feat(writer): 🎉 Enhance relationship field naming and uniqueness

* Update relationship field naming conventions for has-one and has-many relationships.
* Implement logic to ensure unique field names by tracking used names.
* Add tests to verify new naming conventions and uniqueness constraints.

pkg/writers/gorm/writer_test.go

@@ -164,9 +164,309 @@ func TestWriter_WriteDatabase_MultiFile(t *testing.T) {
 		t.Fatalf("Failed to read posts file: %v", err)
 	}
 
-	if !strings.Contains(string(postsContent), "USE *ModelUser") {
-		// Relationship field should be present
-		t.Logf("Posts content:\n%s", string(postsContent))
+	postsStr := string(postsContent)
+
+	// Verify relationship is present with new naming convention
+	// Should now be RelUserID (belongs-to) instead of USE
+	if !strings.Contains(postsStr, "RelUserID") {
+		t.Errorf("Missing relationship field RelUserID (new naming convention)")
+	}
+
+	// Check users file contains has-many relationship
+	usersContent, err := os.ReadFile(filepath.Join(tmpDir, "sql_public_users.go"))
+	if err != nil {
+		t.Fatalf("Failed to read users file: %v", err)
+	}
+
+	usersStr := string(usersContent)
+
+	// Should have RelUserIDPosts (has-many) field
+	if !strings.Contains(usersStr, "RelUserIDPosts") {
+		t.Errorf("Missing has-many relationship field RelUserIDPosts")
+	}
+}
+
+func TestWriter_MultipleReferencesToSameTable(t *testing.T) {
+	// Test scenario: api_event table with multiple foreign keys to filepointer table
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("org")
+
+	// Filepointer table
+	filepointer := models.InitTable("filepointer", "org")
+	filepointer.Columns["id_filepointer"] = &models.Column{
+		Name:         "id_filepointer",
+		Type:         "bigserial",
+		NotNull:      true,
+		IsPrimaryKey: true,
+	}
+	schema.Tables = append(schema.Tables, filepointer)
+
+	// API event table with two foreign keys to filepointer
+	apiEvent := models.InitTable("api_event", "org")
+	apiEvent.Columns["id_api_event"] = &models.Column{
+		Name:         "id_api_event",
+		Type:         "bigserial",
+		NotNull:      true,
+		IsPrimaryKey: true,
+	}
+	apiEvent.Columns["rid_filepointer_request"] = &models.Column{
+		Name:    "rid_filepointer_request",
+		Type:    "bigint",
+		NotNull: false,
+	}
+	apiEvent.Columns["rid_filepointer_response"] = &models.Column{
+		Name:    "rid_filepointer_response",
+		Type:    "bigint",
+		NotNull: false,
+	}
+
+	// Add constraints
+	apiEvent.Constraints["fk_request"] = &models.Constraint{
+		Name:              "fk_request",
+		Type:              models.ForeignKeyConstraint,
+		Columns:           []string{"rid_filepointer_request"},
+		ReferencedTable:   "filepointer",
+		ReferencedSchema:  "org",
+		ReferencedColumns: []string{"id_filepointer"},
+	}
+	apiEvent.Constraints["fk_response"] = &models.Constraint{
+		Name:              "fk_response",
+		Type:              models.ForeignKeyConstraint,
+		Columns:           []string{"rid_filepointer_response"},
+		ReferencedTable:   "filepointer",
+		ReferencedSchema:  "org",
+		ReferencedColumns: []string{"id_filepointer"},
+	}
+
+	schema.Tables = append(schema.Tables, apiEvent)
+	db.Schemas = append(db.Schemas, schema)
+
+	// Create writer
+	tmpDir := t.TempDir()
+	opts := &writers.WriterOptions{
+		PackageName: "models",
+		OutputPath:  tmpDir,
+		Metadata: map[string]interface{}{
+			"multi_file": true,
+		},
+	}
+
+	writer := NewWriter(opts)
+	err := writer.WriteDatabase(db)
+	if err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	// Read the api_event file
