chore(release): update package version to 1.0.68

Existing databases that already ran an old migration kept stale NOT
NULL constraints and mismatched column types/defaults, because the
schema writer only emitted idempotent ADD COLUMN IF NOT EXISTS guards
and never altered columns that already existed.

- Emit guarded ALTER COLUMN ... SET/DROP NOT NULL when a column's
  nullability differs from the model.
- Emit guarded ALTER COLUMN ... TYPE, falling back to renaming the old
  column and adding a fresh one when the in-place conversion fails.
- Emit guarded ALTER COLUMN ... SET/DROP DEFAULT for default drift.
- Collapse the previously duplicated plain/guarded templates so
  WriteSchema (full-schema, live-state-checking) and WriteMigration
  (diff-based) share the same guarded SQL templates and Go helpers
  instead of maintaining the logic twice.

linux/arch/PKGBUILD

@@ -1,6 +1,6 @@
 # Maintainer: Hein (Warky Devs) <hein@warky.dev>
 pkgname=relspec
-pkgver=1.0.66
+pkgver=1.0.68
 pkgrel=1
 pkgdesc="RelSpec is a comprehensive database relations management tool that reads, transforms, and writes database table specifications across multiple formats and ORMs."
 arch=('x86_64' 'aarch64')

linux/centos/relspec.spec

@@ -1,5 +1,5 @@
 Name:           relspec
-Version:        1.0.66
+Version:        1.0.68
 Release:        1%{?dist}
 Summary:        RelSpec is a comprehensive database relations management tool that reads, transforms, and writes database table specifications across multiple formats and ORMs.
 

pkg/writers/pgsql/migration_writer.go

@@ -409,14 +409,7 @@ func (w *MigrationWriter) generateAlterTableScripts(schema *models.Schema, model
 
 		if !exists {
 			// Column doesn't exist, add it
-			defaultVal := ""
+			_, defaultVal := formatColumnDefaultSQL(modelCol)
-			if modelCol.Default != nil {
-				if value, ok := modelCol.Default.(string); ok {
-					defaultVal = writers.QuoteDefaultValue(value, modelCol.Type)
-				} else {
-					defaultVal = fmt.Sprintf("%v", modelCol.Default)
-				}
-			}
 
 			sql, err := w.executor.ExecuteAddColumn(AddColumnData{
 				SchemaName: schema.Name,
@@ -442,12 +435,14 @@ func (w *MigrationWriter) generateAlterTableScripts(schema *models.Schema, model
 		} else if !columnsEqual(modelCol, currentCol) {
 			// Column exists but properties changed
 			if !columnTypesEqual(modelCol, currentCol) {
-				sql, err := w.executor.ExecuteAlterColumnType(AlterColumnTypeData{
+				newType := effectiveAlterColumnSQLType(modelCol)
-					SchemaName: schema.Name,
+				sql, err := w.executor.ExecuteAlterColumnTypeWithCheck(AlterColumnTypeWithCheckData{
-					TableName:  modelTable.Name,
+					SchemaName:      schema.Name,
-					ColumnName: modelCol.Name,
+					TableName:       modelTable.Name,
-					NewType:    effectiveAlterColumnSQLType(modelCol),
+					ColumnName:      modelCol.Name,
-					UsingExpr:  buildAlterColumnUsingExpression(modelCol.Name, effectiveAlterColumnSQLType(modelCol)),
+					NewType:         newType,
+					EquivalentTypes: equivalentTypeListSQL(newType),
+					UsingExpr:       buildAlterColumnUsingExpression(modelCol.Name, newType),
 				})
 				if err != nil {
 					return nil, err
@@ -466,17 +461,9 @@ func (w *MigrationWriter) generateAlterTableScripts(schema *models.Schema, model
 
 			// Check default value changes
 			if fmt.Sprintf("%v", modelCol.Default) != fmt.Sprintf("%v", currentCol.Default) {
-				setDefault := modelCol.Default != nil
+				setDefault, defaultVal := formatColumnDefaultSQL(modelCol)
-				defaultVal := ""
-				if setDefault {
-					if value, ok := modelCol.Default.(string); ok {
-						defaultVal = writers.QuoteDefaultValue(value, modelCol.Type)
-					} else {
-						defaultVal = fmt.Sprintf("%v", modelCol.Default)
-					}
-				}
 
