CSharpMirationStep

.NET assembly with a script implementation

Any assembly script is

• .exe or .dll for target framework is 4.7.2+
• .dll for .net 6.0+
• has exactly one class with script implementation

This project is an example of script implementation. The build output is 2.1_2.2.dll with target framework 4.7.2. Due to the current dependencies, 2.1_2.2.dll works well on .net 6.0+.

Script source

Method SqlDatabaseScript.Execute implements a logic of script

namespace SqlDatabaseCustomScript
{
    public /*sealed*/ class SqlDatabaseScript /*: IDisposable*/
    {
        public void Execute(IDbCommand command, IReadOnlyDictionary<string, string> variables)
        {
            Console.WriteLine("start execution");

            command.CommandText = string.Format("print 'current database name is {0}'", variables["DatabaseName"]);
            command.ExecuteNonQuery();

            command.CommandText = string.Format("print 'version from {0}'", variables["CurrentVersion"]);
            command.ExecuteNonQuery();

            command.CommandText = string.Format("print 'version to {0}'", variables["TargetVersion"]);
            command.ExecuteNonQuery();

            command.CommandText = "create table dbo.DemoTable (Id INT)";
            command.ExecuteNonQuery();

            command.CommandText = "print 'drop table DemoTable'";
            command.ExecuteNonQuery();

            command.CommandText = "drop table dbo.DemoTable";
            command.ExecuteNonQuery();

            Console.WriteLine("finish execution");
        }
    }
}

Use

• method`s parameter "IDbCommand command" to affect database
• Console.WriteLine() to write something into output/log

Runtime .NET desktop

At runtime the assembly will be loaded into A private application domain with

• ApplicationBase: temporary directory
• Location of assembly: ApplicationBase, temporary directory

    public class SqlDatabaseScript
    {
        public void Execute(IDbCommand command, IReadOnlyDictionary<string, string> variables)
        {
            var assemblyLocation = GetType().Assembly.Location;

            // temporary directory
            Console.WriteLine(assemblyLocation);
        }
    }

Instance of migration step will be resolved via reflection: Activator.CreateInstance(typeof(SqlDatabaseScript))

After the migration step is finished or failed

• instance of SqlDatabaseScript will be disposed (if IDisposable)
• the domain will be unloaded
• temporary directory will be deleted

Runtime .NET

At runtime the assembly will be loaded into the current application domain (AssemblyLoadContext.Default).

• ApplicationBase: is a directory of SqlDatabase
• Script assembly has no location:

    public class SqlDatabaseScript
    {
        public void Execute(IDbCommand command, IReadOnlyDictionary<string, string> variables)
        {
            var assemblyLocation = GetType().Assembly.Location;

            // output is empty
            Console.WriteLine(assemblyLocation);
        }
    }

Instance of migration step will be resolved via reflection: Activator.CreateInstance(typeof(SqlDatabaseScript))

After the migration step is finished or failed

• instance of SqlDatabaseScript will be disposed (if IDisposable)

Resolving SqlDatabaseScript.Execute

The assembly must contain exactly one public class SqlDatabaseScript, namespace doesn't matter. Class SqlDatabaseScript must contain instance method public void Execute(...).

Supported signatures of Execute method

• void Execute(IDbCommand command, IReadOnlyDictionary<string, string> variables)
• void Execute(IReadOnlyDictionary<string, string> variables, IDbCommand command)
• void Execute(IDbCommand command)
• void Execute(IDbConnection connection)

Names SqlDatabaseScript and Execute are configurable.

Configuration

name of class SqlDatabaseScript and method Execute can be changed in the configuration file:

<configuration>
  <configSections>
    <section name="sqlDatabase"
             type="SqlDatabase.Configuration.AppConfiguration, SqlDatabase"/>
  </configSections>

  <sqlDatabase>
    <assemblyScript className="SqlDatabaseScript"
                    methodName="Execute" />
  </sqlDatabase>
</configuration>