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authorEric Tune <etune@google.com>2016-01-15 14:34:46 -0800
committerEric Tune <etune@google.com>2016-02-03 13:25:18 -0800
commitdfa00a5742b5eab0df2e98fcc70539cb97e1f876 (patch)
tree0908651831420ba89ae3f85f1a3c580a6b258896 /api-conventions.md
parent7cba47d83d4941948d4c55557f150a25635ca4f4 (diff)
Document Unions, conventions for adding to Unions.
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@@ -53,6 +53,7 @@ using resources with kubectl can be found in [Working with resources](../user-gu
- [Lists of named subobjects preferred over maps](#lists-of-named-subobjects-preferred-over-maps)
- [Primitive types](#primitive-types)
- [Constants](#constants)
+ - [Unions](#unions)
- [Lists and Simple kinds](#lists-and-simple-kinds)
- [Differing Representations](#differing-representations)
- [Verbs on Resources](#verbs-on-resources)
@@ -263,6 +264,15 @@ This rule maintains the invariant that all JSON/YAML keys are fields in API obje
Some fields will have a list of allowed values (enumerations). These values will be strings, and they will be in CamelCase, with an initial uppercase letter. Examples: "ClusterFirst", "Pending", "ClientIP".
+#### Unions
+
+Sometimes, at most one of a set of fields can be set. For example, the [volumes] field of a PodSpec has 17 different volume type-specific
+fields, such as `nfs` and `iscsi`. All fields in the set should be [Optional](#optional-vs-required).
+
+Sometimes, when a new type is created, the api designer may anticipate that a union will be needed in the future, even if only one field is
+allowed initially. In this case, be sure to make the field [Optional](#optional-vs-required) optional. In the validation, you may
+still return an error if the sole field is unset. Do not set a default value for that field.
+
### Lists and Simple kinds
Every list or simple kind SHOULD have the following metadata in a nested object field called "metadata":