Skip to main content

Seeding Data with reusing existing business logic in ASP

Problem

There might be situations, when you need to seed some data with keeping the business logic in mind. Applying business logic and versioning of SQL migration scripts can be time-consuming. We should not forget about it would be great to be able to trace back the changes done in the database.

Examples

  • * You got a legacy project with a db schema you know you will need to modify during your upcoming implementations. You also know that, you will need to move some data from one table to another by applying business logic to it just before the app starts up for the first time with the latest migrations.

  • * You have a missing feature in your system, and you have a repetitive data manipulation (inject) task. For example, you need to modify user access controlled via db tables, because you do not have a UI, feature in the app to do so.
    You also would like to apply the business logic regarding the User Access of the project and you also would like to be able to trace back who modified user data and when?

Please note that, you should not face with these problems. Instead of trying to patch problems like this, it worth to plan ahead and prepare for these kind of problems in the start.

Solution

I will introduce you a package, that can help you in solving out these problems: 

This package helps you to seed data with accessing the IoC container of the application.

You can seed the data with using the existing business logic already composed in your solution and access it later in the IoC of your app. All you need to do is sipmly to register ISeed implementations to your ServiceCollection. Later on, you can see which seeds have been run via the sdr.SeederHistories table.

How to use?

  1. Register your ISeed implementations with the Extensions.RegisterDataSeeder<>
    • Here goes your implementations of ISeed
  2. Register this project's tools and services via the Extensions.RegisterDataSeederServices
    • It is needed to use this project's tools
  3. Replace the IHost.StartAsync with Extensions.MigrateThenRunAsync
    • It is needed to be able to run the ISeed with BeforeAppStart option
    • It is needed to ensure the SeederHistories table got migrated

The example is from the AJProds.EFDataSeeder.Tests.Console project

class Program
{
    public const string CONNECTION_LOCAL_TEST =
    @"Server=localhost\SQLEXPRESS;Initial Catalog=SeederTest;Trusted_Connection=True;MultipleActiveResultSets=true";
    
    static async Task Main(string[] args)
    {
        await Host.CreateDefaultBuilder()
                  .ConfigureServices(ConfigureServices())
                  .Build()
                  .MigrateThenRunAsync(provider =>
                                           // Ensure the TestDbContext's migration is run on start
                                           provider.GetRequiredService<TestDbContext>()
                                                   .Database.MigrateAsync());
    }
    
    private static Action<IServiceCollection> ConfigureServices()
    {
        return collection =>
               {
                   // Register seeders
                   collection.RegisterDataSeeder<AlwaysRunTestSeed>();
                   
                   // My own, custom, test setup
                   collection.AddDbContext<TestDbContext>(builder => builder
                                                             .UseSqlServer(CONNECTION_LOCAL_TEST));
    
                   // EFSeeder setup - with an own EF Migration History table
                   collection.RegisterDataSeederServices(builder =>
                                                         {
                                                             builder
                                                                .UseSqlServer(CONNECTION_LOCAL_TEST);
                                                         });
               };
    }
    
    /// <summary>
    /// My custom seed, that will run after all app start
    /// </summary>
    public class AlwaysRunTestSeed: ISeed
    {
        private readonly TestDbContext _dbContext;

        public int Priority => 50;

        public string SeedName => "Always Run seed";

        public SeedMode Mode => SeedMode.AfterAppStart;

        public bool AlwaysRun => true;

        public AlwaysRunTestSeed(TestDbContext dbContext)
        {
            _dbContext = dbContext;
        }
        
        public async Task SeedAsync()
        {
            _dbContext.Testees.Add(new Testee
                                   {
                                       Description = "Always Run seed"
                                   });

            await _dbContext.SaveChangesAsync();
        }
    }
}
You can define when the ISeed implementations should run:
SeedMode.None
No ISeed logic will be run. You need to find the BaseSeederManager in your ioc and run it with the SeedMode.None argument.
var baseSeederManager = provider.GetRequiredService<BaseSeederManager>();
baseSeederManager.Seed(SeedMode.None);
SeedMode.BeforeAppStart
You must use the Extensions.MigrateThenRunAsync with your HostBuilder, because this procedure will not start up the host until all migration and seed (with SeedMode.BeforeAppStart) has been run successfully.
await Host.CreateDefaultBuilder()
          .ConfigureServices(ConfigureServices())
          .Build()
          .MigrateThenRunAsync();
SeedMode.AfterAppStart
After the host has started successfully, those ISeed classes, that have been set to run AfterAppStart will run in the background, in an IHostedService.
ISeed.RunAlways => true
You can re-run the ISeed procedures every time, when the application starts up. Simply set the RunAlways property to true in your ISeed implementation.



Comments

Post a Comment