Database.cs

using System.Data;

namespace Ledger.Models
{
    public class Database : IDatabase
    {
        readonly IDbConnection _db;

        public Database(IDbConnection db)
        {
            this._db = db;
        }

        public T Query<T>(IQuery<T> query)
        {
            return query.Execute(_db);
        }

        public void Execute(ICommand command)
        {
            command.Execute(_db);
        }
    }
}

ICommand.cs

using System.Data;

namespace Ledger.Models
{
    public interface ICommand
    {
        void Execute(IDbConnection db);
    }
}

IDatabase.cs

using Ledger.Models.CommandQuery;

namespace Ledger.Models
{
    public interface IDatabase
    {
        T Query<T>(IQuery<T> query);
        void Execute(ICommand command);
    }
}

IQuery.cs

using System.Data;

namespace Ledger.Models
{
    public interface IQuery<T>
    {
        T Execute(IDbConnection db);
    }
}