与SqlAlchemy的内部联接 [英] An inner join with SqlAlchemy

问题描述

我有一个带计数的原始内部联接查询，直接在Postgres SQL上编写：

I have a raw inner join query with counting, written directly on Postgres SQL:

    SELECT "films"."id" AS "megaId", 
           COUNT("filmComments"."id") AS "numOfComments" 
      FROM "films"
INNER JOIN "filmComments" 
        ON ("films"."id" = "filmComments"."filmId") 
  GROUP BY "films"."id";

如何使用普通的SqlAlchemy在没有 connection.execute的情况下进行相同的操作（sqlCode）？

How can I make the same, using normal SqlAlchemy, without connection.execute(sqlCode)?

PS我的SqlAlchemy表类：

P.S. My SqlAlchemy table classes:

from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
from sqlalchemy import Column, Integer, String, Date, Float

class Film(Base):
    __tablename__ = "films"
    id = Column(Integer, primary_key = True)
    name = Column(String)
    rating = Column(Float)
    marksCount = Column(Integer)
    commentsCount = Column(Integer, index=True)


class FilmComment(Base):
    __tablename__ = "filmComments"
    id = Column(Integer, primary_key = True)
    filmId = Column(Integer, index=True)
    rating = Column(Integer, index=True)
    text = Column(String)
    votesUp = Column(Integer)
    votesDown = Column(Integer)
    userId = Column(Integer)
    date = Column(Date)

推荐答案

将其映射到SQLAlchemy应该非常简单。出于明显的原因，我没有考虑别名。

Mapping that to SQLAlchemy should be quite straightforward. I'm not considering the aliases, for obvious reasons.

from sqlalchemy import func

megaId, numOfComments = (session.query(Film.id, func.count(FilmComment.id))
                                .join(FilmComment, Film.id == FilmComment.filmId)
                                .group_by(Film.id).first())

这应该有效。如果将 FilmComment.filmId 声明为外键，则不需要显式的 on 子句。

This should work. The explicit on clause wouldn't be needed if FilmComment.filmId were declared as a foreign key.

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