feat(templ): add support for --from-list flag and related tests

cmd/relspec/convert.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/spf13/cobra"
 
+	"git.warky.dev/wdevs/relspecgo/pkg/merge"
 	"git.warky.dev/wdevs/relspecgo/pkg/models"
 	"git.warky.dev/wdevs/relspecgo/pkg/readers"
 	"git.warky.dev/wdevs/relspecgo/pkg/readers/bun"
@@ -45,6 +46,7 @@ var (
 	convertSourceType    string
 	convertSourcePath    string
 	convertSourceConn    string
+	convertFromList      []string
 	convertTargetType    string
 	convertTargetPath    string
 	convertPackageName   string
@@ -166,6 +168,7 @@ func init() {
 	convertCmd.Flags().StringVar(&convertSourceType, "from", "", "Source format (dbml, dctx, drawdb, graphql, json, yaml, gorm, bun, drizzle, prisma, typeorm, pgsql, sqlite)")
 	convertCmd.Flags().StringVar(&convertSourcePath, "from-path", "", "Source file path (for file-based formats)")
 	convertCmd.Flags().StringVar(&convertSourceConn, "from-conn", "", "Source connection string (for pgsql) or file path (for sqlite)")
+	convertCmd.Flags().StringSliceVar(&convertFromList, "from-list", nil, "Comma-separated list of source file paths to read and merge (mutually exclusive with --from-path)")
 
 	convertCmd.Flags().StringVar(&convertTargetType, "to", "", "Target format (dbml, dctx, drawdb, graphql, json, yaml, gorm, bun, drizzle, prisma, typeorm, pgsql)")
 	convertCmd.Flags().StringVar(&convertTargetPath, "to-path", "", "Target output path (file or directory)")
@@ -191,17 +194,29 @@ func runConvert(cmd *cobra.Command, args []string) error {
 	fmt.Fprintf(os.Stderr, "\n=== RelSpec Schema Converter ===\n")
 	fmt.Fprintf(os.Stderr, "Started at: %s\n\n", getCurrentTimestamp())
 
+	// Validate mutually exclusive flags
+	if convertSourcePath != "" && len(convertFromList) > 0 {
+		return fmt.Errorf("--from-path and --from-list are mutually exclusive")
+	}
+
 	// Read source database
 	fmt.Fprintf(os.Stderr, "[1/2] Reading source schema...\n")
 	fmt.Fprintf(os.Stderr, "      Format: %s\n", convertSourceType)
+
+	var db *models.Database
+	var err error
+
+	if len(convertFromList) > 0 {
+		db, err = readDatabaseListForConvert(convertSourceType, convertFromList)
+	} else {
 		if convertSourcePath != "" {
 			fmt.Fprintf(os.Stderr, "      Path:   %s\n", convertSourcePath)
 		}
 		if convertSourceConn != "" {
 			fmt.Fprintf(os.Stderr, "      Conn:   %s\n", maskPassword(convertSourceConn))
 		}
-
+		db, err = readDatabaseForConvert(convertSourceType, convertSourcePath, convertSourceConn)
-	db, err := readDatabaseForConvert(convertSourceType, convertSourcePath, convertSourceConn)
+	}
 	if err != nil {
 		return fmt.Errorf("failed to read source: %w", err)
 	}
@@ -237,6 +252,30 @@ func runConvert(cmd *cobra.Command, args []string) error {
 	return nil
 }
 
+func readDatabaseListForConvert(dbType string, files []string) (*models.Database, error) {
+	if len(files) == 0 {
+		return nil, fmt.Errorf("file list is empty")
+	}
+
+	fmt.Fprintf(os.Stderr, "      Files:  %d file(s)\n", len(files))
+
+	var base *models.Database
+	for i, filePath := range files {
+		fmt.Fprintf(os.Stderr, "      [%d/%d] %s\n", i+1, len(files), filePath)
+		db, err := readDatabaseForConvert(dbType, filePath, "")
+		if err != nil {
+			return nil, fmt.Errorf("failed to read %s: %w", filePath, err)
+		}
+		if base == nil {
+			base = db
+		} else {
+			merge.MergeDatabases(base, db, &merge.MergeOptions{})
+		}
+	}
+
+	return base, nil
+}
+
 func readDatabaseForConvert(dbType, filePath, connString string) (*models.Database, error) {
 	var reader readers.Reader
 

