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[英]Flask + sqlalchemy + marshmallow - Error on relationship - One to Many
[英]Updating one to many relationship in Flask/ SQLAlchemy
我的數據庫中有兩個模型 Parent 和 Child,這兩個模型之間存在一對多的關系,即一個父母可以有多個孩子。
from flask import Flask, request
from flask_restful import Resource
from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow
from flask_restful import Api
from marshmallow import fields
app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///relationships.db"
db = SQLAlchemy(app)
ma = Marshmallow(app)
api = Api(app, prefix="/api")
class Parent(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(20), nullable=False, unique=True)
children = db.relationship("Child", backref="parent")
class Child(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(20), nullable=False, unique=True)
parent_id = db.Column(db.Integer, db.ForeignKey("parent.id"))
class ChildSchema(ma.SQLAlchemyAutoSchema):
class Meta:
model = Child
ordered = True
include_fk = True
dump_only = ("id",)
load_instance = True
class ParentSchema(ma.SQLAlchemyAutoSchema):
children = fields.Pluck(ChildSchema, "name", many=True)
class Meta:
model = Parent
ordered = True
include_relationships = True
dump_only = ("id",)
load_instance = True
class ParentResource(Resource):
@classmethod
def get(cls, _id: int):
parent_schema = ParentSchema()
return parent_schema.dump(parent.query.filter_by(id=_id).first()), 200
@classmethod
def put(cls, _id: int):
parent_json = request.get_json()
parent_schema = ParentSchema()
parent_input_data = parent_schema.load(parent_json)
parent = Parent.query.filter_by(id=_id).first()
parent.name = parent_input_data.name
child_names = [child.name.lower() for child in parent.children]
# Check if child is not already in parent children list
for child_input in parent_input_data.children:
if child_input.name.lower() not in child_names:
parent.children.append(child_input)
db.session.add(parent)
db.session.commit()
return {"message": "Updated"}, 200
api.add_resource(ParentResource, "/parent/<int:_id>")
if __name__ == "__main__":
db.create_all()
app.logger.info("Starting app...")
app.run("127.0.0.1", 3003)
當我嘗試通過添加一些新子項來更新父項時,我收到一個唯一鍵約束錯誤,因為 SQLAlchemy 似乎正在嘗試在父表中運行插入查詢,而不是嘗試更新父表記錄。 父表中已經有一條同名“ABCD”的記錄,即我只是嘗試保持父名稱不變並更新子表。
這是我給 PUT 請求的輸入。
{
"name": "ABCD",
"children": [
"Tom",
"Spot"
]
}
有人可以幫我理解我哪里出錯了嗎? 當我嘗試更新父級而不嘗試更新子級時,更新似乎按預期工作。 僅當我嘗試更新子關系時才會出現此問題。
嘗試將您的查詢從使用INSERT INTO
更改為使用UPDATE
。 INSERT INTO
嘗試添加新記錄,而UPDATE
將修改現有記錄。
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