fix preloading has many with no result (#69)

Author: Fs02

go.mod

@@ -1,15 +1,17 @@
 module github.com/Fs02/grimoire
 
+go 1.14
+
 require (
 	github.com/Fs02/go-paranoid v0.0.0-20180516074805-ab50069def7d
 	github.com/azer/snakecase v0.0.0-20161028114325-c818dddafb5c
-	github.com/davecgh/go-spew v1.1.0
+	github.com/davecgh/go-spew v1.1.0 // indirect
 	github.com/go-sql-driver/mysql v1.3.0
 	github.com/lib/pq v0.0.0-20180327071824-d34b9ff171c2
 	github.com/mattn/go-sqlite3 v1.6.0
-	github.com/pmezard/go-difflib v1.0.0
-	github.com/stretchr/objx v0.1.0
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/objx v0.1.0 // indirect
 	github.com/stretchr/testify v1.2.1
 	github.com/tidwall/gjson v1.1.3
-	github.com/tidwall/match v1.0.0
+	github.com/tidwall/match v1.0.0 // indirect
 )

query.go

@@ -560,7 +560,7 @@ func collectPreloadTarget(preload []preloadTarget, refIndex []int) (map[interfac
 
 		// reset to zero if slice.
 		if fv.Kind() == reflect.Slice || fv.Kind() == reflect.Array {
-			fv.Set(reflect.Zero(fv.Type()))
+			fv.Set(reflect.MakeSlice(fv.Type(), 0, 0))
 		}
 
 		addrs[id] = append(addrs[id], fv)

query_test.go

@@ -1208,6 +1208,23 @@ func TestQuery_Preload_hasMany(t *testing.T) {
 	mock.AssertExpectations(t)
 }
 
+func TestQuery_Preload_hasManyNoResult(t *testing.T) {
+	mock := new(TestAdapter)
+	repo := Repo{adapter: mock}
+
+	user := User{ID: 10}
+	result := []Transaction{}
+
+	query := repo.From("transactions")
+
+	mock.Result(result).On("All", query.Where(In("user_id", 10)), &[]Transaction{}).Return(2, nil)
+
+	assert.Nil(t, query.Preload(&user, "Transactions"))
+	assert.Equal(t, result, user.Transactions)
+	assert.NotPanics(t, func() { query.MustPreload(&user, "Transactions") })
+	mock.AssertExpectations(t)
+}
+
 func TestQuery_Preload_sliceHasMany(t *testing.T) {
 	mock := new(TestAdapter)
 	repo := Repo{adapter: mock}
@@ -1251,6 +1268,23 @@ func TestQuery_Preload_nestedHasMany(t *testing.T) {
 	mock.AssertExpectations(t)
 }
 
+func TestQuery_Preload_nestedHasManyNoResult(t *testing.T) {
+	mock := new(TestAdapter)
+	repo := Repo{adapter: mock}
+
+	address := Address{User: &User{ID: 10}}
+	result := []Transaction{}
+
+	query := repo.From("transactions")
+
+	mock.Result(result).On("All", query.Where(In("user_id", 10)), &[]Transaction{}).Return(2, nil)
+
+	assert.Nil(t, query.Preload(&address, "User.Transactions"))
+	assert.Equal(t, result, address.User.Transactions)
+	assert.NotPanics(t, func() { query.MustPreload(&address, "User.Transactions") })
+	mock.AssertExpectations(t)
+}
+
 func TestQuery_Preload_nestedNullHasMany(t *testing.T) {
 	mock := new(TestAdapter)
 	repo := Repo{adapter: mock}