com.trolltech.qt.sql
Class QSqlQuery

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.sql.QSqlQuery
All Implemented Interfaces:
QtJambiInterface, java.lang.Cloneable

public class QSqlQuery
extends QtJambiObject
implements java.lang.Cloneable

The QSqlQuery class provides a means of executing and manipulating SQL statements. QSqlQuery encapsulates the functionality involved in creating, navigating and retrieving data from SQL queries which are executed on a QSqlDatabase. It can be used to execute DML (data manipulation language) statements, such as SELECT, INSERT, UPDATE and DELETE, as well as DDL (data definition language) statements, such as CREATETABLE. It can also be used to execute database-specific commands which are not standard SQL (e.g. 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 SELECT statement exists when you call commit() or rollback(), the commit or rollback will fail. See isActive() for details. Navigating records is performed with the following functions:

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:

        QSqlQuery query = new QSqlQuery("SELECT * country FROM artist");
        while (query.next()) {
            String country = query.value(0).toString();
            doSomething(country);
        }
    
To access the data returned by a query, use value(int). Each field in the data returned by a SELECT statement is accessed by passing the field's position in the statement, starting from 0. This makes using 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().indexOf(), for example:

        QSqlQuery query = new QSqlQuery("SELECT * FROM artist");
        int fieldNo = query.record().indexOf("country");
        while (query.next()) {
            String country = query.value(fieldNo).toString();
            doSomething(country);
        }
    
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-SELECT query, and size() to find how many were retrieved by a SELECT.

Oracle databases identify placeholders by using a colon-name syntax, e.g :name. ODBC simply uses ? 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().

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.

Named binding using named placeholders:

        QSqlQuery query = new QSqlQuery();
        query.prepare("INSERT INTO person (id, forename, surname) " +
                      "VALUES (:id, :forename, :surname)");
        query.bindValue(":id", 1001);
        query.bindValue(":forename", "Bart");
        query.bindValue(":surname", "Simpson");
        query.exec();
    
Positional binding using named placeholders:
        QSqlQuery query = new QSqlQuery();
        query.prepare("INSERT INTO person (id, forename, surname) " +
                      "VALUES (:id, :forename, :surname)");
        query.bindValue(0, 1001);
        query.bindValue(1, "Bart");
        query.bindValue(2, "Simpson");
        query.exec();
    
Binding values using positional placeholders (version 1):
        QSqlQuery query = new QSqlQuery();
        query.prepare("INSERT INTO person (id, forename, surname) " +
                      "VALUES (?, ?, ?)");
        query.bindValue(0, 1001);
        query.bindValue(1, "Bart");
        query.bindValue(2, "Simpson");
        query.exec();
    
Binding values using positional placeholders (version 2):
        QSqlQuery query = new QSqlQuery();
        query.prepare("INSERT INTO person (id, forename, surname) " +
                      "VALUES (?, ?, ?)");
        query.addBindValue(1001);
        query.addBindValue("Bart");
        query.addBindValue("Simpson");
        query.exec();
    
Binding values to a stored procedure:

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

        QSqlQuery query = new QSqlQuery();
        query.prepare("CALL AsciiToInt(?, ?)");
        query.bindValue(0, "A");
        query.bindValue(1, 0, QSql.ParamTypeFlag.Out);
        query.exec();
        int i = query.boundValue(1).toInt(); // i is 65
    
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 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.

See also:
QSqlDatabase, QSqlQueryModel, QSqlTableModel, and QVariant.


Nested Class Summary
static class QSqlQuery.BatchExecutionMode
           
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QSqlQuery()
          Constructs a QSqlQuery object using the SQL query and the database db.
QSqlQuery(QSqlDatabase db)
          Constructs a QSqlQuery object using the database db.
QSqlQuery(QSqlQuery other)
          Constructs a copy of other.
QSqlQuery(QSqlResult r)
          Constructs a QSqlQuery object which uses the QSqlResultresult to communicate with a database.
QSqlQuery(java.lang.String query)
          Constructs a QSqlQuery object using the SQL query and the database db.
QSqlQuery(java.lang.String query, QSqlDatabase db)
          Constructs a QSqlQuery object using the SQL query and the database db.
 
