Example on how to wrap a transaction datastore in a key-transform dat…

…astore

keytransform/txn.go

@@ -0,0 +1,78 @@
+package keytransform
+
+import (
+	"context"
+
+	ds "github.com/ipfs/go-datastore"
+)
+
+var _ ds.TxnDatastore = (*TxnKeyTransformDatastore)(nil)
+
+// All methods are provided by embedded *Datastore except NewTransaction.
+type TxnKeyTransformDatastore struct {
+	*Datastore
+	txnChild ds.TxnDatastore
+	t        KeyTransform
+}
+
+func WrapTxn(child ds.TxnDatastore, t KeyTransform) ds.TxnDatastore {
+	kt := Wrap(child, t)
+
+	return &TxnKeyTransformDatastore{
+		Datastore: kt,
+		txnChild:  child,
+		t:         t,
+	}
+}
+
+// NewTransaction returns a Txn that runs all Read/Write operations through a key transform datastore
+// backed by the original txn.
+func (txnktds *TxnKeyTransformDatastore) NewTransaction(ctx context.Context, readOnly bool) (ds.Txn, error) {
+	// New transaction - normal
+	txn, err := txnktds.txnChild.NewTransaction(ctx, readOnly)
+	if err != nil {
+		return nil, err
+	}
+
+	// wrap it in an object that augments it to be a Datastore
+	txnKt := &wrappedTxn{
+		Txn: txn,
+	}
+
+	// Make that object a key-transform datastore with the original KeyTransform.
+	kt := Wrap(txnKt, txnktds.t)
+
+	// Finally, ensure that this datastore provides Commit and Discard() so that it can be
+	// a transaction.
+	return &wrappedKt{
+		Datastore: kt,
+		txn:       txnKt,
+	}, nil
+}
+
+// makes a txn a datastore
+type wrappedTxn struct {
+	ds.Txn
+}
+
+func (wtxn *wrappedTxn) Close() error {
+	return nil
+}
+
+func (wtxn *wrappedTxn) Sync(context.Context, ds.Key) error {
+	return nil
+}
+
+// makes a datastore a tnx
+type wrappedKt struct {
+	*Datastore
+	txn ds.Txn
+}
+
+func (wkt *wrappedKt) Commit(ctx context.Context) error {
+	return wkt.txn.Commit(ctx)
+}
+
+func (wkt *wrappedKt) Discard(ctx context.Context) {
+	wkt.txn.Discard(ctx)
+}