There's a movie with a boy named Yao Yongnuo, and there's an interlude in the movie called "Youthful Dance", which is probably about the Republican era.

The story is about a 13-year-old girl, Fang Yilin, who picks up a violin outside a church and meets a boy of the same age, Yao Yongnuo, in 1928 in Qingdao, which is full of European colors. The two of them develop from misunderstanding and understanding to become inseparable best friends. Rather, it's a love story that would hold up just as well if the 13-year-old hero and heroine in the movie were adults. "Yeah, I've thought about that, too, and when we want to do kids' scenes, we're actually doing it from an adult's point of view, i.e. how we think they should be. But when I've come into contact with them, I found that their thought patterns are actually already adults." Chen Jianzhong laughed and said that children are actually adults who are a little more capricious, a little more spontaneous, and who like to say whatever they want. "When they're filming, they'll 'strike' if they're not happy, they won't be the same as professional actors, they're not professional actors, but they're adults."

Most of the scenes for the film were shot on location in Qingdao, with only a portion of the interiors and set pieces shot in Shanghai. Since Chen Jianzhong is more concerned about some historical evidence and doesn't want the movie to come out with a fake period background, he visited many locals and consulted Qingdao historians before shooting. "I wanted to use the hero learning the violin as a backdrop, so I asked them if Qingdao had this kind of musical background at that time, and if music was important in Qingdao. They told me that Qingdao was indeed the capital of music at that time - luckily this matched my imagination. They also said that if you walked around the streets of Qingdao at night, the windows of every house would be open and you would hear them either playing the violin or the piano, as if they were having a concert." Chen Jianzhong wanted to recreate the scene, but the idea failed to materialize because he can no longer find streets of that scale in Qingdao.

"Once Upon a Time" is entirely in Mandarin, and the actors used are all from China. The search for actors brought Chen Jianzhong a lot of pain, and he even said bluntly that if he could not find the right person, the movie would not start shooting. "According to the original idea, the character of Fang Yilin is a girl who knows how to dance and is more boyish and active, and I even designed a scene where she dances. But we searched Shanghai and Beijing and couldn't find a suitable candidate, and finally an art school in Qingdao recommended Ma Xiaoqian, who at first didn't look too special, plus she wore a very rustic school uniform, which made an average impression. Later, when she was asked to act, she was so sharp. The assistant director asked her to fantasize about saying goodbye to her best friend, and she cried at the beginning, and she acted very well."

As for the role of Yao Yongnuo's candidate is even more difficult to find, Chen Jianzhong's requirements are very cute, very shy, do not have to be too handsome, but to play the violin excellent. In China, there are many boys who can play the violin well, but it is not easy to get the right material and appearance. "We searched all the conservatories in Shanghai and Beijing and couldn't find anyone, so we finally decided to 'change direction' and look for someone who didn't know much about violin playing. As a result, my staff found Zhai Tianlin, a boy who had originally auditioned for a supporting role, and changed his hairstyle and clothes for the audition, and I almost didn't recognize him at the time. I ended up casting him."

Asked Chen if he had ever thought of adding a "love triangle" to the innocent friendship and relationship between the male and female leads to create a little more drama? "I don't want to. I wanted to make it straightforward, with two people who are in love with each other, until the end." Yes, it's fresh and pure, so why add salt and vinegar?