QSqlDatabase¶
The
QSqlDatabase
class handles a connection to a database. More…
Synopsis¶
Functions¶
def
close
()def
commit
()def
connectOptions
()def
connectionName
()def
databaseName
()def
driver
()def
driverName
()def
exec_
([query=””])def
hostName
()def
isOpen
()def
isOpenError
()def
isValid
()def
lastError
()def
numericalPrecisionPolicy
()def
open
()def
open
(user, password)def
password
()def
port
()def
primaryIndex
(tablename)def
record
(tablename)def
rollback
()def
setConnectOptions
([options=””])def
setDatabaseName
(name)def
setHostName
(host)def
setNumericalPrecisionPolicy
(precisionPolicy)def
setPassword
(password)def
setPort
(p)def
setUserName
(name)def
tables
([type=QSql.Tables])def
transaction
()def
userName
()
Static functions¶
def
addDatabase
(driver[, connectionName=QLatin1String(defaultConnection)])def
addDatabase
(type[, connectionName=QLatin1String(defaultConnection)])def
cloneDatabase
(other, connectionName)def
cloneDatabase
(other, connectionName)def
connectionNames
()def
contains
([connectionName=QLatin1String(defaultConnection)])def
database
([connectionName=QLatin1String(defaultConnection)[, open=true]])def
drivers
()def
isDriverAvailable
(name)def
registerSqlDriver
(name, creator)def
removeDatabase
(connectionName)
Detailed Description¶
The
QSqlDatabase
class provides an interface for accessing a database through a connection. An instance ofQSqlDatabase
represents the connection. The connection provides access to the database via one of the supported database drivers , which are derived fromQSqlDriver
. Alternatively, you can subclass your own database driver fromQSqlDriver
. See How to Write Your Own Database Driver for more information.Create a connection (i.e., an instance of
QSqlDatabase
) by calling one of the staticaddDatabase()
functions, where you specify the driver or type of driver to use (depending on the type of database) and a connection name. A connection is known by its own name, not by the name of the database it connects to. You can have multiple connections to one database.QSqlDatabase
also supports the concept of a default connection, which is the unnamed connection. To create the default connection, don’t pass the connection name argument when you calladdDatabase()
. Subsequently, the default connection will be assumed if you call any static member function without specifying the connection name. The following snippet shows how to create and open a default connection to a PostgreSQL database:db = QSqlDatabase.addDatabase("QPSQL") db.setHostName("acidalia") db.setDatabaseName("customdb") db.setUserName("mojito") db.setPassword("J0a1m8") ok = db.open()Once the
QSqlDatabase
object has been created, set the connection parameters withsetDatabaseName()
,setUserName()
,setPassword()
,setHostName()
,setPort()
, andsetConnectOptions()
. Then callopen()
to activate the physical connection to the database. The connection is not usable until you open it.The connection defined above will be the default connection, because we didn’t give a connection name to
addDatabase()
. Subsequently, you can get the default connection by callingdatabase()
without the connection name argument:db = QSqlDatabase.database()
QSqlDatabase
is a value class. Changes made to a database connection via one instance ofQSqlDatabase
will affect other instances ofQSqlDatabase
that represent the same connection. UsecloneDatabase()
to create an independent database connection based on an existing one.Warning
It is highly recommended that you do not keep a copy of the
QSqlDatabase
around as a member of a class, as this will prevent the instance from being correctly cleaned up on shutdown. If you need to access an existingQSqlDatabase
, it should be accessed withdatabase()
. If you chose to have aQSqlDatabase
member variable, this needs to be deleted before theQCoreApplication
instance is deleted, otherwise it may lead to undefined behavior.If you create multiple database connections, specify a unique connection name for each one, when you call
addDatabase()
. Usedatabase()
with a connection name to get that connection. UseremoveDatabase()
with a connection name to remove a connection.QSqlDatabase
outputs a warning if you try to remove a connection referenced by otherQSqlDatabase
objects. Usecontains()
to see if a given connection name is in the list of connections.
