Simple SQLite migration for Swift with the SQLite.swift framework

MigrationCreateItems.swift

//
//  MigrationCreateItems.swift
//  Stash
//
//  Created by Andrew C on 8/30/17.
//  Copyright © 2017 Andrew Crookston. All rights reserved.
//  License: MIT
//

import Foundation
import SQLite

final class MigrationCreateItems: SQLiteMigration {
    static let name: String = "create_items"

    static func migrate(connection: Connection) -> Bool {
        do {
            try connection.run(Table(Item.tableName).create { t in
                t.column(Expression<Int64>("id"), primaryKey: .autoincrement)
                t.column(Expression<String>("uid"), unique: true)
                t.column(Expression<Int64>("type"))
                t.column(Expression<String>("content"))
                t.column(Expression<String?>("notes"))
                t.column(Expression<String?>("metadata"))
            })
            return true
        } catch {
            print("#DB MIGRATION ERROR: \(error)")
            return false
        }
    }
}

SQLiteMigration.swift

//
//  SQLiteMigration.swift
//  Stash
//
//  Created by Andrew C on 8/30/17.
//  Copyright © 2017 Andrew Crookston. All rights reserved.
//  License: MIT
//

import Foundation
import SQLite

protocol SQLiteMigration {
    static var name: String { get }
    static func migrate(connection: Connection) -> Bool
}

final class SQLiteMigrator {

    static func register(_ migration: SQLiteMigration.Type) {
        sharedInstance.migrations.append(migration)
    }

    static func register(_ migrations: [SQLiteMigration.Type]) {
        sharedInstance.migrations.append(contentsOf: migrations)
    }

    @discardableResult static func migrate(_ connection: Connection) -> Bool {
        return sharedInstance.migrate(connection)
    }

    // MARK: - private

    private static let schemaTable = Table("db_schema_migration")

    private static let sharedInstance = SQLiteMigrator()

    private var migrations = [SQLiteMigration.Type]()
    private lazy var completed = [String]()


    private init() {}

    private func migrate(connection: Connection, migration: SQLiteMigration.Type) -> Bool {
        print("#DB CHECKING MIGRATION: \(migration.name)")
        if !hasMigrated(migration: migration) {
            print("#DB MIGRATING: \(migration.name)")
            if migration.migrate(connection: connection) {
                completed(migration: migration, connection: connection)
                return true
            }
            return true
        }
        return false
    }

    private func completed(migration: SQLiteMigration.Type, connection: Connection) {
        completed.append(migration.name)

        let name = Expression<String>("name")
        do {
            let insert = SQLiteMigrator.schemaTable.insert(name <- migration.self.name)
            try connection.run(insert)
        } catch {
            print("#DB SAVE MIGRATED ERROR: \(error)")
        }
    }

    private func hasMigrated(migration: SQLiteMigration.Type) -> Bool {
        return completed.contains(migration.name)
    }

    private func setup(connection: Connection) {
        createSchema(connection: connection)
        completed = loadMigrations(connection: connection)
    }

    private func loadMigrations(connection: Connection) -> [String] {
        var migrations = [String]()
        let name = Expression<String>("name")
        do {
            for migration in try connection.prepare(SQLiteMigrator.schemaTable) {
                migrations.append(migration[name])
            }
        } catch {
            print("#DB LOAD MIGRATIONS ERROR: \(error)")
        }
        return migrations
    }

    @discardableResult private func createSchema(connection: Connection) -> Bool {
        do {
            try connection.run(SQLiteMigrator.schemaTable.create(ifNotExists: true) { t in
                t.column(Expression<String>("name"), unique: true)
            })
            return true
        } catch {
            print("#DB MIGRATION ERROR: \(error)")
            return false
        }
    }

    private func migrate(_ connection: Connection) -> Bool {
        setup(connection: connection)
        for migration in migrations {
            if !migrate(connection: connection, migration: migration) {
                return false
            }
        }
        return true
    }
}

usage.swift

// After creating a db connection:
SQLiteMigrator.register(MigrationCreateItems.self)
SQLiteMigrator.migrate(connection)