses removes successes from the result

In order to provide confidence, every validation result includes a result for every rule which was executed, including rules which had passing results. The WithoutSuccesses method filters those results to only rules which did not pass.

ForOnlyThisValue removes results which relate to descendent values

A validation result for a complex object model might include many results relating to descendent values. The ForOnlyThisValue method gets only results which relate to the current root of the validation result. This root is either the primary object being validated, or a different value which has been traversed-to via ForMember and/or ForMatchingMemberItem.