Question

我在语法上做了一些愚蠢的错误，但无法弄清楚是什么。

我正在尝试使用 sqlalchemy func来比较DB字段和变量，方法是将它们都放在较小的情况下，但是输出变为null，就好像条件不满意一样。

如果我不使用func并传递静态变量，那么同样适用。

守则：

question = "Hey"
q1 = QuestionsAndAnswers.query.filter(func.lower(QuestionsAndAnswers.question) == func.lower(question)).all()
q2 = QuestionsAndAnswers.query.filter(QuestionsAndAnswers.question == "Hey").all()
print "q1", q1
print "q2", q2

输出：

q1 []
q2 [<intercom_bot.models.QuestionsAndAnswers object at 0x7f1e2c7add50>]

数据库：

+----+-----------------+--------------------------------------------------+------------+
| id | question        | answer                                           | created_at |
+----+-----------------+--------------------------------------------------+------------+
|  1 | Hi              | Hey, Here I am and here you are. How can I help? | NULL       |
|  2 | Hello           | Hey, Here I am and here you are. How can I help? | NULL       |
|  3 | Helo            | Hey, Here I am and here you are. How can I help? | NULL       |
|  4 | Heelo           | Hey, Here I am and here you are. How can I help? | NULL       |
|  5 | Hell            | Hey, Here I am and here you are. How can I help? | NULL       |
|  6 | Hallo           | Hey, Here I am and here you are. How can I help? | NULL       |
|  7 | Hey             | Hey, Here I am and here you are. How can I help? | NULL       |
|  8 | He              | Hey, Here I am and here you are. How can I help? | NULL       |
|  9 | Ho              | Hey, Here I am and here you are. How can I help? | NULL       |
| 10 | I need help     | Hey, Here I am and here you are. How can I help? | NULL       |
| 11 | Help            | Hey, Here I am and here you are. How can I help? | NULL       |
| 12 | can you help me | Hey, Here I am and here you are. How can I help? | NULL       |
| 13 | Greetings       | Hey, Here I am and here you are. How can I help? | NULL       |
+----+-----------------+--------------------------------------------------+------------+

PS：

print QuestionsAndAnswers.query.filter(func.lower(QuestionsAndAnswers.question) == func.lower(question))

给出了这个：

 SELECT questions_and_answers.id AS questions_and_answers_id, questions_and_answers.question AS questions_and_answers_question, questions_and_answers.answer AS questions_and_answers_answer, questions_and_answers.created_at AS questions_and_answers_created_at 
FROM questions_and_answers 
WHERE lower(questions_and_answers.question) = lower(:lower_1)

PPS：这是模特。

class QuestionsAndAnswers(Base):
    """docstring for QuestionsAndAnswers"""
    __tablename__ = 'questions_and_answers'
    id = Column(BIGINT, primary_key=True)
    question = Column(MEDIUMBLOB, nullable=False)
    answer = Column(MEDIUMBLOB, nullable=False)
    created_at = Column(DATETIME, nullable=True,
                        default=datetime.datetime.now())

Answer 1

问题是MySQL运行LOWER()和UPPER() cannot handle binary string types并且只返回未修改的二进制字符串。

正如相关专栏

question = Column(MEDIUMBLOB, nullable=False)

是二进制字符串类型，函数应用程序

func.lower(QuestionsAndAnswers.question)

是无操作，将按原样返回二进制字符串。这意味着比较将在＆＃34;嘿＆＃34;之间进行。和＆＃34;嘿＆＃34;并且谓词不匹配。

正确的解决方法是更改模型，表格和数据以使用适当的文本类型，例如Unicode和UnicodeText，但快速解决方案是添加强制转换：

from sqlalchemy import Unicode, cast

func.lower(cast(QuestionsAndAnswers.question, Unicode))

无法使用SQLAlchemy func.lower来使用MySQL

1 个答案: