Migration is a standard process for creating and updating the database from our application. After creating the database model, we can transfer it to the real database. But we need to modify our CreateDbContext method first:

var builder = new DbContextOptionsBuilder<RepositoryContext>()
    .UseSqlServer(configuration.GetConnectionString("sqlConnection"), 
        b => b.MigrationsAssembly("CompanyEmployees.Infrastructure.Persistence"));

We have to make this change because migration assembly is not in our main project but in the CompanyEmployees.Infrastructure.Persistence project. So, we’ve just changed the project for the migration assembly. Before we execute our migration commands, we have to install an additional ef core library: Microsoft.EntityFrameworkCore.Tools.

Now, let’s open the Package Manager Console window and create our first migration:

PM> Add-Migration DatabaseCreation

This will likely result in an error on your machine:

Your target project 'CompanyEmployees' doesn't match your migrations assembly 
'CompanyEmployees.Infrastructure.Persistence'. Either change your target project 
or change your migrations assembly. Change your migrations assembly 
by using DbContextOptionsBuilder. 
E.g. options.UseSqlServer(connection, b => b.MigrationsAssembly("CompanyEmployees")). 
By default, the migrations assembly is the assembly containing the DbContext.
Change your target project to the migrations project by using the 
Package Manager Console's Default project drop-down list, 
or by executing "dotnet ef" from the directory containing the migrations project.

In simple terms, we need to change the default project in our Package Manager console to CompanyEmployees.Infrastructure.Persistence since we’ve explicitly defined the migrations assembly. We can pick the default project from the second dropdown in the Package Manager Console. With this command, we are creating migration files, and we can find them in the Migrations folder in our Persistence project:

With those files in place, we can apply migration:

PM> Update-Database

And if you get another exception:

System.Globalization.CultureNotFoundException: Only the invariant culture is supported in 
globalization-invariant mode. See https://aka.ms/GlobalizationInvariantMode 
for more information. (Parameter 'name') en-us is an invalid culture identifier.

You can solve it pretty easily. You need to set the InvarianGlobalization attribute to false in your main project’s .csproj file:

<InvariantGlobalization>false</InvariantGlobalization>

Now, let’s rerun the command. This time, the migrations should be applied, and we can inspect our database:

Now that we’ve created the database and the tables, we should populate them with some initial data. To do that, we are going to create another folder in the CompanyEmployees.Infrastructure.Persistence project called Configurations and add the CompanyConfiguration class:

public class CompanyConfiguration : IEntityTypeConfiguration<Company>
{
    public void Configure(EntityTypeBuilder<Company> builder)
    {
        builder.HasData
        (
            new Company
            {
                Id = new Guid("c9d4c053-49b6-410c-bc78-2d54a9991870"),
                Name = "IT_Solutions Ltd",
                Address = "583 Wall Dr. Gwynn Oak, MD 21207",
                Country = "USA"
            },
            new Company
            {
                Id = new Guid("3d490a70-94ce-4d15-9494-5248280c2ce3"),
                Name = "Admin_Solutions Ltd",
                Address = "312 Forest Avenue, BF 923",
                Country = "USA"
            }
        );
    }
 }

Let’s do the same thing for the EmployeeConfiguration class:

public class EmployeeConfiguration : IEntityTypeConfiguration<Employee>
{
    public void Configure(EntityTypeBuilder<Employee> builder)
    {
        builder.HasData
        (
            new Employee
            {
                Id = new Guid("80abbca8-664d-4b20-b5de-024705497d4a"),
                Name = "Sam Raiden",
                Age = 26,
                Position = "Software developer",
                CompanyId = new Guid("c9d4c053-49b6-410c-bc78-2d54a9991870")
            },
            new Employee
            {
                Id = new Guid("86dba8c0-d178-41e7-938c-ed49778fb52a"),
                Name = "Jana McLeaf",
                Age = 30,
                Position = "Software developer",
                CompanyId = new Guid("c9d4c053-49b6-410c-bc78-2d54a9991870")
            },
            new Employee
            {
                 Id = new Guid("021ca3c1-0deb-4afd-ae94-2159a8479811"),
                 Name = "Kane Miller",
                 Age = 35,
                 Position = "Administrator",
                 CompanyId = new Guid("3d490a70-94ce-4d15-9494-5248280c2ce3")
             }
        );
    }
}

To invoke this configuration, we have to change the RepositoryContext class:

public class RepositoryContext: DbContext
{
    public RepositoryContext(DbContextOptions options)
    : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfiguration(new CompanyConfiguration());
        modelBuilder.ApplyConfiguration(new EmployeeConfiguration());
    }

    public DbSet<Company> Companies { get; set; }
    public DbSet<Employee> Employees { get; set; }
}

Now, we can create and apply another migration to seed these data to the database:

PM> Add-Migration InitialData
PM> Update-Database

These commands will transfer all the data from our configuration files to the respective tables.