-				sql, err := w.executor.ExecuteAlterColumnDefault(AlterColumnDefaultData{
+				sql, err := w.executor.ExecuteAlterColumnDefaultWithCheck(AlterColumnDefaultWithCheckData{
 					SchemaName:   schema.Name,
 					TableName:    modelTable.Name,
 					ColumnName:   modelCol.Name,
@@ -497,6 +484,29 @@ func (w *MigrationWriter) generateAlterTableScripts(schema *models.Schema, model
 				}
 				scripts = append(scripts, script)
 			}
+
+			// Check nullability changes
+			if modelCol.NotNull != currentCol.NotNull {
+				sql, err := w.executor.ExecuteAlterColumnNullabilityWithCheck(AlterColumnNullabilityWithCheckData{
+					SchemaName: schema.Name,
+					TableName:  modelTable.Name,
+					ColumnName: modelCol.Name,
+					NotNull:    modelCol.NotNull,
+				})
+				if err != nil {
+					return nil, err
+				}
+
+				script := MigrationScript{
+					ObjectName: fmt.Sprintf("%s.%s.%s", schema.Name, modelTable.Name, modelCol.Name),
+					ObjectType: "alter column nullability",
+					Schema:     schema.Name,
+					Priority:   145,
+					Sequence:   len(scripts),
+					Body:       sql,
+				}
+				scripts = append(scripts, script)
+			}
 		}
 	}
 

pkg/writers/pgsql/migration_writer_test.go

@@ -136,6 +136,89 @@ func TestWriteMigration_AltersColumnTypeWhenActualTypeDiffers(t *testing.T) {
 	}
 }
 
+func TestWriteMigration_AltersColumnTypeFallsBackToRenameAndAddOnConversionFailure(t *testing.T) {
+	current := models.InitDatabase("testdb")
+	currentSchema := models.InitSchema("public")
+	currentTable := models.InitTable("learnings", "public")
+	currentDetails := models.InitColumn("details", "learnings", "public")
+	currentDetails.Type = "varchar(50)"
+	currentTable.Columns["details"] = currentDetails
+	currentSchema.Tables = append(currentSchema.Tables, currentTable)
+	current.Schemas = append(current.Schemas, currentSchema)
+
+	model := models.InitDatabase("testdb")
+	modelSchema := models.InitSchema("public")
+	modelTable := models.InitTable("learnings", "public")
+	modelDetails := models.InitColumn("details", "learnings", "public")
+	modelDetails.Type = "integer"
+	modelTable.Columns["details"] = modelDetails
+	modelSchema.Tables = append(modelSchema.Tables, modelTable)
+	model.Schemas = append(model.Schemas, modelSchema)
+
+	var buf bytes.Buffer
+	writer, err := NewMigrationWriter(&writers.WriterOptions{})
+	if err != nil {
+		t.Fatalf("Failed to create writer: %v", err)
+	}
+	writer.writer = &buf
+
+	if err := writer.WriteMigration(model, current); err != nil {
+		t.Fatalf("WriteMigration failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "EXCEPTION WHEN OTHERS THEN") {
+		t.Fatalf("expected migration to guard the type conversion with an exception handler, got:\n%s", output)
+	}
+	if !strings.Contains(output, "RENAME COLUMN details TO %I") {
+		t.Fatalf("expected migration to rename the old column (derived from the live type) on conversion failure, got:\n%s", output)
+	}
+	if !strings.Contains(output, "renamed_column := 'details_' || trim(both '_' from regexp_replace(lower(current_type)") {
+		t.Fatalf("expected migration to derive the renamed column name from the live type, got:\n%s", output)
+	}
+	if !strings.Contains(output, "ADD COLUMN details integer") {
+		t.Fatalf("expected migration to add a fresh column with the new type on conversion failure, got:\n%s", output)
+	}
+}
+
+func TestWriteMigration_AltersColumnNullabilityWhenNotNullDiffers(t *testing.T) {
+	current := models.InitDatabase("testdb")
+	currentSchema := models.InitSchema("public")
+	currentTable := models.InitTable("service_instance", "public")
+	currentType := models.InitColumn("rid_service_instance_type", "service_instance", "public")
+	currentType.Type = "text"
+	currentType.NotNull = true
+	currentTable.Columns["rid_service_instance_type"] = currentType
+	currentSchema.Tables = append(currentSchema.Tables, currentTable)
+	current.Schemas = append(current.Schemas, currentSchema)
+
+	model := models.InitDatabase("testdb")
+	modelSchema := models.InitSchema("public")
+	modelTable := models.InitTable("service_instance", "public")
+	modelType := models.InitColumn("rid_service_instance_type", "service_instance", "public")
+	modelType.Type = "text"
+	modelType.NotNull = false
+	modelTable.Columns["rid_service_instance_type"] = modelType
+	modelSchema.Tables = append(modelSchema.Tables, modelTable)
+	model.Schemas = append(model.Schemas, modelSchema)
+
+	var buf bytes.Buffer
+	writer, err := NewMigrationWriter(&writers.WriterOptions{})
+	if err != nil {
+		t.Fatalf("Failed to create writer: %v", err)
+	}
+	writer.writer = &buf
+
+	if err := writer.WriteMigration(model, current); err != nil {
+		t.Fatalf("WriteMigration failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "ALTER COLUMN rid_service_instance_type DROP NOT NULL") {
+		t.Fatalf("expected migration to drop NOT NULL on existing column, got:\n%s", output)
+	}
+}
+
 func TestWriteMigration_UsesStorageTypeForSerialAlterStatements(t *testing.T) {
 	current := models.InitDatabase("testdb")
 	currentSchema := models.InitSchema("public")

pkg/writers/pgsql/templates.go

@@ -89,15 +89,10 @@ type AddColumnData struct {
 	NotNull    bool
 }
 
-// AlterColumnTypeData contains data for alter column type template
+// AlterColumnTypeWithCheckData contains data for the guarded alter column
-type AlterColumnTypeData struct {
+// type template, which only alters existing columns whose live type
-	SchemaName string
+// differs from the desired one, and falls back to renaming the old column
-	TableName  string
+// and adding a fresh one when the in-place conversion is not possible.
-	ColumnName string
-	NewType    string
-	UsingExpr  string
-}
-
 type AlterColumnTypeWithCheckData struct {
 	SchemaName      string
 	TableName       string
@@ -107,8 +102,10 @@ type AlterColumnTypeWithCheckData struct {
 	UsingExpr       string
 }
 
-// AlterColumnDefaultData contains data for alter column default template
+// AlterColumnDefaultWithCheckData contains data for the guarded alter
-type AlterColumnDefaultData struct {
+// column default template, which only alters existing columns whose live
+// default differs from the desired one.
+type AlterColumnDefaultWithCheckData struct {
 	SchemaName   string
 	TableName    string
 	ColumnName   string
@@ -116,6 +113,16 @@ type AlterColumnDefaultData struct {
 	DefaultValue string
 }
 
+// AlterColumnNullabilityWithCheckData contains data for the guarded alter
+// column nullability template, which only alters existing columns whose
+// live NOT NULL state differs from the desired one.
+type AlterColumnNullabilityWithCheckData struct {
+	SchemaName string
+	TableName  string
+	ColumnName string
+	NotNull    bool
+}
+
 // CreatePrimaryKeyData contains data for create primary key template
 type CreatePrimaryKeyData struct {
 	SchemaName     string
@@ -302,16 +309,9 @@ func (te *TemplateExecutor) ExecuteAddColumn(data AddColumnData) (string, error)
 	return buf.String(), nil
 }
 
-// ExecuteAlterColumnType executes the alter column type template
+// ExecuteAlterColumnTypeWithCheck executes the guarded alter column type
-func (te *TemplateExecutor) ExecuteAlterColumnType(data AlterColumnTypeData) (string, error) {
+// template shared by the full-schema writer and the diff-based migration
-	var buf bytes.Buffer
+// writer.
-	err := te.templates.ExecuteTemplate(&buf, "alter_column_type.tmpl", data)
-	if err != nil {
-		return "", fmt.Errorf("failed to execute alter_column_type template: %w", err)
-	}
-	return buf.String(), nil
-}
-
 func (te *TemplateExecutor) ExecuteAlterColumnTypeWithCheck(data AlterColumnTypeWithCheckData) (string, error) {
 	var buf bytes.Buffer
 	err := te.templates.ExecuteTemplate(&buf, "alter_column_type_with_check.tmpl", data)
@@ -321,12 +321,25 @@ func (te *TemplateExecutor) ExecuteAlterColumnTypeWithCheck(data AlterColumnType
 	return buf.String(), nil
 }
 
-// ExecuteAlterColumnDefault executes the alter column default template
+// ExecuteAlterColumnDefaultWithCheck executes the guarded alter column
-func (te *TemplateExecutor) ExecuteAlterColumnDefault(data AlterColumnDefaultData) (string, error) {
+// default template shared by the full-schema writer and the diff-based
+// migration writer.
+func (te *TemplateExecutor) ExecuteAlterColumnDefaultWithCheck(data AlterColumnDefaultWithCheckData) (string, error) {
 	var buf bytes.Buffer
-	err := te.templates.ExecuteTemplate(&buf, "alter_column_default.tmpl", data)
+	err := te.templates.ExecuteTemplate(&buf, "alter_column_default_with_check.tmpl", data)
 	if err != nil {
-		return "", fmt.Errorf("failed to execute alter_column_default template: %w", err)
+		return "", fmt.Errorf("failed to execute alter_column_default_with_check template: %w", err)
+	}
+	return buf.String(), nil
+}
+
+// ExecuteAlterColumnNullabilityWithCheck executes the guarded alter column
+// nullability template.
+func (te *TemplateExecutor) ExecuteAlterColumnNullabilityWithCheck(data AlterColumnNullabilityWithCheckData) (string, error) {
+	var buf bytes.Buffer
+	err := te.templates.ExecuteTemplate(&buf, "alter_column_nullability_with_check.tmpl", data)
+	if err != nil {
+		return "", fmt.Errorf("failed to execute alter_column_nullability_with_check template: %w", err)
 	}
 	return buf.String(), nil
 }

pkg/writers/pgsql/templates/alter_column_default.tmpl

@@ -1,7 +0,0 @@
-{{- if .SetDefault -}}
-ALTER TABLE {{qual_table .SchemaName .TableName}}
-  ALTER COLUMN {{quote_ident .ColumnName}} SET DEFAULT {{.DefaultValue}};
-{{- else -}}
-ALTER TABLE {{qual_table .SchemaName .TableName}}
-  ALTER COLUMN {{quote_ident .ColumnName}} DROP DEFAULT;
-{{- end -}}

pkg/writers/pgsql/templates/alter_column_default_with_check.tmpl

@@ -0,0 +1,29 @@
+DO $$
+DECLARE
+  current_default text;
+BEGIN
+  SELECT pg_catalog.pg_get_expr(d.adbin, d.adrelid)
+    INTO current_default
+  FROM pg_attribute a
+  JOIN pg_class t ON t.oid = a.attrelid
+  JOIN pg_namespace n ON n.oid = t.relnamespace
+  LEFT JOIN pg_attrdef d ON d.adrelid = a.attrelid AND d.adnum = a.attnum
+  WHERE n.nspname = '{{.SchemaName}}'
+    AND t.relname = '{{.TableName}}'
+    AND a.attname = '{{.ColumnName}}'
+    AND a.attnum > 0
+    AND NOT a.attisdropped;
+
+{{- if .SetDefault }}
+  IF current_default IS DISTINCT FROM {{quote .DefaultValue}} THEN
+    ALTER TABLE {{qual_table .SchemaName .TableName}}
+      ALTER COLUMN {{quote_ident .ColumnName}} SET DEFAULT {{.DefaultValue}};
+  END IF;
+{{- else }}
+  IF current_default IS NOT NULL THEN
+    ALTER TABLE {{qual_table .SchemaName .TableName}}
+      ALTER COLUMN {{quote_ident .ColumnName}} DROP DEFAULT;
+  END IF;
+{{- end }}
+END;
+$$;

