key transform wrapper for ds.Txn

Author: i-norden

keytransform/txndatastore.go

@@ -225,26 +225,6 @@ func (d *TxnDatastore) Batch(ctx context.Context) (ds.Batch, error) {
 	}, nil
 }
 
-type transformBatch struct {
-	dst ds.Batch
-
-	f KeyMapping
-}
-
-var _ ds.Batch = (*transformBatch)(nil)
-
-func (t *transformBatch) Put(ctx context.Context, key ds.Key, val []byte) error {
-	return t.dst.Put(ctx, t.f(key), val)
-}
-
-func (t *transformBatch) Delete(ctx context.Context, key ds.Key) error {
-	return t.dst.Delete(ctx, t.f(key))
-}
-
-func (t *transformBatch) Commit(ctx context.Context) error {
-	return t.dst.Commit(ctx)
-}
-
 func (d *TxnDatastore) Check(ctx context.Context) error {
 	if c, ok := d.child.(ds.CheckedDatastore); ok {
 		return c.Check(ctx)
@@ -267,5 +247,169 @@ func (d *TxnDatastore) CollectGarbage(ctx context.Context) error {
 }
 
 func (d *TxnDatastore) NewTransaction(ctx context.Context, readOnly bool) (ds.Txn, error) {
-	panic("implement me")
+	childTxn, err := d.child.NewTransaction(ctx, readOnly)
+	if err != nil {
+		return nil, err
+	}
+	return &txnWrapper{child: childTxn, KeyTransform: d.KeyTransform}, nil
+}
+
+type txnWrapper struct {
+	child ds.Txn
+
+	KeyTransform
+}
+
+var _ ds.Txn = (*txnWrapper)(nil)
+
+func (t *txnWrapper) Get(ctx context.Context, key ds.Key) (value []byte, err error) {
+	return t.child.Get(ctx, t.ConvertKey(key))
+}
+
+func (t *txnWrapper) Has(ctx context.Context, key ds.Key) (exists bool, err error) {
+	return t.child.Has(ctx, t.ConvertKey(key))
+}
+
+func (t *txnWrapper) GetSize(ctx context.Context, key ds.Key) (size int, err error) {
+	return t.child.GetSize(ctx, t.ConvertKey(key))
+}
+
+func (t *txnWrapper) Query(ctx context.Context, q dsq.Query) (dsq.Results, error) {
+	nq, cq := t.prepareQuery(q)
+
+	cqr, err := t.child.Query(ctx, cq)
+	if err != nil {
+		return nil, err
+	}
+
+	qr := dsq.ResultsFromIterator(q, dsq.Iterator{
+		Next: func() (dsq.Result, bool) {
+			r, ok := cqr.NextSync()
+			if !ok {
+				return r, false
+			}
+			if r.Error == nil {
+				r.Entry.Key = t.InvertKey(ds.RawKey(r.Entry.Key)).String()
+			}
+			return r, true
+		},
+		Close: func() error {
+			return cqr.Close()
+		},
+	})
+	return dsq.NaiveQueryApply(nq, qr), nil
+}
+
+// Split the query into a child query and a naive query. That way, we can make
+// the child datastore do as much work as possible.
+func (t *txnWrapper) prepareQuery(q dsq.Query) (naive, child dsq.Query) {
+
+	// First, put everything in the child query. Then, start taking things
+	// out.
+	child = q
+
+	// Always let the child handle the key prefix.
+	child.Prefix = t.ConvertKey(ds.NewKey(child.Prefix)).String()
+
+	// Check if the key transform is order-preserving so we can use the
+	// child datastore's built-in ordering.
+	orderPreserving := false
+	switch t.KeyTransform.(type) {
+	case PrefixTransform, *PrefixTransform:
+		orderPreserving = true
+	}
+
+	// Try to let the child handle ordering.
+orders:
+	for i, o := range child.Orders {
+		switch o.(type) {
+		case dsq.OrderByValue, *dsq.OrderByValue,
+			dsq.OrderByValueDescending, *dsq.OrderByValueDescending:
+			// Key doesn't matter.
+			continue
+		case dsq.OrderByKey, *dsq.OrderByKey,
+			dsq.OrderByKeyDescending, *dsq.OrderByKeyDescending:
+			// if the key transform preserves order, we can delegate
+			// to the child datastore.
+			if orderPreserving {
+				// When sorting, we compare with the first
+				// Order, then, if equal, we compare with the
+				// second Order, etc. However, keys are _unique_
+				// so we'll never apply any additional orders
+				// after ordering by key.
+				child.Orders = child.Orders[:i+1]
+				break orders
+			}
+		}
+
+		// Can't handle this order under transform, punt it to a naive
+		// ordering.
+		naive.Orders = q.Orders
+		child.Orders = nil
+		naive.Offset = q.Offset
+		child.Offset = 0
+		naive.Limit = q.Limit
+		child.Limit = 0
+		break
+	}
+
+	// Try to let the child handle the filters.
+
+	// don't modify the original filters.
+	child.Filters = append([]dsq.Filter(nil), child.Filters...)
+
+	for i, f := range child.Filters {
+		switch f := f.(type) {
+		case dsq.FilterValueCompare, *dsq.FilterValueCompare:
+			continue
+		case dsq.FilterKeyCompare:
+			child.Filters[i] = dsq.FilterKeyCompare{
+				Op:  f.Op,
+				Key: t.ConvertKey(ds.NewKey(f.Key)).String(),
+			}
+			continue
+		case *dsq.FilterKeyCompare:
+			child.Filters[i] = &dsq.FilterKeyCompare{
+				Op:  f.Op,
+				Key: t.ConvertKey(ds.NewKey(f.Key)).String(),
+			}
+			continue
+		case dsq.FilterKeyPrefix:
+			child.Filters[i] = dsq.FilterKeyPrefix{
+				Prefix: t.ConvertKey(ds.NewKey(f.Prefix)).String(),
+			}
+			continue
+		case *dsq.FilterKeyPrefix:
+			child.Filters[i] = &dsq.FilterKeyPrefix{
+				Prefix: t.ConvertKey(ds.NewKey(f.Prefix)).String(),
+			}
+			continue
+		}
+
+		// Not a known filter, defer to the naive implementation.
+		naive.Filters = q.Filters
+		child.Filters = nil
+		naive.Offset = q.Offset
+		child.Offset = 0
+		naive.Limit = q.Limit
+		child.Limit = 0
+		break
+	}
+	return
+}
+
+func (t txnWrapper) Put(ctx context.Context, key ds.Key, value []byte) error {
+	return t.child.Put(ctx, t.ConvertKey(key), value)
+}
+
+func (t txnWrapper) Delete(ctx context.Context, key ds.Key) error {
+	return t.child.Delete(ctx, t.ConvertKey(key))
+}
+
+func (t txnWrapper) Commit(ctx context.Context) error {
+	return t.child.Commit(ctx)
+}
+
+func (t txnWrapper) Discard(ctx context.Context) {
+	t.child.Discard(ctx)
 }