fix: better behavior when saving non-existent instance (#462)

Signed-off-by: Carson Farmer <carson.farmer@gmail.com>

db/collection.go

@@ -553,23 +553,16 @@ func (t *Txn) createSaveActions(identity thread.PubKey, updated ...[]byte) ([]co
 		key := baseKey.ChildString(t.collection.name).ChildString(id.String())
 		previous, err := t.collection.db.datastore.Get(key)
 		if err == ds.ErrNotFound {
-			a := core.Action{
-				Type:           core.Create,
-				InstanceID:     id,
-				CollectionName: t.collection.name,
-				Previous:       nil,
-				Current:        next,
-			}
-			t.actions = append(t.actions, a)
-			// Early out and make this a create event. Assumes valid _id as specified above
-			continue
-		}
-		if err != nil {
-			return nil, err
-		}
-		previous, err = t.collection.filterRead(identity, previous)
-		if err != nil {
+			// Default to an empty doc, downstream reducer will take care of patching, etc
+			previous = []byte("{}")
+		} else if err != nil {
 			return nil, err
+		} else {
+			// No errors, carry on
+			previous, err = t.collection.filterRead(identity, previous)
+			if err != nil {
+				return nil, err
+			}
 		}
 
 		actions = append(actions, core.Action{

db/collection_test.go

@@ -1071,7 +1071,34 @@ func TestSaveInstance(t *testing.T) {
 
 		p := util.JSONFromInstance(Person{Name: "Alice", Age: 42})
 		if err := m.Save(p); err != nil {
-			t.Fatal("should have saved non-existent instasnce")
+			t.Fatal("should have saved non-existent instance")
+		}
+
+		// Create valid, predefined ID
+		ID := core.NewInstanceID()
+		// Update an instance **twice** in the same transaction, **without** a create op
+		err = m.WriteTxn(func(txn *Txn) error {
+			// Save non-existent instance
+			p := Person{Name: "Bob", Age: 37, ID: ID}
+			if err := txn.Save(util.JSONFromInstance(p)); err != nil {
+				return err
+			}
+			// Now update it in the **same** transaction
+			p.Age = 44
+			if err := txn.Save(util.JSONFromInstance(p)); err != nil {
+				return err
+			}
+			return nil
+		})
+		checkErr(t, err)
+
+		// Make sure bob is in there
+		instance, err := m.FindByID(ID)
+		checkErr(t, err)
+		person := &Person{}
+		util.InstanceFromJSON(instance, person)
+		if person.ID != ID || person.Age != 44 || person.Name != "Bob" {
+			t.Fatalf(errInvalidInstanceState)
 		}
 	})
 }

jsonpatcher/jsonpatcher.go

@@ -11,7 +11,7 @@ import (
 
 	jsonpatch "github.com/evanphx/json-patch"
 	cbornode "github.com/ipfs/go-ipld-cbor"
-	"github.com/ipfs/go-ipld-format"
+	format "github.com/ipfs/go-ipld-format"
 	logging "github.com/ipfs/go-log"
 	"github.com/multiformats/go-multihash"
 	ds "github.com/textileio/go-datastore"
@@ -149,9 +149,8 @@ func (jp *jsonPatcher) Reduce(events []core.Event, datastore ds.TxnDatastore, ba
 		case save:
 			value, err := txn.Get(key)
 			if errors.Is(err, ds.ErrNotFound) {
-				return nil, errSavingNonExistentInstance
-			}
-			if err != nil {
+				value = []byte("{}")
+			} else if err != nil {
 				return nil, err
 			}
 			patchedValue, err := jsonpatch.MergePatch(value, je.Patch.JSONPatch)