QueryEngine Class Reference

Class for executing queries and updates. More...

#include <QueryEngine.h>

List of all members.

Public Member Functions
ReturnCode	select (int nAttributes, const RelationAttribute attributes[], int nRelations, const char *relations[], int nConditions, const Condition conditions[])
	Executes a SQL "select-from-where" query.
ReturnCode	insert (const char *relName, int nValues, const TypedValue values[])
	Executes a SQL "insert into" command.
ReturnCode	remove (const char *relName, int nConditions, const Condition conditions[])
	Executes a SQL "delete from" command.
ReturnCode	update (const char *relName, const RelationAttribute *left, const AttributeOrValue *right, int nConditions, const Condition conditions[])
	Executes a SQL "update" command.
Static Public Member Functions
static QueryEngine *	getInstance ()
	Gets the singleton QueryEngine instance.

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Detailed Description

Class for executing queries and updates.

The QueryEngine class is used to execute SQL query and update commands in DavisDB. It contains public methods corresponding to the SQL "select," "insert," "delete," and "update" statements supported by the DavisDB command- line shell. Like SystemManager, it is invoked by the command-line shell as a backend component to actually carry out these commands. QueryEngine is a singleton class; a reference to the singleton object is obtained by calling QueryEngine::getInstance.

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Member Function Documentation

ReturnCode QueryEngine::select	(	int	nAttributes,
		const RelationAttribute	attributes[],
		int	nRelations,
		const char *	relations[],
		int	nConditions,
		const Condition	conditions[]
	)

Executes a SQL "select-from-where" query.

Parameters:

	nAttributes	The number of attributes in the "select" clause
	attributes	The list of attributes in the "select" clause
	nRelations	The number of relations in the "from" clause
	relations	The list of relation names in the "from" clause
	nConditions	The number of conditions in the "where" clause
	conditions	The list of conditions in the "where" clause

Executes a SQL "select-from-where" query issued via the DavisDB command- line shell and prints the result of the query to the console via calls to SystemPrinter. Your implementation should check that the query typechecks with respect to the database schema and return a non-zero RC error code if it does not. Returns RC_OK on success, and other RC error codes otherwise. Parameters nAttributes and nRelations are guaranteed to be non-zero, but nConditions may be zero (for queries with no "where" clause).

ReturnCode QueryEngine::insert	(	const char *	relName,
		int	nValues,
		const TypedValue	values[]
	)

Executes a SQL "insert into" command.

Parameters:

	relName	The name of the target relation
	nValues	The number of values to insert
	TypedValue	The list of values to insert

Executes a SQL "insert" command issued via the DavisDB command-line shell by inserting the specified tuple into the specified relation. Returns RC_OK on success, and other RC error codes otherwise. Your implementation should check that the command as issued typechecks against the database schema and return a non-zero RC error code if it does not.

ReturnCode QueryEngine::remove	(	const char *	relName,
		int	nConditions,
		const Condition	conditions[]
	)

Executes a SQL "delete from" command.

Parameters:

	relName	The name of the target relation
	nConditions	The number of "where" conditions
	conditions	The list of "where" conditions

Executes a SQL "delete from" command by deleting any tuples matching the specified conditions from the specified relation. The list of conditions may be empty (nConditions == 0), in which case all tuples should be deleted from the relation. Returns RC_OK on success, and other RC error codes otherwise. Your implementation should check that the command as issued typechecks against the database schema and return a non-zero RC error code if it does not.

ReturnCode QueryEngine::update	(	const char *	relName,
		const RelationAttribute *	left,
		const AttributeOrValue *	right,
		int	nConditions,
		const Condition	conditions[]
	)

Executes a SQL "update" command.

Parameters:

	relName	The name of the target relation
	left	The attribute to be updated
	right	The attribute name or constant whose value should replace that of left
	nConditions	The number of conditions
	conditions	The list of conditions

Executes a SQL "update" command by replacing the value of the left attribute in any tuple matching the conditions with the value of the right attribute or constant. Returns RC_OK on success, and other RC error codes otherwise. Your implementation should check that the command as issued typechecks against the database schema and return a non-zero RC error code if it does not.

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

• QueryEngine.h
• QueryEngine.cpp