Django rounds left 3 digits while displaying bigint in mysql - mysql

Question

I am using Django to display rows in mysql.
The table in mysql has a primary key which it bigint, and one of them is 871195445245063168, 18 digits.
But on my page, I see 871195445245063200 displayed, the least 3 digits are rounded. I am wondering where I make it wrong.
1, I define a class with a function named data_query to query mysql.
class MyQuery:
self.conn = MySQLdb.connect(host = self.DBHOST, user = self.DBUSER,
passwd = self.DBPWD,port = self.DBPORT,charset = self.CHARSET,connect_timeout=3)
def data_query(self,sql):
cursor = self.conn.cursor(MySQLdb.cursors.DictCursor)
start = time.time()
cursor.execute(sql)
end = time.time()
sql_time = end - start
column_description = cursor.description
column_name = [ column[0] for column in column_description ]
res = cursor.fetchall()
cursor.close()
self.conn.close()
return res,column_name,sql_time
2, I defined a json encoder as follows
class CJsonEncoder(json.JSONEncoder):
def default(self, obj):
if isinstance(obj, datetime.datetime):
try:
return obj.strftime('%Y-%m-%d %H:%M:%S')
except ValueError:
return str(obj)
elif isinstance(obj, datetime.date):
try:
return obj.strftime('%Y-%m-%d')
except ValueError:
return str(obj)
elif isinstance(obj,datetime.timedelta):
return str(obj)
elif isinstance(obj, decimal.Decimal):
return float(obj)
elif isinstance(obj,ObjectId):
return str(obj)
else:
return json.JSONEncoder.default(self, obj)
3, I get my display like this, with sensitive info replaced.
db = MyQuery(host, user, pwd, port)
sql_statement = 'select * from mytable where Findex=871195445245063168 limit 10'
sql_result, table_column_name, sql_time = db.data_query(sql_statement)
query_result = {}
column_name = column_format(table_column_name)
query_result['column'] = column_name
query_result['data'] = list(sql_result)
return HttpResponse(json.dumps(query_result, cls=CJsonEncoder), content_type='application/json')
So, what I go wrong here? Thanks.

Answer 1

This is a JavaScript issue. Your number is bigger than the largest safe integer in JavaScript (Number.MAX_SAFE_INTEGER), so it is rounded.
You can verify this in your browser console or in node.js
$ node
> x = 871195445245063168
871195445245063200
I assume you are either using your response in some kind of JavaScript frontend or you have some Browser extension to render the JSON, which is written in JavaScript.
If you request that URL with a client like curl, you will see that it is returned correctly from the server.