Database Migrations With Vapor

Seeding Data Using Migrations

Migrations are useful for more than just changing the structure of your database.

You can also use them to seed data, such as a list of general categories, or some example data to use in your front end or unit tests.

So, time for you to write your last migration.

Add a new file in the migrations folder named 21-06-03_Tool+Seed.swift and paste the following:

import FluentKit

extension Tool {
  struct Seed: Migration {
    func prepare(on database: Database) -> EventLoopFuture<Void> {
      // 1
      let tools: [Tool] = [
        .init(name: "Hammer", maker: nil),
        .init(name: "Food Processor", maker: "Bosch"),
        .init(name: "Zigsaw", maker: "Makita")
      ]
      // 2
      return tools.map { tool in
        tool.save(on: database)
      }
      .flatten(on: database.eventLoop)
    }

    func revert(on database: Database) -> EventLoopFuture<Void> {
      // 3
      Tool.query(on: database).delete()
    }
  }
}

Here, you:

1. Create a list of three tools, two of which have a maker.
2. Map over the three tools and save each one to the database.
3. Delete all records in tools on revert.

Next, register the migration in configure.swift below the other migrations:

app.migrations.add(Tool.Seed())

Finally, build and run your migration. Then open the tools table in Postico.

Postico view of the tools table after the seed migration runs. It now has three tools.

You can see that the table now has three tools in it.

Where to Go From Here?

Download the completed project files by clicking the Download Materials button at the top or bottom of the tutorial.

In this article, you learned the basics of what a migration is and why you should use migrations to configure your database. You also learned most of the common migration options you'll use in your own apps.

If you want to learn more about migrations, check out Server-Side Swift with Vapor or the official Vapor documentation.

If you're looking for a challenge beyond this tutorial, here are a few things you can try:

• Create a REST API to interact with your app.
• Add a type to the Tool entity (using an Enum).
• Add a quantity property to the Tool entity with a default value of 1.
• Introduce a new Loan entity so you can keep track of which friend borrowed what tool. Remember to set references up correctly in the database!

We hope you enjoyed this tutorial! If you have any questions or comments, please join the forum discussion below!