fix: add schema qualifier to cross-schema foreign key references (#94)

internal/diff/constraint.go

@@ -8,7 +8,7 @@ import (
 )
 
 // generateConstraintSQL generates constraint definition for inline table constraints
-func generateConstraintSQL(constraint *ir.Constraint, _ string) string {
+func generateConstraintSQL(constraint *ir.Constraint, targetSchema string) string {
 	// Helper function to get column names from ConstraintColumn array
 	getColumnNames := func(columns []*ir.ConstraintColumn) []string {
 		var names []string
@@ -27,10 +27,12 @@ func generateConstraintSQL(constraint *ir.Constraint, _ string) string {
 		return fmt.Sprintf("CONSTRAINT %s UNIQUE (%s)", constraint.Name, strings.Join(getColumnNames(constraint.Columns), ", "))
 	case ir.ConstraintTypeForeignKey:
 		// Always include CONSTRAINT name to preserve explicit FK names
+		// Use QualifyEntityNameWithQuotes to add schema qualifier when referencing tables in other schemas
+		qualifiedRefTable := ir.QualifyEntityNameWithQuotes(constraint.ReferencedSchema, constraint.ReferencedTable, targetSchema)
 		stmt := fmt.Sprintf("CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s (%s)",
 			constraint.Name,
 			strings.Join(getColumnNames(constraint.Columns), ", "),
-			ir.QuoteIdentifier(constraint.ReferencedTable), strings.Join(getColumnNames(constraint.ReferencedColumns), ", "))
+			qualifiedRefTable, strings.Join(getColumnNames(constraint.ReferencedColumns), ", "))
 		// Only add ON UPDATE/DELETE if they are not the default "NO ACTION"
 		if constraint.UpdateRule != "" && constraint.UpdateRule != "NO ACTION" {
 			stmt += fmt.Sprintf(" ON UPDATE %s", constraint.UpdateRule)

internal/diff/identifier_quote_test.go

@@ -44,6 +44,7 @@ func TestGenerateConstraintSQL_WithQuoting(t *testing.T) {
 				Columns: []*ir.ConstraintColumn{
 					{Name: "userId", Position: 1},
 				},
+				ReferencedSchema: "public",
 				ReferencedTable: "users",
 				ReferencedColumns: []*ir.ConstraintColumn{
 					{Name: "id", Position: 1},
@@ -65,11 +66,33 @@ func TestGenerateConstraintSQL_WithQuoting(t *testing.T) {
 			},
 			want: `CONSTRAINT test_unique_lower UNIQUE (email, username)`,
 		},
+		{
+			name: "FOREIGN KEY with cross-schema reference",
+			constraint: &ir.Constraint{
+				Name: "test_cross_schema_fk",
+				Type: ir.ConstraintTypeForeignKey,
+				Columns: []*ir.ConstraintColumn{
+					{Name: "category_id", Position: 1},
+				},
+				ReferencedSchema: "public",
+				ReferencedTable: "categories",
+				ReferencedColumns: []*ir.ConstraintColumn{
+					{Name: "id", Position: 1},
+				},
+				IsValid: true,
+			},
+			want: `CONSTRAINT test_cross_schema_fk FOREIGN KEY (category_id) REFERENCES public.categories (id)`,
+		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got := generateConstraintSQL(tt.constraint, "public")
+			// Use "tenant1" as target schema for cross-schema FK test, "public" for others
+			targetSchema := "public"
+			if tt.name == "FOREIGN KEY with cross-schema reference" {
+				targetSchema = "tenant1"
+			}
+			got := generateConstraintSQL(tt.constraint, targetSchema)
 			if got != tt.want {
 				t.Errorf("generateConstraintSQL() = %q, want %q", got, tt.want)
 			}

testdata/dump/tenant/pgschema.sql

@@ -35,9 +35,11 @@ CREATE TABLE IF NOT EXISTS posts (
     title varchar(200) NOT NULL,
     content text,
     author_id integer,
+    category_id integer NOT NULL,
     status public.status DEFAULT 'active',
     created_at timestamp DEFAULT now(),
     CONSTRAINT posts_pkey PRIMARY KEY (id),
-    CONSTRAINT posts_author_id_fkey FOREIGN KEY (author_id) REFERENCES users (id)
+    CONSTRAINT posts_author_id_fkey FOREIGN KEY (author_id) REFERENCES users (id),
+    CONSTRAINT posts_category_id_fkey FOREIGN KEY (category_id) REFERENCES public.categories (id)
 );
 

testdata/dump/tenant/public.sql

@@ -1,2 +1,11 @@
 CREATE TYPE public.user_role AS ENUM ('admin', 'user');
 CREATE TYPE public.status AS ENUM ('active', 'inactive');
+
+--
+-- Shared table in public schema that tenant schemas will reference
+--
+CREATE TABLE public.categories (
+    id SERIAL PRIMARY KEY,
+    name varchar(100) NOT NULL UNIQUE,
+    description text
+);