libpqxx  4.0.1
pqxx::subtransaction Class Reference

"Transaction" nested within another transaction More...

#include <subtransaction.hxx>

Inheritance diagram for pqxx::subtransaction:
pqxx::internal::transactionfocus pqxx::dbtransaction pqxx::internal::namedclass pqxx::transaction_base pqxx::internal::namedclass

Public Member Functions

 subtransaction (dbtransaction &T, const std::string &Name=std::string())
 Nest a subtransaction nested in another transaction. More...
 
 subtransaction (subtransaction &T, const std::string &Name=std::string())
 Nest a subtransaction in another subtransaction. More...
 
- Public Member Functions inherited from pqxx::internal::transactionfocus
 transactionfocus (transaction_base &t)
 
- Public Member Functions inherited from pqxx::internal::namedclass
 namedclass (const std::string &Classname, const std::string &Name="")
 
const std::string & name () const throw ()
 
const std::string & classname () const throw ()
 
std::string description () const
 
- Public Member Functions inherited from pqxx::dbtransaction
virtual ~dbtransaction ()
 
- Public Member Functions inherited from pqxx::transaction_base
virtual ~transaction_base ()=0
 
void commit ()
 Commit the transaction. More...
 
void abort ()
 Abort the transaction. More...
 
std::string esc (const char str[]) const
 Escape string for use as SQL string literal in this transaction. More...
 
std::string esc (const char str[], size_t maxlen) const
 Escape string for use as SQL string literal in this transaction. More...
 
std::string esc (const std::string &str) const
 Escape string for use as SQL string literal in this transaction. More...
 
std::string esc_raw (const unsigned char str[], size_t len) const
 Escape binary data for use as SQL string literal in this transaction. More...
 
std::string esc_raw (const std::string &) const
 Escape binary data for use as SQL string literal in this transaction. More...
 
template<typename T >
std::string quote (const T &t) const
 Represent object as SQL string, including quoting & escaping. More...
 
std::string quote_raw (const unsigned char str[], size_t len) const
 Binary-escape and quote a binarystring for use as an SQL constant. More...
 
std::string quote_raw (const std::string &str) const
 
std::string quote_name (const std::string &identifier) const
 Escape an SQL identifier for use in a query. More...
 
result exec (const std::string &Query, const std::string &Desc=std::string())
 Execute query. More...
 
result exec (const std::stringstream &Query, const std::string &Desc=std::string())
 
internal::parameterized_invocation parameterized (const std::string &query)
 Parameterize a statement. More...
 
connection_baseconn () const
 Connection this transaction is running in. More...
 
void set_variable (const std::string &Var, const std::string &Val)
 Set session variable in this connection. More...
 
std::string get_variable (const std::string &)
 Get currently applicable value of variable. More...
 
prepare::invocation prepared (const std::string &statement=std::string())
 Execute prepared statement. More...
 
void process_notice (const char Msg[]) const
 Have connection process warning message. More...
 
void process_notice (const std::string &Msg) const
 Have connection process warning message. More...
 

Additional Inherited Members

- Public Types inherited from pqxx::transaction_base
typedef isolation_traits< read_committedisolation_tag
 If nothing else is known, our isolation level is at least read_committed. More...
 
- Protected Member Functions inherited from pqxx::internal::transactionfocus
void register_me ()
 
void unregister_me () throw ()
 
void reg_pending_error (const std::string &) throw ()
 
bool registered () const throw ()
 
- Protected Member Functions inherited from pqxx::dbtransaction
 dbtransaction (connection_base &, const std::string &IsolationString, readwrite_policy rw=read_write)
 
 dbtransaction (connection_base &, bool direct=true, readwrite_policy rw=read_write)
 
void start_backend_transaction ()
 Start a transaction on the backend and set desired isolation level. More...
 
virtual result do_exec (const char Query[])
 Sensible default implemented here: perform query. More...
 
- Protected Member Functions inherited from pqxx::transaction_base
 transaction_base (connection_base &c, bool direct=true)
 Create a transaction (to be called by implementation classes only) More...
 
void Begin ()
 Begin transaction (to be called by implementing class) More...
 
void End () throw ()
 End transaction. To be called by implementing class' destructor. More...
 
result DirectExec (const char C[], int Retries=0)
 Execute query on connection directly. More...
 
void reactivation_avoidance_clear () throw ()
 Forget about any reactivation-blocking resources we tried to allocate. More...
 
- Static Protected Member Functions inherited from pqxx::dbtransaction
static std::string fullname (const std::string &ttype, const std::string &isolation)
 
- Protected Attributes inherited from pqxx::internal::transactionfocus
transaction_basem_Trans
 
- Protected Attributes inherited from pqxx::transaction_base
internal::reactivation_avoidance_counter m_reactivation_avoidance
 Resources allocated in this transaction that make reactivation impossible. More...
 

Detailed Description

"Transaction" nested within another transaction

A subtransaction can be executed inside a backend transaction, or inside another subtransaction. This can be useful when, for example, statements in a transaction may harmlessly fail and you don't want them to abort the entire transaction. Here's an example of how a temporary table may be dropped before re-creating it, without failing if the table did not exist:

void do_job(connection_base &C)
{
const string temptable = "fleetingtable";
// Since we're dealing with a temporary table here, disallow automatic
// recovery of the connection in case it breaks.
C.inhibit_reactivation(true);
work W(C, "do_job");
do_firstpart(W);
// Attempt to delete our temporary table if it already existed
try
{
subtransaction S(W, "droptemp");
S.exec("DROP TABLE " + temptable);
S.commit();
}
catch (const undefined_table &)
{
// Table did not exist. Which is what we were hoping to achieve anyway.
// Carry on without regrets.
}
// S may have gone into a failed state and been destroyed, but the
// upper-level transaction W is still fine. We can continue to use it.
W.exec("CREATE TEMP TABLE " + temptable + "(bar integer, splat varchar)");
do_lastpart(W);
}

(This is just an example. If you really wanted to do drop a table without an error if it doesn't exist, you'd use DROP TABLE IF EXISTS.)

There are no isolation levels inside a transaction. They are not needed because all actions within the same backend transaction are always performed sequentially anyway.

Constructor & Destructor Documentation

pqxx::subtransaction::subtransaction ( dbtransaction T,
const std::string &  Name = std::string() 
)
explicit

Nest a subtransaction nested in another transaction.

pqxx::subtransaction::subtransaction ( subtransaction T,
const std::string &  Name = std::string() 
)
explicit

Nest a subtransaction in another subtransaction.


The documentation for this class was generated from the following files: