Add support for pointer FKs when preloading a belongs_to association

pop_test.go

@@ -138,14 +138,16 @@ type Book struct {
 }
 
 type Taxi struct {
-	ID        int       `db:"id"`
-	Model     string    `db:"model"`
-	UserID    nulls.Int `db:"user_id"`
-	AddressID nulls.Int `db:"address_id"`
-	Driver    *User     `belongs_to:"user" fk_id:"user_id"`
-	Address   Address   `belongs_to:"address"`
-	CreatedAt time.Time `db:"created_at"`
-	UpdatedAt time.Time `db:"updated_at"`
+	ID          int       `db:"id"`
+	Model       string    `db:"model"`
+	UserID      nulls.Int `db:"user_id"`
+	AddressID   nulls.Int `db:"address_id"`
+	Driver      *User     `belongs_to:"user" fk_id:"user_id"`
+	Address     Address   `belongs_to:"address"`
+	ToAddressID *int      `db:"to_address_id"`
+	ToAddress   *Address  `belongs_to:"address"`
+	CreatedAt   time.Time `db:"created_at"`
+	UpdatedAt   time.Time `db:"updated_at"`
 }
 
 // Validate gets run every time you call a "Validate*" (ValidateAndSave, ValidateAndCreate, ValidateAndUpdate) method.

preload_associations.go

@@ -355,7 +355,9 @@ func preloadBelongsTo(tx *Connection, asoc *AssociationMetaInfo, mmi *ModelMetaI
 
 	fkids := []interface{}{}
 	mmi.iterate(func(val reflect.Value) {
-		fkids = append(fkids, mmi.mapper.FieldByName(val, fi.Path).Interface())
+		if !isFieldNilPtr(val, fi) {
+			fkids = append(fkids, mmi.mapper.FieldByName(val, fi.Path).Interface())
+		}
 	})
 
 	if len(fkids) == 0 {
@@ -386,11 +388,15 @@ func preloadBelongsTo(tx *Connection, asoc *AssociationMetaInfo, mmi *ModelMetaI
 
 	// 3) iterate over every model and fill it with the assoc.
 	mmi.iterate(func(mvalue reflect.Value) {
+		if isFieldNilPtr(mvalue, fi) {
+			return
+		}
 		modelAssociationField := mmi.mapper.FieldByName(mvalue, asoc.Name)
 		for i := 0; i < slice.Elem().Len(); i++ {
 			asocValue := slice.Elem().Index(i)
-			if mmi.mapper.FieldByName(mvalue, fi.Path).Interface() == mmi.mapper.FieldByName(asocValue, "ID").Interface() ||
-				reflect.DeepEqual(mmi.mapper.FieldByName(mvalue, fi.Path), mmi.mapper.FieldByName(asocValue, "ID")) {
+			fkField := reflect.Indirect(mmi.mapper.FieldByName(mvalue, fi.Path))
+			if fkField.Interface() == mmi.mapper.FieldByName(asocValue, "ID").Interface() ||
+				reflect.DeepEqual(fkField, mmi.mapper.FieldByName(asocValue, "ID")) {
 
 				switch {
 				case modelAssociationField.Kind() == reflect.Slice || modelAssociationField.Kind() == reflect.Array:
@@ -499,3 +505,8 @@ func preloadManyToMany(tx *Connection, asoc *AssociationMetaInfo, mmi *ModelMeta
 	}
 	return nil
 }
+
+func isFieldNilPtr(val reflect.Value, fi *reflectx.FieldInfo) bool {
+	fieldValue := reflectx.FieldByIndexesReadOnly(val, fi.Index)
+	return fieldValue.Kind() == reflect.Ptr && fieldValue.IsNil()
+}

preload_associations_test.go

@@ -231,3 +231,36 @@ func Test_New_Implementation_For_BelongsTo_Multiple_Fields(t *testing.T) {
 		SetEagerMode(EagerDefault)
 	})
 }
+
+func Test_New_Implementation_For_BelongsTo_Ptr_Field(t *testing.T) {
+	if PDB == nil {
+		t.Skip("skipping integration tests")
+	}
+	transaction(func(tx *Connection) {
+		a := require.New(t)
+		toAddress := Address{HouseNumber: 1, Street: "Destination Ave"}
+		a.NoError(tx.Create(&toAddress))
+
+		taxi := Taxi{ToAddressID: &toAddress.ID}
+		a.NoError(tx.Create(&taxi))
+
+		book1 := Book{TaxiID: nulls.NewInt(taxi.ID), Title: "My Book"}
+		a.NoError(tx.Create(&book1))
+
+		taxiNilToAddress := Taxi{ToAddressID: nil}
+		a.NoError(tx.Create(&taxiNilToAddress))
+
+		book2 := Book{TaxiID: nulls.NewInt(taxiNilToAddress.ID), Title: "Another Book"}
+		a.NoError(tx.Create(&book2))
+
+		SetEagerMode(EagerPreload)
+		books := []Book{}
+		a.NoError(tx.EagerPreload("Taxi.ToAddress").Order("created_at").All(&books))
+		a.Len(books, 2)
+		a.Equal(toAddress.Street, books[0].Taxi.ToAddress.Street)
+		a.NotNil(books[0].Taxi.ToAddressID)
+		a.Nil(books[1].Taxi.ToAddress)
+		a.Nil(books[1].Taxi.ToAddressID)
+		SetEagerMode(EagerDefault)
+	})
+}

testdata/migrations/20181104135856_taxis.up.fizz

@@ -2,6 +2,7 @@ create_table("taxis") {
   t.Column("id", "int", {primary: true})
   t.Column("model", "string", {})
   t.Column("user_id", "int", {"null": true})
-  t.Column("address_id", "int",{"null":true})
+  t.Column("address_id", "int", {"null":true})
+  t.Column("to_address_id", "int", {"null":true})
   t.Timestamps()
 }