RWDBDeleter
Module: DB Interface Module Group: Data Manipulation Classes
Does not inherit
- Local Index
- Synopsis
- Description
- Example 1
- Example 2
- Related Classes
- Public Constructors
- Public Member Operator
- Public Member Functions
Local Index
Members
|
acquire() asString() clear() errorHandler() |
execute() isReady() isValid() operator=() |
release() RWDBDeleter() setErrorHandler() status() |
table() where() |
Synopsis
#include <rw/db/deleter.h> RWDBDeleter deleter = myTable.deleter();
Description
RWDBDeleter is an encapsulation of an SQL DELETE statement. The where() method of RWDBDeleter is used to specify a WHERE clause. The WHERE clause is encapsulated by an RWDBCriterion, which is some number of RWDBExprs combined with logical operators.
A DELETE 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 a DELETE statement. Consequently, the execute() method of RWDBDeleter returns an RWDBResult, which is a sequence of zero or more RWDBTables. Applications are not obliged to request any tables from the returned object.
RWDBDeleter is designed around the Interface/Implementation paradigm. An RWDBDeleter instance is an interface to a reference-counted implementation; copy constructors and assignment operators produce additional references to a shared implementation. An RWDBDeleter implementation is a base class from which a family of database-specific deleter implementations is derived.
Example 1
For this example, we delete all the red hubcaps from the autoParts table:
RWDBTable autoParts = myDbase.table("autoParts");
RWDBDeleter deleter = autoParts.deleter();
deleter.where(autoParts["name"] == "hubcap" &&
autoParts["color"] == "red");
deleter.execute();
Example 2
For this example, we delete all parts with a specific id by repeatedly using binding to a variable containing the id:
RWDBTable allParts = myDbase.table( "AllParts" );
RWDBConnection connection = myDbase.connection();
RWDBDeleter deleter = allParts.deleter();
int id = 1001;
deleter.where( allParts["id"] == RWDBBoundExpr( &id ) );
deleter.execute(connection); // delete part number
// 1001
id = 2001;
deleter.execute(connection); // delete part number 2001
Related Classes
The encapsulated WHERE clause of an RWDBDeleter is an RWDBCriterion, which is composed of RWDBExprs. See RWDBCriterion, RWDBExpr, and RWDBColumn for details.
The result of execute() is an RWDBResult, which represents a sequence of zero or more RWDBTables. See RWDBResult and RWDBTable for details.
Public Constructors
RWDBDeleter();
The default constructor creates an RWDBDeleter whose status is RWDBStatus::notInitialized. This constructor is provided as a convenience, for example, to declare an array of RWDBDeleters. Usable RWDBDeleters are obtained from RWDBTables.
RWDBDeleter(const RWDBDeleter& deleter);
Copy constructor. Self shares an implementation with deleter.
Public Member Operator
RWDBDeleter& operator=(const RWDBDeleter& deleter);
Assignment operator. Self shares an implementation with deleter.
Public Member Functions
void acquire() 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 nonmultithreaded builds, this function evaluates to a no-op.
RWCString asString() const;
Returns the SQL equivalent of:
DELETE FROM table [ WHERE ...]
This method returns an SQL statement that would be produced by executing self with an implicit connection. This method however does not produce an implicit connection. It uses the time zone setting of the producer RWDBDatabase instance.
The behavior of this asString() 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 asString() with RWDBDatabase::verboseAsString() set to true will result in a string with blob data returned as hex numbers, such as 0x0A32F5.
RWCString asString(bool verbose) const;
Returns the SQL equivalent of:
DELETE FROM table [ WHERE ...]
This method returns an SQL statement that would be produced by executing self with an implicit connection. This method however does not produce an implicit connection. It uses the time zone setting of the producer RWDBDatabase instance.
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 sent to the database for execution. For example, if an RWDBBlob object is bound, calling asString(true) will result in a string with blob data returned as hex numbers, such as 0x0A32F5.
RWCString asString(const RWDBConnection& conn) const;
Returns the SQL equivalent of:
DELETE FROM table [ WHERE ...]
This method returns an SQL statement that would be produced by executing self with conn. It uses the time zone setting of the RWDBConnection instance conn, which can be set programmatically with RWDBConnection::timeZone().
The behavior of this asString() 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 asString() with RWDBDatabase::verboseAsString() set to true will result in a string with blob data returned as hex numbers, such as 0x0A32F5.
RWCString asString(const RWDBConnection& conn, bool verbose) const;
Returns the SQL equivalent of:
DELETE FROM table [ WHERE ...]
This method returns an SQL statement that would be produced by executing self with conn. It uses the time zone setting of the RWDBConnection instance conn, which can be set programmatically with RWDBConnection::timeZone().
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 sent to the database for execution. For example, if an RWDBBlob object is bound, calling asString(true) will result in a string with blob data returned as hex numbers, such as 0x0A32F5.
void clear();
Clears self's WHERE clause and internal controls.
RWDBStatus::ErrorHandler errorHandler() const;
Returns the error handler attached to self.
RWDBResult execute();
Uses a default database connection to cause the SQL statement encapsulated by self to be executed.
RWDBResult execute(const RWDBConnection& connection);
Uses the supplied connection to cause the SQL statement encapsulated by self to be executed. This function can behave asynchronously if executed using an asynchronous connection.
bool 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 isValid() const;
Returns true if self's status is RWDBStatus::ok, otherwise returns false. Does not return false if the previous executed statement failed. You must check the status of the RWDBResult returned from execute() instead of the status of the RWDBDeleter object.
void release() const;
Releases a previously acquired mutex. This function can be called from a const object. Note: in nonmultithreaded builds, this function evaluates to a no-op.
void setErrorHandler(RWDBStatus::ErrorHandler handler);
Installs handler as self's error handler. The supplied handler is inherited by all objects produced by self. By default, the error handler of an RWDBDeleter is inherited from the object that produced it; this method overrides the default. ErrorHandler is declared as a typedef within the scope of RWDBStatus:
typedef void (*ErrorHandler)(const RWDBStatus&);
RWDBStatus status() const;
Returns the current status of self.
RWDBTable table() const;
Returns the RWDBTable that produced self. Returns an RWDBTable whose status is RWDBStatus::notInitialized if self was produced with the default constructor.
RWDBCriterion where() const;
Returns a copy of self's RWDBCriterion, an encapsulated SQL WHERE clause. Returns an empty RWDBCriterion if self has no WHERE clause.
RWDBDeleter& 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 a deleter without a WHERE clause deletes all rows from its table. Returns a reference to self.
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