Decorators for both commands and queries

1.cs

public sealed class DatabaseCommandRetryDecorator<TCommand> : DatabaseRetryDecorator, ICommandHandler<TCommand>
    where TCommand : ICommand
{
    private readonly ICommandHandler<TCommand> _handler;

    public DatabaseCommandRetryDecorator(ICommandHandler<TCommand> handler, Config config)
        : base(config)
    {
        _handler = handler;
    }

    public Result Handle(TCommand command)
    {
        return InvokeWithRetry(_handler.Handle, command);
    }
}

public sealed class DatabaseQueryRetryDecorator<TQuery, TResult> : DatabaseRetryDecorator, IQueryHandler<TQuery, TResult>
    where TQuery : IQuery<TResult>
{
    private readonly IQueryHandler<TQuery, TResult> _handler;

    public DatabaseQueryRetryDecorator(IQueryHandler<TQuery, TResult> handler, Config config)
        : base(config)
    {
        _handler = handler;
    }

    public TResult Handle(TQuery query)
    {
        return InvokeWithRetry(_handler.Handle, query);
    }
}


public abstract class DatabaseRetryDecorator
{
    private readonly Config _config;

    protected DatabaseRetryDecorator(Config config)
    {
        _config = config;
    }

    protected TOut InvokeWithRetry<TIn, TOut>(Func<TIn, TOut> func, TIn parameter)
    {
        for (int i = 0; ; i++)
        {
            try
            {
                TOut result = func(parameter);
                return result;
            }
            catch (Exception ex)
            {
                if (i >= _config.NumberOfDatabaseRetries || !IsDatabaseException(ex))
                    throw;
            }
        }
    }

    private bool IsDatabaseException(Exception exception)
    {
        string message = exception.InnerException?.Message;

        if (message == null)
            return false;

        return message.Contains("The connection is broken and recovery is not possible")
            || message.Contains("error occurred while establishing a connection");
    }
}