Some utility methods:
returns the list of tables
returns a table’s primary index
returns meta-information about a table’s fields
starts a transaction
saves and completes a transaction
cancels a transaction
hasFeature()
checks if a driver supports transactions
returns information about the last error
returns the names of the available SQL drivers
checks if a particular driver is available
registers a custom-made driver
Note
exec()
is deprecated. Useexec()
instead.Note
When using transactions, you must start the transaction before you create your query.
See also
QSqlDriver
QSqlQuery
Qt SQLThreads and the SQL Module
- class PySide2.QtSql.QSqlDatabase¶
PySide2.QtSql.QSqlDatabase(driver)
PySide2.QtSql.QSqlDatabase(other)
PySide2.QtSql.QSqlDatabase(type)
- param type:
str
- param driver:
- param other:
Creates an empty, invalid
QSqlDatabase
object. UseaddDatabase()
,removeDatabase()
, anddatabase()
to get validQSqlDatabase
objects.This is an overloaded function.
Creates a database connection using the given
driver
.
- PySide2.QtSql.QSqlDatabase.defaultConnection¶
- static PySide2.QtSql.QSqlDatabase.addDatabase(driver[, connectionName=QLatin1String(defaultConnection)])¶
- Parameters:
driver –
PySide2.QtSql.QSqlDriver
connectionName – str
- Return type:
- static PySide2.QtSql.QSqlDatabase.addDatabase(type[, connectionName=QLatin1String(defaultConnection)])
- Parameters:
type – str
connectionName – str
- Return type:
- static PySide2.QtSql.QSqlDatabase.cloneDatabase(other, connectionName)¶
- Parameters:
other –
PySide2.QtSql.QSqlDatabase
connectionName – str
- Return type:
- static PySide2.QtSql.QSqlDatabase.cloneDatabase(other, connectionName)
- Parameters:
other – str
connectionName – str
- Return type:
- PySide2.QtSql.QSqlDatabase.close()¶
Closes the database connection, freeing any resources acquired, and invalidating any existing
QSqlQuery
objects that are used with the database.This will also affect copies of this
QSqlDatabase
object.See also
- PySide2.QtSql.QSqlDatabase.commit()¶
- Return type:
bool
Commits a transaction to the database if the driver supports transactions and a
transaction()
has been started. Returnstrue
if the operation succeeded. Otherwise it returnsfalse
.Note
For some databases, the commit will fail and return
false
if there is anactive query
using the database for aSELECT
. Make the queryinactive
before doing the commit.Call
lastError()
to get information about errors.See also
- PySide2.QtSql.QSqlDatabase.connectOptions()¶
- Return type:
str
Returns the connection options string used for this connection. The string may be empty.
See also
- PySide2.QtSql.QSqlDatabase.connectionName()¶
- Return type:
str
Returns the connection name, which may be empty.
Note
The connection name is not the
database name
.See also
- static PySide2.QtSql.QSqlDatabase.connectionNames()¶
- Return type:
list of strings
Returns a list containing the names of all connections.
See also
contains()
database()
Threads and the SQL Module
- static PySide2.QtSql.QSqlDatabase.contains([connectionName=QLatin1String(defaultConnection)])¶
- Parameters:
connectionName – str
- Return type:
bool
Returns
true
if the list of database connections containsconnectionName
; otherwise returnsfalse
.See also
connectionNames()
database()
Threads and the SQL Module
- static PySide2.QtSql.QSqlDatabase.database([connectionName=QLatin1String(defaultConnection)[, open=true]])¶
- Parameters:
connectionName – str
open – bool
- Return type:
Returns the database connection called
connectionName
. The database connection must have been previously added withaddDatabase()
. Ifopen
is true (the default) and the database connection is not already open it is opened now. If noconnectionName
is specified the default connection is used. IfconnectionName
does not exist in the list of databases, an invalid connection is returned.See also
isOpen()
Threads and the SQL Module
- PySide2.QtSql.QSqlDatabase.databaseName()¶
- Return type:
str
Returns the connection’s database name, which may be empty.
