Documentation ¶
Overview ¶
Package meta provides functions for retrieving API metadata from objects belonging to the Kubernetes API
TODO: move everything in this file to pkg/api/rest
Index ¶
- Constants
- Variables
- func ExtractList(obj runtime.Object) ([]runtime.Object, error)
- func GetItemsPtr(list runtime.Object) (interface{}, error)
- func IsAmbiguousError(err error) bool
- func IsListType(obj runtime.Object) bool
- func IsNoMatchError(err error) bool
- func KindToResource(kind unversioned.GroupVersionKind) (unversioned.GroupVersionResource, unversioned.GroupVersionResource)
- func SetList(list runtime.Object, objects []runtime.Object) error
- type AmbiguousKindError
- type AmbiguousResourceError
- type DefaultRESTMapper
- func (m *DefaultRESTMapper) Add(kind unversioned.GroupVersionKind, scope RESTScope)
- func (m *DefaultRESTMapper) AddResourceAlias(alias string, resources ...string)
- func (m *DefaultRESTMapper) AliasesForResource(alias string) ([]string, bool)
- func (m *DefaultRESTMapper) KindFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionKind, error)
- func (m *DefaultRESTMapper) KindsFor(input unversioned.GroupVersionResource) ([]unversioned.GroupVersionKind, error)
- func (m *DefaultRESTMapper) RESTMapping(gk unversioned.GroupKind, versions ...string) (*RESTMapping, error)
- func (m *DefaultRESTMapper) RESTMappings(gk unversioned.GroupKind) ([]*RESTMapping, error)
- func (m *DefaultRESTMapper) ResourceFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionResource, error)
- func (m *DefaultRESTMapper) ResourceSingularizer(resourceType string) (string, error)
- func (m *DefaultRESTMapper) ResourcesFor(input unversioned.GroupVersionResource) ([]unversioned.GroupVersionResource, error)
- func (m *DefaultRESTMapper) String() string
- type FirstHitRESTMapper
- func (m FirstHitRESTMapper) KindFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionKind, error)
- func (m FirstHitRESTMapper) RESTMapping(gk unversioned.GroupKind, versions ...string) (*RESTMapping, error)
- func (m FirstHitRESTMapper) ResourceFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionResource, error)
- func (m FirstHitRESTMapper) String() string
- type List
- type ListMetaAccessor
- type MetadataAccessor
- type MultiRESTMapper
- func (m MultiRESTMapper) AliasesForResource(alias string) ([]string, bool)
- func (m MultiRESTMapper) KindFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionKind, error)
- func (m MultiRESTMapper) KindsFor(resource unversioned.GroupVersionResource) (gvk []unversioned.GroupVersionKind, err error)
- func (m MultiRESTMapper) RESTMapping(gk unversioned.GroupKind, versions ...string) (*RESTMapping, error)
- func (m MultiRESTMapper) RESTMappings(gk unversioned.GroupKind) ([]*RESTMapping, error)
- func (m MultiRESTMapper) ResourceFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionResource, error)
- func (m MultiRESTMapper) ResourceSingularizer(resource string) (singular string, err error)
- func (m MultiRESTMapper) ResourcesFor(resource unversioned.GroupVersionResource) ([]unversioned.GroupVersionResource, error)
- func (m MultiRESTMapper) String() string
- type NoKindMatchError
- type NoResourceMatchError
- type Object
- type ObjectMetaAccessor
- type PriorityRESTMapper
- func (m PriorityRESTMapper) AliasesForResource(alias string) (aliases []string, ok bool)
- func (m PriorityRESTMapper) KindFor(partiallySpecifiedResource unversioned.GroupVersionResource) (unversioned.GroupVersionKind, error)
- func (m PriorityRESTMapper) KindsFor(partiallySpecifiedResource unversioned.GroupVersionResource) (gvk []unversioned.GroupVersionKind, err error)
- func (m PriorityRESTMapper) RESTMapping(gk unversioned.GroupKind, versions ...string) (mapping *RESTMapping, err error)
- func (m PriorityRESTMapper) RESTMappings(gk unversioned.GroupKind) ([]*RESTMapping, error)
- func (m PriorityRESTMapper) ResourceFor(partiallySpecifiedResource unversioned.GroupVersionResource) (unversioned.GroupVersionResource, error)
- func (m PriorityRESTMapper) ResourceSingularizer(resource string) (singular string, err error)
- func (m PriorityRESTMapper) ResourcesFor(partiallySpecifiedResource unversioned.GroupVersionResource) ([]unversioned.GroupVersionResource, error)
- func (m PriorityRESTMapper) String() string
- type RESTMapper
- type RESTMapping
- type RESTScope
- type RESTScopeName
- type Type
- type VersionInterfaces
- type VersionInterfacesFunc
Constants ¶
const ( AnyGroup = "*" AnyVersion = "*" AnyResource = "*" AnyKind = "*" )
Variables ¶
var RESTScopeNamespace = &restScope{ name: RESTScopeNameNamespace, paramName: "namespaces", argumentName: "namespace", paramDescription: "object name and auth scope, such as for teams and projects", }
var RESTScopeRoot = &restScope{ name: RESTScopeNameRoot, }
Functions ¶
func ExtractList ¶ added in v1.2.0
ExtractList returns obj's Items element as an array of runtime.Objects. Returns an error if obj is not a List type (does not have an Items member).
