Given the following context:

Joanna, a writer, and Michael Reed, a commercial real estate agent, are a married couple who share an apartment in New York City. During a party with Michael's colleagues, Joanna notices him spending time with Laura Nunez, an attractive co-worker, and wonders why he has not previously mentioned her. Joanna suspects Michael is having an affair and confronts him about it when they return home. They have an argument but reconcile later that night. The following day, Michael leaves on a business trip to Philadelphia with his associates Laura and Andy; Joanna stays behind to work on a novel. Joanna meets her ex-boyfriend Alex Mann; they go to a bar later that day, have a dinner with two of Alex's friends, Sandra and Truman, and they discuss their past relationship and Joanna's marriage to Michael; she has never told Michael about Alex.
Joanna and Alex return to Andy's apartment, where they talk about their previous romance, having got back together after Michael briefly broke off his relationship with Joanna. She goes out to walk Andy's dog; he accidentally locks them outside. They go to a party with Sandra, Truman and the dog. Joanna and Alex grow closer over the course of the night, and they eventually kiss. After the party, they return to Alex's hotel room. Joanna refuses to have sex with Alex and they instead spend the night embracing each other in bed. The next day, Joanna and Alex kiss before he leaves New York broken-hearted.

answer the following question:

Besides the dog, who all does Alex attend a party with? 

Sandra