Flask-Sqlalchemy .in_（）方法不适用于我 [英] Flask-Sqlalchemy .in_() method not working for me
问题描述
现在有两个模型，论坛和线程
我有一个应该生成论坛线程的表记录的Jinja模板，请看下面的内容。
{％为线程在Forum.ForumThreads.filter_by（TagID.in_（TagsToShow））中的线程％：
< TR Class =ThreadRecord>
< TD>< a href ={{thread.ForumID}} / Thread / {{thread.ThreadID}}> {{thread.Title}}< / a>< / TD> ;
< TD> {{thread.User.Name}}< / TD>
< TD> {{thread.CreationDate}}< / TD>
< / TR>
{％endfor％}
以下视图（略为简化）
@ app.route（'/ Forum /< int：URLForumID> / ForumThreads'）
def ThreadsTable URLForumID）：
TagsToShow =（1,2,3,4）
Forum = models.Forum.query.filter_by（ForumID = URLForumID）.first（）
return flask.render_template（' ForumThreads.html'，Forum = Forum，TagsToShow = TagsToShow）
然而，每当我尝试运行我得到了错误jinja2.exceptions.UndefinedError：'TagID'是未定义的。
我试着用 {％for thread in Forum .ForumThreads.filter_by（TagID = 1）：％} ，它似乎运行良好，所以我的问题似乎是我如何调用.in_（）方法。我已经搜索了SQLalchemy的文档但一直无法找到答案，任何人都可以指出我在正确的方向吗？
我不知道是否有帮助，但下面是SQLalchemy模型的两个精简版本。
class论坛（db.Model）：
__tablename__ =Forum
ForumID = db.Column（db.Integer，primary_key = True）
ForumName = db.Column（db.Unicode（20），unique = True，nullable = False）
CreationDate = db.Column（db.DateTime，default = datetime.datetime.utcnow（），nullable = False）
ForumThreads = db.relationship（Thread，backref =Forum，lazy ='dynamic' ）
__table_args__ = {'mysql_engine'：'InnoDB'}
类线程（db.Model）：
__tablename__ =线程
ThreadID = db.Column （db.Integer，primary_key = Tr ue）
ForumID = db.Column（db.Integer，db.ForeignKey（Forum.ForumID），nullable = False）
Title = db.Column（db.Unicode（100），nullable = False）
UserID = db.Column（db.Integer，db.ForeignKey（User.UserID），nullable = False）
TagID = db.Column（db.Integer，db.ForeignKey（
CreationDate = db.Column（db.DateTime，default = datetime.datetime.utcnow（），nullable = False）
__table_args__ =（db.ForeignKeyConstraint（[ 'ForumID']，['Forum.ForumID']），
db.ForeignKeyConstraint（['UserID']，['User.UserID']），
db.ForeignKeyConstraint（['TagID'] ，''TagTypes.TagID']），
{'mysql_engine'：'InnoDB'}）
TagID 是未定义的，因为它不能直接访问。它是 Thread 模型的一部分。你需要通过 Thread 来引用它： Thread.TagID 。
然而，一旦你纠正了这个问题，你很可能会遇到一个 TypeError 。 filter_by 接受关键字参数，而不是位置参数。为了在_ 中使用进行过滤，您需要使用过滤器方法。 filter_by 接受关键字参数并基于此建立过滤器。
SomeModel .query.filter_by（a = 1，b = 2）
大致转换为
$ p $
SELECT * FROM somemodel WHERE a = 1 AND b = 2
另一方面，
过滤器接受表达式（类型 BinaryExpression ）作为论据。上面的查询将表示为：
$ p $ SomeModel.query.filter（SomeModel.a == 1，SomeModel.b == 2 ）
这里， SomeModel.a 是 InstrumentedAttribute 。 InstrumentedAttribute 对象拥有的方法允许您执行比较复杂的等式比较。
SomeModel.query.filter（SomeModel.a.in _（（1，2）））
< （1，2）
SELECT * FROM somemodel $ c>
I'm currently working on a project with Flask and SQLAlchemy, basically forum software like discourse but in Python 3.
