title: unresolved attribute "Column" in class "SQLAlchemy"
body: <p>i use pycharm 5.0 and python3.5.And i download all the liarbry by the build-in function of pycharm(setting-project-project interpreter-"+").other libraries appear well,but some problems happens to flask-SQLAlchemy.</p>
  
  <p>i import flask-SQLAlchemy successfully.however,pycharm remind me that "unresolved attribute reference 'Column' in class'SQLAlchemy'"."unresolved attribute reference 'relationship' in class 'SQLAlchemy'" and so on.</p>
  
  <p>I  have try some ways ,but they didn't work.for example:1.restart 2.remove and redownload 3.refresh the cache.which mention in <a href="https://stackoverflow.com/questions/11725519/pycharm-shows-unresolved-references-error-for-valid-code?rq=1">PyCharm shows unresolved references error for valid code</a></p>
  
  <p>code:</p>
  
  <pre><code>from flask import Flask, redirect, render_template, session, url_for, flash
  from flask_sqlalchemy import SQLAlchemy
  from flask_bootstrap import Bootstrap
  from flask_wtf import Form
  from wtforms import StringField, SubmitField
  import os
  from wtforms.validators import data_required
  
  
  basedir = os.path.abspath(os.path.dirname(__file__))
  
  
  app = Flask(__name__)
  app.config['SECRET_KEY'] = 'hard to guess string'
  app.config['SQLALCHEMY_DATABASE_URI'] =\
      'sqlite:///' + os.path.join(basedir, 'data.sqlite')
  app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True
  
  
  bootstrap = Bootstrap(app)
  
  db = SQLAlchemy(app)
  
  
  class Role(db.Model):
      __tablename__ = 'roles'
      id = db.Column(db.Integer, primary_key=True)
      name = db.Column(db.String(64), unique=True)
      users = db.relationship('User', backref='role', lazy='dynamic')
  
      def __repr__(self):
          return '&lt;Role %r&gt;' % self.name
  
  
  class User(db.Model):
      __tablename__ = 'users'
      id = db.Column(db.Integer, primary_key=True)
      username = db.Column(db.String(64), unique=True, index=True)
      role_id = db.Column(db.Integer, db.ForeignKey('roles.id'))
  
      def __repr__(self):
          return '&lt;User %r&gt;' % self.username
  </code></pre>
  
  <p>how can i  solve this problem?</p>