feat: support CONSTRAINT TRIGGER

internal/diff/table.go

@@ -971,17 +971,44 @@ func (td *tableDiff) generateAlterTableStatements(targetSchema string, collector
 
 	// Modify triggers - already sorted by the Diff operation
 	for _, triggerDiff := range td.ModifiedTriggers {
-		// Use CREATE OR REPLACE for modified triggers
-		sql := generateTriggerSQLWithMode(triggerDiff.New, targetSchema)
+		// Constraint triggers don't support CREATE OR REPLACE, so we need to DROP and CREATE
+		if triggerDiff.New.IsConstraint {
+			tableName := getTableNameWithSchema(td.Table.Schema, td.Table.Name, targetSchema)
 
-		context := &diffContext{
-			Type:                DiffTypeTableTrigger,
-			Operation:           DiffOperationAlter,
-			Path:                fmt.Sprintf("%s.%s.%s", td.Table.Schema, td.Table.Name, triggerDiff.New.Name),
-			Source:              triggerDiff,
-			CanRunInTransaction: true,
+			// Step 1: DROP the old trigger
+			dropSQL := fmt.Sprintf("DROP TRIGGER IF EXISTS %s ON %s;", triggerDiff.Old.Name, tableName)
+			dropContext := &diffContext{
+				Type:                DiffTypeTableTrigger,
+				Operation:           DiffOperationDrop,
+				Path:                fmt.Sprintf("%s.%s.%s", td.Table.Schema, td.Table.Name, triggerDiff.Old.Name),
+				Source:              triggerDiff.Old,
+				CanRunInTransaction: true,
+			}
+			collector.collect(dropContext, dropSQL)
+
+			// Step 2: CREATE the new constraint trigger
+			createSQL := generateTriggerSQLWithMode(triggerDiff.New, targetSchema)
+			createContext := &diffContext{
+				Type:                DiffTypeTableTrigger,
+				Operation:           DiffOperationCreate,
+				Path:                fmt.Sprintf("%s.%s.%s", td.Table.Schema, td.Table.Name, triggerDiff.New.Name),
+				Source:              triggerDiff.New,
+				CanRunInTransaction: true,
+			}
+			collector.collect(createContext, createSQL)
+		} else {
+			// Use CREATE OR REPLACE for regular triggers
+			sql := generateTriggerSQLWithMode(triggerDiff.New, targetSchema)
+
+			context := &diffContext{
+				Type:                DiffTypeTableTrigger,
+				Operation:           DiffOperationAlter,
+				Path:                fmt.Sprintf("%s.%s.%s", td.Table.Schema, td.Table.Name, triggerDiff.New.Name),
+				Source:              triggerDiff,
+				CanRunInTransaction: true,
+			}
+			collector.collect(context, sql)
 		}
-		collector.collect(context, sql)
 	}
 
 	// Modify policies - already sorted by the Diff operation

internal/diff/trigger.go

@@ -46,6 +46,17 @@ func triggersEqual(old, new *ir.Trigger) bool {
 		}
 	}
 
+	// Compare constraint trigger properties
+	if old.IsConstraint != new.IsConstraint {
+		return false
+	}
+	if old.Deferrable != new.Deferrable {
+		return false
+	}
+	if old.InitiallyDeferred != new.InitiallyDeferred {
+		return false
+	}
+
 	return true
 }
 
@@ -122,7 +133,7 @@ func generateCreateTriggersSQL(triggers []*ir.Trigger, targetSchema string, coll
 	}
 }
 
-// generateTriggerSQLWithMode generates CREATE [OR REPLACE] TRIGGER statement
+// generateTriggerSQLWithMode generates CREATE [OR REPLACE] TRIGGER or CREATE CONSTRAINT TRIGGER statement
 func generateTriggerSQLWithMode(trigger *ir.Trigger, targetSchema string) string {
 	// Build event list in standard order: INSERT, UPDATE, DELETE, TRUNCATE
 	var events []string
@@ -141,8 +152,26 @@ func generateTriggerSQLWithMode(trigger *ir.Trigger, targetSchema string) string
 	tableName := qualifyEntityName(trigger.Schema, trigger.Table, targetSchema)
 