+	apiEventContent, err := os.ReadFile(filepath.Join(tmpDir, "sql_org_api_event.go"))
+	if err != nil {
+		t.Fatalf("Failed to read api_event file: %v", err)
+	}
+
+	contentStr := string(apiEventContent)
+
+	// Verify both relationships have unique names based on column names
+	expectations := []struct {
+		fieldName string
+		tag       string
+	}{
+		{"RelRIDFilepointerRequest", "foreignKey:RIDFilepointerRequest"},
+		{"RelRIDFilepointerResponse", "foreignKey:RIDFilepointerResponse"},
+	}
+
+	for _, exp := range expectations {
+		if !strings.Contains(contentStr, exp.fieldName) {
+			t.Errorf("Missing relationship field: %s\nGenerated:\n%s", exp.fieldName, contentStr)
+		}
+		if !strings.Contains(contentStr, exp.tag) {
+			t.Errorf("Missing relationship tag: %s\nGenerated:\n%s", exp.tag, contentStr)
+		}
+	}
+
+	// Verify NO duplicate field names (old behavior would create duplicate "FIL" fields)
+	if strings.Contains(contentStr, "FIL *ModelFilepointer") {
+		t.Errorf("Found old prefix-based naming (FIL), should use column-based naming")
+	}
+
+	// Also verify has-many relationships on filepointer table
+	filepointerContent, err := os.ReadFile(filepath.Join(tmpDir, "sql_org_filepointer.go"))
+	if err != nil {
+		t.Fatalf("Failed to read filepointer file: %v", err)
+	}
+
+	filepointerStr := string(filepointerContent)
+
+	// Should have two different has-many relationships with unique names
+	hasManyExpectations := []string{
+		"RelRIDFilepointerRequestAPIEvents",  // Has many via rid_filepointer_request
+		"RelRIDFilepointerResponseAPIEvents", // Has many via rid_filepointer_response
+	}
+
+	for _, exp := range hasManyExpectations {
+		if !strings.Contains(filepointerStr, exp) {
+			t.Errorf("Missing has-many relationship field: %s\nGenerated:\n%s", exp, filepointerStr)
+		}
+	}
+}
+
+func TestWriter_MultipleHasManyRelationships(t *testing.T) {
+	// Test scenario: api_provider table referenced by multiple tables via rid_api_provider
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("org")
+
+	// Owner table
+	owner := models.InitTable("owner", "org")
+	owner.Columns["id_owner"] = &models.Column{
+		Name:         "id_owner",
+		Type:         "bigserial",
+		NotNull:      true,
+		IsPrimaryKey: true,
+	}
+	schema.Tables = append(schema.Tables, owner)
+
+	// API Provider table
+	apiProvider := models.InitTable("api_provider", "org")
+	apiProvider.Columns["id_api_provider"] = &models.Column{
+		Name:         "id_api_provider",
+		Type:         "bigserial",
+		NotNull:      true,
+		IsPrimaryKey: true,
+	}
+	apiProvider.Columns["rid_owner"] = &models.Column{
+		Name:    "rid_owner",
+		Type:    "bigint",
+		NotNull: true,
+	}
+	apiProvider.Constraints["fk_owner"] = &models.Constraint{
+		Name:              "fk_owner",
+		Type:              models.ForeignKeyConstraint,
+		Columns:           []string{"rid_owner"},
+		ReferencedTable:   "owner",
+		ReferencedSchema:  "org",
+		ReferencedColumns: []string{"id_owner"},
+	}
+	schema.Tables = append(schema.Tables, apiProvider)
+
+	// Login table
+	login := models.InitTable("login", "org")
+	login.Columns["id_login"] = &models.Column{
+		Name:         "id_login",
+		Type:         "bigserial",
+		NotNull:      true,
+		IsPrimaryKey: true,
+	}
+	login.Columns["rid_api_provider"] = &models.Column{
+		Name:    "rid_api_provider",
+		Type:    "bigint",
+		NotNull: true,
+	}
+	login.Constraints["fk_api_provider"] = &models.Constraint{
+		Name:              "fk_api_provider",
