使用python转换JSON对象数组

Question

I have the following function in python, which is a query:

The output of this is a table.

def queryNoScan(start_time_prod,date_object,start_time_scan,date_object_scan):
    query_basictable = """
    SELECT t1.Machine, t1.Production, t2.Scanned, (t1.Production-t2.Scanned) as Delta
        FROM
         (SELECT MCH_CODE as Machine, COUNT(CODE) AS Production
                FROM table1
                        WHERE CODE = 'PROD' AND SUBCODE = 'MACH'  
                        AND EVS_START  between '%s'and '%s' and PP_CODE ='A'
                        GROUP BY MCH_CODE) t1 
        INNER JOIN
         (SELECT MCH_CODE as Machine,  COUNT(BARCODE) AS Scanned
                FROM table2
                        WHERE TRC_TIMESTAMP between '%s'and '%s' AND PP_CODE ='A'
                        GROUP BY MCH_CODE) t2 ON t1.Machine=t2.Machine
                        ORDER BY Delta desc
    """ %(start_time_prod,date_object,start_time_scan,date_object_scan)

    scan_data = pd.read_sql(sql=query_basictable, con=engine)

    return scan_data

How can I convert the output of this function to a JSON of strings which I will passed them later in a front end. Like: "machine": {"Machine2": 14317, etc etc

Answer 1

You can use the to_json method from pandas to convert your dataframe into a json string. In the documentation you can also find some helpful examples.

And please don't ignore the comment from chepner since he's right. You should not use the string formatting operation to generate SQL queries.

Instead use the params argument of the read_sql method:

def queryNoScan(start_time_prod, date_object, start_time_scan, date_object_scan):
    query_basictable = """
    SELECT t1.Machine, t1.Production, t2.Scanned, (t1.Production-t2.Scanned) as Delta
        FROM
         (SELECT MCH_CODE as Machine, COUNT(CODE) AS Production
                FROM table1
                        WHERE CODE = 'PROD' AND SUBCODE = 'MACH'  
                        AND EVS_START  between %s and %s and PP_CODE ='A'
                        GROUP BY MCH_CODE) t1 
        INNER JOIN
         (SELECT MCH_CODE as Machine,  COUNT(BARCODE) AS Scanned
                FROM table2
                        WHERE TRC_TIMESTAMP between %s and %s AND PP_CODE ='A'
                        GROUP BY MCH_CODE) t2 ON t1.Machine=t2.Machine
                        ORDER BY Delta desc
    """ 
    params = (start_time_prod, date_object, start_time_scan, date_object_scan)

    scan_data = pd.read_sql(sql=query_basictable, con=engine, params=params)

    return scan_data.to_json()