RWDBUpdater Class Reference

Encapsulates the SQL UPDATE statement. More...

#include <rw/db/updater.h>

Public Member Functions
	RWDBUpdater ()
	RWDBUpdater (const RWDBUpdater &upd)
void	acquire (void) const
RWCString	asString () const
RWCString	asString (const RWDBConnection &conn) const
RWCString	asString (bool verbose) const
RWCString	asString (const RWDBConnection &conn, bool verbose) const
RWDBStatus	clear ()
RWDBStatus::ErrorHandler	errorHandler () const
RWDBResult	execute ()
RWDBResult	execute (const RWDBConnection &connection)
bool	isReady () const
bool	isValid () const
RWDBUpdater &	operator= (const RWDBUpdater &upd)
RWDBUpdater &	operator[] (size_t index)
void	release (void) const
RWDBUpdater &	set (const RWDBAssignment &assignment)
void	setErrorHandler (RWDBStatus::ErrorHandler handler)
RWDBStatus	status () const
RWDBTable	table () const
RWDBUpdater &	where (const RWDBCriterion &criterion)
RWDBCriterion	where () const

Related Functions
(Note that these are not member functions.)
RWDBUpdater &	operator<< (RWDBUpdater &upd, const RWDBAssignment &assignment)

Detailed Description

RWDBUpdater is an encapsulation of an SQL UPDATE statement. Its methods provide an application with explicit control over the UPDATE statement's SET and WHERE clauses.

The insertion operator operator<<() is used to add encapsulated SET clauses to an RWDBUpdater; the where() method specifies a WHERE clause. The items that are inserted into an RWDBUpdater are RWDBAssignment objects, created by the assign() method of RWDBColumn. The WHERE clause is encapsulated by an RWDBCriterion, which is some number of RWDBExpr objects combined with logical operators.

An UPDATE statement does not normally produce results. However, the DB Interface Module recognizes that some database vendors provide triggers, which can cause results to be generated by an UPDATE statement. Consequently, the execute() method of RWDBUpdater returns an RWDBResult, which is a sequence of zero or more RWDBTable objects. Applications are not obliged to request any tables from the returned object.

RWDBUpdater is designed around the Interface/Implementation paradigm. An RWDBUpdater instance is an interface to a reference-counted implementation; copy constructors and assignment operators produce additional references to a shared implementation. An RWDBUpdater implementation is a base class from which a family of database-specific updater implementations is derived.

Synopsis

#include <rw/db/updater.h>

RWDBUpdater updater = myTable.updater();

See also

The encapsulated WHERE clause of an RWDBUpdater is an RWDBCriterion, which is composed of RWDBExpr objects. Each encapsulated SET clause is an RWDBAssignment, produced by the assign() method of RWDBColumn. See RWDBAssignment, RWDBCriterion, RWDBExpr, and RWDBColumn for details.

The result of RWDBUpdater::execute() is an RWDBResult, which represents a sequence of zero or more RWDBTable objects. See RWDBResult and RWDBTable for details.

Example

Example 1

This example uses an RWDBUpdater to increment the number column of the Inventory table by 50 wherever red is found in the color column.

RWDBTable inventory = myDbase.table("Inventory");
RWDBConnection connection = myDbase.connection();
RWDBUpdater update = inventory.updater();
RWDBColumn number = inventory["number"];
update << number.assign(number + 50);
update.where(inventory["color"] == "red");
update.execute(connection);

Example 2

This example accomplishes the same task as Example 1, but provides bindings to an application variable. This allows the application to repeatedly execute the update with different values without reshifting in values.

RWDBTable inventory = myDbase.table("Inventory");
RWDBConnection connection = myDbase.connection();
RWDBUpdater update = inventory.updater();
RWDBColumn number = inventory["number"];
int increment = 50;
RWCString color = "red";
update << number.assign( number + RWDBBoundExpr( &increment) );
update.where( inventory["color"] == RWDBBoundExpr(&color) );
update.execute(connection);
increment = 100;
color = "gold";
update.execute(connection);

Constructor & Destructor Documentation

RWDBUpdater::RWDBUpdater

(

)

The default constructor creates an RWDBUpdater whose status is RWDBStatus::notInitialized. This constructor is provided as a convenience, for example, for declaring an array of RWDBUpdater objects. Usable RWDBUpdater instances are obtained from RWDBTable instances.

