无法为映射表组装任何主键列 | 无法为映射表组装任何主键列

本文介绍了无法为映射表组装任何主键列的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

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?

When I'm trying to create a database schema migration, I'm getting this weird error. Can you please help me to figure out what's wrong?

$ 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'

我的模型:

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")

推荐答案

表中不能有两个主键.相反，您必须使用复合主键.可以通过在模型中添加如下所示的PrimaryKeyConstraint来完成此操作(请记住在关闭__table_args__中的括号之前添加逗号:

You cannot have two primary keys in a table. Instead, you must use a compound primary key.This can be done by adding a PrimaryKeyConstraint in your model as below (remember to add a comma before closing the bracket in __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")

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