我用Python Flask和Flask-SQLAlchemy和sqlalchemy_mptt建表时无法插入节点

Question

当我尝试在 flask shell 中插入根节点时，发生了错误

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/scoping.py", line 553, in commit
    return self._proxied.commit()
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/session.py", line 1903, in commit
    trans.commit(_to_root=True)
  File "<string>", line 2, in commit
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/state_changes.py", line 137, in _go
    ret_value = fn(self, *arg, **kw)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/session.py", line 1218, in commit
    self._prepare_impl()
  File "<string>", line 2, in _prepare_impl
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/state_changes.py", line 137, in _go
    ret_value = fn(self, *arg, **kw)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/session.py", line 1193, in _prepare_impl
    self.session.flush()
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/session.py", line 4155, in flush
    self._flush(objects)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/session.py", line 4292, in _flush
    transaction.rollback(_capture_exception=True)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/util/langhelpers.py", line 147, in __exit__
    raise exc_value.with_traceback(exc_tb)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/session.py", line 4252, in _flush
    flush_context.execute()
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/unitofwork.py", line 467, in execute
    rec.execute(self)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/unitofwork.py", line 644, in execute
    util.preloaded.orm_persistence.save_obj(
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/persistence.py", line 54, in save_obj
    save_obj(base_mapper, [state], uowtransaction, single=True)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/persistence.py", line 60, in save_obj
    for (
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/persistence.py", line 233, in _organize_states_for_save
    mapper.dispatch.before_insert(mapper, connection, state)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/event/attr.py", line 487, in __call__
    fn(*args, **kw)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/orm/events.py", line 889, in wrap
    fn(*arg, **kw)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy_mptt/events.py", line 574, in before_insert
    mptt_before_insert(mapper, connection, instance)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy_mptt/events.py", line 96, in mptt_before_insert
    select(
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/sql/_selectable_constructors.py", line 493, in select
    return Select(*entities)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/sql/selectable.py", line 5161, in __init__
    self._raw_columns = [
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/sql/selectable.py", line 5162, in <listcomp>
    coercions.expect(
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/sql/coercions.py", line 413, in expect
    resolved = impl._literal_coercion(
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/sql/coercions.py", line 652, in _literal_coercion
    self._raise_for_expected(element, argname)
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/sql/coercions.py", line 1143, in _raise_for_expected
    return super()._raise_for_expected(
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/sql/coercions.py", line 711, in _raise_for_expected
    super()._raise_for_expected(
  File "/Users/pingguo/opt/anaconda3/envs/Flask_Web/lib/python3.8/site-packages/sqlalchemy/sql/coercions.py", line 536, in _raise_for_expected
    raise exc.ArgumentError(msg, code=code) from err
sqlalchemy.exc.ArgumentError: Column expression, FROM clause, or other columns clause element expected, got [<sqlalchemy.sql.elements.BinaryExpression object at 0x7fee25170d90>]. Did you mean to say select(<sqlalchemy.sql.elements.BinaryExpression object at 0x7fee25170d90>)?

我认为最重要的信息是这个 这是我的 python 代码

from flask import Flask, render_template
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy_mptt.mixins import BaseNestedSets


app = Flask(__name__)
url = 'sqlite:////' + os.path.join(app.root_path, 'data.db')
app.config['SQLALCHEMY_DATABASE_URI'] = url
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False 

db = SQLAlchemy(app)

class Category(db.Model, BaseNestedSets):
    __tablename__ = 'category'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50), nullable=False)

    def __repr__(self):
        return '<Category {}>'.format(self.name)

这是我的 python 包版本 那是因为 Flask-SQLAlchemy 的版本吗？

遵循最重要的错误提示我在 Github 中找到了 sqlalchemy_mptt 源代码 当我尝试添加根节点时，它似乎会搜索表，并找出当前最大的 tree_id。 如果能找到，root tree_id 就等于它加 1，如果找不到，root tree_id 就等于 1。 但是为什么这部分会出问题，想不通