cmd/relspec/convert_from_list_test.go

@@ -0,0 +1,183 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestReadDatabaseListForConvert_SingleFile(t *testing.T) {
+	dir := t.TempDir()
+	file := filepath.Join(dir, "schema.json")
+	writeTestJSON(t, file, []string{"users"})
+
+	db, err := readDatabaseListForConvert("json", []string{file})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(db.Schemas) == 0 {
+		t.Fatal("expected at least one schema")
+	}
+	if len(db.Schemas[0].Tables) != 1 {
+		t.Errorf("expected 1 table, got %d", len(db.Schemas[0].Tables))
+	}
+}
+
+func TestReadDatabaseListForConvert_MultipleFiles(t *testing.T) {
+	dir := t.TempDir()
+	file1 := filepath.Join(dir, "schema1.json")
+	file2 := filepath.Join(dir, "schema2.json")
+	writeTestJSON(t, file1, []string{"users"})
+	writeTestJSON(t, file2, []string{"comments"})
+
+	db, err := readDatabaseListForConvert("json", []string{file1, file2})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	total := 0
+	for _, s := range db.Schemas {
+		total += len(s.Tables)
+	}
+	if total != 2 {
+		t.Errorf("expected 2 tables (users + comments), got %d", total)
+	}
+}
+
+func TestReadDatabaseListForConvert_PathWithSpaces(t *testing.T) {
+	spacedDir := filepath.Join(t.TempDir(), "my schema files")
+	if err := os.MkdirAll(spacedDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	file := filepath.Join(spacedDir, "my users schema.json")
+	writeTestJSON(t, file, []string{"users"})
+
+	db, err := readDatabaseListForConvert("json", []string{file})
+	if err != nil {
+		t.Fatalf("unexpected error with spaced path: %v", err)
+	}
+	if db == nil {
+		t.Fatal("expected non-nil database")
+	}
+}
+
+func TestReadDatabaseListForConvert_MultipleFilesPathWithSpaces(t *testing.T) {
+	spacedDir := filepath.Join(t.TempDir(), "my schema files")
+	if err := os.MkdirAll(spacedDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	file1 := filepath.Join(spacedDir, "users schema.json")
+	file2 := filepath.Join(spacedDir, "posts schema.json")
+	writeTestJSON(t, file1, []string{"users"})
+	writeTestJSON(t, file2, []string{"posts"})
+
+	db, err := readDatabaseListForConvert("json", []string{file1, file2})
+	if err != nil {
+		t.Fatalf("unexpected error with spaced paths: %v", err)
+	}
+
+	total := 0
+	for _, s := range db.Schemas {
+		total += len(s.Tables)
+	}
+	if total != 2 {
+		t.Errorf("expected 2 tables, got %d", total)
+	}
+}
+
+func TestReadDatabaseListForConvert_EmptyList(t *testing.T) {
+	_, err := readDatabaseListForConvert("json", []string{})
+	if err == nil {
+		t.Error("expected error for empty file list")
+	}
+}
+
+func TestReadDatabaseListForConvert_InvalidFile(t *testing.T) {
+	_, err := readDatabaseListForConvert("json", []string{"/nonexistent/path/file.json"})
+	if err == nil {
+		t.Error("expected error for nonexistent file")
+	}
+}
+
+func TestRunConvert_FromListMutuallyExclusiveWithFromPath(t *testing.T) {
+	saved := saveConvertState()
+	defer restoreConvertState(saved)
+
+	dir := t.TempDir()
+	file := filepath.Join(dir, "schema.json")
+	writeTestJSON(t, file, []string{"users"})
+
+	convertSourceType = "json"
+	convertSourcePath = file
+	convertFromList = []string{file}
+	convertTargetType = "json"
+	convertTargetPath = filepath.Join(dir, "out.json")
+
+	err := runConvert(nil, nil)
+	if err == nil {
+		t.Error("expected error when --from-path and --from-list are both set")
+	}
+}
+
+func TestRunConvert_FromListEndToEnd(t *testing.T) {
+	saved := saveConvertState()
+	defer restoreConvertState(saved)
+
+	dir := t.TempDir()
+	file1 := filepath.Join(dir, "users.json")
+	file2 := filepath.Join(dir, "posts.json")
+	outFile := filepath.Join(dir, "merged.json")
+	writeTestJSON(t, file1, []string{"users"})
+	writeTestJSON(t, file2, []string{"posts"})
+
+	convertSourceType = "json"
+	convertSourcePath = ""
+	convertSourceConn = ""
+	convertFromList = []string{file1, file2}
+	convertTargetType = "json"
+	convertTargetPath = outFile
+	convertPackageName = ""
+	convertSchemaFilter = ""
+	convertFlattenSchema = false
+
+	if err := runConvert(nil, nil); err != nil {
+		t.Fatalf("runConvert() error = %v", err)
+	}
+
+	if _, err := os.Stat(outFile); os.IsNotExist(err) {
+		t.Error("expected output file to be created")
+	}
+}
+
+func TestRunConvert_FromListEndToEndPathWithSpaces(t *testing.T) {
+	saved := saveConvertState()
+	defer restoreConvertState(saved)
+
+	spacedDir := filepath.Join(t.TempDir(), "my schema dir")
+	if err := os.MkdirAll(spacedDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	file1 := filepath.Join(spacedDir, "users schema.json")
+	file2 := filepath.Join(spacedDir, "posts schema.json")
+	outFile := filepath.Join(spacedDir, "merged output.json")
+	writeTestJSON(t, file1, []string{"users"})
+	writeTestJSON(t, file2, []string{"posts"})
+
+	convertSourceType = "json"
+	convertSourcePath = ""
+	convertSourceConn = ""
+	convertFromList = []string{file1, file2}
+	convertTargetType = "json"
+	convertTargetPath = outFile
+	convertPackageName = ""
+	convertSchemaFilter = ""
+	convertFlattenSchema = false
+
+	if err := runConvert(nil, nil); err != nil {
+		t.Fatalf("runConvert() with spaced paths error = %v", err)
+	}
+
+	if _, err := os.Stat(outFile); os.IsNotExist(err) {
+		t.Error("expected output file to be created")
+	}
+}

cmd/relspec/merge.go

@@ -47,6 +47,7 @@ var (
 	mergeSourceType    string
 	mergeSourcePath    string
 	mergeSourceConn    string
+	mergeFromList      []string
 	mergeOutputType    string
 	mergeOutputPath    string
 	mergeOutputConn    string
@@ -109,8 +110,9 @@ func init() {
 
 	// Source database flags
 	mergeCmd.Flags().StringVar(&mergeSourceType, "source", "", "Source format (required): dbml, dctx, drawdb, graphql, json, yaml, gorm, bun, drizzle, prisma, typeorm, pgsql")
-	mergeCmd.Flags().StringVar(&mergeSourcePath, "source-path", "", "Source file path (required for file-based formats)")
+	mergeCmd.Flags().StringVar(&mergeSourcePath, "source-path", "", "Source file path (required for file-based formats, mutually exclusive with --from-list)")
 	mergeCmd.Flags().StringVar(&mergeSourceConn, "source-conn", "", "Source connection string (required for pgsql)")
+	mergeCmd.Flags().StringSliceVar(&mergeFromList, "from-list", nil, "Comma-separated list of source file paths to merge (mutually exclusive with --source-path)")
 
 	// Output flags
 	mergeCmd.Flags().StringVar(&mergeOutputType, "output", "", "Output format (required): dbml, dctx, drawdb, graphql, json, yaml, gorm, bun, drizzle, prisma, typeorm, pgsql")
@@ -144,6 +146,11 @@ func runMerge(cmd *cobra.Command, args []string) error {
 		return fmt.Errorf("--output format is required")
 	}
 
+	// Validate mutually exclusive source flags
+	if mergeSourcePath != "" && len(mergeFromList) > 0 {
+		return fmt.Errorf("--source-path and --from-list are mutually exclusive")
+	}
+
 	// Validate and expand file paths
 	if mergeTargetType != "pgsql" {
 		if mergeTargetPath == "" {
@@ -157,8 +164,8 @@ func runMerge(cmd *cobra.Command, args []string) error {
 	}
 
 	if mergeSourceType != "pgsql" {
-		if mergeSourcePath == "" {
+		if mergeSourcePath == "" && len(mergeFromList) == 0 {
-			return fmt.Errorf("--source-path is required for %s format", mergeSourceType)
+			return fmt.Errorf("--source-path or --from-list is required for %s format", mergeSourceType)
 		}
 		mergeSourcePath = expandPath(mergeSourcePath)
 	} else if mergeSourceConn == "" {
@@ -189,20 +196,37 @@ func runMerge(cmd *cobra.Command, args []string) error {
 	fmt.Fprintf(os.Stderr, "      ✓ Successfully read target database '%s'\n", targetDB.Name)
 	printDatabaseStats(targetDB)
 