func GetItemsPtr ¶ added in v1.2.0
GetItemsPtr returns a pointer to the list object's Items member. If 'list' doesn't have an Items member, it's not really a list type and an error will be returned. This function will either return a pointer to a slice, or an error, but not both.
func IsAmbiguousError ¶ added in v1.4.0
func IsListType ¶ added in v1.2.0
IsListType returns true if the provided Object has a slice called Items
func IsNoMatchError ¶ added in v1.4.0
func KindToResource ¶ added in v1.1.0
func KindToResource(kind unversioned.GroupVersionKind) (unversioned.GroupVersionResource, unversioned.GroupVersionResource)
KindToResource converts Kind to a resource name. Broken. This method only "sort of" works when used outside of this package. It assumes that Kinds and Resources match and they aren't guaranteed to do so.
Types ¶
type AmbiguousKindError ¶ added in v1.4.0
type AmbiguousKindError struct { PartialKind unversioned.GroupVersionKind MatchingResources []unversioned.GroupVersionResource MatchingKinds []unversioned.GroupVersionKind }
AmbiguousKindError is returned if the RESTMapper finds multiple matches for a kind
func (*AmbiguousKindError) Error ¶ added in v1.4.0
func (e *AmbiguousKindError) Error() string
type AmbiguousResourceError ¶ added in v1.2.0
type AmbiguousResourceError struct { PartialResource unversioned.GroupVersionResource MatchingResources []unversioned.GroupVersionResource MatchingKinds []unversioned.GroupVersionKind }
AmbiguousResourceError is returned if the RESTMapper finds multiple matches for a resource
func (*AmbiguousResourceError) Error ¶ added in v1.2.0
func (e *AmbiguousResourceError) Error() string
type DefaultRESTMapper ¶
type DefaultRESTMapper struct {
// contains filtered or unexported fields
}
DefaultRESTMapper exposes mappings between the types defined in a runtime.Scheme. It assumes that all types defined the provided scheme can be mapped with the provided MetadataAccessor and Codec interfaces.
The resource name of a Kind is defined as the lowercase, English-plural version of the Kind string. When converting from resource to Kind, the singular version of the resource name is also accepted for convenience.
TODO: Only accept plural for some operations for increased control? (`get pod bar` vs `get pods bar`)
func NewDefaultRESTMapper ¶
func NewDefaultRESTMapper(defaultGroupVersions []unversioned.GroupVersion, f VersionInterfacesFunc) *DefaultRESTMapper
NewDefaultRESTMapper initializes a mapping between Kind and APIVersion to a resource name and back based on the objects in a runtime.Scheme and the Kubernetes API conventions. Takes a group name, a priority list of the versions to search when an object has no default version (set empty to return an error), and a function that retrieves the correct metadata for a given version.
