Mapping Techniques¶

This is a list of various methods of parsing potentially problematic or difficult input data. Prefer these techniques before having to resort to using HYDMapWithBlock or HYDMapWithPostProcessing

Convert a value or return nil (or another default value)¶

Use the HYDMapOptionally mapper:

id<HYDMapper> mapper1 = HYDMapStringToURL();
id<HYDMapper> mapper2 = HYDMapOptionallyTo(HYDMapStringToURL());

mapper1 one will produce a fatal error if given a value like @1 but mapper2 will return a non-fatal error with nil.

Use it with HYDMapObject, to optionally map properties.

How do I return a source object’s value unchanged?¶

Just use HYDMapIdentity.

Mapping an array of objects, excluding invalid ones instead of failing entirely¶

Depending on the location of HYDMapOptionally in comparison to HYDMapCollectionOf / HYDMapArrayOf, different behavior occurs:

HYDMapOptionallyTo(HYDMapArrayOf(...))

This mapper will return nil if any part of mapping the array fails. Where as:

HYDMapArrayOf(HYDMapOptionallyTo(...))

Will exclude any element that fails to parse from the array. This is due to the way HYDMapArrayOf excludes values from its mapper that produces nil and any kind of error (fatal or non-fatal).

Mapping Two Fields to One Property¶

This applies to any combination of mappings: many-to-one, one-to-many, or many-to-many in a Mapping Data Structure.

Explictly use HYDAccessKeyPath with each key. The accessor will produce an array of the values it has extracted:

HYDMapObject([Employee class],
             @{@[@"date", @"time"]: @[HYDMapByStringJoining(@"T"),
                                      HYDMapStringToDate(HYDDateFormatRFC3339),
                                      @"joinDate"]};