Allow setting the ON DELETE behaviour of foreign key constraints (#297

)

Add support for setting the `ON DELETE` behaviour of a foreign key
constraint.

An example migration that uses the behaviour is:

```json
{
  "name": "21_add_foreign_key_constraint",
  "operations": [
    {
      "alter_column": {
        "table": "posts",
        "column": "user_id",
        "references": {
          "name": "fk_users_id",
          "table": "users",
          "column": "id",
          "on_delete": "CASCADE"
        },
        "up": "(SELECT CASE WHEN EXISTS (SELECT 1 FROM users WHERE users.id = user_id) THEN user_id ELSE NULL END)",
        "down": "user_id"
      }
    }
  ]
}
```

The valid options for `on_delete` are `CASCADE`, `SET NULL`, `RESTRICT`,
or `NO ACTION`. If the field is omitted, the default is `NO ACTION`,

Fixes #221

docs/README.md

@@ -816,7 +816,8 @@ Add foreign key operations add a foreign key constraint to a column.
     "references": {
       "name": "name of foreign key reference",
       "table": "name of referenced table",
-      "column": "name of referenced column"
+      "column": "name of referenced column",
+      "on_delete": "ON DELETE behaviour, can be CASCADE, SET NULL, RESTRICT, or NO ACTION. Default is NO ACTION",
     },
     "up": "SQL expression",
     "down": "SQL expression"

examples/21_add_foreign_key_constraint.json

@@ -8,7 +8,8 @@
         "references": {
           "name": "fk_users_id",
           "table": "users",
-          "column": "id"
+          "column": "id",
+          "on_delete": "CASCADE"
         },
         "up": "(SELECT CASE WHEN EXISTS (SELECT 1 FROM users WHERE users.id = user_id) THEN user_id ELSE NULL END)",
         "down": "user_id"

pkg/migrations/errors.go

@@ -173,3 +173,22 @@ type InvalidReplicaIdentityError struct {
 func (e InvalidReplicaIdentityError) Error() string {
 	return fmt.Sprintf("replica identity on table %q must be one of 'NOTHING', 'DEFAULT', 'INDEX' or 'FULL', found %q", e.Table, e.Identity)
 }
+
+type InvalidOnDeleteSettingError struct {
+	Table   string
+	Column  string
+	Setting string
+}
+
+func (e InvalidOnDeleteSettingError) Error() string {
+	return fmt.Sprintf("foreign key on_delete setting on column %q, table %q must be one of: %q, %q, %q, %q or %q, not %q",
+		e.Column,
+		e.Table,
+		ForeignKeyReferenceOnDeleteNOACTION,
+		ForeignKeyReferenceOnDeleteRESTRICT,
+		ForeignKeyReferenceOnDeleteSETDEFAULT,
+		ForeignKeyReferenceOnDeleteSETNULL,
+		ForeignKeyReferenceOnDeleteCASCADE,
+		e.Setting,
+	)
+}

pkg/migrations/op_common_test.go

@@ -565,6 +565,24 @@ func MustDelete(t *testing.T, db *sql.DB, schema, version, table string, record
 	}
 }
 
+func MustNotDelete(t *testing.T, db *sql.DB, schema, version, table string, record map[string]string, errorCode string) {
+	t.Helper()
+
+	err := delete(t, db, schema, version, table, record)
+	if err == nil {
+		t.Fatal("Expected DELETE to fail")
+	}
+
+	var pqErr *pq.Error
+	if ok := errors.As(err, &pqErr); ok {
+		if pqErr.Code.Name() != errorCode {
+			t.Fatalf("Expected DELETE to fail with %q, got %q", errorCode, pqErr.Code.Name())
+		}
+	} else {
+		t.Fatalf("DELETE failed with unknown error: %v", err)
+	}
+}
+
 func delete(t *testing.T, db *sql.DB, schema, version, table string, record map[string]string) error {
 	t.Helper()
 	versionSchema := roll.VersionedSchemaName(schema, version)

pkg/migrations/op_set_fk.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"strings"
 
 	"github.com/lib/pq"
 	"github.com/xataio/pgroll/pkg/schema"
@@ -160,19 +161,38 @@ func (o *OpSetForeignKey) Validate(ctx context.Context, s *schema.Schema) error
 		return FieldRequiredError{Name: "down"}
 	}
 
+	switch strings.ToUpper(string(o.References.OnDelete)) {
+	case string(ForeignKeyReferenceOnDeleteNOACTION):
+	case string(ForeignKeyReferenceOnDeleteRESTRICT):
+	case string(ForeignKeyReferenceOnDeleteSETDEFAULT):
+	case string(ForeignKeyReferenceOnDeleteSETNULL):
+	case string(ForeignKeyReferenceOnDeleteCASCADE):
+	case "":
+		break
+	default:
+		return InvalidOnDeleteSettingError{Table: o.Table, Column: o.Column, Setting: string(o.References.OnDelete)}
+	}
+
 	return nil
 }
 
 func (o *OpSetForeignKey) addForeignKeyConstraint(ctx context.Context, conn *sql.DB) error {
 	tempColumnName := TemporaryName(o.Column)
 
-	_, err := conn.ExecContext(ctx, fmt.Sprintf("ALTER TABLE %s ADD CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s (%s) NOT VALID",
-		pq.QuoteIdentifier(o.Table),
-		pq.QuoteIdentifier(o.References.Name),
-		pq.QuoteIdentifier(tempColumnName),
-		pq.QuoteIdentifier(o.References.Table),
-		pq.QuoteIdentifier(o.References.Column),
-	))
+	onDelete := "NO ACTION"
+	if o.References.OnDelete != "" {
+		onDelete = strings.ToUpper(string(o.References.OnDelete))
+	}
+
+	_, err := conn.ExecContext(ctx,
+		fmt.Sprintf("ALTER TABLE %s ADD CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s (%s) ON DELETE %s NOT VALID",
+			pq.QuoteIdentifier(o.Table),
+			pq.QuoteIdentifier(o.References.Name),
+			pq.QuoteIdentifier(tempColumnName),
+			pq.QuoteIdentifier(o.References.Table),
+			pq.QuoteIdentifier(o.References.Column),
+			onDelete,
+		))
 
 	return err
 }