The QSqlResult class provides an abstract interface for accessing data from specific SQL databases. 更多...
头: | #include <QSqlResult> |
CMake: |
find_package(Qt6 COMPONENTS Sql REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Sql) |
qmake: | QT += sql |
virtual | ~QSqlResult () |
virtual QVariant | handle () const |
enum | BindingSyntax { PositionalBinding, NamedBinding } |
QSqlResult (const QSqlDriver * db ) | |
void | addBindValue (const QVariant & val , QSql::ParamType paramType ) |
int | at () const |
virtual void | bindValue (int index , const QVariant & val , QSql::ParamType paramType ) |
virtual void | bindValue (const QString & placeholder , const QVariant & val , QSql::ParamType paramType ) |
QSql::ParamType | bindValueType (int index ) const |
QSql::ParamType | bindValueType (const QString & placeholder ) const |
QSqlResult::BindingSyntax | bindingSyntax () const |
QVariant | boundValue (int index ) const |
QVariant | boundValue (const QString & placeholder ) const |
int | boundValueCount () const |
QString | boundValueName (int index ) const |
QList<QVariant> & | boundValues () const |
void | clear () |
virtual QVariant | data (int index ) = 0 |
const QSqlDriver * | driver () const |
virtual bool | exec () |
QString | executedQuery () const |
virtual bool | fetch (int index ) = 0 |
virtual bool | fetchFirst () = 0 |
virtual bool | fetchLast () = 0 |
virtual bool | fetchNext () |
virtual bool | fetchPrevious () |
bool | hasOutValues () const |
bool | isActive () const |
bool | isForwardOnly () const |
virtual bool | isNull (int index ) = 0 |
bool | isSelect () const |
bool | isValid () const |
QSqlError | lastError () const |
virtual QVariant | lastInsertId () const |
QString | lastQuery () const |
virtual int | numRowsAffected () = 0 |
virtual bool | prepare (const QString & query ) |
virtual QSqlRecord | record () const |
virtual bool | reset (const QString & query ) = 0 |
void | resetBindCount () |
virtual bool | savePrepare (const QString & query ) |
virtual void | setActive (bool active ) |
virtual void | setAt (int index ) |
virtual void | setForwardOnly (bool forward ) |
virtual void | setLastError (const QSqlError & error ) |
virtual void | setQuery (const QString & query ) |
virtual void | setSelect (bool select ) |
virtual int | size () = 0 |
Normally, you would use QSqlQuery instead of QSqlResult, since QSqlQuery provides a generic wrapper for database-specific implementations of QSqlResult.
If you are implementing your own SQL driver (by subclassing QSqlDriver ), you will need to provide your own QSqlResult subclass that implements all the pure virtual functions and other virtual functions that you need.
另请参阅 QSqlDriver .
This enum type specifies the different syntaxes for specifying placeholders in prepared queries.
常量 | 值 | 描述 |
---|---|---|
QSqlResult::PositionalBinding
|
0
|
Use the ODBC-style positional syntax, with "?" as placeholders. |
QSqlResult::NamedBinding
|
1
|
Use the Oracle-style syntax with named placeholders (e.g., ":id") |
另请参阅 bindingSyntax ().
[protected]
QSqlResult::
QSqlResult
(const
QSqlDriver
*
db
)
Creates a QSqlResult using database driver db . The object is initialized to an inactive state.
[virtual]
QSqlResult::
~QSqlResult
()
销毁对象并释放任何分配资源。
[protected]
void
QSqlResult::
addBindValue
(const
QVariant
&
val
,
QSql::ParamType
paramType
)
Binds the value val of parameter type paramType to the next available position in the current record (row).
另请参阅 bindValue ().
[protected]
int
QSqlResult::
at
() const
Returns the current (zero-based) row position of the result. May return the special values QSql::BeforeFirstRow or QSql::AfterLastRow .
[virtual protected]
void
QSqlResult::
bindValue
(
int
index
, const
QVariant
&
val
,
QSql::ParamType
paramType
)
Binds the value val of parameter type paramType to position index in the current record (row).
另请参阅 addBindValue ().
[virtual protected]
void
QSqlResult::
bindValue
(const
QString
&
placeholder
, const
QVariant
&
val
,
QSql::ParamType
paramType
)
这是重载函数。
Binds the value val of parameter type paramType 到 placeholder name in the current record (row).
注意: Binding an undefined placeholder will result in undefined behavior.
另请参阅 QSqlQuery::bindValue ().
[protected]
QSql::ParamType
QSqlResult::
bindValueType
(
int
index
) const
Returns the parameter type for the value bound at position index .
另请参阅 boundValue ().
[protected]
QSql::ParamType
QSqlResult::
bindValueType
(const
QString
&
placeholder
) const
这是重载函数。
Returns the parameter type for the value bound with the given placeholder 名称。
[protected]
QSqlResult::BindingSyntax
QSqlResult::
bindingSyntax
() const
Returns the binding syntax used by prepared queries.
[protected]
QVariant
QSqlResult::
boundValue
(
int
index
) const
Returns the value bound at position index in the current record (row).
另请参阅 bindValue () 和 boundValues ().