-	// Step 2: Read source database
+	// Step 2: Read source database(s)
 	fmt.Fprintf(os.Stderr, "\n[2/3] Reading source database...\n")
 	fmt.Fprintf(os.Stderr, "      Format: %s\n", mergeSourceType)
+
+	var sourceDB *models.Database
+	if len(mergeFromList) > 0 {
+		fmt.Fprintf(os.Stderr, "      Files:  %d file(s)\n", len(mergeFromList))
+		for i, filePath := range mergeFromList {
+			fmt.Fprintf(os.Stderr, "      [%d/%d] %s\n", i+1, len(mergeFromList), filePath)
+			db, readErr := readDatabaseForMerge(mergeSourceType, expandPath(filePath), "", "Source")
+			if readErr != nil {
+				return fmt.Errorf("failed to read source file %s: %w", filePath, readErr)
+			}
+			if sourceDB == nil {
+				sourceDB = db
+			} else {
+				merge.MergeDatabases(sourceDB, db, &merge.MergeOptions{})
+			}
+		}
+	} else {
 		if mergeSourcePath != "" {
 			fmt.Fprintf(os.Stderr, "      Path:   %s\n", mergeSourcePath)
 		}
 		if mergeSourceConn != "" {
 			fmt.Fprintf(os.Stderr, "      Conn:   %s\n", maskPassword(mergeSourceConn))
 		}
-
+		sourceDB, err = readDatabaseForMerge(mergeSourceType, mergeSourcePath, mergeSourceConn, "Source")
-	sourceDB, err := readDatabaseForMerge(mergeSourceType, mergeSourcePath, mergeSourceConn, "Source")
 		if err != nil {
 			return fmt.Errorf("failed to read source database: %w", err)
 		}
+	}
 	fmt.Fprintf(os.Stderr, "      ✓ Successfully read source database '%s'\n", sourceDB.Name)
 	printDatabaseStats(sourceDB)
 

cmd/relspec/merge_from_list_test.go

@@ -0,0 +1,162 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestRunMerge_FromListMutuallyExclusiveWithSourcePath(t *testing.T) {
+	saved := saveMergeState()
+	defer restoreMergeState(saved)
+
+	dir := t.TempDir()
+	file := filepath.Join(dir, "schema.json")
+	writeTestJSON(t, file, []string{"users"})
+
+	mergeTargetType = "json"
+	mergeTargetPath = file
+	mergeTargetConn = ""
+	mergeSourceType = "json"
+	mergeSourcePath = file
+	mergeSourceConn = ""
+	mergeFromList = []string{file}
+	mergeOutputType = "json"
+	mergeOutputPath = filepath.Join(dir, "out.json")
+	mergeOutputConn = ""
+	mergeSkipTables = ""
+	mergeReportPath = ""
+
+	err := runMerge(nil, nil)
+	if err == nil {
+		t.Error("expected error when --source-path and --from-list are both set")
+	}
+}
+
+func TestRunMerge_FromListSingleFile(t *testing.T) {
+	saved := saveMergeState()
+	defer restoreMergeState(saved)
+
+	dir := t.TempDir()
+	targetFile := filepath.Join(dir, "target.json")
+	sourceFile := filepath.Join(dir, "source.json")
+	outFile := filepath.Join(dir, "output.json")
+	writeTestJSON(t, targetFile, []string{"users"})
+	writeTestJSON(t, sourceFile, []string{"posts"})
+
+	mergeTargetType = "json"
+	mergeTargetPath = targetFile
+	mergeTargetConn = ""
+	mergeSourceType = "json"
+	mergeSourcePath = ""
+	mergeSourceConn = ""
+	mergeFromList = []string{sourceFile}
+	mergeOutputType = "json"
+	mergeOutputPath = outFile
+	mergeOutputConn = ""
+	mergeSkipTables = ""
+	mergeReportPath = ""
+
+	if err := runMerge(nil, nil); err != nil {
+		t.Fatalf("runMerge() error = %v", err)
+	}
+	if _, err := os.Stat(outFile); os.IsNotExist(err) {
+		t.Error("expected output file to be created")
+	}
+}
+
+func TestRunMerge_FromListMultipleFiles(t *testing.T) {
+	saved := saveMergeState()
+	defer restoreMergeState(saved)
+
+	dir := t.TempDir()
+	targetFile := filepath.Join(dir, "target.json")
+	source1 := filepath.Join(dir, "source1.json")
+	source2 := filepath.Join(dir, "source2.json")
+	outFile := filepath.Join(dir, "output.json")
+	writeTestJSON(t, targetFile, []string{"users"})
+	writeTestJSON(t, source1, []string{"posts"})
+	writeTestJSON(t, source2, []string{"comments"})
+
+	mergeTargetType = "json"
+	mergeTargetPath = targetFile
+	mergeTargetConn = ""
+	mergeSourceType = "json"
+	mergeSourcePath = ""
+	mergeSourceConn = ""
+	mergeFromList = []string{source1, source2}
+	mergeOutputType = "json"
+	mergeOutputPath = outFile
+	mergeOutputConn = ""
+	mergeSkipTables = ""
+	mergeReportPath = ""
+
+	if err := runMerge(nil, nil); err != nil {
+		t.Fatalf("runMerge() error = %v", err)
+	}
+	if _, err := os.Stat(outFile); os.IsNotExist(err) {
+		t.Error("expected output file to be created")
+	}
+}
+
+func TestRunMerge_FromListPathWithSpaces(t *testing.T) {
+	saved := saveMergeState()
+	defer restoreMergeState(saved)
+
+	spacedDir := filepath.Join(t.TempDir(), "my schema files")
+	if err := os.MkdirAll(spacedDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	targetFile := filepath.Join(spacedDir, "target schema.json")
+	sourceFile := filepath.Join(spacedDir, "source schema.json")
+	outFile := filepath.Join(spacedDir, "merged output.json")
+	writeTestJSON(t, targetFile, []string{"users"})
+	writeTestJSON(t, sourceFile, []string{"comments"})
+
+	mergeTargetType = "json"
+	mergeTargetPath = targetFile
+	mergeTargetConn = ""
+	mergeSourceType = "json"
+	mergeSourcePath = ""
+	mergeSourceConn = ""
+	mergeFromList = []string{sourceFile}
+	mergeOutputType = "json"
+	mergeOutputPath = outFile
+	mergeOutputConn = ""
+	mergeSkipTables = ""
+	mergeReportPath = ""
+
+	if err := runMerge(nil, nil); err != nil {
+		t.Fatalf("runMerge() with spaced paths error = %v", err)
+	}
+	if _, err := os.Stat(outFile); os.IsNotExist(err) {
+		t.Error("expected output file to be created")
+	}
+}
+
+func TestRunMerge_FromListMissingSourceType(t *testing.T) {
+	saved := saveMergeState()
+	defer restoreMergeState(saved)
+
+	dir := t.TempDir()
+	file := filepath.Join(dir, "schema.json")
+	writeTestJSON(t, file, []string{"users"})
+
+	mergeTargetType = "json"
+	mergeTargetPath = file
+	mergeTargetConn = ""
+	mergeSourceType = "json"
+	mergeSourcePath = ""
+	mergeSourceConn = ""
+	mergeFromList = []string{} // empty list, no source-path either
+	mergeOutputType = "json"
+	mergeOutputPath = filepath.Join(dir, "out.json")
+	mergeOutputConn = ""
+	mergeSkipTables = ""
+	mergeReportPath = ""
+
+	err := runMerge(nil, nil)
+	if err == nil {
+		t.Error("expected error when neither --source-path nor --from-list is provided")
+	}
+}

