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#ifndef QUERYEXECUTORREPLACEVIEWS_H
#define QUERYEXECUTORREPLACEVIEWS_H
#include "queryexecutorstep.h"
#include "parser/ast/sqlitecreateview.h"
class SchemaResolver;
/**
* @brief Replaces all references to views in query with SELECTs from those views.
*
* Replacing views with their SELECTs (as subselects) simplifies later tasks
* with the query.
*/
class QueryExecutorReplaceViews : public QueryExecutorStep
{
Q_OBJECT
public:
~QueryExecutorReplaceViews();
bool exec();
protected:
void init();
private:
/**
* @brief View representation in context of QueryExecutorReplaceViews step.
*/
struct View
{
/**
* @brief Creates view.
* @param database Database of the view.
* @param view View name.
*/
View(const QString& database, const QString& view);
/**
* @brief Database of the view.
*/
QString database;
/**
* @brief View name.
*/
QString view;
/**
* @brief Checks if it's the same view as the \p other.
* @param other Other view to compare.
* @return 1 if other view is the same one, or 0 otherwise.
*
* Views are equal if they have equal name and database.
*/
int operator==(const View& other) const;
};
friend uint qHash(const View& view);
/**
* @brief Provides all views existing in the database.
* @param database Database name as typed in the query.
* @return List of view names.
*
* Uses internal cache (using views).
*/
QStringList getViews(const QString& database);
/**
* @brief Reads view's DDL, parses it and returns results.
* @param database Database of the view.
* @param viewName View name.
* @return Parsed view or null pointer if view doesn't exist or could not be parsed.
*
* It uses internal cache (using viewStatements).
*/
SqliteCreateViewPtr getView(const QString& database, const QString& viewName);
/**
* @brief Replaces views in the query with SELECT statements.
* @param select SELECT statement to replace views in.
*
* It explores the \p select looking for view names and replaces them with
* apropriate subselect queries, using getView() calls.
*/
void replaceViews(SqliteSelect* select);
/**
* @brief Tells whether particular SELECT statement has any View as a data source.
* @param select Parsed SELECT statement.
* @param viewsInDatabase Prepared list of views existing in the database.
* @return true if the SELECT uses at least one existing View.
*/
bool usesAnyView(SqliteSelect* select, const QStringList& viewsInDatabase);
/**
* @brief Used for caching view list per database.
*/
QHash<QString,QStringList> views;
/**
* @brief Resolver used several time in this step.
*
* It's stored as member of this class, cause otherwise it would be created
* and deleted many times. Instead it's shared across all calls to resolve something
* from schema.
*/
SchemaResolver* schemaResolver = nullptr;
/**
* @brief Used for caching parsed view statement.
*/
QHash<View,SqliteCreateViewPtr> viewStatements;
};
uint qHash(const QueryExecutorReplaceViews::View& view);
#endif // QUERYEXECUTORREPLACEVIEWS_H
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