[protected]
QVariant
QSqlResult::
boundValue
(const
QString
&
placeholder
) const
这是重载函数。
Returns the value bound by the given placeholder name in the current record (row).
另请参阅 bindValueType ().
[protected]
int
QSqlResult::
boundValueCount
() const
Returns the number of bound values in the result.
另请参阅 boundValues ().
[protected]
QString
QSqlResult::
boundValueName
(
int
index
) const
Returns the name of the bound value at position index in the current record (row).
另请参阅 boundValue ().
[protected]
QList
<
QVariant
> &QSqlResult::
boundValues
() const
Returns a vector of the result's bound values for the current record (row).
另请参阅 boundValueCount ().
[protected]
void
QSqlResult::
clear
()
Clears the entire result set and releases any associated resources.
[pure virtual protected]
QVariant
QSqlResult::
data
(
int
index
)
Returns the data for field index in the current row as a QVariant . This function is only called if the result is in an active state and is positioned on a valid record and index is non-negative. Derived classes must reimplement this function and return the value of field index , or QVariant() if it cannot be determined.
[protected]
const
QSqlDriver
*QSqlResult::
driver
() const
Returns the driver associated with the result. This is the object that was passed to the constructor.
[virtual protected]
bool
QSqlResult::
exec
()
Executes the query, returning true if successful; otherwise returns false.
另请参阅 prepare ().
[protected]
QString
QSqlResult::
executedQuery
() const
Returns the query that was actually executed. This may differ from the query that was passed, for example if bound values were used with a prepared query and the underlying database doesn't support prepared queries.
[pure virtual protected]
bool
QSqlResult::
fetch
(
int
index
)
Positions the result to an arbitrary (zero-based) row index .
This function is only called if the result is in an active state. Derived classes must reimplement this function and position the result to the row index ,和调用 setAt () with an appropriate value. Return true to indicate success, or false to signify failure.
另请参阅 isActive (), fetchFirst (), fetchLast (), fetchNext (),和 fetchPrevious ().
[pure virtual protected]
bool
QSqlResult::
fetchFirst
()
Positions the result to the first record (row 0) in the result.
This function is only called if the result is in an active state. Derived classes must reimplement this function and position the result to the first record, and call setAt () with an appropriate value. Return true to indicate success, or false to signify failure.
[pure virtual protected]
bool
QSqlResult::
fetchLast
()
Positions the result to the last record (last row) in the result.
This function is only called if the result is in an active state. Derived classes must reimplement this function and position the result to the last record, and call setAt () with an appropriate value. Return true to indicate success, or false to signify failure.
另请参阅 fetch () 和 fetchFirst ().
[virtual protected]
bool
QSqlResult::
fetchNext
()
Positions the result to the next available record (row) in the result.
This function is only called if the result is in an active state. The default implementation calls fetch () with the next index. Derived classes can reimplement this function and position the result to the next record in some other way, and call setAt () with an appropriate value. Return true to indicate success, or false to signify failure.
另请参阅 fetch () 和 fetchPrevious ().
[virtual protected]
bool
QSqlResult::
fetchPrevious
()
Positions the result to the previous record (row) in the result.
This function is only called if the result is in an active state. The default implementation calls fetch () with the previous index. Derived classes can reimplement this function and position the result to the next record in some other way, and call setAt () with an appropriate value. Return true to indicate success, or false to signify failure.
[virtual]
QVariant
QSqlResult::
handle
() const
Returns the low-level database handle for this result set wrapped in a QVariant or an invalid QVariant if there is no handle.
警告: Use this with uttermost care and only if you know what you're doing.
警告: The handle returned here can become a stale pointer if the result is modified (for example, if you clear it).
警告: The handle can be NULL if the result was not executed yet.
警告: PostgreSQL: in forward-only mode, the handle of QSqlResult can change after calling fetch (), fetchFirst (), fetchLast (), fetchNext (), fetchPrevious (), nextResult().
The handle returned here is database-dependent, you should query the type name of the variant before accessing it.
This example retrieves the handle for a sqlite result:
QSqlDatabase db = QSqlDatabase::database("sales"); QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db); QVariant v = query.result()->handle(); if (v.isValid() && qstrcmp(v.typeName(), "sqlite3_stmt*") == 0) { // v.data() returns a pointer to the handle sqlite3_stmt *handle = *static_cast<sqlite3_stmt **>(v.data()); if (handle) { // ... } }
This snippet returns the handle for PostgreSQL or MySQL:
if (qstrcmp(v.typeName(), "PGresult*") == 0) { PGresult *handle = *static_cast<PGresult **>(v.data()); if (handle) { // ... } } if (qstrcmp(v.typeName(), "MYSQL_STMT*") == 0) { MYSQL_STMT *handle = *static_cast<MYSQL_STMT **>(v.data()); if (handle) { // ... } }
另请参阅 QSqlDriver::handle ().
[protected]
bool
QSqlResult::
hasOutValues
() const
返回
true
if at least one of the query's bound values is a
QSql::Out
或
QSql::InOut
;否则返回
false
.
另请参阅 bindValueType ().
