设计多态一对多关系数据库。烧瓶

Question

我正在寻找创建多态的一对多关系，例如here我很难解释，所以让我使用示例：

假设我们有三个表书籍、杂志、报纸，它们都有标题为标题和文本的列。 文本列有多个翻译，我想通过多态一对多关系存储。

SQL-Alchemy 中的概念：

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///database.db"
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
db = SQLAlchemy(app)


class Book(db.Model):
    __tablename__ = "books"
    id = db.Column(db.Integer, primary_key=True)
    author = db.Column(db.String)
    # text_translations = db.relationship("Description", backref="book")


class Magazine(db.Model):
    __tablename__ = "magazines"
    id = db.Column(db.Integer, primary_key=True)
    author = db.Column(db.String)
    # text_translations = db.relationship("Description", backref="book")


class Newspaper(db.Model):
    __tablename__ = "newspapers"
    id = db.Column(db.Integer, primary_key=True)
    author = db.Column(db.String)
    # text_translations = db.relationship("Description", backref="book")


class Translation(db.Model):
    __tablename__ = "translations"
    id = db.Column(db.Integer, primary_key=True)
    # source_type =  # This supposed to be either Book, Magazine, Newspaper
    # source_id =  # This suppossed to be id of the Book/Magazine/Newspaper (depends on source_type)
    language = db.Column(db.String)  # this chooses language
    text = db.Column(db.String)  # this is the text in said language

当然，有一个选项可以使翻译类看起来像这样：

class Translation(db.Model):
    __tablename__ = "translations"
    id = db.Column(db.Integer, primary_key=True)
    book_id = db.Column(db.Integer, db.ForeignKey(Book.id))
    magazine_id = db.Column(db.Integer, db.ForeignKey(Magazine.id))
    newspaper_id = db.Column(db.Integer, db.ForeignKey(Newspaper.id))
    language = db.Column(db.String)  # this chooses language
    text = db.Column(db.String)  # this is the text in said language

但是，如果表的数量远多于 3 个，那么效率就低了。 我尝试通过 SQLAlchemy 执行此操作，但我不确定这是否可能，如果在 SQLAlchemy 中确实无法执行此操作，我可以使用哪种替代方法？

Answer 1

你的做法是正确的。你可以试试这个修改后的代码

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy.orm import generic_relationship

app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///database.db"
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
db = SQLAlchemy(app)

class Translation(db.Model):
    __tablename__ = "translations"
    id = db.Column(db.Integer, primary_key=True)
    source_type = db.Column(db.String) 
    source_id = db.Column(db.Integer)  
    language = db.Column(db.String)  
    text = db.Column(db.String)  

class Content(db.Model):
    __abstract__ = True
    id = db.Column(db.Integer, primary_key=True)
    author = db.Column(db.String)
    translations = generic_relationship(Translation, source_type, source_id)

class Book(Content):
    __tablename__ = "books"

class Magazine(Content):
    __tablename__ = "magazines"

class Newspaper(Content):
    __tablename__ = "newspapers"