func (*DefaultRESTMapper) Add ¶
func (m *DefaultRESTMapper) Add(kind unversioned.GroupVersionKind, scope RESTScope)
func (*DefaultRESTMapper) AddResourceAlias ¶ added in v0.16.0
func (m *DefaultRESTMapper) AddResourceAlias(alias string, resources ...string)
AddResourceAlias maps aliases to resources
func (*DefaultRESTMapper) AliasesForResource ¶ added in v0.16.0
func (m *DefaultRESTMapper) AliasesForResource(alias string) ([]string, bool)
AliasesForResource returns whether a resource has an alias or not
func (*DefaultRESTMapper) KindFor ¶ added in v1.2.0
func (m *DefaultRESTMapper) KindFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionKind, error)
func (*DefaultRESTMapper) KindsFor ¶ added in v1.2.0
func (m *DefaultRESTMapper) KindsFor(input unversioned.GroupVersionResource) ([]unversioned.GroupVersionKind, error)
func (*DefaultRESTMapper) RESTMapping ¶
func (m *DefaultRESTMapper) RESTMapping(gk unversioned.GroupKind, versions ...string) (*RESTMapping, error)
RESTMapping returns a struct representing the resource path and conversion interfaces a RESTClient should use to operate on the provided group/kind in order of versions. If a version search order is not provided, the search order provided to DefaultRESTMapper will be used to resolve which version should be used to access the named group/kind. TODO: consider refactoring to use RESTMappings in a way that preserves version ordering and preference
func (*DefaultRESTMapper) RESTMappings ¶ added in v1.4.0
func (m *DefaultRESTMapper) RESTMappings(gk unversioned.GroupKind) ([]*RESTMapping, error)
RESTMappings returns the RESTMappings for the provided group kind in a rough internal preferred order. If no kind is found it will return a NoResourceMatchError.
func (*DefaultRESTMapper) ResourceFor ¶ added in v1.2.0
func (m *DefaultRESTMapper) ResourceFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionResource, error)
func (*DefaultRESTMapper) ResourceSingularizer ¶ added in v1.1.0
func (m *DefaultRESTMapper) ResourceSingularizer(resourceType string) (string, error)
ResourceSingularizer implements RESTMapper It converts a resource name from plural to singular (e.g., from pods to pod)
func (*DefaultRESTMapper) ResourcesFor ¶ added in v1.2.0
func (m *DefaultRESTMapper) ResourcesFor(input unversioned.GroupVersionResource) ([]unversioned.GroupVersionResource, error)
func (*DefaultRESTMapper) String ¶ added in v1.2.0
func (m *DefaultRESTMapper) String() string
type FirstHitRESTMapper ¶ added in v1.5.0
type FirstHitRESTMapper struct {
MultiRESTMapper
}
FirstHitRESTMapper is a wrapper for multiple RESTMappers which returns the first successful result for the singular requests
func (FirstHitRESTMapper) KindFor ¶ added in v1.5.0
func (m FirstHitRESTMapper) KindFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionKind, error)
func (FirstHitRESTMapper) RESTMapping ¶ added in v1.5.0
func (m FirstHitRESTMapper) RESTMapping(gk unversioned.GroupKind, versions ...string) (*RESTMapping, error)
RESTMapping provides the REST mapping for the resource based on the kind and version. This implementation supports multiple REST schemas and return the first match.
func (FirstHitRESTMapper) ResourceFor ¶ added in v1.5.0
func (m FirstHitRESTMapper) ResourceFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionResource, error)
func (FirstHitRESTMapper) String ¶ added in v1.5.0
func (m FirstHitRESTMapper) String() string
type List ¶ added in v1.2.0
type List unversioned.List
List lets you work with list metadata from any of the versioned or internal API objects. Attempting to set or retrieve a field on an object that does not support that field will be a no-op and return a default value.