pkg/writers/pgsql/templates/alter_column_nullability_with_check.tmpl

@@ -0,0 +1,26 @@
+DO $$
+DECLARE
+  current_not_null boolean;
+BEGIN
+  SELECT a.attnotnull
+    INTO current_not_null
+  FROM pg_attribute a
+  JOIN pg_class t ON t.oid = a.attrelid
+  JOIN pg_namespace n ON n.oid = t.relnamespace
+  WHERE n.nspname = '{{.SchemaName}}'
+    AND t.relname = '{{.TableName}}'
+    AND a.attname = '{{.ColumnName}}'
+    AND a.attnum > 0
+    AND NOT a.attisdropped;
+
+  IF current_not_null IS NOT NULL AND current_not_null IS DISTINCT FROM {{.NotNull}} THEN
+{{- if .NotNull }}
+    ALTER TABLE {{qual_table .SchemaName .TableName}}
+      ALTER COLUMN {{quote_ident .ColumnName}} SET NOT NULL;
+{{- else }}
+    ALTER TABLE {{qual_table .SchemaName .TableName}}
+      ALTER COLUMN {{quote_ident .ColumnName}} DROP NOT NULL;
+{{- end }}
+  END IF;
+END;
+$$;

pkg/writers/pgsql/templates/alter_column_type.tmpl

@@ -1,2 +0,0 @@
-ALTER TABLE {{qual_table .SchemaName .TableName}}
-  ALTER COLUMN {{quote_ident .ColumnName}} TYPE {{.NewType}}{{if .UsingExpr}} USING {{.UsingExpr}}{{end}};

pkg/writers/pgsql/templates/alter_column_type_with_check.tmpl

@@ -1,6 +1,7 @@
 DO $$
 DECLARE
   current_type text;
+  renamed_column text;
 BEGIN
   SELECT pg_catalog.format_type(a.atttypid, a.atttypmod)
     INTO current_type
@@ -15,8 +16,15 @@ BEGIN
 
   IF current_type IS NOT NULL
      AND current_type <> ALL(ARRAY[{{.EquivalentTypes}}]) THEN
-    ALTER TABLE {{qual_table .SchemaName .TableName}}
+    BEGIN
-      ALTER COLUMN {{quote_ident .ColumnName}} TYPE {{.NewType}}{{if .UsingExpr}} USING {{.UsingExpr}}{{end}};
+      ALTER TABLE {{qual_table .SchemaName .TableName}}
+        ALTER COLUMN {{quote_ident .ColumnName}} TYPE {{.NewType}}{{if .UsingExpr}} USING {{.UsingExpr}}{{end}};
+    EXCEPTION WHEN OTHERS THEN
+      renamed_column := '{{.ColumnName}}_' || trim(both '_' from regexp_replace(lower(current_type), '[^a-z0-9]+', '_', 'g'));
+      EXECUTE format('ALTER TABLE {{qual_table .SchemaName .TableName}} RENAME COLUMN {{quote_ident .ColumnName}} TO %I', renamed_column);
+      ALTER TABLE {{qual_table .SchemaName .TableName}}
+        ADD COLUMN {{quote_ident .ColumnName}} {{.NewType}};
+    END;
   END IF;
 END;
 $$;

pkg/writers/pgsql/writer.go

@@ -475,6 +475,75 @@ func (w *Writer) GenerateAlterColumnTypeStatements(schema *models.Schema) ([]str
 	return statements, nil
 }
 
+// GenerateAlterColumnDefaultStatements generates guarded ALTER TABLE
+// statements to bring existing columns' DEFAULT clause in line with the
+// model, safe to run against a database that already has the columns.
+func (w *Writer) GenerateAlterColumnDefaultStatements(schema *models.Schema) ([]string, error) {
+	statements := []string{}
+
+	statements = append(statements, fmt.Sprintf("-- Alter column defaults for schema: %s", schema.Name))
+
+	for _, table := range schema.Tables {
+		columns := getSortedColumns(table.Columns)
+		for _, col := range columns {
+			setDefault, defaultVal := formatColumnDefaultSQL(col)
+			stmt, err := w.executor.ExecuteAlterColumnDefaultWithCheck(AlterColumnDefaultWithCheckData{
+				SchemaName:   schema.Name,
+				TableName:    table.Name,
+				ColumnName:   col.Name,
+				SetDefault:   setDefault,
+				DefaultValue: defaultVal,
+			})
+			if err != nil {
+				return nil, fmt.Errorf("failed to generate alter column default for %s.%s.%s: %w", schema.Name, table.Name, col.Name, err)
+			}
+			statements = append(statements, stmt)
+		}
+	}
+
+	return statements, nil
+}
+
+// formatColumnDefaultSQL renders a column's model-level default into the
+// SQL literal/expression used by ALTER COLUMN ... SET DEFAULT, shared by
+// the full-schema writer and the diff-based migration writer.
+func formatColumnDefaultSQL(col *models.Column) (setDefault bool, defaultVal string) {
+	if col.Default == nil {
+		return false, ""
+	}
+	if value, ok := col.Default.(string); ok {
+		return true, writers.QuoteDefaultValue(value, col.Type)
+	}
+	return true, fmt.Sprintf("%v", col.Default)
+}
+
+// GenerateAlterColumnNullabilityStatements generates guarded ALTER TABLE
+// statements to bring existing columns' NOT NULL state in line with the
+// model, safe to run against a database that already has the columns.
+func (w *Writer) GenerateAlterColumnNullabilityStatements(schema *models.Schema) ([]string, error) {
+	statements := []string{}
+
+	statements = append(statements, fmt.Sprintf("-- Alter column nullability for schema: %s", schema.Name))
+
+	for _, table := range schema.Tables {
+		columns := getSortedColumns(table.Columns)
+		for _, col := range columns {
+			stmt, err := w.executor.ExecuteAlterColumnNullabilityWithCheck(AlterColumnNullabilityWithCheckData{
+				SchemaName: schema.Name,
+				TableName:  table.Name,
+				ColumnName: col.Name,
+				NotNull:    col.NotNull,
+			})
+			if err != nil {
+				return nil, fmt.Errorf("failed to generate alter column nullability for %s.%s.%s: %w", schema.Name, table.Name, col.Name, err)
+			}
+			statements = append(statements, stmt)
+		}
+	}
+
+	return statements, nil
+}
+
 // GenerateAddColumnsForDatabase generates ALTER TABLE ADD COLUMN statements for the entire database
 func (w *Writer) GenerateAddColumnsForDatabase(db *models.Database) ([]string, error) {
 	statements := []string{}
@@ -641,6 +710,14 @@ func (w *Writer) WriteSchema(schema *models.Schema) error {
 		return err
 	}
 
+	if err := w.writeAlterColumnDefaults(schema); err != nil {
+		return err
+	}
+
+	if err := w.writeAlterColumnNullability(schema); err != nil {
+		return err
+	}
+
 	// Phase 4: Create primary keys (priority 160)
 	if err := w.writePrimaryKeys(schema); err != nil {
 		return err
@@ -859,6 +936,36 @@ func (w *Writer) writeAlterColumnTypes(schema *models.Schema) error {
 	return nil
 }
 
+func (w *Writer) writeAlterColumnDefaults(schema *models.Schema) error {
+	fmt.Fprintf(w.writer, "-- Alter column defaults for schema: %s\n", schema.Name)
+
+	statements, err := w.GenerateAlterColumnDefaultStatements(schema)
+	if err != nil {
+		return err
+	}
+	for _, stmt := range statements[1:] {
+		fmt.Fprint(w.writer, stmt)
+		fmt.Fprint(w.writer, "\n")
+	}
+
+	return nil
+}
+
+func (w *Writer) writeAlterColumnNullability(schema *models.Schema) error {
+	fmt.Fprintf(w.writer, "-- Alter column nullability for schema: %s\n", schema.Name)
+
+	statements, err := w.GenerateAlterColumnNullabilityStatements(schema)
+	if err != nil {
+		return err
+	}
+	for _, stmt := range statements[1:] {
+		fmt.Fprint(w.writer, stmt)
+		fmt.Fprint(w.writer, "\n")
+	}
+
+	return nil
+}
+
 // writePrimaryKeys generates ALTER TABLE statements for primary keys
 func (w *Writer) writePrimaryKeys(schema *models.Schema) error {
 	fmt.Fprintf(w.writer, "-- Primary keys for schema: %s\n", schema.Name)

pkg/writers/pgsql/writer_test.go

@@ -1106,6 +1106,113 @@ func TestWriteSchema_EmitsGuardedAlterColumnTypeStatements(t *testing.T) {
 	}
 }
 
