python - Flask SQL 没有这样的表

Question

我以前尝试过这个方法并且有效，现在我又这样做了，但还是不行。我使用虚拟环境。

db 文件与 init 和 models 位于同一目录中。导入 db 后，我还在 python shell 中执行了 db.create_all() 。当我执行 Students.query.all() 时发生错误。我现在真的很困惑。我将我的代码与我现有的项目进行了比较，结果是相同的。我不明白为什么它不起作用。

Traceback (most recent call last):
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1246, in _execute_context
    cursor, statement, parameters, context
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\engine\default.py", line 581, in do_execute
    cursor.execute(statement, parameters)
sqlite3.OperationalError: no such table: students

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\orm\query.py", line 3211, in all
    return list(self)
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\orm\query.py", line 3367, in __iter__
    return self._execute_and_instances(context)
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\orm\query.py", line 3392, in _execute_and_instances
    result = conn.execute(querycontext.statement, self._params)
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\engine\base.py", line 982, in execute
    return meth(self, multiparams, params)
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\sql\elements.py", line 287, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1101, in _execute_clauseelement
    distilled_params,
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1250, in _execute_context
    e, statement, parameters, cursor, context
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1476, in _handle_dbapi_exception
    util.raise_from_cause(sqlalchemy_exception, exc_info)
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\util\compat.py", line 398, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\util\compat.py", line 152, in reraise
    raise value.with_traceback(tb)
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1246, in _execute_context
    cursor, statement, parameters, context
  File "C:\Users\Martin\Desktop\regtry\venv\lib\site-packages\sqlalchemy\engine\default.py", line 581, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) no such table: students
[SQL: SELECT students.id AS students_id, students.last_name AS students_last_name, students.college AS students_college, students.email AS students_email
FROM students]
(Background on this error at: http://sqlalche.me/e/e3q8)

_ _ 初始化 _ _.py:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

main = Flask(__name__)
main.config['SECRET_KEY'] = '3bce79429ad6b79670e4e800fb4a57b9'
main.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///site.db'

db = SQLAlchemy(main)

from reg import routes

模型.py:

from reg import db

class Students(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    last_name = db.Column(db.String(60), nullable=False)
    college = db.Column(db.String(60), nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)

    def __repr__(self):
        return f"Student('{self.last_name}','{self.college}','{self.email}')"

Answer 1

这可能与您调用 db.create_all() 的位置有关。您必须在定义所有模型后调用它。以下是一个模块中的一个工作示例:

import flask
from flask_sqlalchemy import SQLAlchemy

app = flask.Flask(__name__)
app.config['SECRET_KEY'] = '3bce79429ad6b79670e4e800fb4a57b9'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///site.db'

db = SQLAlchemy(app)


class Students(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    last_name = db.Column(db.String(60), nullable=False)
    college = db.Column(db.String(60), nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)

    def __repr__(self):
        return f"Student('{self.last_name}','{self.college}','{self.email}')"

db.create_all()


@app.route("/students", methods=["GET"])
def all_students():
    students = Students.query.all()
    resp = []
    for student in students:
        resp.append(dict(
            id=student.id,
            last_name=student.last_name,
            college=student.college,
            email=student.email
        ))
    return flask.jsonify(resp), 200


@app.route("/students/<_id>", methods=["GET"])
def student_by_id(_id):
    student = Students.query.get(_id)
    if student:
        resp = dict(
            id=student.id,
            last_name=student.last_name,
            college=student.college,
            email=student.email
        )
        return flask.jsonify(resp), 200
    else:
        return "", 404


@app.route("/students", methods=["POST"])
def add_student():
    req = flask.request.get_json()
    student = Students(**req)
    db.session.add(student)
    db.session.commit()
    resp = flask.make_response()
    resp.headers["Location"] = flask.url_for("student_by_id", _id=student.id)
    return resp, 201

在您的示例中，我没有看到对 db.create_all() 的调用，但我怀疑它位于错误的位置。使用您的示例，我相信如果您将调用从您所在的位置移动到 __init__.py 的末尾，它会起作用:

__init__.py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

main = Flask(__name__)
main.config['SECRET_KEY'] = '3bce79429ad6b79670e4e800fb4a57b9'
main.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///site.db'

db = SQLAlchemy(main)

from reg import routes
db.create_all()