source: trunk/src/sql/kernel/qsqlquery.cpp@ 1061

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#include "qsqlquery.h"

//#define QT_DEBUG_SQL

#include "qatomic.h"
#include "qsqlrecord.h"
#include "qsqlresult.h"
#include "qsqldriver.h"
#include "qsqldatabase.h"
#include "private/qsqlnulldriver_p.h"
#include "qvector.h"
#include "qmap.h"

QT_BEGIN_NAMESPACE

class QSqlQueryPrivate
{
public:
    QSqlQueryPrivate(QSqlResult* result);
    ~QSqlQueryPrivate();
    QAtomicInt ref;
    QSqlResult* sqlResult;

    static QSqlQueryPrivate* shared_null();
};

Q_GLOBAL_STATIC_WITH_ARGS(QSqlQueryPrivate, nullQueryPrivate, (0))
Q_GLOBAL_STATIC(QSqlNullDriver, nullDriver)
Q_GLOBAL_STATIC_WITH_ARGS(QSqlNullResult, nullResult, (nullDriver()))

QSqlQueryPrivate* QSqlQueryPrivate::shared_null()
{
    QSqlQueryPrivate *null = nullQueryPrivate();
    null->ref.ref();
    return null;
}

/*!
\internal
*/
QSqlQueryPrivate::QSqlQueryPrivate(QSqlResult* result)
    : ref(1), sqlResult(result)
{
    if (!sqlResult)
        sqlResult = nullResult();
}

QSqlQueryPrivate::~QSqlQueryPrivate()
{
    QSqlResult *nr = nullResult();
    if (!nr || sqlResult == nr)
        return;
    delete sqlResult;
}

/*!
    \class QSqlQuery
    \brief The QSqlQuery class provides a means of executing and
    manipulating SQL statements.

    \ingroup database
    \ingroup shared

    \inmodule QtSql

    QSqlQuery encapsulates the functionality involved in creating,
    navigating and retrieving data from SQL queries which are
    executed on a \l QSqlDatabase. It can be used to execute DML
    (data manipulation language) statements, such as \c SELECT, \c
    INSERT, \c UPDATE and \c DELETE, as well as DDL (data definition
    language) statements, such as \c{CREATE} \c{TABLE}. It can also
    be used to execute database-specific commands which are not
    standard SQL (e.g. \c{SET DATESTYLE=ISO} for PostgreSQL).

    Successfully executed SQL statements set the query's state to
    active so that isActive() returns true. Otherwise the query's
    state is set to inactive. In either case, when executing a new SQL
    statement, the query is positioned on an invalid record. An active
    query must be navigated to a valid record (so that isValid()
    returns true) before values can be retrieved.

    For some databases, if an active query that is a \c{SELECT}
    statement exists when you call \l{QSqlDatabase::}{commit()} or
    \l{QSqlDatabase::}{rollback()}, the commit or rollback will
    fail. See isActive() for details.

    \target QSqlQuery examples

    Navigating records is performed with the following functions:

    \list
    \o next()
    \o previous()
    \o first()
    \o last()
    \o seek()
    \endlist

    These functions allow the programmer to move forward, backward
    or arbitrarily through the records returned by the query. If you
    only need to move forward through the results (e.g., by using
    next()), you can use setForwardOnly(), which will save a
    significant amount of memory overhead and improve performance on
    some databases. Once an active query is positioned on a valid
    record, data can be retrieved using value(). All data is
    transferred from the SQL backend using QVariants.

    For example:

    \snippet doc/src/snippets/sqldatabase/sqldatabase.cpp 7

    To access the data returned by a query, use value(int). Each
    field in the data returned by a \c SELECT statement is accessed
    by passing the field's position in the statement, starting from
    0. This makes using \c{SELECT *} queries inadvisable because the
    order of the fields returned is indeterminate.

    For the sake of efficiency, there are no functions to access a
    field by name (unless you use prepared queries with names, as
    explained below). To convert a field name into an index, use
    record().\l{QSqlRecord::indexOf()}{indexOf()}, for example:

    \snippet doc/src/snippets/sqldatabase/sqldatabase.cpp 8

    QSqlQuery supports prepared query execution and the binding of
    parameter values to placeholders. Some databases don't support
    these features, so for those, Qt emulates the required
    functionality. For example, the Oracle and ODBC drivers have
    proper prepared query support, and Qt makes use of it; but for
    databases that don't have this support, Qt implements the feature
    itself, e.g. by replacing placeholders with actual values when a
    query is executed. Use numRowsAffected() to find out how many rows
    were affected by a non-\c SELECT query, and size() to find how
    many were retrieved by a \c SELECT.

    Oracle databases identify placeholders by using a colon-name
    syntax, e.g \c{:name}. ODBC simply uses \c ? characters. Qt
    supports both syntaxes, with the restriction that you can't mix
    them in the same query.

    You can retrieve the values of all the fields in a single variable
    (a map) using boundValues().

    \section1 Approaches to Binding Values

    Below we present the same example using each of the four
    different binding approaches, as well as one example of binding
    values to a stored procedure.

    \bold{Named binding using named placeholders:}

    \snippet doc/src/snippets/sqldatabase/sqldatabase.cpp 9

    \bold{Positional binding using named placeholders:}

    \snippet doc/src/snippets/sqldatabase/sqldatabase.cpp 10

    \bold{Binding values using positional placeholders (version 1):}

    \snippet doc/src/snippets/sqldatabase/sqldatabase.cpp 11

    \bold{Binding values using positional placeholders (version 2):}

    \snippet doc/src/snippets/sqldatabase/sqldatabase.cpp 12

    \bold{Binding values to a stored procedure:}

    This code calls a stored procedure called \c AsciiToInt(), passing
    it a character through its in parameter, and taking its result in
    the out parameter.

