python - 创建 db.connection 自定义类包装器，不断收到“django.db.utils.InterfaceError: cursor already closed”

Question

我试图为“django.db.connection”制作自定义类包装器，但我不断收到“django.db.utils.InterfaceError：游标已关闭”。

如果没有自定义类包装器（复制自），则工作代码是这样的./manage.py shell：

>>> from django.db import (connection as con)
>>> with con.cursor() as q:
...     q.execute('select * from master.years a where a.years = %s', [str(2019)])
...     f = [f.name for f in q.description]
...     for b in q:
...             print(dict(zip(f,b)))

我的包装webapp/mine/db.py：

class query_00:
    def __init__(self, db_con, db_sql, db_stmt = []):
        self.db_con = db_con
        self.db_sql = db_sql
        self.fields = []

        with db_con.cursor() as self.query:
            self.query.execute(db_sql, db_stmt)
            self.fields = [f.name for f in self.query.description]

        # for entry in self.query:
            # yield dict(zip(self.fields, entry))

        # self.query = db_con.cursor()

    # must return self, because
    # AttributeError: 'NoneType' object has no attribute 'result'
    def __enter__(self):
        return self
        # self.query.execute(self.db_sql, self.db_stmt)
        # self.fields = [f.name for f in self.query.description]
        # pass

    def __exit__(self, exc_type, exc_value, traceback):
        # is this necessary?
        # self.db_con.close()
        pass

    def result(self):
        for entry in self.query.fetchall():
            yield dict(zip(self.fields, entry))

        # not working
        # for entry in self.query:
            # yield dict(zip(self.fields, entry))

        # not working
        # yield dict(zip(self.fields, entry))

        # pass

./manage.py shell然后我通过输入试一下

from django.db import (connection as con)
from mine.db import query_00

# expected usage, attempt 1
q = query_00(con, 'SELECT * FROM master.years a where a.year = %s', [str(2019),])
for b in q.result():
    print(b)

# expected usage, attempt 2
with query_00(con, 'SELECT * FROM master.years a where a.year = %s', [str(2019),]) as q:
    for b in q.result():
        print(b)

python-3，django-2，postgresql-9

（对不起我的英语不好）

标签： pythondjangoclassdjango-database

Answer 1

所以，在阅读了文档之后，我意识到连接在我的 init 方法中被关闭了。

class query_00:
    def __init__(self, db_con, db_sql, db_stmt = []):
        self.db_con = db_con
        self.db_sql = db_sql
        self.fields = []

        with db_con.cursor() as self.query:
            self.query.execute(db_sql, db_stmt)
            self.fields = [f.name for f in self.query.description]
        # the connection only happend inside "with:" block
        # the connection, was already closed here (after with:)

所以，我只需要将 cursor() 保留在变量上

class query_01:
    def __init__(self, db_sql, db_stmt):
        self.db_sql = db_sql
        self.db_stmt = db_stmt
        self.query = connection.cursor()
...

换query.execute()一种方法

...
    def execute(self):
        self.query.execute(self.db_sql, self.db_stmt)
        self.fields = [f.name for f in self.query.description]
...

结果（）

...
    def result(self):
        self.execute()
        for entry in self.query:
            yield self.keyvalue(entry)
...

然后我的课正在工作

with query_00('SELECT * FROM master.years a where a.year = %s', [str(2019),]) as q:
    for b in q.result():
        print(b)