+func TestWriteSchema_EmitsGuardedAlterColumnDefaultStatements(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+
+	table := models.InitTable("agent_skills", "public")
+
+	statusCol := models.InitColumn("status", "agent_skills", "public")
+	statusCol.Type = "text"
+	statusCol.Default = "active"
+	table.Columns["status"] = statusCol
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	writer := NewWriter(&writers.WriterOptions{})
+	writer.writer = &buf
+
+	if err := writer.WriteDatabase(db); err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "-- Alter column defaults for schema: public") {
+		t.Fatalf("expected alter column default section, got:\n%s", output)
+	}
+	if !strings.Contains(output, "pg_get_expr(d.adbin, d.adrelid)") {
+		t.Fatalf("expected guarded live-default check, got:\n%s", output)
+	}
+	if !strings.Contains(output, "ALTER COLUMN status SET DEFAULT 'active'") {
+		t.Fatalf("expected guarded SET DEFAULT for status column, got:\n%s", output)
+	}
+}
+
+func TestWriteSchema_GuardedAlterColumnTypeFallsBackOnConversionFailure(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+
+	table := models.InitTable("agent_skills", "public")
+
+	nameCol := models.InitColumn("name", "agent_skills", "public")
+	nameCol.Type = "integer"
+	table.Columns["name"] = nameCol
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	writer := NewWriter(&writers.WriterOptions{})
+	writer.writer = &buf
+
+	if err := writer.WriteDatabase(db); err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "EXCEPTION WHEN OTHERS THEN") {
+		t.Fatalf("expected guarded alter to fall back on conversion failure, got:\n%s", output)
+	}
+	if !strings.Contains(output, "renamed_column := 'name_' || trim(both '_' from regexp_replace(lower(current_type)") {
+		t.Fatalf("expected fallback to derive a renamed column name from the live type, got:\n%s", output)
+	}
+	if !strings.Contains(output, "RENAME COLUMN name TO %I") {
+		t.Fatalf("expected fallback to rename the existing column, got:\n%s", output)
+	}
+	if !strings.Contains(output, "ADD COLUMN name integer") {
+		t.Fatalf("expected fallback to add a fresh column with the new type, got:\n%s", output)
+	}
+}
+
+func TestWriteSchema_EmitsGuardedAlterColumnNullabilityStatements(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("origin")
+
+	table := models.InitTable("service_instance", "origin")
+
+	typeCol := models.InitColumn("rid_service_instance_type", "service_instance", "origin")
+	typeCol.Type = "text"
+	typeCol.NotNull = false
+	table.Columns["rid_service_instance_type"] = typeCol
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	writer := NewWriter(&writers.WriterOptions{})
+	writer.writer = &buf
+
+	if err := writer.WriteDatabase(db); err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "-- Alter column nullability for schema: origin") {
+		t.Fatalf("expected alter column nullability section, got:\n%s", output)
+	}
+	if !strings.Contains(output, "a.attnotnull") {
+		t.Fatalf("expected guarded live-nullability check, got:\n%s", output)
+	}
+	if !strings.Contains(output, "current_not_null IS DISTINCT FROM false") {
+		t.Fatalf("expected guard comparing live nullability against desired value, got:\n%s", output)
+	}
+	if !strings.Contains(output, "ALTER COLUMN rid_service_instance_type DROP NOT NULL") {
+		t.Fatalf("expected guarded DROP NOT NULL for nullable column, got:\n%s", output)
+	}
+}
+
 func TestWriteSchema_UsesStorageTypeForSerialAlterStatements(t *testing.T) {
 	db := models.InitDatabase("testdb")
 	schema := models.InitSchema("public")