[FastAPI] 14. SQLAlchemy์˜ One-to-Many, Many-to-Many, Self referential relationship

์ง€๋‚œ ํฌ์ŠคํŠธ์—์„œ๋Š” ๋‹จ์ˆœ Column ๋ฐ์ดํ„ฐ์™€ ๊ทธ๋ฆฌ๊ณ , ๋‹จ์ผ ์™ธ๋ž˜ํ‚ค ํ•˜๋‚˜์˜ ๊ด€๊ณ„ ๋ฐ์ดํ„ฐ๋ฅผ Pydantic์œผ๋กœ ๋งคํ•‘ํ•˜์—ฌ Serialize/Deserialize ํ•˜๋Š” ๊ฒƒ์— ๋Œ€ํ•ด ์•Œ์•„๋ดค์Šต๋‹ˆ๋‹ค. ์ด๋ฒˆ ํฌ์ŠคํŠธ์—์„œ๋Š” Many-to-Many, One-to-Many ํ˜•ํƒœ์˜ Foreign Key๊ฐ€ ๊ฑธ๋ ค ์žˆ๋Š” ๊ด€๊ณ„ํ˜• ๋ฐ์ดํ„ฐ๋ฅผ Joinํ•ด์„œ ๊ฐ€์ ธ์˜ฌ ๋–„ ์–ด๋–ป๊ฒŒ Pydantic ๋ชจ๋ธ๊ณผ ๋งคํ•‘ํ•  ์ˆ˜ ์žˆ๋Š”์ง€์— ๋Œ€ํ•ด ์•Œ์•„๋ณด๊ฒ ์Šต๋‹ˆ๋‹ค. DB์—์„œ ๋‹จ์ˆœํ•˜๊ฒŒ ์ ‘๊ทผ ์ง€๋‚œ ํฌ์ŠคํŠธ์—์„œ ์‚ฌ์šฉํ•œ ERD๋ฅผ ๊ทธ๋Œ€๋กœ ์‚ฌ์šฉํ•ด๋ณด๊ฒ ์Šต๋‹ˆ๋‹ค. Category์™€ Post๊ฐ€ ์žˆ๊ณ , Post๋Š” category_id๋ฅผ ์™ธ๋ž˜ํ‚ค๋กœ ์‚ฌ์šฉํ•˜๊ณ  ์žˆ์Šต๋‹ˆ๋‹ค. ๋”ฐ๋ผ์„œ ์นดํ…Œ๊ณ ๋ฆฌ์˜ ๋ฐ์ดํ„ฐ๋ฅผ category ํ…Œ์ด๋ธ”์ด ๊ฐ€์ง€๊ณ  ์žˆ๋Š”๊ฑด๋ฐ, ์šฐ๋ฆฌ๊ฐ€ ์ด ์ •๋ณด๋ฅผ ๋ชจ๋‘ ๋ฐ์ดํ„ฐ๋ฒ ์ด์Šค๋กœ ๊ฐ€์ ธ์˜ค๋ ค๋ฉด ์–ด๋–ป๊ฒŒ ํ•ด์•ผ ..