Note
The database name is not the connection name.
See also
- PySide2.QtSql.QSqlDatabase.driver()¶
- Return type:
Returns the database driver used to access the database connection.
See also
- PySide2.QtSql.QSqlDatabase.driverName()¶
- Return type:
str
Returns the connection’s driver name.
See also
- static PySide2.QtSql.QSqlDatabase.drivers()¶
- Return type:
list of strings
Returns a list of all the available database drivers.
See also
- PySide2.QtSql.QSqlDatabase.exec_([query=""])¶
- Parameters:
query – str
- Return type:
Executes a SQL statement on the database and returns a
QSqlQuery
object. UselastError()
to retrieve error information. Ifquery
is empty, an empty, invalid query is returned andlastError()
is not affected.See also
- PySide2.QtSql.QSqlDatabase.hostName()¶
- Return type:
str
Returns the connection’s host name; it may be empty.
See also
- static PySide2.QtSql.QSqlDatabase.isDriverAvailable(name)¶
- Parameters:
name – str
- Return type:
bool
Returns
true
if a driver calledname
is available; otherwise returnsfalse
.See also
- PySide2.QtSql.QSqlDatabase.isOpen()¶
- Return type:
bool
Returns
true
if the database connection is currently open; otherwise returnsfalse
.
- PySide2.QtSql.QSqlDatabase.isOpenError()¶
- Return type:
bool
Returns
true
if there was an error opening the database connection; otherwise returnsfalse
. Error information can be retrieved using thelastError()
function.
- PySide2.QtSql.QSqlDatabase.isValid()¶
- Return type:
bool
Returns
true
if theQSqlDatabase
has a valid driver.Example:
QSqlDatabase db; qDebug() << db.isValid(); // Returns false db = QSqlDatabase::database("sales"); qDebug() << db.isValid(); // Returns \c true if "sales" connection exists QSqlDatabase::removeDatabase("sales"); qDebug() << db.isValid(); // Returns false
- PySide2.QtSql.QSqlDatabase.lastError()¶
- Return type:
Returns information about the last error that occurred on the database.
Failures that occur in conjunction with an individual query are reported by
lastError()
.See also
- PySide2.QtSql.QSqlDatabase.numericalPrecisionPolicy()¶
- Return type:
Returns the current default precision policy for the database connection.
See also
NumericalPrecisionPolicy
setNumericalPrecisionPolicy()
numericalPrecisionPolicy()
setNumericalPrecisionPolicy()
- PySide2.QtSql.QSqlDatabase.open()¶
- Return type:
bool
Opens the database connection using the current connection values. Returns
true
on success; otherwise returnsfalse
. Error information can be retrieved usinglastError()
.
- PySide2.QtSql.QSqlDatabase.open(user, password)
- Parameters:
user – str
password – str
- Return type:
bool
This is an overloaded function.
Opens the database connection using the given
user
name andpassword
. Returnstrue
on success; otherwise returnsfalse
. Error information can be retrieved using thelastError()
function.This function does not store the password it is given. Instead, the password is passed directly to the driver for opening the connection and it is then discarded.
See also
- PySide2.QtSql.QSqlDatabase.password()¶
- Return type:
str
Returns the connection’s password. An empty string will be returned if the password was not set with
setPassword()
, and if the password was given in theopen()
call, or if no password was used.See also
- PySide2.QtSql.QSqlDatabase.port()¶
- Return type:
int
Returns the connection’s port number. The value is undefined if the port number has not been set.
See also
- PySide2.QtSql.QSqlDatabase.primaryIndex(tablename)¶
- Parameters:
tablename – str
- Return type:
Returns the primary index for table
tablename
. If no primary index exists, an emptyQSqlIndex
is returned.Note
Some drivers, such as the QPSQL driver, may may require you to pass
tablename
in lower case if the table was not quoted when created. See the Qt SQL driver documentation for more information.