Method Summary
 void addBindValue(java.lang.Object val)
          Adds the value val to the list of values when using positional value binding.
 void addBindValue(java.lang.Object val, QSql.ParamType type)
          Adds the value val to the list of values when using positional value binding.
 void addBindValue(java.lang.Object val, QSql.ParamTypeFlag[] type)
          This is an overloaded method provided for convenience.
 int at()
          Returns the current internal position of the query.
 void bindValue(int pos, java.lang.Object val)
          Set the placeholder in position pos to be bound to value val in the prepared statement.
 void bindValue(int pos, java.lang.Object val, QSql.ParamType type)
          Set the placeholder in position pos to be bound to value val in the prepared statement.
 void bindValue(int pos, java.lang.Object val, QSql.ParamTypeFlag[] type)
          This is an overloaded method provided for convenience.
 void bindValue(java.lang.String placeholder, java.lang.Object val)
          Set the placeholder placeholder to be bound to value val in the prepared statement.
 void bindValue(java.lang.String placeholder, java.lang.Object val, QSql.ParamType type)
          Set the placeholder placeholder to be bound to value val in the prepared statement.
 void bindValue(java.lang.String placeholder, java.lang.Object val, QSql.ParamTypeFlag[] type)
          This is an overloaded method provided for convenience.
 java.lang.Object boundValue(int pos)
          Returns the value for the placeholder at position pos.
 java.lang.Object boundValue(java.lang.String placeholder)
          Returns the value for the placeholder.
 java.util.SortedMap boundValues()
          Returns a map of the bound values.
 void clear()
          Clears the result set and releases any resources held by the query.
 QSqlQuery clone()
          This method is reimplemented for internal reasons
 QSqlDriver driver()
          Returns the database driver associated with the query.
 boolean exec()
          Executes a previously prepared SQL query.
 boolean exec(java.lang.String query)
          Executes the SQL in query.
 boolean execBatch()
          Executes a previously prepared SQL query in a batch.
 boolean execBatch(QSqlQuery.BatchExecutionMode mode)
          Executes a previously prepared SQL query in a batch.
 java.lang.String executedQuery()
          Returns the last query that was successfully executed.
 void finish()
          Instruct the database driver that no more data will be fetched from this query until it is re-executed.
 boolean first()
          Retrieves the first record in the result, if available, and positions the query on the retrieved record.
 boolean isActive()
          Returns true if the query is active.
 boolean isForwardOnly()
          Returns true if you can only scroll forward through a result set; otherwise returns false.
 boolean isNull(int field)
          Returns true if the query is active and positioned on a valid record and the field is NULL; otherwise returns false.
 boolean isSelect()
          Returns true if the current query is a SELECT statement; otherwise returns false.
 boolean isValid()
          Returns true if the query is currently positioned on a valid record; otherwise returns false.
 boolean last()
          Retrieves the last record in the result, if available, and positions the query on the retrieved record.
 QSqlError lastError()
          Returns error information about the last error (if any) that occurred with this query.
 java.lang.Object lastInsertId()
          Returns the object ID of the most recent inserted row if the database supports it.
 java.lang.String lastQuery()
          Returns the text of the current query being used, or an empty string if there is no current query text.
 boolean next()
          Retrieves the next record in the result, if available, and positions the query on the retrieved record.
 boolean nextResult()
          Discards the current result set and navigates to the next if available.
 QSql.NumericalPrecisionPolicy numericalPrecisionPolicy()
          Returns the current precision policy.
 int numRowsAffected()
          Returns the number of rows affected by the result's SQL statement, or -1 if it cannot be determined.
 boolean prepare(java.lang.String query)
          Prepares the SQL query query for execution.
 boolean previous()
          Retrieves the previous record in the result, if available, and positions the query on the retrieved record.
 QSqlRecord record()
          Returns a QSqlRecord containing the field information for the current query.
 QSqlResult result()
          Returns the result associated with the query.
 boolean seek(int i)
          Retrieves the record at position index, if available, and positions the query on the retrieved record.
 boolean seek(int i, boolean relative)
          Retrieves the record at position index, if available, and positions the query on the retrieved record.
 void setForwardOnly(boolean forward)
          Sets forward only mode to forward.
 void setNumericalPrecisionPolicy(QSql.NumericalPrecisionPolicy precisionPolicy)
          Instruct the database driver to return numerical values with a precision specified by precisionPolicy.
 int size()
          Returns the size of the result (number of rows returned), or -1 if the size cannot be determined or if the database does not support reporting information about query sizes.
 java.lang.Object value(int i)
          Returns the value of field index in the current record.
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Constructor Detail

QSqlQuery

public QSqlQuery(QSqlDatabase db)
Constructs a QSqlQuery object using the database db.