RWDBUpdater::RWDBUpdater

(

const RWDBUpdater &

upd

)

Copy constructor. Self shares an implementation with upd.

Member Function Documentation

void RWDBUpdater::acquire

(

void

)

const

Attempts to acquire the internal mutex lock. If the mutex is already locked by another thread, the function blocks until the mutex is released. This function can be called from a const object.

Note

In single-threaded builds, this function evaluates to a no-op.

RWCString RWDBUpdater::asString ( ) const

inline

Returns the SQL equivalent of:

UPDATE table SET ... [ WHERE ...]

This method returns an SQL statement that would be produced by executing self with an implicit RWDBConnection object. An implicit RWDBConnection object inherits the time zone setting from the producer RWDBDatabase instance. Hence, the time zone setting of the producer RWDBDatabase object will be used for creating the string representations of any RWDateTime instances in self.

The behavior of this method depends upon the RWDBDatabase::verboseAsString() setting in the producer RWDBDatabase instance.

• If verboseAsString() is false, the SQL returned is the same as that passed to the database for execution. This is the default.
• If verboseAsString() is true, any placeholders in the returned SQL are replaced with their bound values.

Note

When the RWDBDatabase::verboseAsString() option is set to true, the SQL returned by this method may not be a valid SQL statement. However, this method's return value is not necessarily the same SQL that is sent to the database for execution. For example, if an RWDBBlob object is bound, calling this method with RWDBDatabase::verboseAsString() set to true will result in a string with blob data returned as hex numbers, such as 0x0A32F5.

See also

RWDBDatabase::timeZone(const RWZone*) for time zone setting on RWDBDatabase.

RWCString RWDBUpdater::asString ( const RWDBConnection &  conn ) const

inline

Returns the SQL equivalent of:

UPDATE table SET ... [ WHERE ...]

This method returns an SQL statement that would be produced by executing self with conn. The time zone setting of conn will be used for creating string representations of any RWDateTime instances in self.

The behavior of this method depends upon the RWDBDatabase::verboseAsString() setting in the producer RWDBDatabase instance.

• If verboseAsString() is false, the SQL returned is the same as that passed to the database for execution. This is the default.
• If verboseAsString() is true, any placeholders in the returned SQL are replaced with their bound values.

Note

When the RWDBDatabase::verboseAsString() option is set to true, the SQL returned by this method may not be a valid SQL statement. However, this method's return value is not necessarily the same SQL that is sent to the database for execution. For example, if an RWDBBlob object is bound, calling this method with RWDBDatabase::verboseAsString() set to true will result in a string with blob data returned as hex numbers, such as 0x0A32F5.

See also

RWDBConnection::timeZone(const RWZone*) for time zone setting on RWDBConnection.

RWCString RWDBUpdater::asString ( bool  verbose ) const

inline

Returns the SQL equivalent of:

UPDATE table SET ... [ WHERE ...]

This method returns an SQL statement that would be produced by executing self with an implicit RWDBConnection object. An implicit RWDBConnection object inherits the time zone setting from the producer RWDBDatabase instance. Hence, the time zone setting of the producer RWDBDatabase object will be used for creating the string representations of any RWDateTime instances in self.

The behavior of this method depends on the value of verbose, and is independent of the RWDBDatabase::verboseAsString() setting.

• If verbose is false, the SQL returned is the same as that passed to the database for execution.
• If verbose is true, any placeholders in the returned SQL are replaced with their bound values although the SQL passed to the database for execution will not be affected.

Note

The SQL returned by this method when verbose is true may not be a valid SQL statement. However, this is not necessarily the same SQL that is sent to the database for execution. For example, if an RWDBBlob object is bound, calling this method with verbose as true will result in a string with blob data returned as hex numbers, such as 0x0A32F5.

