fix Query.One + Filter behavior (#248)

query.go

@@ -239,34 +239,19 @@ func (q *Query) One(ctx context.Context, out interface{}) error {
 	}
 
 	// If not, try a Query.
-	req := q.queryInput()
-
-	var res *dynamodb.QueryOutput
-	err := q.table.db.retry(ctx, func() error {
-		var err error
-		res, err = q.table.db.client.Query(ctx, req)
-		q.cc.incRequests()
-		if err != nil {
-			return err
-		}
-
-		switch {
-		case len(res.Items) == 0:
-			return ErrNotFound
-		case len(res.Items) > 1 && q.limit != 1:
-			return ErrTooMany
-		case res.LastEvaluatedKey != nil && q.searchLimit != 0:
-			return ErrTooMany
-		}
-
-		return nil
-	})
-	if err != nil {
+	iter := q.Iter().(*queryIter)
+	ok := iter.Next(ctx, out)
+	if err := iter.Err(); err != nil {
 		return err
 	}
-	q.cc.add(res.ConsumedCapacity)
-
-	return unmarshalItem(res.Items[0], out)
+	if !ok {
+		return ErrNotFound
+	}
+	// Best effort: do we have any pending unused items?
+	if iter.hasMore() {
+		return ErrTooMany
+	}
+	return nil
 }
 
 // Count executes this request, returning the number of results.
@@ -422,6 +407,13 @@ func (itr *queryIter) Next(ctx context.Context, out interface{}) bool {
 	return itr.err == nil
 }
 
+func (itr *queryIter) hasMore() bool {
+	if itr.query.limit > 0 && itr.n == itr.query.limit {
+		return false
+	}
+	return itr.output != nil && itr.idx < len(itr.output.Items)
+}
+
 // Err returns the error encountered, if any.
 // You should check this after Next is finished.
 func (itr *queryIter) Err() error {

query_test.go

@@ -2,6 +2,7 @@ package dynamo
 
 import (
 	"context"
+	"errors"
 	"reflect"
 	"testing"
 	"time"
@@ -111,6 +112,30 @@ func TestGetAllCount(t *testing.T) {
 		t.Errorf("bad result for get one. %v ≠ %v", one, item)
 	}
 
+	// trigger ErrTooMany
+	one = widget{}
+	err = table.Get("UserID", 42).Range("Time", Greater, "0").Consistent(true).One(ctx, &one)
+	if !errors.Is(err, ErrTooMany) {
+		t.Errorf("bad error from get one. %v ≠ %v", err, ErrTooMany)
+	}
+
+	// suppress ErrTooMany with Limit(1)
+	one = widget{}
+	err = table.Get("UserID", 42).Range("Time", Greater, "0").Consistent(true).Limit(1).One(ctx, &one)
+	if err != nil {
+		t.Error("unexpected error:", err)
+	}
+	if one.UserID == 0 {
+		t.Errorf("bad result for get one: %v", one)
+	}
+
+	// trigger ErrNotFound via SearchLimit + Filter + One
+	one = widget{}
+	err = table.Get("UserID", 42).Range("Time", Greater, "0").Filter("Msg = ?", item.Msg).Consistent(true).SearchLimit(1).One(ctx, &one)
+	if !errors.Is(err, ErrNotFound) {
+		t.Errorf("bad error from get one. %v ≠ %v", err, ErrNotFound)
+	}
+
 	// GetItem + Project
 	one = widget{}
 	projected := widget{