feat: add --type-map to override SQL-to-Go types in bun and gorm writers

Adds WriterOptions.TypeMappings and a repeatable --type-map sqltype=gotype
flag. Defaults are unchanged when no mapping is given. Closes #36 (bun/gorm).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

pkg/writers/bun/type_mapper.go

@@ -12,6 +12,7 @@ import (
 // TypeMapper handles type conversions between SQL and Go types for Bun
 type TypeMapper struct {
 	sqlTypesAlias string
+	typeMappings  map[string]string
 	typeStyle     string // writers.NullableTypeSqlTypes | writers.NullableTypeStdlib | writers.NullableTypeBaselib
 	arrayNullable string // writers.NullableArraysSlice | writers.NullableArraysPointerSlice
 }
@@ -37,6 +38,10 @@ func NewTypeMapper(typeStyle, arrayNullable string) *TypeMapper {
 
 // SQLTypeToGoType converts a SQL type to its Go equivalent.
 func (tm *TypeMapper) SQLTypeToGoType(sqlType string, notNull bool) string {
+	if goType, ok := tm.overrideGoType(sqlType, notNull); ok {
+		return goType
+	}
+
 	// Array columns always use a native Go slice, regardless of typeStyle.
 	if pgsql.IsArrayType(sqlType) {
 		goType := tm.arrayGoType(tm.extractBaseType(sqlType))
@@ -68,6 +73,26 @@ func (tm *TypeMapper) SQLTypeToGoType(sqlType string, notNull bool) string {
 	return tm.bunGoType(baseType)
 }
 
+// SetTypeMappings installs user-configured SQL-to-Go type overrides.
+func (tm *TypeMapper) SetTypeMappings(mappings map[string]string) {
+	tm.typeMappings = mappings
+}
+
+// overrideGoType applies a configured override, if any, for the column type.
+func (tm *TypeMapper) overrideGoType(sqlType string, notNull bool) (string, bool) {
+	if len(tm.typeMappings) == 0 {
+		return "", false
+	}
+	goType, ok := writers.LookupTypeMapping(tm.typeMappings, tm.extractBaseType(sqlType))
+	if !ok {
+		return "", false
+	}
+	if pgsql.IsArrayType(sqlType) {
+		return "[]" + goType, true
+	}
+	return writers.ApplyTypeMapping(goType, notNull), true
+}
+
 // extractBaseType extracts the base type from a SQL type string
 func (tm *TypeMapper) extractBaseType(sqlType string) string {
 	return pgsql.CanonicalizeBaseType(pgsql.ExtractBaseTypeLower(sqlType))

pkg/writers/bun/type_mapper_override_test.go

@@ -0,0 +1,25 @@
+package bun
+
+import "testing"
+
+func TestTypeMapper_CustomTypeMappings(t *testing.T) {
+	mapper := NewTypeMapper("", "")
+	mapper.SetTypeMappings(map[string]string{"uuid": "uuid.UUID", "numeric": "decimal.Decimal"})
+
+	tests := []struct {
+		sqlType string
+		notNull bool
+		want    string
+	}{
+		{"uuid", true, "uuid.UUID"},
+		{"uuid", false, "*uuid.UUID"},
+		{"numeric(10,2)", true, "decimal.Decimal"},
+		{"UUID[]", false, "[]uuid.UUID"},
+		{"bigint", true, "int64"}, // unmapped types keep defaults
+	}
+	for _, tt := range tests {
+		if got := mapper.SQLTypeToGoType(tt.sqlType, tt.notNull); got != tt.want {
+			t.Errorf("SQLTypeToGoType(%q, %v) = %q, want %q", tt.sqlType, tt.notNull, got, tt.want)
+		}
+	}
+}

pkg/writers/bun/writer.go

@@ -28,6 +28,8 @@ func NewWriter(options *writers.WriterOptions) *Writer {
 		config:     LoadMethodConfigFromMetadata(options.Metadata),
 	}
 
+	w.typeMapper.SetTypeMappings(options.TypeMappings)
+
 	// Initialize templates
 	tmpl, err := NewTemplates()
 	if err != nil {