Question

我正在开发的“ Reddit clone” Web应用程序中使用Elasticsearch实现搜索功能。我想支持搜索线程，用户和子索引，但是当我输入搜索查询并搜索上述3个类别中不包含任何匹配项之一时，我得到了意外的“ OperationalError”，而不是空的结果集。

如我所包含的代码所示，我尝试使用sqlalchemy.orm.query.Query.all（）函数，该函数返回以下错误：

OperationalError: (sqlite3.OperationalError) near "END": syntax error
[SQL: SELECT user.id AS user_id, user.username AS user_username, user.email AS user_email, user.password_hash AS user_password_hash, user.last_sign_in AS user_last_sign_in 
FROM user 
WHERE 1 != 1 ORDER BY CASE user.id END]
(Background on this error at: http://sqlalche.me/e/e3q8)

我研究了其他StackOverflow帖子，发现first（）函数在内部处理数据库结果，如果未找到结果，则返回None，但是当我切换到该函数时，遇到了此错误：

OperationalError: (sqlite3.OperationalError) near "END": syntax error
[SQL: SELECT user.id AS user_id, user.username AS user_username, user.email AS user_email, user.password_hash AS user_password_hash, user.last_sign_in AS user_last_sign_in 
FROM user 
WHERE 1 != 1 ORDER BY CASE user.id END
 LIMIT ? OFFSET ?]
[parameters: (1, 0)]
(Background on this error at: http://sqlalche.me/e/e3q8)

在检查SqlAlchemy的文档时，在任何一个函数中我都没有提到此错误，并且阅读了OperationalError的含义，我担心数据库设置可能不正确。

app / routes.py：这是处理对以下URL发出的搜索请求的路由：http://localhost:5000/search?q=＆index =

@app.route('/search', methods=['GET'])
def search():
    print 'Hit the /search route!'
    if not g.search_form.validate():
        return redirect(url_for('index'))
    page = request.args.get('page', 1, type=int)
    target_index = request.args.get('index', 'thread')
    if target_index == 'thread':
        results, total = Thread.search(g.search_form.q.data, page, app.config['POSTS_PER_PAGE'])
        print 'Called Thread.search(), total results = {}'.format(total['value'])
    elif target_index == 'user':
        results, total = User.search(g.search_form.q.data, page, app.config['POSTS_PER_PAGE'])
        print 'Called User.search(), total results = {}'.format(total['value'])
    elif target_index == 'subreddit':
        results, total = Subreddit.search(g.search_form.q.data, page, app.config['POSTS_PER_PAGE'])
        print 'Called Subreddit.search(), total results = {}'.format(total['value'])
    else:
        return render_template('404.html')
    try:
        results = results.all()
    except OperationalError:
        results = [None]
    total = total['value']
    next_url = url_for('search', index=target_index, q=g.search_form.q.data, page=page + 1) if total > page * app.config['POSTS_PER_PAGE'] else None
    prev_url = url_for('search', index=target_index, q=g.search_form.q.data, page=page - 1) if page > 1 else None
    results_list = zip(results, [None] * len(results)) # Temporarily to match expected input for template
    return render_template('search.html', title=_('Search'), results_list=results_list, next_url=next_url, prev_url=prev_url, query=g.search_form.q.data, index=target_index)

app / models.py：

class SearchableMixin(object):
    @classmethod
    def search(cls, expression, page, per_page):
        ids, total = query_index(cls.__tablename__, expression, page, per_page)
        if total == 0:
            return cls.query.filter_by(id=0), 0
        when = []
        for i in range(len(ids)):
            when.append((ids[i], i))
        return cls.query.filter(cls.id.in_(ids)).order_by(
            db.case(when, value=cls.id)), total

    @classmethod
    def before_commit(cls, session):
        session._changes = {
            'add': list(session.new),
            'update': list(session.dirty),
            'delete': list(session.deleted)
        }

    @classmethod
    def after_commit(cls, session):
        for obj in session._changes['add']:
            if isinstance(obj, SearchableMixin):
                add_to_index(obj.__tablename__, obj)
        for obj in session._changes['update']:
            if isinstance(obj, SearchableMixin):
                add_to_index(obj.__tablename__, obj)
        for obj in session._changes['delete']:
            if isinstance(obj, SearchableMixin):
                remove_from_index(obj.__tablename__, obj)
        session._changes = None

    @classmethod
    def reindex(cls):
        for obj in cls.query:
            add_to_index(cls.__tablename__, obj)

db.event.listen(db.session, 'before_commit', SearchableMixin.before_commit)
db.event.listen(db.session, 'after_commit', SearchableMixin.after_commit)

# Below is one model that implements SearchableMixin to allow searching # for users. Thread and Subreddit models follow the same logic.
class User(db.Model, UserMixin, SearchableMixin):
    __searchable__ = ['username']
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), index=True, unique=True)
    # <Remaining User model fields here...>

app / search.py ：（保留基础搜索功能以查询Elasticsearch索引）

def add_to_index(index, model):
    if not app.elasticsearch:
        return
    payload = {}
    for field in model.__searchable__:
        payload[field] = getattr(model, field)
    app.elasticsearch.index(index=index, doc_type=index, id=model.id,
                                    body=payload)

def remove_from_index(index, model):
    if not app.elasticsearch:
        return
    app.elasticsearch.delete(index=index, doc_type=index, id=model.id)

def query_index(index, query, page, per_page):
    if not app.elasticsearch:
        return [], 0
    search = app.elasticsearch.search(
        index=index,
        body={'query': {'multi_match': {'query': query, 'fields': ['*']}},
              'from': (page - 1) * per_page, 'size': per_page})
    ids = [int(hit['_id']) for hit in search['hits']['hits']]
    return ids, search['hits']['total']

正如我包含的app / routes.py所示，我通过捕获OperationalError并将其视为未找到结果的指示符来进行变通，但是由于all（）文档没有提及它，所以我没想到会引发这种异常。

Answer 1

通过将您检索到的所有字段隐藏在星号后面，我对生成的查询进行了一些简化。

SELECT user.*
FROM user 
WHERE 1 != 1
ORDER BY CASE user.id END

首先，只要1 != 1是where子句，此查询将不返回任何值，因为根据定义，该子句为false。 ids是否为空？这也可能很大程度上解释了格式错误的CASE语句，这是错误的根源。通常，case(dict(a=1, b=2), value=User.name)会产生CASE WHEN name = 'a' THEN 1 WHEN name = 'b' THEN 2 END，可以正确执行。

SqlAlchemy Query.All（）意外返回OperationalError

1 个答案: