How to create initializer to create and migrate my

问题:

I have been learning how to use EF for a week or so now and am stuck on the issue of creating/updating my database. I am able to create an initializer to create the database if it is not there:

static class Program
{
    static void Main()
    {
        Database.SetInitializer<GumpDatabase>(new GumpDatabaseInitializer());
....

class GumpDatabaseInitializer : CreateDatabaseIfNotExists<GumpDatabase>
{
    public GumpDatabaseInitializer()
    {
    }
    protected override void Seed(GumpDatabase context)
    {
        context.Database.ExecuteSqlCommand("CREATE UNIQUE INDEX Name ON Stations (Name)");
        // Other stuff
    }
}

Or I can create a Configuration to migrate the db

static class Program
{
    static void Main()
    {
        Database.SetInitializer<GumpDatabase>(new MigrateDatabaseToLatestVersion<GumpDatabase, Configuration>());
....

internal sealed class Configuration : DbMigrationsConfiguration<GumpDatabase>
{
    public Configuration()
    {
        AutomaticMigrationsEnabled = true;
        SetSqlGenerator("MySql.Data.MySqlClient", new MySql.Data.Entity.MySqlMigrationSqlGenerator()); 
    }

    protected override void Seed(GumpDatabase context)
    {

    }

Each works correctly but I haven't figured out a way to do both. I can switch between the two initializers by changing the SetInitializer call but if I want to create the database if it is not there and also migrate it if it is what do I do? Do I need to create a custom initializer?

Thanks

Edit based on NSGaga answer

class CreateOrMigrateDatabaseInitializer<TContext, TConfiguration> : CreateDatabaseIfNotExists<TContext>, IDatabaseInitializer<TContext>
    where TContext : DbContext
    where TConfiguration : DbMigrationsConfiguration<TContext>, new()
{
    private readonly DbMigrationsConfiguration _configuration;
    public CreateOrMigrateDatabaseInitializer()
    {
        _configuration = new TConfiguration();
    }
    public CreateOrMigrateDatabaseInitializer(string connection)
    {
        Contract.Requires(!string.IsNullOrEmpty(connection), "connection");

        _configuration = new TConfiguration
        {
            TargetDatabase = new DbConnectionInfo(connection)
        };
    }
    void IDatabaseInitializer<TContext>.InitializeDatabase(TContext context)
    {
        Contract.Requires(context != null, "context");

        if (context.Database.Exists())
        {
            if (!context.Database.CompatibleWithModel(throwIfNoMetadata: false))
            {
                var migrator = new DbMigrator(_configuration);
                migrator.Update();
            }
        }
        else
        {
            context.Database.Create();
            Seed(context);
            context.SaveChanges();
        }


    }
    protected virtual void Seed(TContext context)
    {
    }
}

and

internal sealed class Configuration : DbMigrationsConfiguration<GumpDatabase>
{
    public Configuration()
    {
        AutomaticMigrationsEnabled = true;
        AutomaticMigrationDataLossAllowed = false;
        SetSqlGenerator("MySql.Data.MySqlClient", new MySql.Data.Entity.MySqlMigrationSqlGenerator()); 
    }

    protected override void Seed(GumpDatabase context)
    {
    }
}

and

class GumpDatabaseInitializer : CreateOrMigrateDatabaseInitializer<GumpDatabase,Gump.Migrations.Configuration>
{
    public GumpDatabaseInitializer()
    {
    }
    protected override void Seed(GumpDatabase context)
    {
        context.Database.ExecuteSqlCommand("CREATE UNIQUE INDEX Name ON Stations (Name)");
        context.Database.ExecuteSqlCommand("CREATE UNIQUE INDEX Name ON Sequences (Name)");
        context.Database.ExecuteSqlCommand("CREATE UNIQUE INDEX StationPartNumber ON StationPartNumbers (StationId,PartNumberId)");
    }
}

and finally

static void Main()
{
    Database.SetInitializer<GumpDatabase>(new GumpDatabaseInitializer());

回答1:

I think you're pretty much there - you can lookup the source code for MigrateDatabaseToLatestVersion (it's open source http://entityframework.codeplex.com/) - it's pretty simplistic, what it does pretty much is call the DbMigrator - as far as I could see.

All you have to do seems is to merge the two - use one or the other as a basis, add other functionality in there - that should work fine I think.

class CreateAndMigrateDatabaseInitializer<TContext, TConfiguration> : CreateDatabaseIfNotExists<TContext>, IDatabaseInitializer<TContext> 
    where TContext : DbContext
    where TConfiguration : DbMigrationsConfiguration<TContext>, new()
{
    private readonly DbMigrationsConfiguration _configuration;
    public CreateAndMigrateDatabaseInitializer()
    {
        _configuration = new TConfiguration();
    }
    public CreateAndMigrateDatabaseInitializer(string connection)
    {
        Contract.Requires(!string.IsNullOrEmpty(connection), "connection");

        _configuration = new TConfiguration
        {
            TargetDatabase = new DbConnectionInfo(connection)
        };
    }
    void IDatabaseInitializer<TContext>.InitializeDatabase(TContext context)
    {
        Contract.Requires(context != null, "context");

        var migrator = new DbMigrator(_configuration);
        migrator.Update();

        // move on with the 'CreateDatabaseIfNotExists' for the 'Seed'
        base.InitializeDatabase(context);
    }
    protected override void Seed(TContext context)
    {
    }
}

call it like this...

Database.SetInitializer(new CreateAndMigrateDatabaseInitializer<GumpDatabase, YourNamespace.Migrations.Configuration>());

...actually, override it (since it's generic implementation) like you were doing for CreateDatabaseIfNotExists (you just have extra 'param' for Configuration) - and just supply the 'Seed'.

class GumpDatabaseInitializer : CreateAndMigrateDatabaseInitializer<GumpDatabase, YourNamespace.Migrations.Configuration>
{
    protected override void Seed(GumpDatabase context)
    {
        context.Database.ExecuteSqlCommand("CREATE UNIQUE INDEX Name ON Stations (Name)");
    }
}

...and call it something like

Database.SetInitializer(new GumpDatabaseInitializer());

EDIT: Based on the comments - DbMigrator should not run twice. It always checks (spends a bit of time) and does a 'blank' update and moves on. However just in case if you'd like to remove that and 'check' before entering - this should work (change the similar piece above)...

var migrator = new DbMigrator(_configuration);
if (!context.Database.CompatibleWithModel(throwIfNoMetadata: false))
    if (migrator.GetPendingMigrations().Any())
        migrator.Update();

(this is a redundant / double-check - one of the if-s should be enough. Put a break there - and see exactly what's happening, it should not get in - once Db is migrated. As I mentioned, works fine when I test it.

EDIT:

Replace the inside of InitializeDatabase with...

var doseed = !context.Database.Exists();
// && new DatabaseTableChecker().AnyModelTableExists(context);
// check to see if to seed - we 'lack' the 'AnyModelTableExists' - could be copied/done otherwise if needed...

var migrator = new DbMigrator(_configuration);
// if (doseed || !context.Database.CompatibleWithModel(throwIfNoMetadata: false))
    if (migrator.GetPendingMigrations().Any())
        migrator.Update();

// move on with the 'CreateDatabaseIfNotExists' for the 'Seed'
base.InitializeDatabase(context);
if (doseed)
{
    Seed(context);
    context.SaveChanges();
}

This works around (half-way) not-seeding - if migration goes first. And migrations have to be first, otherwise you have issues.

You still need to do it properly - this is the gist if not all you might need - but if any issues w/ MySQL etc., probably some more leg work here.

Note: Still seeding doesn't call if you have a db, but it's empty. Problem is mixing of the two different initializers. So you'll have to work that out - either by implementing what Create... does inside (that call we can't call) or something else.

回答2:

Actually it should be:

var migrator = new DbMigrator(_configuration);
if (!context.Database.CompatibleWithModel(false) || migrator.GetPendingMigrations().Any())
    migrator.Update();

because if we have a migration, that is not related to our db model, for example inserting a row in any of our tables, the migration won't be executed.

回答3:

To do both (seed and migrate) you really only have to use migrations with a MigrateDatabaseToLatestVersion initializer. When you enable migrations for your context a Configuration class derived from DbMigrationsConfiguration is created and you can override the Seed method to seed your database. Note that the database may already contain seed data when this method executes but the AddOrUpdate extension method conveniently helps you make "upserts" in your database.

This is different compared to the Seed method of some of the other database intitializers where the database is only seeded when it is initially created. However, when you are using migrations you may want to change your seed data when the database changes and using MigrateDatabaseToLatestVersion makes that possible.

To combine seeding with migrations you will have to perform the following steps in a new project:

1. Create a code-first DbContext with associated entities

2. In the package manager console execute the command Enable-Migrations

3. In the Migrations folder a Configuration class is generated with a Seed method. You can modify this method to seed your database:

   protected override void Seed(MyContext context) {
     // Add two entities with name "Foo" and "Bar".
     context.MyEntities.AddOrUpdate(
       e => e.Name,
       new MyEntity { Name = "Foo" },
       new MyEntity { Name = "Bar" }
     );
   }
   

4. You need to create a database initializer that derives from MigrateDatabaseToLatestVersion:

   class MyContextInitializer
     : MigrateDatabaseToLatestVersion<MyContext, Migrations.Configuration> { }
   

   You will also have to configure the initializer either by calling Database.SetInitializer(new MyContextInitializer()) when you application starts or in the App.config file by using the <databaseInitializer/> element.

5. In the constructor for the generated Configuration class you can enable automatic migrations:

   public Configuration() {
     AutomaticMigrationsEnabled = true
   }
   

   However, in a team you might prefer to not do that. In that case you will have to create an initial migration (unless it was created when you did Enable-Migrations). In the package manager execute the command Add-Migration InitialCreate. This creates the first migration required to create your database.

At this point you have a DbContext with migrations and a Seed method.

So to sum it: Enable migrations, use the MigrateDatabaseToLatestVersion initializer and add seed data in the Configuration class that was generated when migrations were enabled.

回答4:

While MigrateDatabaseToLatestVersion does actually create the DB if it does not exist and even allows you to seed it, if you already have a working solution based on CreateDatabaseIfNotExists and/or don't want to complicate it with testing for existence of seed data, you can just use the below by inheriting from it rather than from CreateDatabaseIfNotExists:

public class CreateOrMigrateDatabaseInitializer<TContext, TConfiguration> : CreateDatabaseIfNotExists<TContext>, IDatabaseInitializer<TContext>
        where TContext : DbContext
        where TConfiguration : DbMigrationsConfiguration<TContext>, new()
    {

        void IDatabaseInitializer<TContext>.InitializeDatabase(TContext context)
        {
            if (context.Database.Exists())
            {
                if (!context.Database.CompatibleWithModel(throwIfNoMetadata: false))
                {
                    var migrationInitializer = new MigrateDatabaseToLatestVersion<TContext, TConfiguration>(true);
                    migrationInitializer.InitializeDatabase(context);
                }
            }

            base.InitializeDatabase(context);
        }
    }

This is based on previous answers and OP's own solution. This should work with other providers as well, but I only tested with SQL Server.