- PySide2.QtSql.QSqlDatabase.record(tablename)¶
- Parameters:
tablename – str
- Return type:
Returns a
QSqlRecord
populated with the names of all the fields in the table (or view) calledtablename
. The order in which the fields appear in the record is undefined. If no such table (or view) exists, an empty record is returned.Note
Some drivers, such as the QPSQL driver, may may require you to pass
tablename
in lower case if the table was not quoted when created. See the Qt SQL driver documentation for more information.
- static PySide2.QtSql.QSqlDatabase.registerSqlDriver(name, creator)¶
- Parameters:
name – str
creator –
PySide2.QtSql.QSqlDriverCreatorBase
This function registers a new SQL driver called
name
, within the SQL framework. This is useful if you have a custom SQL driver and don’t want to compile it as a plugin.Example:
QSqlDatabase::registerSqlDriver("MYDRIVER", new QSqlDriverCreator<QSqlDriver>); QVERIFY(QSqlDatabase::drivers().contains("MYDRIVER")); QSqlDatabase db = QSqlDatabase::addDatabase("MYDRIVER"); QVERIFY(db.isValid());
QSqlDatabase
takes ownership of thecreator
pointer, so you mustn’t delete it yourself.See also
- static PySide2.QtSql.QSqlDatabase.removeDatabase(connectionName)¶
- Parameters:
connectionName – str
Removes the database connection
connectionName
from the list of database connections.Warning
There should be no open queries on the database connection when this function is called, otherwise a resource leak will occur.
Example:
// WRONG QSqlDatabase db = QSqlDatabase::database("sales"); QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db); QSqlDatabase::removeDatabase("sales"); // will output a warning // "db" is now a dangling invalid database connection, // "query" contains an invalid result set
The correct way to do it:
{ QSqlDatabase db = QSqlDatabase::database("sales"); QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db); } // Both "db" and "query" are destroyed because they are out of scope QSqlDatabase::removeDatabase("sales"); // correct
To remove the default connection, which may have been created with a call to
addDatabase()
not specifying a connection name, you can retrieve the default connection name by callingconnectionName()
on the database returned bydatabase()
. Note that if a default database hasn’t been created an invalid database will be returned.See also
database()
connectionName()
Threads and the SQL Module
- PySide2.QtSql.QSqlDatabase.rollback()¶
- Return type:
bool
Rolls back a transaction on the database, if the driver supports transactions and a
transaction()
has been started. Returnstrue
if the operation succeeded. Otherwise it returnsfalse
.Note
For some databases, the rollback will fail and return
false
if there is anactive query
using the database for aSELECT
. Make the queryinactive
before doing the rollback.Call
lastError()
to get information about errors.See also
- PySide2.QtSql.QSqlDatabase.setConnectOptions([options=""])¶
- Parameters:
options – str
Sets database-specific
options
. This must be done before the connection is opened, otherwise it has no effect. Another possibility is to close the connection, call , andopen()
the connection again.The format of the
options
string is a semicolon separated list of option names or option=value pairs. The options depend on the database client used:Examples:
db.setConnectOptions("SSL_KEY=client-key.pem;SSL_CERT=client-cert.pem;SSL_CA=ca-cert.pem;CLIENT_IGNORE_SPACE=1"); // use an SSL connection to the server if (!db.open()) { db.setConnectOptions(); // clears the connect option string // ... } // ... // PostgreSQL connection db.setConnectOptions("requiressl=1"); // enable PostgreSQL SSL connections if (!db.open()) { db.setConnectOptions(); // clear options // ... } // ... // ODBC connection db.setConnectOptions("SQL_ATTR_ACCESS_MODE=SQL_MODE_READ_ONLY;SQL_ATTR_TRACE=SQL_OPT_TRACE_ON"); // set ODBC options if (!db.open()) { db.setConnectOptions(); // don't try to set this option // ... } }
Refer to the client library documentation for more information about the different options.