+		Type:              models.ForeignKeyConstraint,
+		Columns:           []string{"rid_api_provider"},
+		ReferencedTable:   "api_provider",
+		ReferencedSchema:  "org",
+		ReferencedColumns: []string{"id_api_provider"},
+	}
+	schema.Tables = append(schema.Tables, login)
+
+	// Filepointer table
+	filepointer := models.InitTable("filepointer", "org")
+	filepointer.Columns["id_filepointer"] = &models.Column{
+		Name:         "id_filepointer",
+		Type:         "bigserial",
+		NotNull:      true,
+		IsPrimaryKey: true,
+	}
+	filepointer.Columns["rid_api_provider"] = &models.Column{
+		Name:    "rid_api_provider",
+		Type:    "bigint",
+		NotNull: true,
+	}
+	filepointer.Constraints["fk_api_provider"] = &models.Constraint{
+		Name:              "fk_api_provider",
+		Type:              models.ForeignKeyConstraint,
+		Columns:           []string{"rid_api_provider"},
+		ReferencedTable:   "api_provider",
+		ReferencedSchema:  "org",
+		ReferencedColumns: []string{"id_api_provider"},
+	}
+	schema.Tables = append(schema.Tables, filepointer)
+
+	// API Event table
+	apiEvent := models.InitTable("api_event", "org")
+	apiEvent.Columns["id_api_event"] = &models.Column{
+		Name:         "id_api_event",
+		Type:         "bigserial",
+		NotNull:      true,
+		IsPrimaryKey: true,
+	}
+	apiEvent.Columns["rid_api_provider"] = &models.Column{
+		Name:    "rid_api_provider",
+		Type:    "bigint",
+		NotNull: true,
+	}
+	apiEvent.Constraints["fk_api_provider"] = &models.Constraint{
+		Name:              "fk_api_provider",
+		Type:              models.ForeignKeyConstraint,
+		Columns:           []string{"rid_api_provider"},
+		ReferencedTable:   "api_provider",
+		ReferencedSchema:  "org",
+		ReferencedColumns: []string{"id_api_provider"},
+	}
+	schema.Tables = append(schema.Tables, apiEvent)
+
+	db.Schemas = append(db.Schemas, schema)
+
+	// Create writer
+	tmpDir := t.TempDir()
+	opts := &writers.WriterOptions{
+		PackageName: "models",
+		OutputPath:  tmpDir,
+		Metadata: map[string]interface{}{
+			"multi_file": true,
+		},
+	}
+
+	writer := NewWriter(opts)
+	err := writer.WriteDatabase(db)
+	if err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	// Read the api_provider file
+	apiProviderContent, err := os.ReadFile(filepath.Join(tmpDir, "sql_org_api_provider.go"))
+	if err != nil {
+		t.Fatalf("Failed to read api_provider file: %v", err)
+	}
+
+	contentStr := string(apiProviderContent)
+
+	// Verify all has-many relationships have unique names
+	hasManyExpectations := []string{
+		"RelRIDAPIProviderLogins",      // Has many via Login
+		"RelRIDAPIProviderFilepointers", // Has many via Filepointer
+		"RelRIDAPIProviderAPIEvents",   // Has many via APIEvent
+		"RelRIDOwner",                  // Belongs to via rid_owner
+	}
+
+	for _, exp := range hasManyExpectations {
+		if !strings.Contains(contentStr, exp) {
+			t.Errorf("Missing relationship field: %s\nGenerated:\n%s", exp, contentStr)
+		}
+	}
+
+	// Verify NO duplicate field names
+	// Count occurrences of "RelRIDAPIProvider" fields - should have 3 unique ones
+	count := strings.Count(contentStr, "RelRIDAPIProvider")
+	if count != 3 {
+		t.Errorf("Expected 3 RelRIDAPIProvider* fields, found %d\nGenerated:\n%s", count, contentStr)
+	}
+
+	// Verify no duplicate declarations (would cause compilation error)
+	duplicatePattern := "RelRIDAPIProviders []*Model"
+	if strings.Contains(contentStr, duplicatePattern) {
+		t.Errorf("Found duplicate field declaration pattern, fields should be unique")
 	}
 }