There are Two models at the moment, Forum and Threads
I've got a Jinja template that should be generating table records of forum threads, please see below.
{% for thread in Forum.ForumThreads.filter_by(TagID.in_(TagsToShow)): %}
<TR Class="ThreadRecord">
<TD><a href="{{thread.ForumID}}/Thread/{{thread.ThreadID}}">{{thread.Title}}</a></TD>
<TD class="ThreadTag{{thread.TagID}}">{{thread.Tag.Name}}</TD>
<TD>{{thread.PostList.count()}}</TD>
<TD>{{thread.User.Name}}</TD>
<TD>{{thread.CreationDate}}</TD>
</TR>
{% endfor %}
This is called by the following view (slightly simplified).
@app.route('/Forum/<int:URLForumID>/ForumThreads')
def ThreadsTable(URLForumID):
TagsToShow = (1,2,3,4)
Forum = models.Forum.query.filter_by(ForumID=URLForumID).first()
return flask.render_template('ForumThreads.html', Forum=Forum, TagsToShow=TagsToShow)
However, every time I try to run it I get the error "jinja2.exceptions.UndefinedError: 'TagID' is undefined".
I've tried running it with {% for thread in Forum.ForumThreads.filter_by(TagID=1): %} and it seems to run fine, so my problem appears to be in how I am calling the .in_() method. I've searched through the documentation for SQLalchemy but have been unable to find the answer, would anyone be able to point me in the right direction?
I don't know if it helps, but below are the two stripped down versions of the SQLalchemy models used.
class Forum(db.Model):
__tablename__ = "Forum"
ForumID = db.Column(db.Integer, primary_key=True)
ForumName = db.Column(db.Unicode(20), unique=True, nullable=False)
CreationDate = db.Column(db.DateTime, default=datetime.datetime.utcnow(), nullable=False)
ForumThreads = db.relationship("Thread", backref="Forum", lazy='dynamic')
__table_args__ = {'mysql_engine': 'InnoDB'}
class Thread(db.Model):
__tablename__ = "Thread"
ThreadID = db.Column(db.Integer, primary_key=True)
ForumID = db.Column(db.Integer, db.ForeignKey("Forum.ForumID"), nullable=False)
Title = db.Column(db.Unicode(100), nullable=False)
UserID = db.Column(db.Integer, db.ForeignKey("User.UserID"), nullable=False)
TagID = db.Column(db.Integer, db.ForeignKey("TagTypes.TagID"), nullable=False)
CreationDate = db.Column(db.DateTime, default=datetime.datetime.utcnow(), nullable=False)
__table_args__ = (db.ForeignKeyConstraint(['ForumID'], ['Forum.ForumID']),
db.ForeignKeyConstraint(['UserID'], ['User.UserID']),
db.ForeignKeyConstraint(['TagID'], ['TagTypes.TagID']),
{'mysql_engine': 'InnoDB'})
TagID is undefined because it isn't directly accessible. It is part of your Thread model. You need to go through Thread in order to reference it: Thread.TagID.
Once you correct this, however, you will most likely encounter a TypeError. filter_by accepts keyword arguments, not positional ones. In order to filter using in_, you need to use the filter method. filter_by accepts keyword arguments and builds the filters based on that.
SomeModel.query.filter_by(a=1, b=2)
will roughly translate to
SELECT * FROM somemodel WHERE a = 1 AND b = 2
filter, on the other hand, accepts expressions (type BinaryExpression) as arguments. The above query would be expressed as
SomeModel.query.filter(SomeModel.a == 1, SomeModel.b == 2)
Here, SomeModel.a is an InstrumentedAttribute. InstrumentedAttribute objects possess methods that allow you to perform comparisons that are more complex that equality.
SomeModel.query.filter(SomeModel.a.in_((1, 2)))
will roughly translate to
SELECT * FROM somemodel WHERE a IN (1, 2)
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