feat(writer): 🎉 Enhance primary key handling and add tests

* Implement checks for existing primary keys before adding new ones.
* Drop auto-generated primary keys if they exist.
* Add tests for primary key existence and column size specifiers.
* Improve type conversion handling for PostgreSQL compatibility.

pkg/writers/pgsql/writer.go

@@ -179,27 +179,67 @@ func (w *Writer) GenerateSchemaStatements(schema *models.Schema) ([]string, erro
 			}
 		}
 
+		var pkColumns []string
+		var pkName string
+
 		if pkConstraint != nil {
-			stmt := fmt.Sprintf("ALTER TABLE %s.%s ADD CONSTRAINT %s PRIMARY KEY (%s)",
-				schema.SQLName(), table.SQLName(), pkConstraint.Name, strings.Join(pkConstraint.Columns, ", "))
-			statements = append(statements, stmt)
+			pkColumns = pkConstraint.Columns
+			pkName = pkConstraint.Name
 		} else {
 			// No explicit constraint, check for columns with IsPrimaryKey = true
-			pkColumns := []string{}
+			pkCols := []string{}
 			for _, col := range table.Columns {
 				if col.IsPrimaryKey {
-					pkColumns = append(pkColumns, col.SQLName())
+					pkCols = append(pkCols, col.SQLName())
 				}
 			}
-			if len(pkColumns) > 0 {
+			if len(pkCols) > 0 {
 				// Sort for consistent output
-				sort.Strings(pkColumns)
-				pkName := fmt.Sprintf("pk_%s_%s", schema.SQLName(), table.SQLName())
-				stmt := fmt.Sprintf("ALTER TABLE %s.%s ADD CONSTRAINT %s PRIMARY KEY (%s)",
-					schema.SQLName(), table.SQLName(), pkName, strings.Join(pkColumns, ", "))
-				statements = append(statements, stmt)
+				sort.Strings(pkCols)
+				pkColumns = pkCols
+				pkName = fmt.Sprintf("pk_%s_%s", schema.SQLName(), table.SQLName())
 			}
 		}
+
+		if len(pkColumns) > 0 {
+			// Auto-generated primary key names to check for and drop
+			autoGenPKNames := []string{
+				fmt.Sprintf("%s_pkey", table.Name),
+				fmt.Sprintf("%s_%s_pkey", schema.Name, table.Name),
+			}
+
+			// Wrap in DO block to drop auto-generated PK and add our named PK
+			stmt := fmt.Sprintf("DO $$\nDECLARE\n"+
+				"  auto_pk_name text;\n"+
+				"BEGIN\n"+
+				"  -- Drop auto-generated primary key if it exists\n"+
+				"  SELECT constraint_name INTO auto_pk_name\n"+
+				"  FROM information_schema.table_constraints\n"+
+				"  WHERE table_schema = '%s'\n"+
+				"    AND table_name = '%s'\n"+
+				"    AND constraint_type = 'PRIMARY KEY'\n"+
+				"    AND constraint_name IN (%s);\n"+
+				"\n"+
+				"  IF auto_pk_name IS NOT NULL THEN\n"+
+				"    EXECUTE 'ALTER TABLE %s.%s DROP CONSTRAINT ' || quote_ident(auto_pk_name);\n"+
+				"  END IF;\n"+
+				"\n"+
+				"  -- Add named primary key if it doesn't exist\n"+
+				"  IF NOT EXISTS (\n"+
+				"    SELECT 1 FROM information_schema.table_constraints\n"+
+				"    WHERE table_schema = '%s'\n"+
+				"      AND table_name = '%s'\n"+
+				"      AND constraint_name = '%s'\n"+
+				"  ) THEN\n"+
+				"    ALTER TABLE %s.%s ADD CONSTRAINT %s PRIMARY KEY (%s);\n"+
+				"  END IF;\n"+
+				"END;\n$$",
+				schema.Name, table.Name, formatStringList(autoGenPKNames),
+				schema.SQLName(), table.SQLName(),
+				schema.Name, table.Name, pkName,
+				schema.SQLName(), table.SQLName(), pkName, strings.Join(pkColumns, ", "))
+			statements = append(statements, stmt)
+		}
 	}
 
 	// Phase 5: Indexes
@@ -270,7 +310,18 @@ func (w *Writer) GenerateSchemaStatements(schema *models.Schema) ([]string, erro
 				onUpdate = "NO ACTION"
 			}
 
-			stmt := fmt.Sprintf("ALTER TABLE %s.%s ADD CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s.%s(%s) ON DELETE %s ON UPDATE %s",
+			// Wrap in DO block to check for existing constraint
+			stmt := fmt.Sprintf("DO $$\nBEGIN\n"+
+				"  IF NOT EXISTS (\n"+
+				"    SELECT 1 FROM information_schema.table_constraints\n"+
+				"    WHERE table_schema = '%s'\n"+
+				"      AND table_name = '%s'\n"+
+				"      AND constraint_name = '%s'\n"+
+				"  ) THEN\n"+
+				"    ALTER TABLE %s.%s ADD CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s.%s(%s) ON DELETE %s ON UPDATE %s;\n"+
+				"  END IF;\n"+
+				"END;\n$$",
+				schema.Name, table.Name, constraint.Name,
 				schema.SQLName(), table.SQLName(), constraint.Name,
 				strings.Join(constraint.Columns, ", "),
 				strings.ToLower(refSchema), strings.ToLower(constraint.ReferencedTable),
@@ -336,14 +387,25 @@ func (w *Writer) generateColumnDefinition(col *models.Column) string {
 	// Type with length/precision - convert to valid PostgreSQL type
 	baseType := pgsql.ConvertSQLType(col.Type)
 	typeStr := baseType
+
+	// Only add size specifiers for types that support them
 	if col.Length > 0 && col.Precision == 0 {
-		typeStr = fmt.Sprintf("%s(%d)", baseType, col.Length)
-	} else if col.Precision > 0 {
-		if col.Scale > 0 {
-			typeStr = fmt.Sprintf("%s(%d,%d)", baseType, col.Precision, col.Scale)
-		} else {
-			typeStr = fmt.Sprintf("%s(%d)", baseType, col.Precision)
+		if supportsLength(baseType) {
+			typeStr = fmt.Sprintf("%s(%d)", baseType, col.Length)
+		} else if isTextTypeWithoutLength(baseType) {
+			// Convert text with length to varchar
+			typeStr = fmt.Sprintf("varchar(%d)", col.Length)
 		}
+		// For types that don't support length (integer, bigint, etc.), ignore the length
+	} else if col.Precision > 0 {
+		if supportsPrecision(baseType) {
+			if col.Scale > 0 {
+				typeStr = fmt.Sprintf("%s(%d,%d)", baseType, col.Precision, col.Scale)
+			} else {
+				typeStr = fmt.Sprintf("%s(%d)", baseType, col.Precision)
+			}
+		}
+		// For types that don't support precision, ignore it
 	}
 	parts = append(parts, typeStr)
 
@@ -490,15 +552,8 @@ func (w *Writer) writeCreateTables(schema *models.Schema) error {
 		columnDefs := make([]string, 0, len(columns))
 
 		for _, col := range columns {
-			colDef := fmt.Sprintf("  %s %s", col.SQLName(), pgsql.ConvertSQLType(col.Type))
-
-			// Add default value if present
-			if col.Default != nil && col.Default != "" {
-				// Strip backticks - DBML uses them for SQL expressions but PostgreSQL doesn't
-				defaultVal := fmt.Sprintf("%v", col.Default)
-				colDef += fmt.Sprintf(" DEFAULT %s", stripBackticks(defaultVal))
-			}
-
+			// Use generateColumnDefinition to properly handle type, length, precision, and defaults
+			colDef := "  " + w.generateColumnDefinition(col)
 			columnDefs = append(columnDefs, colDef)
 		}
 
@@ -550,7 +605,32 @@ func (w *Writer) writePrimaryKeys(schema *models.Schema) error {
 			continue
 		}
 
-		fmt.Fprintf(w.writer, "DO $$\nBEGIN\n")
+		// Auto-generated primary key names to check for and drop
+		autoGenPKNames := []string{
+			fmt.Sprintf("%s_pkey", table.Name),
+			fmt.Sprintf("%s_%s_pkey", schema.Name, table.Name),
+		}
+
+		fmt.Fprintf(w.writer, "DO $$\nDECLARE\n")
+		fmt.Fprintf(w.writer, "  auto_pk_name text;\nBEGIN\n")
+
+		// Check for and drop auto-generated primary keys
+		fmt.Fprintf(w.writer, "  -- Drop auto-generated primary key if it exists\n")
+		fmt.Fprintf(w.writer, "  SELECT constraint_name INTO auto_pk_name\n")
+		fmt.Fprintf(w.writer, "  FROM information_schema.table_constraints\n")
+		fmt.Fprintf(w.writer, "  WHERE table_schema = '%s'\n", schema.Name)
+		fmt.Fprintf(w.writer, "    AND table_name = '%s'\n", table.Name)
+		fmt.Fprintf(w.writer, "    AND constraint_type = 'PRIMARY KEY'\n")
+		fmt.Fprintf(w.writer, "    AND constraint_name IN (%s);\n", formatStringList(autoGenPKNames))
+		fmt.Fprintf(w.writer, "\n")
+		fmt.Fprintf(w.writer, "  IF auto_pk_name IS NOT NULL THEN\n")
+		fmt.Fprintf(w.writer, "    EXECUTE 'ALTER TABLE %s.%s DROP CONSTRAINT ' || quote_ident(auto_pk_name);\n",
+			schema.SQLName(), table.SQLName())
+		fmt.Fprintf(w.writer, "  END IF;\n")
+		fmt.Fprintf(w.writer, "\n")
+
+		// Add our named primary key if it doesn't exist
+		fmt.Fprintf(w.writer, "  -- Add named primary key if it doesn't exist\n")
 		fmt.Fprintf(w.writer, "  IF NOT EXISTS (\n")
 		fmt.Fprintf(w.writer, "    SELECT 1 FROM information_schema.table_constraints\n")
 		fmt.Fprintf(w.writer, "    WHERE table_schema = '%s'\n", schema.Name)
@@ -711,13 +791,6 @@ func (w *Writer) writeForeignKeys(schema *models.Schema) error {
 				onUpdate = strings.ToUpper(fkConstraint.OnUpdate)
 			}
 
