QSqlDatabase ¶

概要 ¶

详细描述 ¶

QSqlDatabase class provides an interface for accessing a database through a connection. An instance of QSqlDatabase represents the connection. The connection provides access to the database via one of the supported database drivers , which are derived from QSqlDriver . Alternatively, you can subclass your own database driver from QSqlDriver 。见 How to Write Your Own Database Driver 了解更多信息。

Create a connection (i.e., an instance of QSqlDatabase ) by calling one of the static addDatabase() 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 call addDatabase() . 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 with setDatabaseName() , setUserName() , setPassword() , setHostName() , setPort() ，和 setConnectOptions() . Then call open() 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 calling database() without the connection name argument:

db = QSqlDatabase.database()
											

QSqlDatabase is a value class. Changes made to a database connection via one instance of QSqlDatabase will affect other instances of QSqlDatabase that represent the same connection. Use cloneDatabase() to create an independent database connection based on an existing one.

警告

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 existing QSqlDatabase , it should be accessed with database() . If you chose to have a QSqlDatabase member variable, this needs to be deleted before the QCoreApplication 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() 。使用 database() with a connection name to get that connection. Use removeDatabase() with a connection name to remove a connection. QSqlDatabase outputs a warning if you try to remove a connection referenced by other QSqlDatabase objects. Use contains() to see if a given connection name is in the list of connections.

Some utility methods:
tables()	returns the list of tables
primaryIndex()	returns a table’s primary index
record()	returns meta-information about a table’s fields
transaction()	starts a transaction
commit()	saves and completes a transaction
rollback()	cancels a transaction
hasFeature()	checks if a driver supports transactions
lastError()	returns information about the last error
drivers()	returns the names of the available SQL drivers
isDriverAvailable()	checks if a particular driver is available
registerSqlDriver()	registers a custom-made driver

注意

exec() is deprecated. Use exec() 代替。

注意

When using transactions, you must start the transaction before you create your query.

另请参阅

QSqlDriver QSqlQuery Qt SQL Threads and the SQL 模块

class QSqlDatabase ¶

QSqlDatabase(driver)

QSqlDatabase(other)

QSqlDatabase(type)

param type

unicode

param driver

QSqlDriver

param other

QSqlDatabase

Creates an empty, invalid QSqlDatabase 对象。使用 addDatabase() , removeDatabase() ，和 database() to get valid QSqlDatabase 对象。

这是重载函数。

Creates a database connection using the given driver .

PySide2.QtSql.QSqlDatabase. defaultConnection ¶

static PySide2.QtSql.QSqlDatabase. addDatabase ( driver [ , connectionName=QLatin1String(defaultConnection) ] ) ¶

参数

• driver – QSqlDriver

• connectionName – unicode

返回类型

QSqlDatabase

static PySide2.QtSql.QSqlDatabase. addDatabase ( type [ , connectionName=QLatin1String(defaultConnection) ] ) ¶

参数

• type – unicode

• connectionName – unicode

返回类型

QSqlDatabase

static PySide2.QtSql.QSqlDatabase. cloneDatabase ( other , connectionName ) ¶

参数

• other – QSqlDatabase

• connectionName – unicode

返回类型

QSqlDatabase

static PySide2.QtSql.QSqlDatabase. cloneDatabase ( other , connectionName ) ¶

参数

• other – unicode

• connectionName – unicode

返回类型

QSqlDatabase

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 对象。

另请参阅

removeDatabase()

PySide2.QtSql.QSqlDatabase. commit ( ) ¶

返回类型

bool

Commits a transaction to the database if the driver supports transactions and a transaction() has been started. Returns true if the operation succeeded. Otherwise it returns false .

注意

For some databases, the commit will fail and return false if there is an active query using the database for a SELECT . Make the query inactive before doing the commit.

调用 lastError() to get information about errors.

另请参阅

isActive() hasFeature() rollback()

PySide2.QtSql.QSqlDatabase. connectOptions ( ) ¶

返回类型

unicode

Returns the connection options string used for this connection. The string may be empty.

另请参阅

setConnectOptions()

PySide2.QtSql.QSqlDatabase. connectionName ( ) ¶

返回类型

unicode

Returns the connection name, which may be empty.

注意

The connection name is not the database name .

另请参阅

addDatabase()

static PySide2.QtSql.QSqlDatabase. connectionNames ( ) ¶

返回类型

字符串列表

Returns a list containing the names of all connections.

另请参阅

contains() database() Threads and the SQL 模块

static PySide2.QtSql.QSqlDatabase. contains ( [ connectionName=QLatin1String(defaultConnection) ] ) ¶

参数

connectionName – unicode

返回类型

bool

返回 true if the list of database connections contains connectionName ；否则返回 false .