cmd/relspec/templ.go

@@ -15,6 +15,7 @@ var (
 	templSourceType      string
 	templSourcePath      string
 	templSourceConn      string
+	templFromList        []string
 	templTemplatePath    string
 	templOutputPath      string
 	templSchemaFilter    string
@@ -78,8 +79,9 @@ Examples:
 
 func init() {
 	templCmd.Flags().StringVar(&templSourceType, "from", "", "Source format (dbml, pgsql, json, etc.)")
-	templCmd.Flags().StringVar(&templSourcePath, "from-path", "", "Source file path (for file-based sources)")
+	templCmd.Flags().StringVar(&templSourcePath, "from-path", "", "Source file path (for file-based sources, mutually exclusive with --from-list)")
 	templCmd.Flags().StringVar(&templSourceConn, "from-conn", "", "Source connection string (for database sources)")
+	templCmd.Flags().StringSliceVar(&templFromList, "from-list", nil, "Comma-separated list of source file paths to read and merge (mutually exclusive with --from-path)")
 	templCmd.Flags().StringVar(&templTemplatePath, "template", "", "Template file path (required)")
 	templCmd.Flags().StringVar(&templOutputPath, "output", "", "Output path (file or directory, empty for stdout)")
 	templCmd.Flags().StringVar(&templSchemaFilter, "schema", "", "Filter to specific schema")
@@ -95,9 +97,20 @@ func runTempl(cmd *cobra.Command, args []string) error {
 	fmt.Fprintf(os.Stderr, "=== RelSpec Template Execution ===\n")
 	fmt.Fprintf(os.Stderr, "Started at: %s\n\n", getCurrentTimestamp())
 
+	// Validate mutually exclusive flags
+	if templSourcePath != "" && len(templFromList) > 0 {
+		return fmt.Errorf("--from-path and --from-list are mutually exclusive")
+	}
+
 	// Read database using the same function as convert
 	fmt.Fprintf(os.Stderr, "Reading from %s...\n", templSourceType)
-	db, err := readDatabaseForConvert(templSourceType, templSourcePath, templSourceConn)
+	var db *models.Database
+	var err error
+	if len(templFromList) > 0 {
+		db, err = readDatabaseListForConvert(templSourceType, templFromList)
+	} else {
+		db, err = readDatabaseForConvert(templSourceType, templSourcePath, templSourceConn)
+	}
 	if err != nil {
 		return fmt.Errorf("failed to read source: %w", err)
 	}

cmd/relspec/templ_from_list_test.go

@@ -0,0 +1,134 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// writeTestTemplate writes a minimal Go text template file.
+func writeTestTemplate(t *testing.T, path string) {
+	t.Helper()
+	content := []byte(`{{.Name}}`)
+	if err := os.WriteFile(path, content, 0644); err != nil {
+		t.Fatalf("failed to write template file %s: %v", path, err)
+	}
+}
+
+func TestRunTempl_FromListMutuallyExclusiveWithFromPath(t *testing.T) {
+	saved := saveTemplState()
+	defer restoreTemplState(saved)
+
+	dir := t.TempDir()
+	file := filepath.Join(dir, "schema.json")
+	tmpl := filepath.Join(dir, "tmpl.tmpl")
+	writeTestJSON(t, file, []string{"users"})
+	writeTestTemplate(t, tmpl)
+
+	templSourceType = "json"
+	templSourcePath = file
+	templFromList = []string{file}
+	templTemplatePath = tmpl
+	templOutputPath = ""
+	templMode = "database"
+	templFilenamePattern = "{{.Name}}.txt"
+
+	err := runTempl(nil, nil)
+	if err == nil {
+		t.Error("expected error when --from-path and --from-list are both set")
+	}
+}
+
+func TestRunTempl_FromListSingleFile(t *testing.T) {
+	saved := saveTemplState()
+	defer restoreTemplState(saved)
+
+	dir := t.TempDir()
+	file := filepath.Join(dir, "schema.json")
+	tmpl := filepath.Join(dir, "tmpl.tmpl")
+	outFile := filepath.Join(dir, "output.txt")
+	writeTestJSON(t, file, []string{"users"})
+	writeTestTemplate(t, tmpl)
+
+	templSourceType = "json"
+	templSourcePath = ""
+	templSourceConn = ""
+	templFromList = []string{file}
+	templTemplatePath = tmpl
+	templOutputPath = outFile
+	templSchemaFilter = ""
+	templMode = "database"
+	templFilenamePattern = "{{.Name}}.txt"
+
+	if err := runTempl(nil, nil); err != nil {
+		t.Fatalf("runTempl() error = %v", err)
+	}
+	if _, err := os.Stat(outFile); os.IsNotExist(err) {
+		t.Error("expected output file to be created")
+	}
+}
+
+func TestRunTempl_FromListMultipleFiles(t *testing.T) {
+	saved := saveTemplState()
+	defer restoreTemplState(saved)
+
+	dir := t.TempDir()
+	file1 := filepath.Join(dir, "users.json")
+	file2 := filepath.Join(dir, "posts.json")
+	tmpl := filepath.Join(dir, "tmpl.tmpl")
+	outFile := filepath.Join(dir, "output.txt")
+	writeTestJSON(t, file1, []string{"users"})
+	writeTestJSON(t, file2, []string{"posts"})
+	writeTestTemplate(t, tmpl)
+
+	templSourceType = "json"
+	templSourcePath = ""
+	templSourceConn = ""
+	templFromList = []string{file1, file2}
+	templTemplatePath = tmpl
+	templOutputPath = outFile
+	templSchemaFilter = ""
+	templMode = "database"
+	templFilenamePattern = "{{.Name}}.txt"
+
+	if err := runTempl(nil, nil); err != nil {
+		t.Fatalf("runTempl() error = %v", err)
+	}
+	if _, err := os.Stat(outFile); os.IsNotExist(err) {
+		t.Error("expected output file to be created")
+	}
+}
+
+func TestRunTempl_FromListPathWithSpaces(t *testing.T) {
+	saved := saveTemplState()
+	defer restoreTemplState(saved)
+
+	spacedDir := filepath.Join(t.TempDir(), "my schema files")
+	if err := os.MkdirAll(spacedDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	file1 := filepath.Join(spacedDir, "users schema.json")
+	file2 := filepath.Join(spacedDir, "posts schema.json")
+	tmpl := filepath.Join(spacedDir, "my template.tmpl")
+	outFile := filepath.Join(spacedDir, "output file.txt")
+	writeTestJSON(t, file1, []string{"users"})
+	writeTestJSON(t, file2, []string{"posts"})
+	writeTestTemplate(t, tmpl)
+
+	templSourceType = "json"
+	templSourcePath = ""
+	templSourceConn = ""
+	templFromList = []string{file1, file2}
+	templTemplatePath = tmpl
+	templOutputPath = outFile
+	templSchemaFilter = ""
+	templMode = "database"
+	templFilenamePattern = "{{.Name}}.txt"
+
+	if err := runTempl(nil, nil); err != nil {
+		t.Fatalf("runTempl() with spaced paths error = %v", err)
+	}
+	if _, err := os.Stat(outFile); os.IsNotExist(err) {
+		t.Error("expected output file to be created")
+	}
+}

cmd/relspec/testhelpers_test.go

@@ -0,0 +1,219 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"testing"
+)
+
+// minimalColumn is used to build test JSON fixtures.
+type minimalColumn struct {
+	Name          string `json:"name"`
+	Table         string `json:"table"`
+	Schema        string `json:"schema"`
+	Type          string `json:"type"`
+	NotNull       bool   `json:"not_null"`
+	IsPrimaryKey  bool   `json:"is_primary_key"`
+	AutoIncrement bool   `json:"auto_increment"`
+}
+
+type minimalTable struct {
+	Name    string                   `json:"name"`
+	Schema  string                   `json:"schema"`
+	Columns map[string]minimalColumn `json:"columns"`
+}
+
+type minimalSchema struct {
+	Name   string         `json:"name"`
+	Tables []minimalTable `json:"tables"`
+}
+
+type minimalDatabase struct {
+	Name    string          `json:"name"`
+	Schemas []minimalSchema `json:"schemas"`
+}
+
+// writeTestJSON writes a minimal JSON database file with one schema ("public")
+// containing tables with the given names. Each table has a single "id" PK column.
+func writeTestJSON(t *testing.T, path string, tableNames []string) {
+	t.Helper()
+
+	tables := make([]minimalTable, len(tableNames))
+	for i, name := range tableNames {
+		tables[i] = minimalTable{
+			Name:   name,
+			Schema: "public",
+			Columns: map[string]minimalColumn{
+				"id": {
+					Name:          "id",
+					Table:         name,
+					Schema:        "public",
+					Type:          "bigint",
+					NotNull:       true,
+					IsPrimaryKey:  true,
+					AutoIncrement: true,
+				},
+			},
+		}
+	}
+
+	db := minimalDatabase{
+		Name:    "test_db",
+		Schemas: []minimalSchema{{Name: "public", Tables: tables}},
+	}
+
+	data, err := json.Marshal(db)
+	if err != nil {
+		t.Fatalf("failed to marshal test JSON: %v", err)
+	}
+	if err := os.WriteFile(path, data, 0644); err != nil {
+		t.Fatalf("failed to write test file %s: %v", path, err)
+	}
+}
+
+// convertState captures and restores all convert global vars.
+type convertState struct {
+	sourceType    string
+	sourcePath    string
+	sourceConn    string
+	fromList      []string
+	targetType    string
+	targetPath    string
+	packageName   string
+	schemaFilter  string
+	flattenSchema bool
+}
+
+func saveConvertState() convertState {
+	return convertState{
+		sourceType:    convertSourceType,
+		sourcePath:    convertSourcePath,
+		sourceConn:    convertSourceConn,
+		fromList:      convertFromList,
+		targetType:    convertTargetType,
+		targetPath:    convertTargetPath,
+		packageName:   convertPackageName,
+		schemaFilter:  convertSchemaFilter,
+		flattenSchema: convertFlattenSchema,
+	}
+}
+
+func restoreConvertState(s convertState) {
+	convertSourceType = s.sourceType
+	convertSourcePath = s.sourcePath
+	convertSourceConn = s.sourceConn
+	convertFromList = s.fromList
+	convertTargetType = s.targetType
+	convertTargetPath = s.targetPath
+	convertPackageName = s.packageName
+	convertSchemaFilter = s.schemaFilter
+	convertFlattenSchema = s.flattenSchema
+}
+
+// templState captures and restores all templ global vars.
+type templState struct {
+	sourceType      string
+	sourcePath      string
+	sourceConn      string
+	fromList        []string
+	templatePath    string
+	outputPath      string
+	schemaFilter    string
+	mode            string
+	filenamePattern string
+}
+
+func saveTemplState() templState {
+	return templState{
+		sourceType:      templSourceType,
+		sourcePath:      templSourcePath,
+		sourceConn:      templSourceConn,
+		fromList:        templFromList,
+		templatePath:    templTemplatePath,
+		outputPath:      templOutputPath,
+		schemaFilter:    templSchemaFilter,
+		mode:            templMode,
+		filenamePattern: templFilenamePattern,
+	}
+}
+
+func restoreTemplState(s templState) {
+	templSourceType = s.sourceType
+	templSourcePath = s.sourcePath
+	templSourceConn = s.sourceConn
+	templFromList = s.fromList
+	templTemplatePath = s.templatePath
+	templOutputPath = s.outputPath
+	templSchemaFilter = s.schemaFilter
+	templMode = s.mode
+	templFilenamePattern = s.filenamePattern
+}
+
+// mergeState captures and restores all merge global vars.
+type mergeState struct {
+	targetType    string
+	targetPath    string
+	targetConn    string
+	sourceType    string
+	sourcePath    string
+	sourceConn    string
+	fromList      []string
+	outputType    string
+	outputPath    string
+	outputConn    string
+	skipDomains   bool
+	skipRelations bool
+	skipEnums     bool
+	skipViews     bool
+	skipSequences bool
+	skipTables    string
+	verbose       bool
+	reportPath    string
+	flattenSchema bool
+}
+
+func saveMergeState() mergeState {
+	return mergeState{
+		targetType:    mergeTargetType,
+		targetPath:    mergeTargetPath,
+		targetConn:    mergeTargetConn,
+		sourceType:    mergeSourceType,
+		sourcePath:    mergeSourcePath,
+		sourceConn:    mergeSourceConn,
+		fromList:      mergeFromList,
+		outputType:    mergeOutputType,
+		outputPath:    mergeOutputPath,
+		outputConn:    mergeOutputConn,
+		skipDomains:   mergeSkipDomains,
+		skipRelations: mergeSkipRelations,
+		skipEnums:     mergeSkipEnums,
+		skipViews:     mergeSkipViews,
+		skipSequences: mergeSkipSequences,
+		skipTables:    mergeSkipTables,
+		verbose:       mergeVerbose,
+		reportPath:    mergeReportPath,
+		flattenSchema: mergeFlattenSchema,
+	}
+}
+
+func restoreMergeState(s mergeState) {
+	mergeTargetType = s.targetType
+	mergeTargetPath = s.targetPath
+	mergeTargetConn = s.targetConn
+	mergeSourceType = s.sourceType
+	mergeSourcePath = s.sourcePath
+	mergeSourceConn = s.sourceConn
+	mergeFromList = s.fromList
+	mergeOutputType = s.outputType
+	mergeOutputPath = s.outputPath
+	mergeOutputConn = s.outputConn
+	mergeSkipDomains = s.skipDomains
+	mergeSkipRelations = s.skipRelations
+	mergeSkipEnums = s.skipEnums
+	mergeSkipViews = s.skipViews
+	mergeSkipSequences = s.skipSequences
+	mergeSkipTables = s.skipTables
+	mergeVerbose = s.verbose
+	mergeReportPath = s.reportPath
+	mergeFlattenSchema = s.flattenSchema
+}

