Python Flask app.run是否创建实体副本？

我使用了Python（3.6.4）、Flask（0.12.2）、Flask_admin（1.5.1）和Flask_sqlalchemy（2.3.2）的简单堆栈。我选择SQLite作为我的数据库

我的项目结构相当简单：

1） shared_db.py

from flask_sqlalchemy import SQLAlchemy 
db = SQLAlchemy()

from shared_db import db

class City(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)

def fill_data(app):
    with app.app_context():
        db.create_all()
        db.session.add(City(name="Moscow"))
        db.session.add(City(name="New York"))
        db.session.add(City(name="London"))
        db.session.add(City(name="Paris"))
        db.session.commit()

from flask_admin.contrib.sqla import ModelView

from models import City

class CityView(ModelView):
    column_display_pk = True    # to force ids to appear in the Admin panel
    column_hide_backrefs = False
    column_list = ("id", "name")


def create_views(admin, db):
    admin.add_view(CityView(City, db.session))

import os

from flask_admin import Admin
from flask import Flask, jsonify, make_response, request

from shared_db import db
from models import fill_data
from model_views import create_views

app = Flask(__name__)
app.config["SECRET_KEY"] = "123456790"
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////<path to the project>/myDB'
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False

db.init_app(app)
fill_data(app)

admin = Admin(app, 'My app')
create_views(admin, db)

if __name__ == "__main__":
    port = int(os.environ.get('PORT', 5000))
    app.run(host='0.0.0.0', port=port, debug=True)

2） 型号.py

from flask_sqlalchemy import SQLAlchemy 
db = SQLAlchemy()

from shared_db import db

class City(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)

def fill_data(app):
    with app.app_context():
        db.create_all()
        db.session.add(City(name="Moscow"))
        db.session.add(City(name="New York"))
        db.session.add(City(name="London"))
        db.session.add(City(name="Paris"))
        db.session.commit()

from flask_admin.contrib.sqla import ModelView

from models import City

class CityView(ModelView):
    column_display_pk = True    # to force ids to appear in the Admin panel
    column_hide_backrefs = False
    column_list = ("id", "name")


def create_views(admin, db):
    admin.add_view(CityView(City, db.session))

import os

from flask_admin import Admin
from flask import Flask, jsonify, make_response, request

from shared_db import db
from models import fill_data
from model_views import create_views

app = Flask(__name__)
app.config["SECRET_KEY"] = "123456790"
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////<path to the project>/myDB'
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False

db.init_app(app)
fill_data(app)

admin = Admin(app, 'My app')
create_views(admin, db)

if __name__ == "__main__":
    port = int(os.environ.get('PORT', 5000))
    app.run(host='0.0.0.0', port=port, debug=True)

3） 模型视图.py

from flask_sqlalchemy import SQLAlchemy 
db = SQLAlchemy()

from shared_db import db

class City(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)

def fill_data(app):
    with app.app_context():
        db.create_all()
        db.session.add(City(name="Moscow"))
        db.session.add(City(name="New York"))
        db.session.add(City(name="London"))
        db.session.add(City(name="Paris"))
        db.session.commit()

from flask_admin.contrib.sqla import ModelView

from models import City

class CityView(ModelView):
    column_display_pk = True    # to force ids to appear in the Admin panel
    column_hide_backrefs = False
    column_list = ("id", "name")


def create_views(admin, db):
    admin.add_view(CityView(City, db.session))

import os

from flask_admin import Admin
from flask import Flask, jsonify, make_response, request

from shared_db import db
from models import fill_data
from model_views import create_views

app = Flask(__name__)
app.config["SECRET_KEY"] = "123456790"
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////<path to the project>/myDB'
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False

db.init_app(app)
fill_data(app)

admin = Admin(app, 'My app')
create_views(admin, db)

if __name__ == "__main__":
    port = int(os.environ.get('PORT', 5000))
    app.run(host='0.0.0.0', port=port, debug=True)

4） app.py

from flask_sqlalchemy import SQLAlchemy 
db = SQLAlchemy()

from shared_db import db

class City(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)

def fill_data(app):
    with app.app_context():
        db.create_all()
        db.session.add(City(name="Moscow"))
        db.session.add(City(name="New York"))
        db.session.add(City(name="London"))
        db.session.add(City(name="Paris"))
        db.session.commit()

from flask_admin.contrib.sqla import ModelView

from models import City

class CityView(ModelView):
    column_display_pk = True    # to force ids to appear in the Admin panel
    column_hide_backrefs = False
    column_list = ("id", "name")


def create_views(admin, db):
    admin.add_view(CityView(City, db.session))

import os

from flask_admin import Admin
from flask import Flask, jsonify, make_response, request

from shared_db import db
from models import fill_data
from model_views import create_views

app = Flask(__name__)
app.config["SECRET_KEY"] = "123456790"
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////<path to the project>/myDB'
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False

db.init_app(app)
fill_data(app)

admin = Admin(app, 'My app')
create_views(admin, db)

if __name__ == "__main__":
    port = int(os.environ.get('PORT', 5000))
    app.run(host='0.0.0.0', port=port, debug=True)

导入操作系统
从flask_admin导入admin
从烧瓶导入烧瓶，jsonify，作出响应，请求
从共享数据库导入数据库
从模型导入填充数据
从模型视图导入创建视图
app=烧瓶（名称）
app.config[“密钥”]=“123456790”
app.config['SQLALCHEMY\u DATABASE\u URI']='sqlite://///myDB'
app.config[“SQLALCHEMY\u TRACK\u MODIFICATIONS”]=False
db.init_应用程序（应用程序）
填充数据（应用程序）
admin=admin（应用程序“我的应用程序”）
创建视图（管理员、数据库）
如果名称=“\uuuuu main\uuuuuuuu”：
port=int（os.environ.get（'port'，5000））
app.run（host='0.0.0.0'，port=port，debug=True）

---

最后，我删除了

myDB

-文件（如果存在），并使用

python3app.py

运行该应用程序

令人惊讶的是，我最终得到了8个城市，而不是4个城市！我用DB Browser进行了一些调试，发现重复的4个城市就在最后一行代码--

app.run（…）

执行之后创建

---

如何使用预填充的数据库正确运行flask应用程序

如果每次应用程序启动时都需要对数据库进行种子设定，则需要进行填充数据库幂等元的操作。换句话说，在创建对象之前，您需要检查对象是否已经存在（因为当您没有删除数据库时，应用程序完全有可能重新启动）。可能会帮助您通过SQLAlchemy完成此行为