func ListAccessor ¶ added in v1.3.1
ListAccessor returns a List interface for the provided object or an error if the object does not provide List. IMPORTANT: Objects are a superset of lists, so all Objects return List metadata. Do not use this check to determine whether an object *is* a List. TODO: return bool instead of error
type ListMetaAccessor ¶ added in v1.3.1
type ListMetaAccessor interface {
GetListMeta() List
}
type MetadataAccessor ¶
type MetadataAccessor interface { APIVersion(obj runtime.Object) (string, error) SetAPIVersion(obj runtime.Object, version string) error Kind(obj runtime.Object) (string, error) SetKind(obj runtime.Object, kind string) error Namespace(obj runtime.Object) (string, error) SetNamespace(obj runtime.Object, namespace string) error Name(obj runtime.Object) (string, error) SetName(obj runtime.Object, name string) error GenerateName(obj runtime.Object) (string, error) SetGenerateName(obj runtime.Object, name string) error UID(obj runtime.Object) (types.UID, error) SetUID(obj runtime.Object, uid types.UID) error SelfLink(obj runtime.Object) (string, error) SetSelfLink(obj runtime.Object, selfLink string) error Labels(obj runtime.Object) (map[string]string, error) SetLabels(obj runtime.Object, labels map[string]string) error Annotations(obj runtime.Object) (map[string]string, error) SetAnnotations(obj runtime.Object, annotations map[string]string) error runtime.ResourceVersioner }
MetadataAccessor lets you work with object and list metadata from any of the versioned or internal API objects. Attempting to set or retrieve a field on an object that does not support that field (Name, UID, Namespace on lists) will be a no-op and return a default value.
MetadataAccessor exposes Interface in a way that can be used with multiple objects.
func NewAccessor ¶
func NewAccessor() MetadataAccessor
NewAccessor returns a MetadataAccessor that can retrieve or manipulate resource version on objects derived from core API metadata concepts.
type MultiRESTMapper ¶ added in v0.16.0
type MultiRESTMapper []RESTMapper
MultiRESTMapper is a wrapper for multiple RESTMappers.
func (MultiRESTMapper) AliasesForResource ¶ added in v0.16.0
func (m MultiRESTMapper) AliasesForResource(alias string) ([]string, bool)
AliasesForResource finds the first alias response for the provided mappers.
func (MultiRESTMapper) KindFor ¶ added in v1.2.0
func (m MultiRESTMapper) KindFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionKind, error)
func (MultiRESTMapper) KindsFor ¶ added in v1.2.0
func (m MultiRESTMapper) KindsFor(resource unversioned.GroupVersionResource) (gvk []unversioned.GroupVersionKind, err error)
func (MultiRESTMapper) RESTMapping ¶ added in v0.16.0
func (m MultiRESTMapper) RESTMapping(gk unversioned.GroupKind, versions ...string) (*RESTMapping, error)
RESTMapping provides the REST mapping for the resource based on the kind and version. This implementation supports multiple REST schemas and return the first match.
func (MultiRESTMapper) RESTMappings ¶ added in v1.4.0
func (m MultiRESTMapper) RESTMappings(gk unversioned.GroupKind) ([]*RESTMapping, error)
RESTMappings returns all possible RESTMappings for the provided group kind, or an error if the type is not recognized.
func (MultiRESTMapper) ResourceFor ¶ added in v1.2.0
func (m MultiRESTMapper) ResourceFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionResource, error)
func (MultiRESTMapper) ResourceSingularizer ¶ added in v1.1.0
func (m MultiRESTMapper) ResourceSingularizer(resource string) (singular string, err error)
ResourceSingularizer converts a REST resource name from plural to singular (e.g., from pods to pod) This implementation supports multiple REST schemas and return the first match.
func (MultiRESTMapper) ResourcesFor ¶ added in v1.2.0
func (m MultiRESTMapper) ResourcesFor(resource unversioned.GroupVersionResource) ([]unversioned.GroupVersionResource, error)
func (MultiRESTMapper) String ¶ added in v1.2.0
func (m MultiRESTMapper) String() string
type NoKindMatchError ¶ added in v1.4.0
type NoKindMatchError struct {
PartialKind unversioned.GroupVersionKind
}
NoKindMatchError is returned if the RESTMapper can't find any match for a kind
func (*NoKindMatchError) Error ¶ added in v1.4.0
func (e *NoKindMatchError) Error() string
type NoResourceMatchError ¶ added in v1.2.0
type NoResourceMatchError struct {
PartialResource unversioned.GroupVersionResource
}
NoResourceMatchError is returned if the RESTMapper can't find any match for a resource
func (*NoResourceMatchError) Error ¶ added in v1.2.0
func (e *NoResourceMatchError) Error() string
type Object ¶ added in v1.2.0
type Object interface { GetNamespace() string SetNamespace(namespace string) GetName() string SetName(name string) GetGenerateName() string SetGenerateName(name string) GetUID() types.UID SetUID(uid types.UID) GetResourceVersion() string SetResourceVersion(version string) GetSelfLink() string SetSelfLink(selfLink string) GetCreationTimestamp() unversioned.Time SetCreationTimestamp(timestamp unversioned.Time) GetDeletionTimestamp() *unversioned.Time SetDeletionTimestamp(timestamp *unversioned.Time) GetLabels() map[string]string SetLabels(labels map[string]string) GetAnnotations() map[string]string SetAnnotations(annotations map[string]string) GetFinalizers() []string SetFinalizers(finalizers []string) GetOwnerReferences() []metatypes.OwnerReference SetOwnerReferences([]metatypes.OwnerReference) GetClusterName() string SetClusterName(clusterName string) }
Object lets you work with object metadata from any of the versioned or internal API objects. Attempting to set or retrieve a field on an object that does not support that field (Name, UID, Namespace on lists) will be a no-op and return a default value.
func Accessor ¶
Accessor takes an arbitrary object pointer and returns meta.Interface. obj must be a pointer to an API type. An error is returned if the minimum required fields are missing. Fields that are not required return the default value and are a no-op if set. TODO: return bool instead of error
type ObjectMetaAccessor ¶ added in v1.2.0
type ObjectMetaAccessor interface {
GetObjectMeta() Object
}
type PriorityRESTMapper ¶ added in v1.2.0
type PriorityRESTMapper struct { // Delegate is the RESTMapper to use to locate all the Kind and Resource matches Delegate RESTMapper // ResourcePriority is a list of priority patterns to apply to matching resources. // The list of all matching resources is narrowed based on the patterns until only one remains. // A pattern with no matches is skipped. A pattern with more than one match uses its // matches as the list to continue matching against. ResourcePriority []unversioned.GroupVersionResource // KindPriority is a list of priority patterns to apply to matching kinds. // The list of all matching kinds is narrowed based on the patterns until only one remains. // A pattern with no matches is skipped. A pattern with more than one match uses its // matches as the list to continue matching against. KindPriority []unversioned.GroupVersionKind }
PriorityRESTMapper is a wrapper for automatically choosing a particular Resource or Kind when multiple matches are possible
func (PriorityRESTMapper) AliasesForResource ¶ added in v1.2.0
func (m PriorityRESTMapper) AliasesForResource(alias string) (aliases []string, ok bool)
func (PriorityRESTMapper) KindFor ¶ added in v1.2.0
func (m PriorityRESTMapper) KindFor(partiallySpecifiedResource unversioned.GroupVersionResource) (unversioned.GroupVersionKind, error)
KindFor finds all kinds, then passes them through the KindPriority patterns to find a single matching hit.
func (PriorityRESTMapper) KindsFor ¶ added in v1.2.0
func (m PriorityRESTMapper) KindsFor(partiallySpecifiedResource unversioned.GroupVersionResource) (gvk []unversioned.GroupVersionKind, err error)
func (PriorityRESTMapper) RESTMapping ¶ added in v1.2.0
func (m PriorityRESTMapper) RESTMapping(gk unversioned.GroupKind, versions ...string) (mapping *RESTMapping, err error)
func (PriorityRESTMapper) RESTMappings ¶ added in v1.4.0
func (m PriorityRESTMapper) RESTMappings(gk unversioned.GroupKind) ([]*RESTMapping, error)
func (PriorityRESTMapper) ResourceFor ¶ added in v1.2.0
func (m PriorityRESTMapper) ResourceFor(partiallySpecifiedResource unversioned.GroupVersionResource) (unversioned.GroupVersionResource, error)
ResourceFor finds all resources, then passes them through the ResourcePriority patterns to find a single matching hit.