pkg/inspector/report.go

@@ -60,19 +60,19 @@ func (f *MarkdownFormatter) Format(report *InspectorReport) (string, error) {
 	// Summary
 	sb.WriteString(f.formatHeader("Summary"))
 	sb.WriteString("\n")
-	sb.WriteString(fmt.Sprintf("- Rules Checked: %d\n", report.Summary.RulesChecked))
+	fmt.Fprintf(&sb, "- Rules Checked: %d\n", report.Summary.RulesChecked)
 
 	// Color-code error and warning counts
 	if report.Summary.ErrorCount > 0 {
 		sb.WriteString(f.colorize(fmt.Sprintf("- Errors: %d\n", report.Summary.ErrorCount), colorRed))
 	} else {
-		sb.WriteString(fmt.Sprintf("- Errors: %d\n", report.Summary.ErrorCount))
+		fmt.Fprintf(&sb, "- Errors: %d\n", report.Summary.ErrorCount)
 	}
 
 	if report.Summary.WarningCount > 0 {
 		sb.WriteString(f.colorize(fmt.Sprintf("- Warnings: %d\n", report.Summary.WarningCount), colorYellow))
 	} else {
-		sb.WriteString(fmt.Sprintf("- Warnings: %d\n", report.Summary.WarningCount))
+		fmt.Fprintf(&sb, "- Warnings: %d\n", report.Summary.WarningCount)
 	}
 
 	if report.Summary.PassedCount > 0 {

pkg/readers/gorm/reader.go

@@ -676,8 +676,19 @@ func (r *Reader) extractTableFromGormTag(tag string) (tablename string, schemaNa
 
 // deriveTableName derives a table name from struct name
 func (r *Reader) deriveTableName(structName string) string {
-	// Remove "Model" prefix if present, use the name as-is without transformation
+	// Remove "Model" prefix if present
-	return strings.TrimPrefix(structName, "Model")
+	name := strings.TrimPrefix(structName, "Model")
+
+	// Convert PascalCase to snake_case
+	var result strings.Builder
+	for i, r := range name {
+		if i > 0 && r >= 'A' && r <= 'Z' {
+			result.WriteRune('_')
+		}
+		result.WriteRune(r)
+	}
+
+	return strings.ToLower(result.String())
 }
 
 // parseColumn parses a struct field into a Column model

pkg/writers/dbml/writer.go

@@ -62,10 +62,10 @@ func (w *Writer) databaseToDBML(d *models.Database) string {
 	var sb strings.Builder
 
 	if d.Description != "" {
-		sb.WriteString(fmt.Sprintf("// %s\n", d.Description))
+		fmt.Fprintf(&sb, "// %s\n", d.Description)
 	}
 	if d.Comment != "" {
-		sb.WriteString(fmt.Sprintf("// %s\n", d.Comment))
+		fmt.Fprintf(&sb, "// %s\n", d.Comment)
 	}
 	if d.Description != "" || d.Comment != "" {
 		sb.WriteString("\n")
@@ -94,7 +94,7 @@ func (w *Writer) schemaToDBML(schema *models.Schema) string {
 	var sb strings.Builder
 
 	if schema.Description != "" {
-		sb.WriteString(fmt.Sprintf("// Schema: %s - %s\n", schema.Name, schema.Description))
+		fmt.Fprintf(&sb, "// Schema: %s - %s\n", schema.Name, schema.Description)
 	}
 
 	for _, table := range schema.Tables {
@@ -110,10 +110,10 @@ func (w *Writer) tableToDBML(t *models.Table) string {
 	var sb strings.Builder
 
 	tableName := fmt.Sprintf("%s.%s", t.Schema, t.Name)
-	sb.WriteString(fmt.Sprintf("Table %s {\n", tableName))
+	fmt.Fprintf(&sb, "Table %s {\n", tableName)
 
 	for _, column := range t.Columns {
-		sb.WriteString(fmt.Sprintf("  %s %s", column.Name, column.Type))
+		fmt.Fprintf(&sb, "  %s %s", column.Name, column.Type)
 
 		var attrs []string
 		if column.IsPrimaryKey {
@@ -138,11 +138,11 @@ func (w *Writer) tableToDBML(t *models.Table) string {
 		}
 
 		if len(attrs) > 0 {
-			sb.WriteString(fmt.Sprintf(" [%s]", strings.Join(attrs, ", ")))
+			fmt.Fprintf(&sb, " [%s]", strings.Join(attrs, ", "))
 		}
 
 		if column.Comment != "" {
-			sb.WriteString(fmt.Sprintf(" // %s", column.Comment))
+			fmt.Fprintf(&sb, " // %s", column.Comment)
 		}
 		sb.WriteString("\n")
 	}
@@ -161,9 +161,9 @@ func (w *Writer) tableToDBML(t *models.Table) string {
 				indexAttrs = append(indexAttrs, fmt.Sprintf("type: %s", index.Type))
 			}
 
-			sb.WriteString(fmt.Sprintf("    (%s)", strings.Join(index.Columns, ", ")))
+			fmt.Fprintf(&sb, "    (%s)", strings.Join(index.Columns, ", "))
 			if len(indexAttrs) > 0 {
-				sb.WriteString(fmt.Sprintf(" [%s]", strings.Join(indexAttrs, ", ")))
+				fmt.Fprintf(&sb, " [%s]", strings.Join(indexAttrs, ", "))
 			}
 			sb.WriteString("\n")
 		}
@@ -172,7 +172,7 @@ func (w *Writer) tableToDBML(t *models.Table) string {
 
 	note := strings.TrimSpace(t.Description + " " + t.Comment)
 	if note != "" {
-		sb.WriteString(fmt.Sprintf("\n  Note: '%s'\n", note))
+		fmt.Fprintf(&sb, "\n  Note: '%s'\n", note)
 	}
 
 	sb.WriteString("}\n")

pkg/writers/graphql/writer.go

@@ -52,7 +52,7 @@ func (w *Writer) databaseToGraphQL(db *models.Database) string {
 	if w.shouldIncludeComments() {
 		sb.WriteString("# Generated GraphQL Schema\n")
 		if db.Name != "" {
-			sb.WriteString(fmt.Sprintf("# Database: %s\n", db.Name))
+			fmt.Fprintf(&sb, "# Database: %s\n", db.Name)
 		}
 		sb.WriteString("\n")
 	}
@@ -62,7 +62,7 @@ func (w *Writer) databaseToGraphQL(db *models.Database) string {
 		scalars := w.collectCustomScalars(db)
 		if len(scalars) > 0 {
 			for _, scalar := range scalars {
-				sb.WriteString(fmt.Sprintf("scalar %s\n", scalar))
+				fmt.Fprintf(&sb, "scalar %s\n", scalar)
 			}
 			sb.WriteString("\n")
 		}
@@ -176,9 +176,9 @@ func (w *Writer) isJoinTable(table *models.Table) bool {
 func (w *Writer) enumToGraphQL(enum *models.Enum) string {
 	var sb strings.Builder
 
-	sb.WriteString(fmt.Sprintf("enum %s {\n", enum.Name))
+	fmt.Fprintf(&sb, "enum %s {\n", enum.Name)
 	for _, value := range enum.Values {
-		sb.WriteString(fmt.Sprintf("  %s\n", value))
+		fmt.Fprintf(&sb, "  %s\n", value)
 	}
 	sb.WriteString("}\n")
 
@@ -197,10 +197,10 @@ func (w *Writer) tableToGraphQL(table *models.Table, db *models.Database, schema
 		if desc == "" {
 			desc = table.Comment
 		}
-		sb.WriteString(fmt.Sprintf("# %s\n", desc))
+		fmt.Fprintf(&sb, "# %s\n", desc)
 	}
 
-	sb.WriteString(fmt.Sprintf("type %s {\n", typeName))
+	fmt.Fprintf(&sb, "type %s {\n", typeName)
 
 	// Collect and categorize fields
 	var idFields, scalarFields, relationFields []string

pkg/writers/prisma/writer.go

@@ -125,9 +125,9 @@ func (w *Writer) generateGenerator() string {
 func (w *Writer) enumToPrisma(enum *models.Enum) string {
 	var sb strings.Builder
 
-	sb.WriteString(fmt.Sprintf("enum %s {\n", enum.Name))
+	fmt.Fprintf(&sb, "enum %s {\n", enum.Name)
 	for _, value := range enum.Values {
-		sb.WriteString(fmt.Sprintf("  %s\n", value))
+		fmt.Fprintf(&sb, "  %s\n", value)
 	}
 	sb.WriteString("}\n")
 
@@ -179,7 +179,7 @@ func (w *Writer) identifyJoinTables(schema *models.Schema) map[string]bool {
 func (w *Writer) tableToPrisma(table *models.Table, schema *models.Schema, joinTables map[string]bool) string {
 	var sb strings.Builder
 
-	sb.WriteString(fmt.Sprintf("model %s {\n", table.Name))
+	fmt.Fprintf(&sb, "model %s {\n", table.Name)
 
 	// Collect columns to write
 	columns := make([]*models.Column, 0, len(table.Columns))
@@ -219,11 +219,11 @@ func (w *Writer) columnToField(col *models.Column, table *models.Table, schema *
 	var sb strings.Builder
 
 	// Field name
-	sb.WriteString(fmt.Sprintf("  %s", col.Name))
+	fmt.Fprintf(&sb, "  %s", col.Name)
 
 	// Field type
 	prismaType := w.sqlTypeToPrisma(col.Type, schema)
-	sb.WriteString(fmt.Sprintf(" %s", prismaType))
+	fmt.Fprintf(&sb, " %s", prismaType)
 
 	// Optional modifier
 	if !col.NotNull && !col.IsPrimaryKey {
@@ -413,7 +413,7 @@ func (w *Writer) generateRelationFields(table *models.Table, schema *models.Sche
 			relationName = relationName[:len(relationName)-1]
 		}
 
