Lintel Technologies: Asynchronous DB Operations in Twisted

Twisted is an asynchronous networking framework. Other Database API Implementations have blocking interfaces.

For this reason, twisted.enterprise.adbapi was created. It is a non-blocking interface,which allows you to access a number of different RDBMSes.

General Method to access DB API.

1 ) Create a Connection with db.

db = dbmodule.connect('dbname','user','password')

2) create a cursor.

cursor = db.cursor()

3) do a query.

resultset = cursor.query('SELECT * FROM table WHERE condition=expression')

Cursor blocks to response in asynchronous framework. Those delays are unacceptable when using an asynchronous framework such as Twisted.

To Overcome blocking interface, twisted provides asynchronous wrapper for db module such as twisted.enterprise.adbapi

Database Connection using adbapi API.

To use adbapi, we import dependencies as below

fromtwisted.enterpriseimportadbapi

1) Connect Database using adbapi.ConnectionPool

db = adbapi.ConnectionPool("mysqldb",db="agentdata",user="root",passwd="<yourpassword>")

Here, We do not need to import dbmodule directly.

dbmodule.connect are passed as extra arguments to adbapi.ConnectionPool’s Constructor.

2) Run Database Query

query = ("SELECT * FROM agentdetails WHERE name = '%s'" % (name)) return dbpool.runQuery(query).addCallback(self.receiveResult).addErrback(self.errorquery)

Here, I used ‘%s’ paramstyle for mysql. if you use another database module, you need to use compatible paramstyle. for more, use DB-API specification.

Twisted doesn’t attempt to offer any sort of magic parameter munging runQuery(query,params,…) maps directly onto cursor.execute(query,params,…).

This query returns Deferred, which allows arbitrary callbacks to be called upon completion (or failure).

Demo : Select, Insert and Update query in Database. fromtwisted.enterpriseimportadbapi importdatetime,logging fromtwisted.internetimportreactor """ Test DB : This File do database connection and basic operation. """ log = logging.getLogger("Test DB") dbpool = adbapi.ConnectionPool("MySQLdb",db="agentdata",user="root",passwd="<yourpassword>") class AgentDB(): defgetTime(self): log.info("Get Current Time from System.") time = str(datetime.datetime.now()).split('.')[0] return time defdoSelect(self,name): log.info("Select operation in Database.") query = ("SELECT * FROM agentdetails WHERE name = '%s'" % (name)) return dbpool.runQuery(query).addCallback(self.receiveResult).addErrback(self.errorquery) defreceiveResult(self,result): print "Receive Result" printresult # general purpose method to receive result from defer. return result deferrorquery(self,result): print "error received", result return result defdoInsert(self,name,status,state): log.info("Insert operation in Database.") query = """INSERT INTO agentdetails (name,state,status,logtime) values('%s','%s','%s','%s')""" % ( name,state,status,self.getTime()) return dbpool.runQuery(query).addCallback(self.receiveResult) defdoUpdate(self,name,status,state): log.info("Update operation in Database.") query = ("UPDATE agentdetails SET status = '%s', state = '%s',logtime = '%s' WHERE name = '%s'" % ( status,state, self.getTime(),name)) return dbpool.runQuery(query).addCallback(self.receiveResult) defcheckDB(self): self.doSelect('1011') self.doInsert('Test','Test','Test') self.doUpdate('Test','SecondTest','SecondTest') a= AgentDB() a.checkDB() reactor.run()

Here, I have used MySQLdb api, agentdata as a database name, root as a user, 123456 as a password.

Also, I have created select, insert and update query for select, insert and update operation respectively.

runQuery method returns deferred. for this, add callback and error back to handle success and failure respectively.