Manage your database schema

Use Data Definition Language (DDL) to create and update database objects (such as tables and indexes) in your provisioned SQL database. Forge SQL supports MySQL-compatible DDL operations like CREATE, ALTER, and DROP (for more details, see SQL Statement Overview in the TiDB documentation).

You can create as many DDL operations as needed. Forge SQL can use scheduledTrigger to execute each operation on each provisioned SQL database in the sequence you specify.

You can also update your app’s database schema by adding new DDL operations over time. Forge SQL can:

1. Track which operations have already been executed on any installation of your app.
2. Track failed DDL operations, and re-run them later.
3. Migrate data between old and new database schemas.

Before you begin

The sql package provides the necessary methods for interacting with Forge SQL. To start using Forge SQL’s capabilities, you’ll need to install it in your project:

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npm install @forge/sql

You'll need the migrationRunner SDK to execute DDL operations. To import it:

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import migrationRunner from `@forge/sql` ; 

Define schema updates

Use DDL operations to create and update each database object in your schema. Use the migrationRunner.enqueue method to queue these operations in the order they should be executed. This method accepts a list of ordered DDL operations, with each one defined as a key/value pair consisting of:

• a unique operationName
• a pre-defined DDL function

Example

The following snippet defines two DDL operations, CREATE_USERS_TABLE and CREATE_BOOKS_TABLE, both of which create tables for our provisioned database.

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import { migrationRunner } from '@forge/sql';

export const CREATE_USERS_TABLE = `CREATE TABLE IF NOT EXISTS Users (
    user_id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(100) NOT NULL,
    email VARCHAR(100) UNIQUE NOT NULL,
)`;

export const CREATE_BOOKS_TABLE = `CREATE TABLE IF NOT EXISTS Books (
    book_id INT PRIMARY KEY AUTO_INCREMENT,
    title VARCHAR(200) NOT NULL,
    author VARCHAR(100) NOT NULL,
    published_date DATE
)`;

To invoke both DDL operations through migrationRunner.enqueue, assign an operationName to each one (v001_create_users_table and v002_create_books_table):

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const createDBobjects = migrationRunner
  .enqueue('v001_create_users_table', CREATE_USERS_TABLE)
  .enqueue('v002_create_books_table', CREATE_BOOKS_TABLE)

Next, wrap createDBobjects in a single database object creation function (runMigration). This will let you map its key to a scheduled trigger, which Forge will use to execute it (this is covered in the next section):

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export const runMigration = async () => {
  try {
    await applyMigrations();
  };

export const applyMigrations = async () => {
  const migrationsRun = await createDBobjects.run();
};

Orchestrate schema updates

Database object creation (that is, your DDL operations) needs to be executed as part of the app installation process. One way to orchestrate this is through scheduled triggers. Doing so assigns the entire lifecycle of creating your database objects to Forge SQL.

Map your database object creation function to a scheduled trigger module in your manifest. Forge will use the trigger to execute your migrationRunner invocation according to your defined interval (we recommend hourly or daily).

Example

The following declaration triggers the runMigration function from the previous example:

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modules:
  scheduledTrigger:
    - key: my-db-schema
      function: runMigration
      interval: hour 
  function:
    - key: runMigration
      handler: index.trigger

Here, Forge will execute runMigration within the hour after app installation. As such, it is possible for customers to have your app already installed, without the database schema applied yet.

Forge SQL will check each app installation hourly if there are any failed or pending DDL functions (tracking them based on their operationName). Forge SQL will run pending DDL functions and re-run failed ones.

Log schema updates

The migrationRunner.list method lists all the DDL operations you queued (through migrationRunner.enqueue), along with the status of each one. Use it to generate logs for your database object creation function; this will allow you to track its progress for each app installation.

Use your app logs in the Developer Console to view these generated logs. From there, you can filter for errors against your database object creation function.

Example

The following snippet expands on our earlier example by adding a migrationRunner.list invocation to create logs for the runMigration function:

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export const applyMigrations = async () => {
  const migrationsRun = await createDBobjects.run();

  console.log('Migrations checkpoint [after running migrations]:');
  await migrationRunner
    .list()
    .then((migration) => migration.map((y) => console.log(`${y.name} migrated at ${y.migratedAt.toUTCString()}`)));
  };

Monitoring

You can inspect each installation's SQL database schema through the developer console. The developer console can display:

• Which schema updates have already been applied
• The databae objects present in the current schema.

See Monitoring SQL for more information.

Recommendations

• Your app should only have one migrationRunner invocation.

• Ensure that each change to your SQL database is backwards compatible to all schema versions that are currently in use. Every DDL operation you define should introduce schema changes that won’t block data migrations from previous versions.

• Likewise, each SQL database change should be compatible to all versions of your app currently installed on a customer site. This means, for example, that every SQL query used by previous versions of your app should also work in the latest version of your SQL database.

• Avoid destructive changes to your SQL database, as these risk breaking compatibility between database schema versions.