See also:
QSqlDatabase.


QSqlQuery

public QSqlQuery(QSqlResult r)
Constructs a QSqlQuery object which uses the QSqlResultresult to communicate with a database.


QSqlQuery

public QSqlQuery(QSqlQuery other)
Constructs a copy of other.


QSqlQuery

public QSqlQuery(java.lang.String query)
Constructs a QSqlQuery object using the SQL query and the database db. If db is not specified, the application's default database is used. If query is not an empty string, it will be executed.

See also:
QSqlDatabase.


QSqlQuery

public QSqlQuery()
Constructs a QSqlQuery object using the SQL query and the database db. If db is not specified, the application's default database is used. If query is not an empty string, it will be executed.

See also:
QSqlDatabase.


QSqlQuery

public QSqlQuery(java.lang.String query,
                 QSqlDatabase db)
Constructs a QSqlQuery object using the SQL query and the database db. If db is not specified, the application's default database is used. If query is not an empty string, it will be executed.

See also:
QSqlDatabase.

Method Detail

addBindValue

public final void addBindValue(java.lang.Object val,
                               QSql.ParamTypeFlag[] type)
This is an overloaded method provided for convenience.


addBindValue

public final void addBindValue(java.lang.Object val)
Adds the value val to the list of values when using positional value binding. The order of the addBindValue() calls determines which placeholder a value will be bound to in the prepared query. If paramType is QSql::Out or QSql::InOut , the placeholder will be overwritten with data from the database after the exec() call.

To bind a NULL value, use a null QVariant; for example, use QVariant(QVariant::String) if you are binding a string.

See also:
bindValue(), prepare(), exec(), boundValue(), and boundValues().


addBindValue

public final void addBindValue(java.lang.Object val,
                               QSql.ParamType type)
Adds the value val to the list of values when using positional value binding. The order of the addBindValue() calls determines which placeholder a value will be bound to in the prepared query. If paramType is QSql::Out or QSql::InOut , the placeholder will be overwritten with data from the database after the exec() call.

To bind a NULL value, use a null QVariant; for example, use QVariant(QVariant::String) if you are binding a string.

See also:
bindValue(), prepare(), exec(), boundValue(), and boundValues().


at

public final int at()
Returns the current internal position of the query. The first record is at position zero. If the position is invalid, the function returns QSql::BeforeFirstRow or QSql::AfterLastRow , which are special negative values.

See also:
previous(), next(), first(), last(), seek(), isActive(), and isValid().


bindValue

public final void bindValue(java.lang.String placeholder,
                            java.lang.Object val,
                            QSql.ParamTypeFlag[] type)
This is an overloaded method provided for convenience.


bindValue

public final void bindValue(java.lang.String placeholder,
                            java.lang.Object val)
Set the placeholder placeholder to be bound to value val in the prepared statement. Note that the placeholder mark (e.g :) must be included when specifying the placeholder name. If paramType is QSql::Out or QSql::InOut , the placeholder will be overwritten with data from the database after the exec() call.

To bind a NULL value, use a null QVariant; for example, use QVariant(QVariant::String) if you are binding a string.

See also:
addBindValue(), prepare(), exec(), boundValue(), and boundValues().


bindValue

public final void bindValue(java.lang.String placeholder,
                            java.lang.Object val,
                            QSql.ParamType type)
Set the placeholder placeholder to be bound to value val in the prepared statement. Note that the placeholder mark (e.g :) must be included when specifying the placeholder name. If paramType is QSql::Out or QSql::InOut , the placeholder will be overwritten with data from the database after the exec() call.

To bind a NULL value, use a null QVariant; for example, use QVariant(QVariant::String) if you are binding a string.

See also:
addBindValue(), prepare(), exec(), boundValue(), and boundValues().


bindValue

public final void bindValue(int pos,
                            java.lang.Object val,
                            QSql.ParamTypeFlag[] type)
This is an overloaded method provided for convenience.


bindValue

public final void bindValue(int pos,
                            java.lang.Object val)
Set the placeholder in position pos to be bound to value val in the prepared statement. Field numbering starts at 0. If paramType is QSql::Out or QSql::InOut , the placeholder will be overwritten with data from the database after the exec() call.


bindValue

public final void bindValue(int pos,
                            java.lang.Object val,
                            QSql.ParamType type)
Set the placeholder in position pos to be bound to value val in the prepared statement. Field numbering starts at 0. If paramType is QSql::Out or QSql::InOut , the placeholder will be overwritten with data from the database after the exec() call.


boundValue

public final java.lang.Object boundValue(java.lang.String placeholder)
Returns the value for the placeholder.