-		sb.WriteString(fmt.Sprintf("  %s %s", strings.ToLower(relationName), relationType))
+		fmt.Fprintf(&sb, "  %s %s", strings.ToLower(relationName), relationType)
 
 		if isOptional {
 			sb.WriteString("?")
@@ -479,8 +479,8 @@ func (w *Writer) generateInverseRelations(table *models.Table, schema *models.Sc
 					if fk.ReferencedTable != table.Name {
 						// This is the other side
 						otherSide := fk.ReferencedTable
-						sb.WriteString(fmt.Sprintf("  %ss %s[]\n",
+						fmt.Fprintf(&sb, "  %ss %s[]\n",
-							strings.ToLower(otherSide), otherSide))
+							strings.ToLower(otherSide), otherSide)
 						break
 					}
 				}
@@ -497,8 +497,8 @@ func (w *Writer) generateInverseRelations(table *models.Table, schema *models.Sc
 					pluralName += "s"
 				}
 
-				sb.WriteString(fmt.Sprintf("  %s %s[]\n",
+				fmt.Fprintf(&sb, "  %s %s[]\n",
-					strings.ToLower(pluralName), otherTable.Name))
+					strings.ToLower(pluralName), otherTable.Name)
 			}
 		}
 	}
@@ -530,20 +530,20 @@ func (w *Writer) generateBlockAttributes(table *models.Table) string {
 
 	if len(pkCols) > 1 {
 		sort.Strings(pkCols)
-		sb.WriteString(fmt.Sprintf("  @@id([%s])\n", strings.Join(pkCols, ", ")))
+		fmt.Fprintf(&sb, "  @@id([%s])\n", strings.Join(pkCols, ", "))
 	}
 
 	// @@unique for multi-column unique constraints
 	for _, constraint := range table.Constraints {
 		if constraint.Type == models.UniqueConstraint && len(constraint.Columns) > 1 {
-			sb.WriteString(fmt.Sprintf("  @@unique([%s])\n", strings.Join(constraint.Columns, ", ")))
+			fmt.Fprintf(&sb, "  @@unique([%s])\n", strings.Join(constraint.Columns, ", "))
 		}
 	}
 
 	// @@index for indexes
 	for _, index := range table.Indexes {
 		if !index.Unique { // Unique indexes are handled by @@unique
-			sb.WriteString(fmt.Sprintf("  @@index([%s])\n", strings.Join(index.Columns, ", ")))
+			fmt.Fprintf(&sb, "  @@index([%s])\n", strings.Join(index.Columns, ", "))
 		}
 	}
 

pkg/writers/typeorm/writer.go

@@ -207,7 +207,7 @@ func (w *Writer) tableToEntity(table *models.Table, schema *models.Schema, joinT
 
 	// Generate @Entity decorator with options
 	entityOptions := w.buildEntityOptions(table)
-	sb.WriteString(fmt.Sprintf("@Entity({\n%s\n})\n", entityOptions))
+	fmt.Fprintf(&sb, "@Entity({\n%s\n})\n", entityOptions)
 
 	// Get class name (from metadata if different from table name)
 	className := table.Name
@@ -219,7 +219,7 @@ func (w *Writer) tableToEntity(table *models.Table, schema *models.Schema, joinT
 		}
 	}
 
-	sb.WriteString(fmt.Sprintf("export class %s {\n", className))
+	fmt.Fprintf(&sb, "export class %s {\n", className)
 
 	// Collect and sort columns
 	columns := make([]*models.Column, 0, len(table.Columns))
@@ -272,7 +272,7 @@ func (w *Writer) viewToEntity(view *models.View) string {
 	sb.WriteString("})\n")
 
 	// Generate class
-	sb.WriteString(fmt.Sprintf("export class %s {\n", view.Name))
+	fmt.Fprintf(&sb, "export class %s {\n", view.Name)
 
 	// Generate field definitions (without decorators for view fields)
 	columns := make([]*models.Column, 0, len(view.Columns))
@@ -285,7 +285,7 @@ func (w *Writer) viewToEntity(view *models.View) string {
 
 	for _, col := range columns {
 		tsType := w.sqlTypeToTypeScript(col.Type)
-		sb.WriteString(fmt.Sprintf("  %s: %s;\n", col.Name, tsType))
+		fmt.Fprintf(&sb, "  %s: %s;\n", col.Name, tsType)
 	}
 
 	sb.WriteString("}\n")
@@ -314,7 +314,7 @@ func (w *Writer) columnToField(col *models.Column, table *models.Table) string {
 		// Regular @Column decorator
 		options := w.buildColumnOptions(col, table)
 		if options != "" {
-			sb.WriteString(fmt.Sprintf("  @Column({ %s })\n", options))
+			fmt.Fprintf(&sb, "  @Column({ %s })\n", options)
 		} else {
 			sb.WriteString("  @Column()\n")
 		}
@@ -327,7 +327,7 @@ func (w *Writer) columnToField(col *models.Column, table *models.Table) string {
 		nullable = " | null"
 	}
 
-	sb.WriteString(fmt.Sprintf("  %s: %s%s;", col.Name, tsType, nullable))
+	fmt.Fprintf(&sb, "  %s: %s%s;", col.Name, tsType, nullable)
 
 	return sb.String()
 }
@@ -464,17 +464,17 @@ func (w *Writer) generateRelationFields(table *models.Table, schema *models.Sche
 		inverseField := w.findInverseFieldName(table.Name, relatedTable, schema)
 
 		if inverseField != "" {
-			sb.WriteString(fmt.Sprintf("  @ManyToOne(() => %s, %s => %s.%s)\n",
+			fmt.Fprintf(&sb, "  @ManyToOne(() => %s, %s => %s.%s)\n",
-				relatedTable, strings.ToLower(relatedTable), strings.ToLower(relatedTable), inverseField))
+				relatedTable, strings.ToLower(relatedTable), strings.ToLower(relatedTable), inverseField)
 		} else {
 			if isNullable {
-				sb.WriteString(fmt.Sprintf("  @ManyToOne(() => %s, { nullable: true })\n", relatedTable))
+				fmt.Fprintf(&sb, "  @ManyToOne(() => %s, { nullable: true })\n", relatedTable)
 			} else {
-				sb.WriteString(fmt.Sprintf("  @ManyToOne(() => %s)\n", relatedTable))
+				fmt.Fprintf(&sb, "  @ManyToOne(() => %s)\n", relatedTable)
 			}
 		}
 
-		sb.WriteString(fmt.Sprintf("  %s: %s%s;\n", fieldName, relatedTable, nullable))
+		fmt.Fprintf(&sb, "  %s: %s%s;\n", fieldName, relatedTable, nullable)
 		sb.WriteString("\n")
 	}