 	// Build the trigger statement with proper formatting
-	stmt := fmt.Sprintf("CREATE OR REPLACE TRIGGER %s\n    %s %s ON %s\n    FOR EACH %s",
-		trigger.Name, trigger.Timing, eventList, tableName, trigger.Level)
+	// Use CREATE CONSTRAINT TRIGGER for constraint triggers (cannot use OR REPLACE)
+	var stmt string
+	if trigger.IsConstraint {
+		stmt = fmt.Sprintf("CREATE CONSTRAINT TRIGGER %s\n    %s %s ON %s",
+			trigger.Name, trigger.Timing, eventList, tableName)
+
+		// Add deferrable clause for constraint triggers
+		if trigger.Deferrable {
+			if trigger.InitiallyDeferred {
+				stmt += "\n    DEFERRABLE INITIALLY DEFERRED"
+			} else {
+				stmt += "\n    DEFERRABLE INITIALLY IMMEDIATE"
+			}
+		}
+
+		stmt += fmt.Sprintf("\n    FOR EACH %s", trigger.Level)
+	} else {
+		stmt = fmt.Sprintf("CREATE OR REPLACE TRIGGER %s\n    %s %s ON %s\n    FOR EACH %s",
+			trigger.Name, trigger.Timing, eventList, tableName, trigger.Level)
+	}
 
 	// Add WHEN clause if present
 	if trigger.Condition != "" {

ir/ir.go

@@ -227,15 +227,18 @@ const (
 
 // Trigger represents a database trigger
 type Trigger struct {
-	Schema    string         `json:"schema"`
-	Table     string         `json:"table"`
-	Name      string         `json:"name"`
-	Timing    TriggerTiming  `json:"timing"` // BEFORE, AFTER, INSTEAD OF
-	Events    []TriggerEvent `json:"events"` // INSERT, UPDATE, DELETE
-	Level     TriggerLevel   `json:"level"`  // ROW, STATEMENT
-	Function  string         `json:"function"`
-	Condition string         `json:"condition,omitempty"` // WHEN condition
-	Comment   string         `json:"comment,omitempty"`
+	Schema            string         `json:"schema"`
+	Table             string         `json:"table"`
+	Name              string         `json:"name"`
+	Timing            TriggerTiming  `json:"timing"` // BEFORE, AFTER, INSTEAD OF
+	Events            []TriggerEvent `json:"events"` // INSERT, UPDATE, DELETE
+	Level             TriggerLevel   `json:"level"`  // ROW, STATEMENT
+	Function          string         `json:"function"`
+	Condition         string         `json:"condition,omitempty"` // WHEN condition
+	Comment           string         `json:"comment,omitempty"`
+	IsConstraint      bool           `json:"is_constraint,omitempty"`       // Whether this is a constraint trigger
+	Deferrable        bool           `json:"deferrable,omitempty"`          // Can be deferred until end of transaction
+	InitiallyDeferred bool           `json:"initially_deferred,omitempty"`  // Whether deferred by default
 }
 
 // TriggerTiming represents the timing of trigger execution

ir/parser.go

@@ -3239,14 +3239,17 @@ func (p *Parser) parseCreateTrigger(triggerStmt *pg_query.CreateTrigStmt) error
 
 	// Create trigger
 	trigger := &Trigger{
-		Schema:    schemaName,
-		Table:     tableName,
-		Name:      triggerStmt.Trigname,
-		Timing:    timing,
-		Events:    events,
-		Level:     level,
-		Function:  function,
-		Condition: condition,
+		Schema:            schemaName,
+		Table:             tableName,
+		Name:              triggerStmt.Trigname,
+		Timing:            timing,
+		Events:            events,
+		Level:             level,
+		Function:          function,
+		Condition:         condition,
+		IsConstraint:      triggerStmt.Isconstraint,
+		Deferrable:        triggerStmt.Deferrable,
+		InitiallyDeferred: triggerStmt.Initdeferred,
 	}
 
 	// Add trigger to table only

ir/queries/queries.sql

@@ -176,8 +176,8 @@ SELECT
         WHEN 'x' THEN 'EXCLUDE'
         ELSE 'UNKNOWN'
     END AS constraint_type,
-    a.attname AS column_name,
-    a.attnum AS ordinal_position,
+    COALESCE(a.attname, '') AS column_name,
+    COALESCE(a.attnum, 0) AS ordinal_position,
     COALESCE(fn.nspname, '') AS foreign_table_schema,
     COALESCE(fcl.relname, '') AS foreign_table_name,
     COALESCE(fa.attname, '') AS foreign_column_name,
@@ -663,8 +663,8 @@ SELECT
         WHEN 'x' THEN 'EXCLUDE'
         ELSE 'UNKNOWN'
     END AS constraint_type,
-    a.attname AS column_name,
-    a.attnum AS ordinal_position,
+    COALESCE(a.attname, '') AS column_name,
+    COALESCE(a.attnum, 0) AS ordinal_position,
     COALESCE(fn.nspname, '') AS foreign_table_schema,
     COALESCE(fcl.relname, '') AS foreign_table_name,
     COALESCE(fa.attname, '') AS foreign_column_name,

testdata/diff/create_trigger/add_trigger_constraint/diff.sql

@@ -0,0 +1,6 @@
+CREATE CONSTRAINT TRIGGER prevent_code_update_trigger
+    AFTER UPDATE ON products
+    DEFERRABLE INITIALLY IMMEDIATE
+    FOR EACH ROW
+    EXECUTE FUNCTION prevent_code_update();
+

testdata/diff/create_trigger/add_trigger_constraint/new.sql

@@ -0,0 +1,20 @@
+CREATE TABLE public.products (
+    id integer PRIMARY KEY,
+    code text NOT NULL
+);
+
+CREATE OR REPLACE FUNCTION public.prevent_code_update()
+RETURNS trigger AS $$
+BEGIN
+    IF OLD.code IS DISTINCT FROM NEW.code THEN
+        RAISE EXCEPTION 'Product code cannot be updated';
+    END IF;
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE CONSTRAINT TRIGGER prevent_code_update_trigger
+    AFTER UPDATE ON public.products
+    DEFERRABLE INITIALLY IMMEDIATE
+    FOR EACH ROW
+    EXECUTE FUNCTION public.prevent_code_update();

testdata/diff/create_trigger/add_trigger_constraint/old.sql

@@ -0,0 +1,14 @@
+CREATE TABLE public.products (
+    id integer PRIMARY KEY,
+    code text NOT NULL
+);
+
+CREATE OR REPLACE FUNCTION public.prevent_code_update()
+RETURNS trigger AS $$
+BEGIN
+    IF OLD.code IS DISTINCT FROM NEW.code THEN
+        RAISE EXCEPTION 'Product code cannot be updated';
+    END IF;
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;

testdata/diff/create_trigger/add_trigger_constraint/plan.json

@@ -0,0 +1,20 @@
+{
+  "version": "1.0.0",
+  "pgschema_version": "1.2.1",
+  "created_at": "1970-01-01T00:00:00Z",
+  "source_fingerprint": {
+    "hash": "08f4c7258568484a7571fb1a332a97279e6dcb5336ddbbf021d777cc1b73730d"
+  },
+  "groups": [
+    {
+      "steps": [
+        {
+          "sql": "CREATE CONSTRAINT TRIGGER prevent_code_update_trigger\n    AFTER UPDATE ON products\n    DEFERRABLE INITIALLY IMMEDIATE\n    FOR EACH ROW\n    EXECUTE FUNCTION prevent_code_update();",
+          "type": "table.trigger",
+          "operation": "create",
+          "path": "public.products.prevent_code_update_trigger"
+        }
+      ]
+    }
+  ]
+}

testdata/diff/create_trigger/add_trigger_constraint/plan.sql

@@ -0,0 +1,5 @@
+CREATE CONSTRAINT TRIGGER prevent_code_update_trigger
+    AFTER UPDATE ON products
+    DEFERRABLE INITIALLY IMMEDIATE
+    FOR EACH ROW
+    EXECUTE FUNCTION prevent_code_update();

testdata/diff/create_trigger/add_trigger_constraint/plan.txt

@@ -0,0 +1,17 @@
+Plan: 1 to modify.
+
+Summary by type:
+  tables: 1 to modify
+
+Tables:
+  ~ products
+    + prevent_code_update_trigger (trigger)
+
+DDL to be executed:
+--------------------------------------------------
+
+CREATE CONSTRAINT TRIGGER prevent_code_update_trigger
+    AFTER UPDATE ON products
+    DEFERRABLE INITIALLY IMMEDIATE
+    FOR EACH ROW
+    EXECUTE FUNCTION prevent_code_update();