-			fmt.Fprintf(w.writer, "ALTER TABLE %s.%s\n", schema.SQLName(), table.SQLName())
-			fmt.Fprintf(w.writer, "  DROP CONSTRAINT IF EXISTS %s;\n", fkName)
-			fmt.Fprintf(w.writer, "\n")
-			fmt.Fprintf(w.writer, "ALTER TABLE %s.%s\n", schema.SQLName(), table.SQLName())
-			fmt.Fprintf(w.writer, "  ADD CONSTRAINT %s\n", fkName)
-			fmt.Fprintf(w.writer, "  FOREIGN KEY (%s)\n", strings.Join(sourceColumns, ", "))
-
 			// Use constraint's referenced schema/table or relationship's ToSchema/ToTable
 			refSchema := fkConstraint.ReferencedSchema
 			if refSchema == "" {
@@ -728,11 +801,24 @@ func (w *Writer) writeForeignKeys(schema *models.Schema) error {
 				refTable = rel.ToTable
 			}
 
-			fmt.Fprintf(w.writer, "  REFERENCES %s.%s (%s)\n",
+			// Use DO block to check if constraint exists before adding
+			fmt.Fprintf(w.writer, "DO $$\nBEGIN\n")
+			fmt.Fprintf(w.writer, "  IF NOT EXISTS (\n")
+			fmt.Fprintf(w.writer, "    SELECT 1 FROM information_schema.table_constraints\n")
+			fmt.Fprintf(w.writer, "    WHERE table_schema = '%s'\n", schema.Name)
+			fmt.Fprintf(w.writer, "      AND table_name = '%s'\n", table.Name)
+			fmt.Fprintf(w.writer, "      AND constraint_name = '%s'\n", fkName)
+			fmt.Fprintf(w.writer, "  ) THEN\n")
+			fmt.Fprintf(w.writer, "    ALTER TABLE %s.%s\n", schema.SQLName(), table.SQLName())
+			fmt.Fprintf(w.writer, "      ADD CONSTRAINT %s\n", fkName)
+			fmt.Fprintf(w.writer, "      FOREIGN KEY (%s)\n", strings.Join(sourceColumns, ", "))
+			fmt.Fprintf(w.writer, "      REFERENCES %s.%s (%s)\n",
 				refSchema, refTable, strings.Join(targetColumns, ", "))
-			fmt.Fprintf(w.writer, "  ON DELETE %s\n", onDelete)
-			fmt.Fprintf(w.writer, "  ON UPDATE %s\n", onUpdate)
-			fmt.Fprintf(w.writer, "  DEFERRABLE;\n\n")
+			fmt.Fprintf(w.writer, "      ON DELETE %s\n", onDelete)
+			fmt.Fprintf(w.writer, "      ON UPDATE %s\n", onUpdate)
+			fmt.Fprintf(w.writer, "      DEFERRABLE;\n")
+			fmt.Fprintf(w.writer, "  END IF;\n")
+			fmt.Fprintf(w.writer, "END;\n$$;\n\n")
 		}
 	}
 
@@ -844,6 +930,44 @@ func isTextType(colType string) bool {
 	return false
 }
 
+// supportsLength checks if a PostgreSQL type supports length specification
+func supportsLength(colType string) bool {
+	lengthTypes := []string{"varchar", "character varying", "char", "character", "bit", "bit varying", "varbit"}
+	lowerType := strings.ToLower(colType)
+	for _, t := range lengthTypes {
+		if lowerType == t || strings.HasPrefix(lowerType, t+"(") {
+			return true
+		}
+	}
+	return false
+}
+
+// supportsPrecision checks if a PostgreSQL type supports precision/scale specification
+func supportsPrecision(colType string) bool {
+	precisionTypes := []string{"numeric", "decimal", "time", "timestamp", "timestamptz", "timestamp with time zone", "timestamp without time zone", "time with time zone", "time without time zone", "interval"}
+	lowerType := strings.ToLower(colType)
+	for _, t := range precisionTypes {
+		if lowerType == t || strings.HasPrefix(lowerType, t+"(") {
+			return true
+		}
+	}
+	return false
+}
+
+// isTextTypeWithoutLength checks if type is text (which should convert to varchar when length is specified)
+func isTextTypeWithoutLength(colType string) bool {
+	return strings.EqualFold(colType, "text")
+}
+
+// formatStringList formats a list of strings as a SQL-safe comma-separated quoted list
+func formatStringList(items []string) string {
+	quoted := make([]string, len(items))
+	for i, item := range items {
+		quoted[i] = fmt.Sprintf("'%s'", escapeQuote(item))
+	}
+	return strings.Join(quoted, ", ")
+}
+
 // extractOperatorClass extracts operator class from index comment/note
 // Looks for common operator classes like gin_trgm_ops, gist_trgm_ops, etc.
 func extractOperatorClass(comment string) string {