@cds-pgroll/postgres

Complementary migration toolkit for @cap-js/postgres. Handles destructive DDL operations (DROP, RENAME) that CAP's schema_evolution: 'alter' cannot perform.

Why?

SAP CAP with @cap-js/postgres supports schema_evolution: 'alter' which can:

• ✅ ADD tables, ADD columns, ALTER column types

But it cannot:

• ❌ DROP tables, DROP columns
• ❌ RENAME tables, RENAME columns
• ❌ DROP NOT NULL, SET DEFAULT

@cds-pgroll/postgres fills this gap with pgroll-inspired migrations that run before CAP's cds-deploy, handling the destructive/rename DDL that CAP leaves behind.

Architecture

┌─────────────────────────────────────────────────────┐
│                  CF Deployment                       │
│                                                      │
│  1. pgroll-migrator (CF task)                       │
│     ├── Phase 1: Auto-detect CSN delta              │
│     │   Compare old cds_model with new csn.json     │
│     │   → Generate DROP operations automatically     │
│     └── Phase 2: Apply manual migration files       │
│         → Run *.json from migrations/ directory      │
│                                                      │
│  2. db-deployer (deployed-after pgroll-migrator)    │
│     └── cds-deploy --model-only                     │
│         → ADD tables, ALTER columns, update cds_model│
│                                                      │
│  3. srv (deployed-after db-deployer)                │
│     └── Application server                           │
└─────────────────────────────────────────────────────┘

Installation

npm install @cds-pgroll/postgres --save-dev

Quick Start

1. Initialize

npx cds-pgroll init

Creates a schema snapshot in migrations/.schema-snapshot.json.

2. Make schema changes

Edit db/schema.cds — remove a column, drop an entity, etc.

3. Generate migration

npx cds-pgroll generate

Interactive CLI that creates a migration JSON file in migrations/.

4. Apply locally

npx cds-pgroll apply

5. Check status

npx cds-pgroll status

Configuration

Add to your package.json:

{
  "cds-pgroll": {
    "schema": "cap_tva",
    "migrationsDir": "migrations",
    "schemaPath": "db/schema.cds",
    "dataDir": "db/data",
    "schemaEvolution": "alter"
  }
}

Or use environment variables:

• CAP_DB_SCHEMA — PostgreSQL schema name
• CAP_SCHEMA_EVOLUTION — Schema evolution mode

Migration File Format

Migration files are JSON with a name and operations array:

{
  "name": "20260311_120000_drop_payment_category",
  "operations": [
    {
      "drop_column": {
        "table": "CAP_TVA_DB_FINANCIALDOCUMENTS",
        "column": "paymentcategory",
        "down": "SELECT NULL"
      }
    }
  ]
}

Supported Operations

Operation	Description	Example
drop_column	Remove a column	{ "table": "T", "column": "C", "down": "SELECT NULL" }
drop_table	Remove a table	{ "table": "T" }
rename_column	Rename a column	{ "table": "T", "from": "old", "to": "new" }
rename_table	Rename a table	{ "from": "OLD_T", "to": "NEW_T" }
alter_column	Change column type	{ "table": "T", "column": "C", "type": "VARCHAR(500)", "up": "CAST...", "down": "CAST..." }
add_column	Add a column	{ "table": "T", "column": { "name": "C", "type": "VARCHAR(100)" } }
set_not_null	Add NOT NULL	{ "table": "T", "column": "C" }
drop_not_null	Remove NOT NULL	{ "table": "T", "column": "C" }
set_default	Set default value	{ "table": "T", "column": "C", "default": "'value'" }
drop_default	Remove default	{ "table": "T", "column": "C" }
create_table	Create a table	{ "table": "T", "columns": [...], "data": [...] }
raw_sql	Raw SQL statement	{ "up": "CREATE INDEX ...", "down": "DROP INDEX ..." }

MTA Integration

For Cloud Foundry deployments, add a pgroll-migrator module to your mta.yaml. See examples/mta-module.yaml for a complete example.

Key points:

1. Add npx cds-pgroll prepare to before-all build commands
2. Copy migration files to gen/migrations/ during build
3. Set deployed-after on db-deployer to ensure correct ordering
4. Use --model-only flag for cds-deploy so CAP doesn't attempt DDL

Build Commands

build-parameters:
  before-all:
    - builder: custom
      commands:
        - npm ci
        - npx cds build --production
        - npx cds-pgroll prepare
        - 'sed -i ''s/"start": "cds-deploy"/"start": "cds-deploy --model-only"/'' gen/pg/package.json'
        - mkdir -p gen/migrations
        - cp migrations/package.json gen/migrations/
        - cp migrations/run-pgroll.js gen/migrations/
        - bash -c "cp migrations/*.json gen/migrations/ 2>/dev/null; exit 0"
        - cp gen/pg/db/csn.json gen/migrations/csn.json

API Reference

Core Functions

const {
  // Type mapping
  cdsTypeToSql,        // Convert CDS type to PostgreSQL type
  
  // Naming
  entityToTableName,   // CDS entity → PG table name
  quoteIdent,          // Safe SQL identifier quoting
  
  // Operations
  applyOperation,      // Execute a pgroll operation against PG
  tableExists,         // Check if table exists
  columnExists,        // Check if column exists
  
  // CSN comparison
  detectSchemaChanges, // Compare CSNs for destructive changes
  parseStoredCSN,      // Parse CSN from cds_model TEXT column
  
  // SQL helpers
  PgRollSql,           // Migration tracking (init, record, query)
  
  // High-level
  runMigrations,       // Full 2-phase pipeline
  generate,            // Interactive migration generator
  prepareDeployer,     // Prepare gen/pg for deployment
} = require('@cds-pgroll/postgres');

PgRollSql Class

const { PgRollSql } = require('@cds-pgroll/postgres');
const { Client } = require('pg');

const client = new Client({ /* connection config */ });
await client.connect();

const sql = new PgRollSql(client, 'cap_tva');
await sql.initializeSchema();

// Query migrations
const migrations = await sql.getMigrations();
const pending = await sql.getPendingMigrations(['file1', 'file2']);
const health = await sql.healthCheck();

// Record a migration
await sql.recordMigration('my_migration', [{ drop_table: { table: 'T' } }]);

CDS Type Mapping

CDS Type	PostgreSQL Type
cds.UUID	VARCHAR(36)
cds.String	VARCHAR(length) or VARCHAR(5000)
cds.LargeString	TEXT
cds.Integer	INTEGER
cds.Integer64	BIGINT
cds.Decimal	DECIMAL(p,s) or DECIMAL
cds.Double	FLOAT8
cds.Boolean	BOOLEAN
cds.Date	DATE
cds.Time	TIME
cds.DateTime	TIMESTAMP
cds.Timestamp	TIMESTAMP
cds.Binary	BYTEA
cds.LargeBinary	BYTEA

How It Differs from pgroll

This is not the pgroll binary. It is a lightweight, CDS-aware migration runner that borrows pgroll's JSON operation format. Key differences:

• No expand/contract pattern (CAP handles schema evolution)
• No shadow columns or views
• Direct DDL execution with proper identifier quoting
• Integrated CSN delta detection
• CDS type system awareness

License

MIT