Repeatedly creating and deleting databases in Entity Framework

Question

When writing some unit tests for our application, I stumbled upon some weird behaviour in EF6 (tested with 6.1 and 6.1.2): apparently it is impossible to repeatedly create and delete databases (same name/same connection string) within the same application context.

Test setup:

public class A
{
    public int Id { get; set; }
    public string Name { get; set; }
}

class AMap : EntityTypeConfiguration<A>
{
    public AMap()
    {
        HasKey(a => a.Id);
        Property(a => a.Name).IsRequired().IsMaxLength().HasColumnName("Name");
        Property(a => a.Id).HasColumnName("ID");
    }
}

public class SomeContext : DbContext
{
    public SomeContext(DbConnection connection, bool ownsConnection) : base(connection, ownsConnection)
    {

    }

    public DbSet<A> As { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Configurations.Add(new AMap());
    }
}

[TestFixture]
public class BasicTest
{
    private readonly HashSet<string> m_databases = new HashSet<string>();

    #region SetUp/TearDown

    [TestFixtureSetUp]
    public void SetUp()
    {
        System.Data.Entity.Database.SetInitializer(
            new CreateDatabaseIfNotExists<SomeContext>());
    }


    [TestFixtureTearDown]
    public void TearDown()
    {
        foreach (var database in m_databases)
        {
            if (!string.IsNullOrWhiteSpace(database))
                DeleteDatabase(database);
        }
    }

    #endregion


    [Test]
    public void RepeatedCreateDeleteSameName()
    {
        var dbName = Guid.NewGuid().ToString();
        m_databases.Add(dbName);
        for (int i = 0; i < 2; i++)
        {
            Assert.IsTrue(CreateDatabase(dbName), "failed to create database");
            Assert.IsTrue(DeleteDatabase(dbName), "failed to delete database");
        }

        Console.WriteLine();
    }

    [Test]
    public void RepeatedCreateDeleteDifferentName()
    {
        for (int i = 0; i < 2; i++)
        {
            var dbName = Guid.NewGuid().ToString();
            if (m_databases.Add(dbName))
            {
                Assert.IsTrue(CreateDatabase(dbName), "failed to create database");
                Assert.IsTrue(DeleteDatabase(dbName), "failed to delete database");
            }
        }

        Console.WriteLine();
    }

    [Test]
    public void RepeatedCreateDeleteReuseName()
    {
        var testDatabases = new HashSet<string>();
        for (int i = 0; i < 3; i++)
        {
            var dbName = Guid.NewGuid().ToString();
            if (m_databases.Add(dbName))
            {
                testDatabases.Add(dbName);
                Assert.IsTrue(CreateDatabase(dbName), "failed to create database");
                Assert.IsTrue(DeleteDatabase(dbName), "failed to delete database");
            }
        }
        var repeatName = testDatabases.OrderBy(n => n).FirstOrDefault();
        Assert.IsTrue(CreateDatabase(repeatName), "failed to create database");
        Assert.IsTrue(DeleteDatabase(repeatName), "failed to delete database");

        Console.WriteLine();
    }

    #region Helpers

    private static bool CreateDatabase(string databaseName)
    {
        Console.Write("creating database '" + databaseName + "'...");
        using (var connection = CreateConnection(CreateConnectionString(databaseName)))
        {
            using (var context = new SomeContext(connection, false))
            {
                var a = context.As.ToList(); // CompatibleWithModel must not be the first call
                var result = context.Database.CompatibleWithModel(false);
                Console.WriteLine(result ? "DONE" : "FAIL");
                return result;
            }
        }
    }


    private static bool DeleteDatabase(string databaseName)
    {
        using (var connection = CreateConnection(CreateConnectionString(databaseName)))
        {
            if (System.Data.Entity.Database.Exists(connection))
            {
                Console.Write("deleting database '" + databaseName + "'...");
                var result = System.Data.Entity.Database.Delete(connection);
                Console.WriteLine(result ? "DONE" : "FAIL");
                return result;
            }
            return true;
        }
    }

    private static DbConnection CreateConnection(string connectionString)
    {
        return new SqlConnection(connectionString);
    }

    private static string CreateConnectionString(string databaseName)
    {
        var builder = new SqlConnectionStringBuilder
        {
            DataSource = "server",
            InitialCatalog = databaseName,
            IntegratedSecurity = false,
            MultipleActiveResultSets = false,
            PersistSecurityInfo = true,
            UserID = "username",
            Password = "password"
        };
        return builder.ConnectionString;
    }

    #endregion

}

RepeatedCreateDeleteDifferentName completes successfully, the other two fail. According to this, you cannot create a database with the same name, already used once before. When trying to create the database for the second time, the test (and application) throws a SqlException, noting a failed login. Is this a bug in Entity Framework or is this behaviour intentional (with what explanation)?

I tested this on a Ms SqlServer 2012 and Express 2014, not yet on Oracle. By the way: EF seems to have a problem with CompatibleWithModel being the very first call to the database.

Update: Submitted an issue on the EF bug tracker (link)

Answer 1

Database initializers only run once per context per AppDomain. So if you delete the database at some arbitrary point they aren't going to automatically re-run and recreate the database. You can use DbContext.Database.Initialize(force: true) to force the initializer to run again.