Field methods to access through properties

Author: Miguel Molina

generator/types.go

@@ -611,6 +611,8 @@ type ImplicitFK struct {
 }
 
 // Field is the representation of a model field.
+// TODO(erizocosmico): please, refactor all this structure to use precomputed
+// data instead of calculating it upon each call.
 type Field struct {
 	// Name is the field name.
 	Name string
@@ -807,8 +809,12 @@ func (f *Field) IsInverse() bool {
 		return false
 	}
 
-	for _, part := range strings.Split(f.Tag.Get("fk"), ",") {
-		if part == "inverse" {
+	if f.IsManyToManyRelationship() {
+		return f.isInverseThrough()
+	}
+
+	for i, part := range strings.Split(f.Tag.Get("fk"), ",") {
+		if i > 0 && part == "inverse" {
 			return true
 		}
 	}
@@ -822,6 +828,58 @@ func (f *Field) IsOneToManyRelationship() bool {
 	return f.Kind == Relationship && strings.HasPrefix(f.Type, "[]")
 }
 
+// IsManyToManyRelationship reports whether the field is a many to many
+// relationship.
+func (f *Field) IsManyToManyRelationship() bool {
+	return f.Kind == Relationship && f.Tag.Get("through") != ""
+}
+
+// ThroughTable returns the name of the intermediate table used to access the
+// current field.
+func (f *Field) ThroughTable() string {
+	return f.getThroughTablePart(0)
+}
+
+// LeftForeignKey is the name of the column used to join the current model with
+// the intermediate table.
+func (f *Field) LeftForeignKey() string {
+	fk := f.getThroughTablePart(1)
+	if fk == "" {
+		fk = foreignKeyForModel(f.Model.Name)
+	}
+	return fk
+}
+
+// RightForeignKey is the name of the column used to join the relationship
+// model with the intermediate table.
+func (f *Field) RightForeignKey() string {
+	fk := f.getThroughTablePart(2)
+	if fk == "" {
+		fk = foreignKeyForModel(f.TypeSchemaName())
+	}
+	return fk
+}
+
+func (f *Field) isInverseThrough() bool {
+	return f.getThroughPart(1) == "inverse"
+}
+
+func (f *Field) getThroughPart(idx int) string {
+	parts := strings.Split(f.Tag.Get("through"), ",")
+	if len(parts) > idx {
+		return strings.TrimSpace(parts[idx])
+	}
+	return ""
+}
+
+func (f *Field) getThroughTablePart(idx int) string {
+	parts := strings.Split(f.getThroughPart(0), ":")
+	if len(parts) > idx {
+		return strings.TrimSpace(parts[idx])
+	}
+	return ""
+}
+
 func foreignKeyForModel(model string) string {
 	return toLowerSnakeCase(model) + "_id"
 }

generator/types_test.go

@@ -194,6 +194,79 @@ func (s *FieldSuite) TestValue() {
 	}
 }
 
+func (s *FieldSuite) TestIsInverse() {
+	cases := []struct {
+		tag      string
+		expected bool
+	}{
+		{"", false},
+		{`inverse:"true"`, false},
+		{`fk:"inverse"`, false},
+		{`through:"inverse"`, false},
+		{`fk:"foo,inverse"`, true},
+		{`fk:",inverse"`, true},
+		{`through:"foo,inverse"`, true},
+		{`through:"foo:a:b,inverse"`, true},
+	}
+
+	for _, tt := range cases {
+		f := withTag(mkField("", ""), tt.tag)
+		f.Kind = Relationship
+		s.Equal(tt.expected, f.IsInverse(), tt.tag)
+	}
+}
+
+func (s *FieldSuite) TestThroughTable() {
+	cases := []struct {
+		tag, expected string
+	}{
+		{``, ""},
+		{`through:"foo"`, "foo"},
+		{`through:"foo,inverse"`, "foo"},
+		{`through:"foo:a:b,inverse"`, "foo"},
+	}
+
+	for _, tt := range cases {
+		s.Equal(tt.expected, withTag(mkField("", ""), tt.tag).ThroughTable(), tt.tag)
+	}
+}
+
+func (s *FieldSuite) TestLeftForeignKey() {
+	cases := []struct {
+		tag, expected string
+	}{
+		{``, "bar_id"},
+		{`through:"foo"`, "bar_id"},
+		{`through:"foo,inverse"`, "bar_id"},
+		{`through:"foo:a,inverse"`, "a"},
+		{`through:"foo:a:b,inverse"`, "a"},
+	}
+
+	for _, tt := range cases {
+		f := withTag(mkField("", ""), tt.tag)
+		f.Model = &Model{Name: "Bar"}
+		s.Equal(tt.expected, f.LeftForeignKey(), tt.tag)
+	}
+}
+
+func (s *FieldSuite) TestRightForeignKey() {
+	cases := []struct {
+		tag, expected string
+	}{
+		{``, "foo_id"},
+		{`through:"foo"`, "foo_id"},
+		{`through:"foo,inverse"`, "foo_id"},
+		{`through:"foo:a,inverse"`, "foo_id"},
+		{`through:"foo:a:b,inverse"`, "b"},
+	}
+
+	for _, tt := range cases {
+		f := withTag(mkField("", ""), tt.tag)
+		f.Type = "Foo"
+		s.Equal(tt.expected, f.RightForeignKey(), tt.tag)
+	}
+}
+
 type ModelSuite struct {
 	suite.Suite
 	model    *Model