New migration handler that came in v4.3.0

BookStoreTenantDatabaseMigrationHandler.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using Volo.Abp.Data;
using Volo.Abp.DependencyInjection;
using Volo.Abp.EventBus.Distributed;
using Volo.Abp.Identity;
using Volo.Abp.MultiTenancy;
using Volo.Abp.Uow;

namespace Acme.BookStore.Data
{
    public class MyProjectNameTenantDatabaseMigrationHandler :
        IDistributedEventHandler<TenantCreatedEto>,
        IDistributedEventHandler<TenantConnectionStringUpdatedEto>,
        IDistributedEventHandler<ApplyDatabaseMigrationsEto>,
        ITransientDependency
    {
        private readonly IEnumerable<IMyProjectNameDbSchemaMigrator> _dbSchemaMigrators;
        private readonly ICurrentTenant _currentTenant;
        private readonly IUnitOfWorkManager _unitOfWorkManager;
        private readonly IDataSeeder _dataSeeder;
        private readonly ITenantStore _tenantStore;
        private readonly ILogger<MyProjectNameTenantDatabaseMigrationHandler> _logger;

        public MyProjectNameTenantDatabaseMigrationHandler(
            IEnumerable<IMyProjectNameDbSchemaMigrator> dbSchemaMigrators,
            ICurrentTenant currentTenant,
            IUnitOfWorkManager unitOfWorkManager,
            IDataSeeder dataSeeder,
            ITenantStore tenantStore,
            ILogger<MyProjectNameTenantDatabaseMigrationHandler> logger)
        {
            _dbSchemaMigrators = dbSchemaMigrators;
            _currentTenant = currentTenant;
            _unitOfWorkManager = unitOfWorkManager;
            _dataSeeder = dataSeeder;
            _tenantStore = tenantStore;
            _logger = logger;
        }

        public async Task HandleEventAsync(TenantCreatedEto eventData)
        {
            await MigrateAndSeedForTenantAsync(
                eventData.Id,
                eventData.Properties.GetOrDefault("AdminEmail") ?? MyProjectNameConsts.AdminEmailDefaultValue,
                eventData.Properties.GetOrDefault("AdminPassword") ?? MyProjectNameConsts.AdminPasswordDefaultValue
            );
        }

        public async Task HandleEventAsync(TenantConnectionStringUpdatedEto eventData)
        {
            if (eventData.ConnectionStringName != ConnectionStrings.DefaultConnectionStringName ||
                eventData.NewValue.IsNullOrWhiteSpace())
            {
                return;
            }

            await MigrateAndSeedForTenantAsync(
                eventData.Id,
                MyProjectNameConsts.AdminEmailDefaultValue,
                MyProjectNameConsts.AdminPasswordDefaultValue
            );

            /* You may want to move your data from the old database to the new database!
             * It is up to you. If you don't make it, new database will be empty
             * (and tenant's admin password is reset to 1q2w3E*).
             */
        }

        public async Task HandleEventAsync(ApplyDatabaseMigrationsEto eventData)
        {
            if (eventData.TenantId == null)
            {
                return;
            }

            await MigrateAndSeedForTenantAsync(
                eventData.TenantId.Value,
                MyProjectNameConsts.AdminEmailDefaultValue,
                MyProjectNameConsts.AdminPasswordDefaultValue
            );
        }

        private async Task MigrateAndSeedForTenantAsync(
            Guid tenantId,
            string adminEmail,
            string adminPassword)
        {
            try
            {
                using (_currentTenant.Change(tenantId))
                {
                    // Create database tables if needed
                    using (var uow = _unitOfWorkManager.Begin(requiresNew: false, isTransactional: false))
                    {
                        var tenantConfiguration = await _tenantStore.FindAsync(tenantId);
                        if (tenantConfiguration?.ConnectionStrings != null &&
                            !tenantConfiguration.ConnectionStrings.Default.IsNullOrWhiteSpace())
                        {
                            foreach (var migrator in _dbSchemaMigrators)
                            {
                                await migrator.MigrateAsync();
                            }
                        }

                        await uow.CompleteAsync();
                    }

                    // Seed data
                    using (var uow = _unitOfWorkManager.Begin(requiresNew: false, isTransactional: true))
                    {
                        await _dataSeeder.SeedAsync(
                            new DataSeedContext(tenantId)
                                .WithProperty(IdentityDataSeedContributor.AdminEmailPropertyName, adminEmail)
                                .WithProperty(IdentityDataSeedContributor.AdminPasswordPropertyName, adminPassword)
                        );

                        await uow.CompleteAsync();
                    }
                }
            }
            catch (Exception ex)
            {
                _logger.LogException(ex);
            }
        }
    }
}

You need to put this class into /aspnet-core/src/Acme.BookStore/Domain/Data/ directory.

I don't know whether this solution work for anybody, I'm new in abp angular and the create tenant modal form save button is even disabled. How will I go around it?