Breastfeeding and drinking beer.

I'm a ftm so I'm new to all of this. I plan to breastfeed and I know you cannot drink alcohol because it will pass to your baby. So what if I want to go to dinner with my husband and have some drinks? Do I feed her formula? How do I know how long the alcohol stays in my milk? I know this might be a dumb post but I'm very curious & want to take precautions.