无法为映射表组装任何主键列

Question

当我尝试创建数据库架构迁移时，遇到了这个奇怪的错误。您能帮我找出问题所在吗？

$ python app.py db upgrade
[skipped]
sqlalchemy.exc.ArgumentError: Mapper Mapper|EssayStateAssociations|essay_associations could not assemble any primary key columns for mapped table 'essay_associations'

我的模特：

class EssayStateAssociations(db.Model):
    __tablename__ = 'essay_associations'

    application_essay_id = db.Column(
        db.Integer,
        db.ForeignKey("application_essay.id"),
        primary_key=True),
    theme_essay_id = db.Column(
        db.Integer,
        db.ForeignKey("theme_essay.id"),
        primary_key=True),
    state = db.Column(db.String, default="pending")

Answer 1

一个表中不能有两个主键。相反，您必须使用复合主键。可以通过PrimaryKeyConstraint在模型中添加，如下所示来完成此操作（请记住在闭合括号之前，请添加逗号__table_args__：

from db import PrimaryKeyConstraint

class EssayStateAssociations(db.Model):
    __tablename__ = 'essay_associations'
    __table_args__ = (
        PrimaryKeyConstraint('application_essay_id', 'theme_essay_id'),
    )

    application_essay_id = db.Column(
        db.Integer,
        db.ForeignKey("application_essay.id"))
    theme_essay_id = db.Column(
        db.Integer,
        db.ForeignKey("theme_essay.id"))
    state = db.Column(db.String, default="pending")