另请参阅

connectionNames() database() Threads and the SQL 模块

static PySide2.QtSql.QSqlDatabase. database ( [ connectionName=QLatin1String(defaultConnection) [ , open=true ] ] ) ¶

参数

• connectionName – unicode

• open – bool

返回类型

QSqlDatabase

Returns the database connection called connectionName . The database connection must have been previously added with addDatabase() 。若 open is true (the default) and the database connection is not already open it is opened now. If no connectionName is specified the default connection is used. If connectionName does not exist in the list of databases, an invalid connection is returned.

另请参阅

isOpen() Threads and the SQL 模块

PySide2.QtSql.QSqlDatabase. databaseName ( ) ¶

返回类型

unicode

Returns the connection’s database name, which may be empty.

注意

The database name is not the connection name.

另请参阅

setDatabaseName()

PySide2.QtSql.QSqlDatabase. driver ( ) ¶

返回类型

QSqlDriver

Returns the database driver used to access the database connection.

另请参阅

addDatabase() drivers()

PySide2.QtSql.QSqlDatabase. driverName ( ) ¶

返回类型

unicode

Returns the connection’s driver name.

另请参阅

addDatabase() driver()

static PySide2.QtSql.QSqlDatabase. drivers ( ) ¶

返回类型

字符串列表

Returns a list of all the available database drivers.

另请参阅

registerSqlDriver()

PySide2.QtSql.QSqlDatabase. exec_ ( [ query="" ] ) ¶

参数

query – unicode

返回类型

QSqlQuery

Executes a SQL statement on the database and returns a QSqlQuery 对象。使用 lastError() to retrieve error information. If query is empty, an empty, invalid query is returned and lastError() is not affected.

另请参阅

QSqlQuery lastError()

PySide2.QtSql.QSqlDatabase. hostName ( ) ¶

返回类型

unicode

Returns the connection’s host name; it may be empty.

另请参阅

setHostName()

static PySide2.QtSql.QSqlDatabase. isDriverAvailable ( name ) ¶

参数

name – unicode

返回类型

bool

返回 true if a driver called name is available; otherwise returns false .

另请参阅

drivers()

PySide2.QtSql.QSqlDatabase. isOpen ( ) ¶

返回类型

bool

返回 true if the database connection is currently open; otherwise returns false .

PySide2.QtSql.QSqlDatabase. isOpenError ( ) ¶

返回类型

bool

返回 true if there was an error opening the database connection; otherwise returns false . Error information can be retrieved using the lastError() 函数。

PySide2.QtSql.QSqlDatabase. isValid ( ) ¶

返回类型

bool

返回 true 若 QSqlDatabase has a valid driver.

范例：

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 ( ) ¶

返回类型

QSqlError

Returns information about the last error that occurred on the database.

Failures that occur in conjunction with an individual query are reported by lastError() .

另请参阅

QSqlError lastError()

PySide2.QtSql.QSqlDatabase. numericalPrecisionPolicy ( ) ¶

返回类型

NumericalPrecisionPolicy

Returns the current default precision policy for the database connection.

另请参阅

NumericalPrecisionPolicy setNumericalPrecisionPolicy() numericalPrecisionPolicy() setNumericalPrecisionPolicy()

PySide2.QtSql.QSqlDatabase. open ( ) ¶

返回类型

bool

Opens the database connection using the current connection values. Returns true 当成功时；否则返回 false . Error information can be retrieved using lastError() .

另请参阅

lastError() setDatabaseName() setUserName() setPassword() setHostName() setPort() setConnectOptions()

PySide2.QtSql.QSqlDatabase. open ( user , password ) ¶

参数

• user – unicode

• password – unicode

返回类型

bool

这是重载函数。

Opens the database connection using the given user name and password 。返回 true 当成功时；否则返回 false . Error information can be retrieved using the lastError() 函数。

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.

另请参阅

lastError()

PySide2.QtSql.QSqlDatabase. password ( ) ¶

返回类型

unicode

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 the open() call, or if no password was used.

另请参阅

setPassword()

PySide2.QtSql.QSqlDatabase. port ( ) ¶

返回类型

int

Returns the connection’s port number. The value is undefined if the port number has not been set.

另请参阅

setPort()

PySide2.QtSql.QSqlDatabase. primaryIndex ( tablename ) ¶

参数

tablename – unicode

返回类型

QSqlIndex

Returns the primary index for table tablename . If no primary index exists, an empty QSqlIndex 被返回。

注意

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 文档编制，了解更多信息。

另请参阅

tables() record()

PySide2.QtSql.QSqlDatabase. record ( tablename ) ¶

参数

tablename – unicode

返回类型

QSqlRecord

返回 QSqlRecord populated with the names of all the fields in the table (or view) called tablename . The order in which the fields appear in the record is undefined. If no such table (or view) exists, an empty record is returned.