[protected]
bool
QSqlResult::
isActive
() const
返回
true
if the result has records to be retrieved; otherwise returns
false
.
[protected]
bool
QSqlResult::
isForwardOnly
() const
返回
true
if you can only scroll forward through the result set; otherwise returns
false
.
另请参阅 setForwardOnly ().
[pure virtual protected]
bool
QSqlResult::
isNull
(
int
index
)
返回
true
if the field at position
index
in the current row is null; otherwise returns
false
.
[protected]
bool
QSqlResult::
isSelect
() const
返回
true
if the current result is from a
SELECT
statement; otherwise returns
false
.
另请参阅 setSelect ().
[protected]
bool
QSqlResult::
isValid
() const
返回
true
if the result is positioned on a valid record (that is, the result is not positioned before the first or after the last record); otherwise returns
false
.
另请参阅 at ().
[protected]
QSqlError
QSqlResult::
lastError
() const
Returns the last error associated with the result.
另请参阅 setLastError ().
[virtual protected]
QVariant
QSqlResult::
lastInsertId
() const
Returns the object ID of the most recent inserted row if the database supports it. An invalid QVariant will be returned if the query did not insert any value or if the database does not report the id back. If more than one row was touched by the insert, the behavior is undefined.
Note that for Oracle databases the row's ROWID will be returned, while for MySQL databases the row's auto-increment field will be returned.
另请参阅 QSqlDriver::hasFeature ().
[protected]
QString
QSqlResult::
lastQuery
() const
Returns the current SQL query text, or an empty string if there isn't one.
另请参阅 setQuery ().
[pure virtual protected]
int
QSqlResult::
numRowsAffected
()
Returns the number of rows affected by the last query executed, or -1 if it cannot be determined or if the query is a
SELECT
语句。
另请参阅 size ().
[virtual protected]
bool
QSqlResult::
prepare
(const
QString
&
query
)
Prepares the given
query
for execution; the query will normally use placeholders so that it can be executed repeatedly. Returns true if the query is prepared successfully; otherwise returns
false
.
另请参阅 exec ().
[virtual protected]
QSqlRecord
QSqlResult::
record
() const
Returns the current record if the query is active; otherwise returns an empty QSqlRecord .
The default implementation always returns an empty QSqlRecord .
另请参阅 isActive ().
[pure virtual protected]
bool
QSqlResult::
reset
(const
QString
&
query
)
Sets the result to use the SQL statement query for subsequent data retrieval.
Derived classes must reimplement this function and apply the query to the database. This function is only called after the result is set to an inactive state and is positioned before the first record of the new result. Derived classes should return true if the query was successful and ready to be used, or false otherwise.
另请参阅 setQuery ().
[protected]
void
QSqlResult::
resetBindCount
()
Resets the number of bind parameters.
[virtual protected]
bool
QSqlResult::
savePrepare
(const
QString
&
query
)
Prepares the given
query
, using the underlying database functionality where possible. Returns
true
if the query is prepared successfully; otherwise returns
false
.
Note: This method should have been called "safePrepare()".
另请参阅 prepare ().
[virtual protected]
void
QSqlResult::
setActive
(
bool
active
)
This function is provided for derived classes to set the internal active state to active .
另请参阅 isActive ().
[virtual protected]
void
QSqlResult::
setAt
(
int
index
)
This function is provided for derived classes to set the internal (zero-based) row position to index .
另请参阅 at ().
[virtual protected]
void
QSqlResult::
setForwardOnly
(
bool
forward
)
Sets forward only mode to forward 。若 forward is true, only fetchNext () is allowed for navigating the results. Forward only mode needs much less memory since results do not have to be cached. By default, this feature is disabled.
Setting forward only to false is a suggestion to the database engine, which has the final say on whether a result set is forward only or scrollable. isForwardOnly () will always return the correct status of the result set.
注意: Calling setForwardOnly after execution of the query will result in unexpected results at best, and crashes at worst.
注意: To make sure the forward-only query completed successfully, the application should check lastError () for an error not only after executing the query, but also after navigating the query results.
警告: PostgreSQL: While navigating the query results in forward-only mode, do not execute any other SQL command on the same database connection. This will cause the query results to be lost.
另请参阅 isForwardOnly (), fetchNext (),和 QSqlQuery::setForwardOnly ().
[virtual protected]
void
QSqlResult::
setLastError
(const
QSqlError
&
error
)
This function is provided for derived classes to set the last error to error .
另请参阅 lastError ().
[virtual protected]
void
QSqlResult::
setQuery
(const
QString
&
query
)
Sets the current query for the result to query . You must call reset () to execute the query on the database.
[virtual protected]
void
QSqlResult::
setSelect
(
bool
select
)
This function is provided for derived classes to indicate whether or not the current statement is a SQL
SELECT
statement. The
select
parameter should be true if the statement is a
SELECT
statement; otherwise it should be false.
另请参阅 isSelect ().
[pure virtual protected]
int
QSqlResult::
size
()
Returns the size of the
SELECT
result, or -1 if it cannot be determined or if the query is not a
SELECT
语句。
另请参阅 numRowsAffected ().