how do i skip empty values supplied to %s in python flask mysql connector

Question

For example im doing a query to my database

try:
            dbConn = DatabasePool.getConnection()
            cursor = dbConn.cursor(dictionary=True)
            sqlquery = f"update table set name=%s if(name=%s is not null),description=%s if(description=%s is not null) where jsonid=%s"
            cursor.execute(
                sqlquery, (JSON['name'], JSON['description'], jsonid))

            dbConn.commit()
            rows = cursor.rowcount
            return rows

        finally:
            dbConn.close()

if i leave the name field blank. i will still be able to update my description likewise for my name.

how do i go about it doing it with the %s

i have also tried another way

sql = f"update table set name=if(name is null, name, %s), description = if(description is null, description, %s) where jsonID=%s"
            cursor.execute(
                sql, (JSON['name'], JSON['description'], jsonid))

i have to provide the 2 fields, if not it will throw me an 500 internal server error if one of the field is less.

Answer 1

If the set of fields you're updating is variable, then you need to build your query dynamically. Note here that I add additional "SET" clauses based on which fields are present.

        clauses = []
        values = []
        if JSON['name']:
            clauses.append( 'name=%s' )
            values.append( JSON['name'] )
        if JSON['description']:
            clauses.append( 'description=%s' )
            values.append( JSON['description'] )
        if values:
            values.append( jsonid )
            cursor = dbConn.cursor(dictionary=True)
            sqlquery = "UPDATE table SET " + (','.join(clauses)) + " WHERE jsonid=%s;"
            cursor.execute( sqlquery, values )
            rows = cursor.rowcount
            dbConn.commit()
            return rows

If you have more than just these two fields, you can make it even more automated:

        for column in ('name','description'):
            if JSON[column]:
                clauses.append( column + '=%s' )
                values.append( JSON[column] )

Answer 2

I'm not sure why I'm still facing this error

here is the put route

@app.route('/movie/<int:movieid>', methods=['PUT'])
def updateMovie(movieid):
    try:
        movieJSON = request.json  # body JSON data
        rows = Movie.updateMovie(movieid, movieJSON)
        msg = str(rows)+" row(s) updated"
        output = {"message": msg}
        return jsonify(output), 200
    except Exception as err:
        print(err)
        return jsonify({}), 500

while my movie class

@classmethod
    def updateMovie(cls, movieid, movieJSON):
        clauses = []
        values = []

        if movieJSON['name']:
            clauses.append('name=%s')
            values.append(movieJSON['name'])
        if movieJSON['description']:
            clauses.append('description=%s')
            values.append(movieJSON['description'])
        try:
            if values:
                values.append(movieid)
                dbConn = DatabasePool.getConnection()
                cursor = dbConn.cursor(dictionary=True)
                sql = "update movie set " + \
                    (','.join(clauses)) + " where movieID=%s"
                print(sql)
                print(values)
                cursor.execute(sql, (values))
                dbConn.commit()
                rows = cursor.rowcount
                return rows

        finally:
            dbConn.close()

the print statement which work

update movie set name=%s,description=%s where movieID=%s
['asdasd', 'asdasda123', 21]
127.0.0.1 - - [03/Feb/2022 20:20:22] "PUT /movie/21 HTTP/1.1" 200 -

if i provide 1 of the fields i get

'description'
127.0.0.1 - - [03/Feb/2022 20:14:50] "PUT /movie/21 HTTP/1.1" 500 -

or

'name'
127.0.0.1 - - [03/Feb/2022 20:25:27] "PUT /movie/21 HTTP/1.1" 500 -