Is there a good way to extend the Code-First Migrations

I have found a solution though I am not sure if it is good. I had to go a little farther down the rabbit hole than I wanted to get it, and it is not really an extension point.

It allows me to write statements such as:

CreateTable(    "dbo.CustomerDirectory",     c => new        {            Uid = c.Int(nullable: false),            CustomerUid = c.Int(nullable: false),            Description = c.String(nullable: false, maxLength: 50, unicode: false),            RowGuid = c.Guid(nullable: false),        })    .PrimaryKey(t => t.Uid)    .ForeignKey("dbo.Customer", t => t.CustomerUid)      //SqlValue is a custom static helper class    .DefaultConstraint( t => t.Description, SqlValue.EmptyString)      //This is a convention in the project      //Equivalent to      //  .DefaultConstraint( t => t.RowGuid, SqlValue.EmptyString)      //  .RowGuid( t => t.RowGuid )    .StandardRowGuid()      //For one-offs    .Sql( tableName => string.Format( "ALTER TABLE {0} ...", tableName" );

I do not like:

• The fact that I am reflecting on private members, and normally would not use such a solution
• That the lambda to select a column could return the wrong column name if the "name" optional parameter of the column definition was used.

I am only considering using it here because:

• We ship the EF assembly so we are sure the one used will have these members.
• A couple unit tests will tell us if a new version will break these.
• It is isolated to migrations.
• We have all the information we are reflecting to get, so if a new version does break this, we could put in place a hack to replace this functionality.

internal static class TableBuilderExtentions{    internal static TableBuilder<TColumns> Sql<TColumns>(        this TableBuilder<TColumns> tableBuilder,        Func<string, string> sql,        bool suppressTransaction = false,        object anonymousArguments = null)    {        string sqlStatement = sql(tableBuilder.GetTableName());        DbMigration dbMigration = tableBuilder.GetDbMigration();        Action<string, bool, object> executeSql = dbMigration.GetSqlMethod();        executeSql(sqlStatement, suppressTransaction, anonymousArguments);        return tableBuilder;    }    [Pure]    private static DbMigration GetDbMigration<TColumns>(this TableBuilder<TColumns> tableBuilder)    {        var field = tableBuilder.GetType().GetField(            "_migration", BindingFlags.NonPublic | BindingFlags.Instance);        return (DbMigration)field.GetValue(tableBuilder);    }    /// <summary>    ///   Caution: This implementation only works on single properties.    ///   Also, coder may have specified the 'name' parameter which would make this invalid.    /// </summary>    private static string GetPropertyName<TColumns>(Expression<Func<TColumns, object>> someObject)    {        MemberExpression e = (MemberExpression)someObject.Body;        return e.Member.Name;    }    [Pure]    private static Action<string, bool, object> GetSqlMethod(this DbMigration migration)    {        MethodInfo methodInfo = typeof(DbMigration).GetMethod(            "Sql", BindingFlags.NonPublic | BindingFlags.Instance);        return (s, b, arg3) => methodInfo.Invoke(migration, new[] { s, b, arg3 });    }    [Pure]    private static string GetTableName<TColumns>(this TableBuilder<TColumns> tableBuilder)    {        var field = tableBuilder.GetType().GetField(            "_createTableOperation", BindingFlags.NonPublic | BindingFlags.Instance);        var createTableOperation = (CreateTableOperation)field.GetValue(tableBuilder);        return createTableOperation.Name;    }}

To piggyback on what ravi said, you could extend the DbMigration class:

using System;using System.Collections.Generic;using System.Data.Entity.Migrations;using System.Linq;using System.Text;using System.Threading.Tasks;public abstract class ExtendedDbMigration : DbMigration{    public void DoCommonTask(string parameter)    {        Sql("** DO SOMETHING HERE **");    }    public void UndoCommonTask(string parameter)    {        Sql("** DO SOMETHING HERE **");    }}

Then, when you create a migration, change it from DbMigration to ExtendedDbMigration:

using System.Data.Entity.Migrations;public partial class some_migration : ExtendedDbMigration{    public override void Up()    {        DoCommonTask("Up");    }    public override void Down()    {        UndoCommonTask("Down");    }}

Not a generic solution, but you can inherit from an abstract/interface class. Given this would need some code changes but its reasonably clean.

I have used this pattern to define my audit columns (UpdatedBy, UpdateDate etc.,) for all the tables.