See also:
boundValues(), bindValue(), and addBindValue().


boundValue

public final java.lang.Object boundValue(int pos)
Returns the value for the placeholder at position pos.


boundValues

public final java.util.SortedMap boundValues()
Returns a map of the bound values.

With named binding, the bound values can be examined in the following ways:

        Map<String, Object> map = query.boundValues();

        for (String key : map.keySet()) {
            Object value = map.get(key);
            System.out.println(i.key().toAscii().data() << ": "
                 << i.value().toString().toAscii().data());
        }
    
With positional binding, the code becomes:
        int i = 0;
        for (Object value : query.boundValues().values())
            System.err.println(String.valueOf(i++) + ": " + value);
    

See also:
boundValue(), bindValue(), and addBindValue().


clear

public final void clear()
Clears the result set and releases any resources held by the query. Sets the query state to inactive. You should rarely if ever need to call this function.


driver

public final QSqlDriver driver()
Returns the database driver associated with the query.


exec

public final boolean exec()
Executes a previously prepared SQL query. Returns true if the query executed successfully; otherwise returns false.

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

See also:
prepare(), bindValue(), addBindValue(), boundValue(), and boundValues().


exec

public final boolean exec(java.lang.String query)
Executes the SQL in query. Returns true and sets the query state to active if the query was successful; otherwise returns false. The 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 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:

        QSqlQuery query = new QSqlQuery();
        query.exec("INSERT INTO employee (id, name, salary) " +
                   "VALUES (1001, 'Thad Beaumont', 65000)");
    

See also:
isActive(), isValid(), next(), previous(), first(), last(), and seek().


execBatch

public final boolean execBatch()
Executes a previously prepared SQL query in a batch. All the bound parameters have to be lists of variants. If the database doesn't support batch executions, the driver will simulate it using conventional exec() calls.

Returns true if the query is executed successfully; otherwise returns false.

Example:

        QSqlQuery q = new QSqlQuery();
        q.prepare("insert into myTable values (?, ?)");

    List<Integer> ints = new ArrayList<Integer>();
        ints.add(1);
    ints.add(2);
    ints.add(3);
    ints.add(4);
        q.addBindValue(ints);

    List<String> names = new ArrayList<String>();
    names.add("Harald");
    names.add("Boris");
    names.add("Trond");
    names.add(null);
        q.addBindValue(names);

        if (!q.execBatch())
            System.out.println(q.lastError());
The example above inserts four new rows into myTable:
    1  Harald
    2  Boris
    3  Trond
        4  NULL
To bind NULL values, a null QVariant of the relevant type has to be added to the bound QVariantList; for example, QVariant(QVariant::String) should be used if you are using strings.

Note: Every bound QVariantList must contain the same amount of variants.

Note: The type of the QVariants in a list must not change. For example, you cannot mix integer and string variants within a QVariantList.

The mode parameter indicates how the bound QVariantList will be interpreted. If mode is ValuesAsRows, every variant within the QVariantList will be interpreted as a value for a new row. ValuesAsColumns is a special case for the Oracle driver. In this mode, every entry within a QVariantList will be interpreted as array-value for an IN or OUT value within a stored procedure. Note that this will only work if the IN or OUT value is a table-type consisting of only one column of a basic type, for example TYPE myType IS TABLE OF VARCHAR(64) INDEX BY BINARY_INTEGER;

See also:
prepare(), bindValue(), and addBindValue().


execBatch

public final boolean execBatch(QSqlQuery.BatchExecutionMode mode)
Executes a previously prepared SQL query in a batch. All the bound parameters have to be lists of variants. If the database doesn't support batch executions, the driver will simulate it using conventional exec() calls.

Returns true if the query is executed successfully; otherwise returns false.

