feat: Add unique secondary index

cli/index_create.go

@@ -21,12 +21,14 @@ func MakeIndexCreateCommand() *cobra.Command {
 	var collectionArg string
 	var nameArg string
 	var fieldsArg []string
+	var uniqueArg bool
 	var cmd = &cobra.Command{
-		Use:   "create -c --collection <collection> --fields <fields> [-n --name <name>]",
+		Use:   "create -c --collection <collection> --fields <fields> [-n --name <name>] [--unique]",
 		Short: "Creates a secondary index on a collection's field(s)",
 		Long: `Creates a secondary index on a collection's field(s).
 
 The --name flag is optional. If not provided, a name will be generated automatically.
+The --unique flag is optional. If provided, the index will be unique.
 
 Example: create an index for 'Users' collection on 'name' field:
   defradb client index create --collection Users --fields name
@@ -44,6 +46,7 @@ Example: create a named index for 'Users' collection on 'name' field:
 			desc := client.IndexDescription{
 				Name:   nameArg,
 				Fields: fields,
+				Unique: uniqueArg,
 			}
 			col, err := store.GetCollectionByName(cmd.Context(), collectionArg)
 			if err != nil {
@@ -62,6 +65,7 @@ Example: create a named index for 'Users' collection on 'name' field:
 	cmd.Flags().StringVarP(&collectionArg, "collection", "c", "", "Collection name")
 	cmd.Flags().StringVarP(&nameArg, "name", "n", "", "Index name")
 	cmd.Flags().StringSliceVar(&fieldsArg, "fields", []string{}, "Fields to index")
+	cmd.Flags().BoolVarP(&uniqueArg, "unique", "u", false, "Make the index unique")
 
 	return cmd
 }

client/index.go

@@ -36,6 +36,8 @@ type IndexDescription struct {
 	ID uint32
 	// Fields contains the fields that are being indexed.
 	Fields []IndexedFieldDescription
+	// Unique indicates whether the index is unique.
+	Unique bool
 }
 
 // CollectIndexedFields returns all fields that are indexed by all collection indexes.

db/errors.go

@@ -86,6 +86,7 @@ const (
 	errExpectedJSONArray                  string = "expected JSON array"
 	errOneOneAlreadyLinked                string = "target document is already linked to another document"
 	errIndexDoesNotMatchName              string = "the index used does not match the given name"
+	errCanNotIndexNonUniqueField          string = "can not create doc that violates unique index"
 )
 
 var (
@@ -631,3 +632,12 @@ func NewErrIndexDoesNotMatchName(index, name string) error {
 		errors.NewKV("Name", name),
 	)
 }
+
+func NewErrCanNotIndexNonUniqueField(dockey, fieldName string, value any) error {
+	return errors.New(
+		errCanNotIndexNonUniqueField,
+		errors.NewKV("Dockey", dockey),
+		errors.NewKV("Field name", fieldName),
+		errors.NewKV("Field value", value),
+	)
+}

db/fetcher/indexer.go

@@ -32,6 +32,7 @@ type IndexFetcher struct {
 	mapping           *core.DocumentMapping
 	indexedField      client.FieldDescription
 	docFields         []client.FieldDescription
+	indexDesc         client.IndexDescription
 	indexIter         indexIterator
 	indexDataStoreKey core.IndexDataStoreKey
 	execInfo          ExecInfo
@@ -70,6 +71,7 @@ func (f *IndexFetcher) Init(
 
 	for _, index := range col.Description().Indexes {
 		if index.Fields[0].Name == f.indexedField.Name {
+			f.indexDesc = index
 			f.indexDataStoreKey.IndexID = index.ID
 			break
 		}
@@ -84,7 +86,7 @@ func (f *IndexFetcher) Init(
 		}
 	}
 
-	iter, err := createIndexIterator(f.indexDataStoreKey, f.indexFilter, &f.execInfo)
+	iter, err := createIndexIterator(f.indexDataStoreKey, f.indexFilter, &f.execInfo, f.indexDesc.Unique)
 	if err != nil {
 		return err
 	}
@@ -112,28 +114,32 @@ func (f *IndexFetcher) FetchNext(ctx context.Context) (EncodedDocument, ExecInfo
 	for {
 		f.doc.Reset()
 
-		indexKey, hasValue, err := f.indexIter.Next()
+		res, err := f.indexIter.Next()
 		if err != nil {
 			return nil, ExecInfo{}, err
 		}
 
-		if !hasValue {
+		if !res.foundKey {
 			return nil, f.execInfo, nil
 		}
 
 		property := &encProperty{
 			Desc: f.indexedField,
-			Raw:  indexKey.FieldValues[0],
+			Raw:  res.key.FieldValues[0],
 		}
 
-		f.doc.key = indexKey.FieldValues[1]
+		if f.indexDesc.Unique {
+			f.doc.key = res.value
+		} else {
+			f.doc.key = res.key.FieldValues[1]
+		}
 		f.doc.properties[f.indexedField] = property
 		f.execInfo.FieldsFetched++
 
 		if f.docFetcher != nil && len(f.docFields) > 0 {
 			targetKey := base.MakeDocKey(f.col.Description(), string(f.doc.key))
 			spans := core.NewSpans(core.NewSpan(targetKey, targetKey.PrefixEnd()))
-			err = f.docFetcher.Start(ctx, spans)
+			err := f.docFetcher.Start(ctx, spans)
 			if err != nil {
 				return nil, ExecInfo{}, err
 			}