See also

RWDBDatabase::timeZone(const RWZone*) for time zone setting on RWDBDatabase.

RWCString RWDBUpdater::asString ( const RWDBConnection &  conn, bool  verbose  ) const

inline

Returns the SQL equivalent of:

UPDATE table SET ... [ WHERE ...]

This method returns an SQL statement that would be produced by executing self with conn. The time zone setting of conn will be used for creating string representations of any RWDateTime instances in self.

The behavior of this method depends on the value of verbose, and is independent of the RWDBDatabase::verboseAsString() setting.

• If verbose is false, the SQL returned is the same as that passed to the database for execution.
• If verbose is true, any placeholders in the returned SQL are replaced with their bound values although the SQL passed to the database for execution will not be affected.

Note

The SQL returned by this method when verbose is true may not be a valid SQL statement. However, this is not necessarily the same SQL that is sent to the database for execution. For example, if an RWDBBlob object is bound, calling this method with verbose as true will result in a string with blob data returned as hex numbers, such as 0x0A32F5.

See also

RWDBConnection::timeZone(const RWZone*) for time zone setting on RWDBConnection.

RWDBStatus RWDBUpdater::clear

(

)

Clears self's list of assignments, WHERE clauses, and internal controls.

RWDBStatus::ErrorHandler RWDBUpdater::errorHandler

(

)

const

Returns the error handler attached to self.

RWDBResult RWDBUpdater::execute

(

)

Uses a default database connection to execute the SQL statement encapsulated by self.

RWDBResult RWDBUpdater::execute

(

const RWDBConnection &

connection

)

Uses the supplied connection to execute the SQL statement encapsulated by self. This function can behave asynchronously if executed using an asynchronous connection.

bool RWDBUpdater::isReady

(

)

const

Returns true if the object is in ready state, indicating that accessing the object will not block. Accessing a nonready object may potentially block.

bool RWDBUpdater::isValid

(

)

const

Returns true if self's status is RWDBStatus::ok, otherwise returns false. Does not return false if the previously executed statement failed. In this case, you must check the status of the RWDBResult returned from execute() instead of the status of the RWDBUpdater object.

RWDBUpdater& RWDBUpdater::operator=

(

const RWDBUpdater &

upd

)

Assignment operator. Self shared an implementation with upd.

RWDBUpdater& RWDBUpdater::operator[]

(

size_t

index

)

Sets self's current position to index.

void RWDBUpdater::release

(

void

)

const

Releases a previously acquired mutex. This function can be called from a const object.

Note

In single-threaded builds, this function evaluates to a no-op.

RWDBUpdater& RWDBUpdater::set

(

const RWDBAssignment &

assignment

)

Adds the encapsulated SET clause represented by assignment to self. Equivalent to inserting assignment into self. Returns a reference to self.

void RWDBUpdater::setErrorHandler

(

RWDBStatus::ErrorHandler

handler

)

Installs handler as self's error handler. The supplied handler is inherited by all objects produced by self. By default, an RWDBStatus::ErrorHandler is inherited from the object that produced self; this method overrides the default.

RWDBStatus RWDBUpdater::status

(

)

const

Returns the current status of self.

RWDBTable RWDBUpdater::table

(

)

const

Returns the RWDBTable that produced self. Returns an RWDBTable whose status is RWDBStatus::notInitialized if self was created with the default constructor.

RWDBUpdater& RWDBUpdater::where

(

const RWDBCriterion &

criterion

)

Specifies criterion as self's SQL WHERE clause. If self already has a WHERE clause, this method replaces it. Specifying an empty criterion clears self's WHERE clause. Notice that an updater without a WHERE clause updates all rows in its table. Returns a reference to self.

RWDBCriterion RWDBUpdater::where

(

)

const

Returns a copy of self's RWDBCriterion, an encapsulated SQL WHERE clause. Returns an empty RWDBCriterion if self has no WHERE clause.

Friends And Related Function Documentation

RWDBUpdater& operator<< ( RWDBUpdater &  upd, const RWDBAssignment &  assignment  )

friend

Appends assignment to the encapsulated SET clause in upd. Returns a reference to upd.