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// Copyright 2014 Canonical Ltd.
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// Licensed under the LGPLv3, see LICENCE file for details.
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"github.com/juju/errors"
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// Convert turns a Document into a Metadata if possible.
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func Convert(doc Document) (Metadata, error) {
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meta, ok := doc.(Metadata)
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return nil, errors.Errorf("expected a Metadata doc, got %v", doc)
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// MetadataDocStorage provides the MetadataStorage methods than can be
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// derived from DocStorage methods. To fully implement MetadataStorage,
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// this type must be embedded in a type that implements the remaining
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type MetadataDocStorage struct {
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// Metadata implements MetadataStorage.Metadata.
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func (s *MetadataDocStorage) Metadata(id string) (Metadata, error) {
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return nil, errors.Trace(err)
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meta, err := Convert(doc)
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return meta, errors.Trace(err)
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// ListMetadata implements MetadataStorage.ListMetadata.
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func (s *MetadataDocStorage) ListMetadata() ([]Metadata, error) {
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docs, err := s.ListDocs()
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return nil, errors.Trace(err)
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var metaList []Metadata
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for _, doc := range docs {
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meta, err := Convert(doc)
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return nil, errors.Trace(err)
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metaList = append(metaList, meta)
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// ListMetadata implements MetadataStorage.ListMetadata.
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func (s *MetadataDocStorage) AddMetadata(meta Metadata) (string, error) {
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id, err := s.AddDoc(meta)
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return id, errors.Trace(err)
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// ListMetadata implements MetadataStorage.ListMetadata.
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func (s *MetadataDocStorage) RemoveMetadata(id string) error {
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return errors.Trace(s.RemoveDoc(id))