func (PriorityRESTMapper) ResourceSingularizer ¶ added in v1.2.0
func (m PriorityRESTMapper) ResourceSingularizer(resource string) (singular string, err error)
func (PriorityRESTMapper) ResourcesFor ¶ added in v1.2.0
func (m PriorityRESTMapper) ResourcesFor(partiallySpecifiedResource unversioned.GroupVersionResource) ([]unversioned.GroupVersionResource, error)
func (PriorityRESTMapper) String ¶ added in v1.2.0
func (m PriorityRESTMapper) String() string
type RESTMapper ¶
type RESTMapper interface { // KindFor takes a partial resource and returns the single match. Returns an error if there are multiple matches KindFor(resource unversioned.GroupVersionResource) (unversioned.GroupVersionKind, error) // KindsFor takes a partial resource and returns the list of potential kinds in priority order KindsFor(resource unversioned.GroupVersionResource) ([]unversioned.GroupVersionKind, error) // ResourceFor takes a partial resource and returns the single match. Returns an error if there are multiple matches ResourceFor(input unversioned.GroupVersionResource) (unversioned.GroupVersionResource, error) // ResourcesFor takes a partial resource and returns the list of potential resource in priority order ResourcesFor(input unversioned.GroupVersionResource) ([]unversioned.GroupVersionResource, error) // RESTMapping identifies a preferred resource mapping for the provided group kind. RESTMapping(gk unversioned.GroupKind, versions ...string) (*RESTMapping, error) // RESTMappings returns all resource mappings for the provided group kind. RESTMappings(gk unversioned.GroupKind) ([]*RESTMapping, error) AliasesForResource(resource string) ([]string, bool) ResourceSingularizer(resource string) (singular string, err error) }
RESTMapper allows clients to map resources to kind, and map kind and version to interfaces for manipulating those objects. It is primarily intended for consumers of Kubernetes compatible REST APIs as defined in docs/devel/api-conventions.md.
The Kubernetes API provides versioned resources and object kinds which are scoped to API groups. In other words, kinds and resources should not be assumed to be unique across groups.
TODO: split into sub-interfaces
type RESTMapping ¶
type RESTMapping struct { // Resource is a string representing the name of this resource as a REST client would see it Resource string GroupVersionKind unversioned.GroupVersionKind // Scope contains the information needed to deal with REST Resources that are in a resource hierarchy Scope RESTScope runtime.ObjectConvertor MetadataAccessor }
RESTMapping contains the information needed to deal with objects of a specific resource and kind in a RESTful manner.
type RESTScope ¶ added in v0.10.0
type RESTScope interface { // Name of the scope Name() RESTScopeName // ParamName is the optional name of the parameter that should be inserted in the resource url // If empty, no param will be inserted ParamName() string // ArgumentName is the optional name that should be used for the variable holding the value. ArgumentName() string // ParamDescription is the optional description to use to document the parameter in api documentation ParamDescription() string }
RESTScope contains the information needed to deal with REST resources that are in a resource hierarchy
type RESTScopeName ¶ added in v0.10.0
type RESTScopeName string
const ( RESTScopeNameNamespace RESTScopeName = "namespace" RESTScopeNameRoot RESTScopeName = "root" )
type Type ¶ added in v1.2.0
type Type unversioned.Type
Type exposes the type and APIVersion of versioned or internal API objects.
func TypeAccessor ¶ added in v0.9.0
TypeAccessor returns an interface that allows retrieving and modifying the APIVersion and Kind of an in-memory internal object. TODO: this interface is used to test code that does not have ObjectMeta or ListMeta in round tripping (objects which can use apiVersion/kind, but do not fit the Kube api conventions).
type VersionInterfaces ¶
type VersionInterfaces struct { runtime.ObjectConvertor MetadataAccessor }
VersionInterfaces contains the interfaces one should use for dealing with types of a particular version.
func InterfacesForUnstructured ¶ added in v1.4.0
func InterfacesForUnstructured(unversioned.GroupVersion) (*VersionInterfaces, error)
InterfacesForUnstructured returns VersionInterfaces suitable for dealing with runtime.Unstructured objects.
type VersionInterfacesFunc ¶
type VersionInterfacesFunc func(version unversioned.GroupVersion) (*VersionInterfaces, error)
VersionInterfacesFunc returns the appropriate typer, and metadata accessor for a given api version, or an error if no such api version exists.