According to Freud's interpretation of dreams, dreaming of long eggplant (cylindrical, long and smooth) is no different from dreaming of snakes. They are symbols of male genitalia and represent your desire for sex. Dream interpretation is often from the perspective of summing up the past, so this shows that your sexual repression is relatively strong, and purple shows that your sexual repression is hidden and not exposed.
Of course, whether it is Duke Zhou or Freud, dreams should be analyzed in combination with your recent life. Dreams are the embodiment of your own subconscious. It is possible that purple eggplant doesn't mean anything, but you have encountered purple or eggplant-related foods in your recent life, so they remain in your subconscious and are reflected in your dreams.