    \snippet doc/src/snippets/sqldatabase/sqldatabase.cpp 13

    Note that unbound parameters will retain their values.

    Stored procedures that uses the return statement to return values,
    or return multiple result sets, are not fully supported. For specific
    details see \l{SQL Database Drivers}.

    \warning You must load the SQL driver and open the connection before a
    QSqlQuery is created. Also, the connection must remain open while the
    query exists; otherwise, the behavior of QSqlQuery is undefined.

    \sa QSqlDatabase, QSqlQueryModel, QSqlTableModel, QVariant
*/

/*!
    Constructs a QSqlQuery object which uses the QSqlResult \a result
    to communicate with a database.
*/

QSqlQuery::QSqlQuery(QSqlResult *result)
{
    d = new QSqlQueryPrivate(result);
}

/*!
    Destroys the object and frees any allocated resources.
*/

QSqlQuery::~QSqlQuery()
{
    if (!d->ref.deref())
        delete d;
}

/*!
    Constructs a copy of \a other.
*/

QSqlQuery::QSqlQuery(const QSqlQuery& other)
{
    d = other.d;
    d->ref.ref();
}

/*!
    \internal
*/
static void qInit(QSqlQuery *q, const QString& query, QSqlDatabase db)
{
    QSqlDatabase database = db;
    if (!database.isValid())
        database = QSqlDatabase::database(QLatin1String(QSqlDatabase::defaultConnection), false);
    if (database.isValid()) {
        *q = QSqlQuery(database.driver()->createResult());
    }
    if (!query.isEmpty())
        q->exec(query);
}

/*!
    Constructs a QSqlQuery object using the SQL \a query and the
    database \a db. If \a db is not specified, or is invalid, the application's
    default database is used. If \a query is not an empty string, it
    will be executed.

    \sa QSqlDatabase
*/
QSqlQuery::QSqlQuery(const QString& query, QSqlDatabase db)
{
    d = QSqlQueryPrivate::shared_null();
    qInit(this, query, db);
}

/*!
    Constructs a QSqlQuery object using the database \a db.
    If \a db is invalid, the application's default database will be used.

    \sa QSqlDatabase
*/

QSqlQuery::QSqlQuery(QSqlDatabase db)
{
    d = QSqlQueryPrivate::shared_null();
    qInit(this, QString(), db);
}


/*!
    Assigns \a other to this object.
*/

QSqlQuery& QSqlQuery::operator=(const QSqlQuery& other)
{
    qAtomicAssign(d, other.d);
    return *this;
}

/*!
  Returns true if the query is \l{isActive()}{active} and positioned
  on a valid record and the \a field is NULL; otherwise returns
  false. Note that for some drivers, isNull() will not return accurate
  information until after an attempt is made to retrieve data.

  \sa isActive(), isValid(), value()
*/

bool QSqlQuery::isNull(int field) const
{
    if (d->sqlResult->isActive() && d->sqlResult->isValid())
        return d->sqlResult->isNull(field);
    return true;
}

/*!
  
  Executes the SQL in \a query. Returns true and sets the query state
  to \l{isActive()}{active} if the query was successful; otherwise
  returns false. The \a query string must use syntax appropriate for
  the SQL database being queried (for example, standard SQL).

  After the query is executed, the query is positioned on an \e
  invalid record and must be navigated to a valid record before data
  values can be retrieved (for example, using next()).

  Note that the last error for this query is reset when exec() is
  called.

  Example:

  \snippet doc/src/snippets/sqldatabase/sqldatabase.cpp 34

  \sa isActive(), isValid(), next(), previous(), first(), last(),
  seek()
*/

bool QSqlQuery::exec(const QString& query)
{
    if (d->ref != 1) {
        bool fo = isForwardOnly();
        *this = QSqlQuery(driver()->createResult());
        d->sqlResult->setNumericalPrecisionPolicy(d->sqlResult->numericalPrecisionPolicy());
        setForwardOnly(fo);
    } else {
        d->sqlResult->clear();
        d->sqlResult->setActive(false);
        d->sqlResult->setLastError(QSqlError());
        d->sqlResult->setAt(QSql::BeforeFirstRow);
        d->sqlResult->setNumericalPrecisionPolicy(d->sqlResult->numericalPrecisionPolicy());
    }
    d->sqlResult->setQuery(query.trimmed());
    if (!driver()->isOpen() || driver()->isOpenError()) {
        qWarning("QSqlQuery::exec: database not open");
        return false;
    }
    if (query.isEmpty()) {
        qWarning("QSqlQuery::exec: empty query");
        return false;
    }
#ifdef QT_DEBUG_SQL
    qDebug("\n QSqlQuery: %s", query.toLocal8Bit().constData());
#endif
    return d->sqlResult->reset(query);
}

/*!
    Returns the value of field \a index in the current record.

    The fields are numbered from left to right using the text of the
    \c SELECT statement, e.g. in

    \snippet doc/src/snippets/code/src_sql_kernel_qsqlquery.cpp 0

    field 0 is \c forename and field 1 is \c
    surname. Using \c{SELECT *} is not recommended because the order
    of the fields in the query is undefined.

    An invalid QVariant is returned if field \a index does not
    exist, if the query is inactive, or if the query is positioned on
    an invalid record.

    \sa previous() next() first() last() seek() isActive() isValid()
*/

QVariant QSqlQuery::value(int index) const
{
    if (isActive() && isValid() && (index > QSql::BeforeFirstRow))
        return d->sqlResult->data(index);