schemer-migrations

Schemer Migrations (New Package)

This example demonstrates the new database/schemer package, which provides a cleaner API for managing database schema migrations with automatic schema injection and tracking.

Features Demonstrated

New Schemer Package

• Simplified API: No need to manually register migrations with schema
• Automatic Schema Injection: Schema is automatically injected into each migration
• Context Support: All operations support context for cancellation and timeout handling
• Clean Interface Naming: Uses SchemerInterface and SchemerImplementation pattern
• Flexible Migration Addition: Add migrations individually or in batches
• Migration Tracking: Automatically tracks executed migrations in migration_tracker table
• Advanced Rollback: Support for rolling back by steps or by batch

Migration Operations

• Creating tables with various column types
• Adding indexes to existing tables
• Adding columns to existing tables
• Rolling back migrations (single, by steps, or by batch)
• Migration status checking
• Fresh and reset operations

Advantages Over Old System

1. No Manual Registration: No need to call schema.Register()
2. Simpler API: Pass neat db instance directly instead of separate schema and orm
3. Auto-injection: Schema is automatically injected into migrations
4. Context Support: All operations support context for proper cancellation/timeout handling
5. Clear Rollback Methods: RollbackSteps() and RollbackToBatch() instead of confusing parameters
6. Auto-creation: Automatically creates migration_tracker table on first run
7. Better Organization: Clear separation between schema building and migration execution

Running the Example

cd examples/schemer-migrations
go run main.go

This will:

1. Create a SQLite database (example_schema_migrations.db)
2. Run all migrations using the new schemer package
3. Demonstrate rolling back the last migration
4. Show migration status

Migration Structure

Each migration follows the same pattern as before, but now uses the schemer package for execution:

type CreateUsersTable struct {
    schema.BaseMigration
}

func (m *CreateUsersTable) Signature() string {
    return "2024_06_15_120000_create_users_table"
}

func (m *CreateUsersTable) Description() string {
    return "Creates users table"
}

func (m *CreateUsersTable) Up() error {
    return m.GetSchema().Create("users", func(blueprint contractsschema.Blueprint) {
        blueprint.ID()
        blueprint.String("name")
        blueprint.String("email")
        blueprint.Unique("email")
        blueprint.Timestamps()
    })
}

func (m *CreateUsersTable) Down() error {
    return m.GetSchema().DropIfExists("users")
}

Usage Pattern

// Create schemer instance with neat db
schemer := schemer.NewSchemer(db)

// Add migrations
schemer.AddMigration(&CreateUsersTable{})
schemer.AddMigration(&CreatePostsTable{})

// Or add multiple at once
schemer.AddMigrations([]contractsschema.MigrationInterface{
    &CreateUsersTable{},
    &CreatePostsTable{},
})

// Run migrations
ctx := context.Background()
if err := schemer.Up(ctx); err != nil {
    log.Fatal(err)
}

// Rollback last migration
if err := schemer.Down(ctx); err != nil {
    log.Fatal(err)
}

// Check status
status, err := schemer.Status()

API Methods

AddMigration

Adds a single migration to the schemer instance.

AddMigrations

Adds multiple migrations at once.

Up

Runs all pending migrations. Automatically creates the migration_tracker table if it doesn't exist.

Down

Rolls back the last migration.

RollbackSteps

Rolls back the specified number of migrations.

RollbackToBatch

Rolls back all migrations to the specified batch.

Status

Returns the current status of all migrations.

Fresh

Drops all tables except migration_tracker and clears the tracker.

Reset

Rolls back all migrations.

Migration Tracking

The schemer automatically tracks migrations in a migration_tracker table with the following structure:

type MigrationTracker struct {
    ID          string    // Migration signature
    Batch       int       // Batch number (timestamp)
    Description string    // Migration description
    StartedAt   time.Time // When migration started
    CompletedAt time.Time // When migration finished
}

Best Practices

1. Migration Naming: Use timestamp-based signatures for ordering

   "2024_06_15_120000_create_users_table"
   

2. Idempotent Up Methods: Check if resources exist before creating

   func (m *CreateUsersTable) Up() error {
       if m.GetSchema().HasTable("users") {
           return nil
       }
       // Create table
   }
   

3. Context Usage: Always use context for production applications

   ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
   defer cancel()
   err := schemer.Up(ctx)
   

Migration from Old System

Before (Old System):

schema := db.Schema()
schema.Register(migrations)
manager := schema.NewMigrationManager(db)
manager.Run(migrations)

After (New Schemer Package):

schemer := schemer.NewSchemer(db)
schemer.AddMigrations(migrations)
schemer.Up(context.Background())

Testing

Run the tests with:

cd examples/schemer-migrations
go test -v

Prerequisites

• SQLite database (or modify the DSN to use your preferred database)
• Neat ORM with schemer package support

Related Documentation

• Schemer Package README
• Schemer Package Proposal