注意

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 文档编制，了解更多信息。

static PySide2.QtSql.QSqlDatabase. registerSqlDriver ( name , creator ) ¶

参数

• name – unicode

• creator – 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.

范例：

QSqlDatabase::registerSqlDriver("MYDRIVER", new QSqlDriverCreator<QSqlDriver>);
QVERIFY(QSqlDatabase::drivers().contains("MYDRIVER"));
QSqlDatabase db = QSqlDatabase::addDatabase("MYDRIVER");
QVERIFY(db.isValid());
											

QSqlDatabase 拥有所有权对于 creator pointer, so you mustn’t delete it yourself.

另请参阅

drivers()

static PySide2.QtSql.QSqlDatabase. removeDatabase ( connectionName ) ¶

参数

connectionName – unicode

Removes the database connection connectionName from the list of database connections.

警告

There should be no open queries on the database connection when this function is called, otherwise a resource leak will occur.

范例：

// 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 calling connectionName() on the database returned by database() . Note that if a default database hasn’t been created an invalid database will be returned.

另请参阅

database() connectionName() Threads and the SQL 模块

PySide2.QtSql.QSqlDatabase. rollback ( ) ¶

返回类型

bool

Rolls back a transaction on the database, if the driver supports transactions and a transaction() has been started. Returns true if the operation succeeded. Otherwise it returns false .

注意

For some databases, the rollback will fail and return false if there is an active query using the database for a SELECT . Make the query inactive before doing the rollback.

调用 lastError() to get information about errors.

另请参阅

isActive() hasFeature() commit()

PySide2.QtSql.QSqlDatabase. setConnectOptions ( [ options="" ] ) ¶

参数

options – unicode

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 , and open() 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:

范例：

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.

另请参阅

connectOptions()

PySide2.QtSql.QSqlDatabase. setDatabaseName ( name ) ¶

参数

name – unicode

Sets the connection’s database name to name . To have effect, the database name must be set before the connection is opened . Alternatively, you can close() the connection, set the database name, and call open() 再次。

注意

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.

另请参阅

databaseName() setUserName() setPassword() setHostName() setPort() setConnectOptions() open()

PySide2.QtSql.QSqlDatabase. setHostName ( host ) ¶

参数

host – unicode

Sets the connection’s host name to host . To have effect, the host name must be set before the connection is opened . Alternatively, you can close() the connection, set the host name, and call open() 再次。

There is no default value.

另请参阅

hostName() setUserName() setPassword() setDatabaseName() setPort() setConnectOptions() open()

PySide2.QtSql.QSqlDatabase. setNumericalPrecisionPolicy ( precisionPolicy ) ¶

参数

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.

另请参阅

NumericalPrecisionPolicy numericalPrecisionPolicy() setNumericalPrecisionPolicy() numericalPrecisionPolicy()

PySide2.QtSql.QSqlDatabase. setPassword ( password ) ¶

参数

password – unicode

Sets the connection’s password to password . To have effect, the password must be set before the connection is opened . Alternatively, you can close() the connection, set the password, and call open() 再次。

There is no default value.

警告

This function stores the password in plain text within Qt. Use the open() call that takes a password as parameter to avoid this behavior.

另请参阅

password() setUserName() setDatabaseName() setHostName() setPort() setConnectOptions() open()

PySide2.QtSql.QSqlDatabase. setPort ( p ) ¶

参数

p – int

Sets the connection’s port number to port . To have effect, the port number must be set before the connection is opened . Alternatively, you can close() the connection, set the port number, and call open() again..

There is no default value.

另请参阅

port() setUserName() setPassword() setHostName() setDatabaseName() setConnectOptions() open()

PySide2.QtSql.QSqlDatabase. setUserName ( name ) ¶

参数

name – unicode

Sets the connection’s user name to name . To have effect, the user name must be set before the connection is opened . Alternatively, you can close() the connection, set the user name, and call open() 再次。

There is no default value.

另请参阅

userName() setDatabaseName() setPassword() setHostName() setPort() setConnectOptions() open()

PySide2.QtSql.QSqlDatabase. tables ( [ type=QSql.Tables ] ) ¶

参数

type – TableType

返回类型

字符串列表

Returns a list of the database’s tables, system tables and views, as specified by the parameter type .

另请参阅

primaryIndex() record()

PySide2.QtSql.QSqlDatabase. transaction ( ) ¶

返回类型

bool

Begins a transaction on the database if the driver supports transactions. Returns true if the operation succeeded. Otherwise it returns false .

另请参阅

hasFeature() commit() rollback()

PySide2.QtSql.QSqlDatabase. userName ( ) ¶

返回类型

unicode

Returns the connection’s user name; it may be empty.

另请参阅

setUserName()