See also
- PySide2.QtSql.QSqlDatabase.setDatabaseName(name)¶
- Parameters:
name – str
Sets the connection’s database name to
name
. To have effect, the database name must be set before the connection isopened
. Alternatively, you canclose()
the connection, set the database name, and callopen()
again.Note
The database name is not the connection name . The connection name must be passed to
addDatabase()
at connection object create time.For the QSQLITE driver, if the database name specified does not exist, then it will create the file for you unless the QSQLITE_OPEN_READONLY option is set.
Additionally,
name
can be set to":memory:"
which will create a temporary database which is only available for the lifetime of the application.For the QOCI (Oracle) driver, the database name is the TNS Service Name.
For the QODBC driver, the
name
can either be a DSN, a DSN filename (in which case the file must have a.dsn
extension), or a connection string.For example, Microsoft Access users can use the following connection string to open an
.mdb
file directly, instead of having to create a DSN entry in the ODBC manager:// ... QSqlDatabase db = QSqlDatabase::addDatabase("QODBC"); db.setDatabaseName("DRIVER={Microsoft Access Driver (*.mdb, *.accdb)};FIL={MS Access};DBQ=myaccessfile.mdb"); if (db.open()) { // success! } // ...
There is no default value.
- PySide2.QtSql.QSqlDatabase.setHostName(host)¶
- Parameters:
host – str
Sets the connection’s host name to
host
. To have effect, the host name must be set before the connection isopened
. Alternatively, you canclose()
the connection, set the host name, and callopen()
again.There is no default value.
- PySide2.QtSql.QSqlDatabase.setNumericalPrecisionPolicy(precisionPolicy)¶
- Parameters:
precisionPolicy –
NumericalPrecisionPolicy
Sets the default numerical precision policy used by queries created on this database connection to
precisionPolicy
.Note: Drivers that don’t support fetching numerical values with low precision will ignore the precision policy. You can use
hasFeature()
to find out whether a driver supports this feature.Note: Setting the default precision policy to
precisionPolicy
doesn’t affect any currently active queries.See also
NumericalPrecisionPolicy
numericalPrecisionPolicy()
setNumericalPrecisionPolicy()
numericalPrecisionPolicy()
- PySide2.QtSql.QSqlDatabase.setPassword(password)¶
- Parameters:
password – str
Sets the connection’s password to
password
. To have effect, the password must be set before the connection isopened
. Alternatively, you canclose()
the connection, set the password, and callopen()
again.There is no default value.
Warning
This function stores the password in plain text within Qt. Use the
open()
call that takes a password as parameter to avoid this behavior.
- PySide2.QtSql.QSqlDatabase.setPort(p)¶
- Parameters:
p – int
Sets the connection’s port number to
port
. To have effect, the port number must be set before the connection isopened
. Alternatively, you canclose()
the connection, set the port number, and callopen()
again..There is no default value.
- PySide2.QtSql.QSqlDatabase.setUserName(name)¶
- Parameters:
name – str
Sets the connection’s user name to
name
. To have effect, the user name must be set before the connection isopened
. Alternatively, you canclose()
the connection, set the user name, and callopen()
again.There is no default value.
- PySide2.QtSql.QSqlDatabase.tables([type=QSql.Tables])¶
- Parameters:
type –
TableType
- Return type:
list of strings
Returns a list of the database’s tables, system tables and views, as specified by the parameter
type
.See also
- PySide2.QtSql.QSqlDatabase.transaction()¶
- Return type:
bool
Begins a transaction on the database if the driver supports transactions. Returns
true
if the operation succeeded. Otherwise it returnsfalse
.See also
- PySide2.QtSql.QSqlDatabase.userName()¶
- Return type:
str
Returns the connection’s user name; it may be empty.
See also
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