我已经学习了一个星期左右的时间来使用EF，并且一直困扰于创建/更新数据库的问题。如果数据库不存在，我可以创建一个初始化器来创建数据库：

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
    }
}

或者我可以创建一个配置来迁移数据库

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)
    {

    }

每个都可以正常工作，但我还没有想办法做到这两个。我可以通过更改SetInitializer调用在两个初始值设定项之间进行切换，但是如果我想创建数据库（如果该数据库不存在的话），并且还要迁移它（如果这样做的话）呢？我需要创建自定义初始化程序吗？

谢谢

根据NSGaga答案进行编辑

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)
    {
    }
}

和

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)
    {
    }
}

和

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)");
    }
}

最后

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