Example:

        QSqlQuery q = new QSqlQuery();
        q.prepare("insert into myTable values (?, ?)");

    List<Integer> ints = new ArrayList<Integer>();
        ints.add(1);
    ints.add(2);
    ints.add(3);
    ints.add(4);
        q.addBindValue(ints);

    List<String> names = new ArrayList<String>();
    names.add("Harald");
    names.add("Boris");
    names.add("Trond");
    names.add(null);
        q.addBindValue(names);

        if (!q.execBatch())
            System.out.println(q.lastError());
The example above inserts four new rows into myTable:
    1  Harald
    2  Boris
    3  Trond
        4  NULL
To bind NULL values, a null QVariant of the relevant type has to be added to the bound QVariantList; for example, QVariant(QVariant::String) should be used if you are using strings.

Note: Every bound QVariantList must contain the same amount of variants.

Note: The type of the QVariants in a list must not change. For example, you cannot mix integer and string variants within a QVariantList.

The mode parameter indicates how the bound QVariantList will be interpreted. If mode is ValuesAsRows, every variant within the QVariantList will be interpreted as a value for a new row. ValuesAsColumns is a special case for the Oracle driver. In this mode, every entry within a QVariantList will be interpreted as array-value for an IN or OUT value within a stored procedure. Note that this will only work if the IN or OUT value is a table-type consisting of only one column of a basic type, for example TYPE myType IS TABLE OF VARCHAR(64) INDEX BY BINARY_INTEGER;

See also:
prepare(), bindValue(), and addBindValue().


executedQuery

public final java.lang.String executedQuery()
Returns the last query that was successfully executed.

In most cases this function returns the same string as lastQuery(). If a prepared query with placeholders is executed on a DBMS that does not support it, the preparation of this query is emulated. The placeholders in the original query are replaced with their bound values to form a new query. This function returns the modified query. It is mostly useful for debugging purposes.

See also:
lastQuery().


finish

public final void finish()
Instruct the database driver that no more data will be fetched from this query until it is re-executed. There is normally no need to call this function, but it may be helpful in order to free resources such as locks or cursors if you intend to re-use the query at a later time.

Sets the query to inactive. Bound values retain their values.

See also:
prepare(), exec(), and isActive().


first

public final boolean first()
Retrieves the first record in the result, if available, and positions the query on the retrieved record. Note that the result must be in the active state and isSelect() must return true before calling this function or it will do nothing and return false. Returns true if successful. If unsuccessful the query position is set to an invalid position and false is returned.

See also:
next(), previous(), last(), seek(), at(), isActive(), and isValid().


isActive

public final boolean isActive()
Returns true if the query is active. An active QSqlQuery is one that has been exec()'d successfully but not yet finished with. When you are finished with an active query, you can make make the query inactive by calling finish() or clear(), or you can delete the QSqlQuery instance.

Note: Of particular interest is an active query that is a SELECT statement. For some databases that support transactions, an active query that is a SELECT statement can cause a commit() or a rollback() to fail, so before committing or rolling back, you should make your active SELECT statement query inactive using one of the ways listed above.

See also:
isSelect().


isForwardOnly

public final boolean isForwardOnly()
Returns true if you can only scroll forward through a result set; otherwise returns false.

See also:
setForwardOnly(), and next().


isNull

public final boolean isNull(int field)
Returns true if the query is active and positioned on a valid record and the 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.

See also:
isActive(), isValid(), and value().


isSelect

public final boolean isSelect()
Returns true if the current query is a SELECT statement; otherwise returns false.


isValid

public final boolean isValid()
Returns true if the query is currently positioned on a valid record; otherwise returns false.


last

public final boolean last()
Retrieves the last record in the result, if available, and positions the query on the retrieved record. Note that the result must be in the active state and isSelect() must return true before calling this function or it will do nothing and return false. Returns true if successful. If unsuccessful the query position is set to an invalid position and false is returned.

See also:
next(), previous(), first(), seek(), at(), isActive(), and isValid().


lastError

public final QSqlError lastError()
Returns error information about the last error (if any) that occurred with this query.

See also:
QSqlError, and QSqlDatabase::lastError().


lastInsertId

public final java.lang.Object lastInsertId()
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.

For MySQL databases the row's auto-increment field will be returned.

Note: For this function to work in PSQL, the table table must contain OIDs, which may not have been created by default. Check the default_with_oids configuration variable to be sure.

See also:
QSqlDriver::hasFeature().


lastQuery

public final java.lang.String lastQuery()
Returns the text of the current query being used, or an empty string if there is no current query text.

See also:
executedQuery().


next

public final boolean next()
Retrieves the next record in the result, if available, and positions the query on the retrieved record. Note that the result must be in the active state and isSelect() must return true before calling this function or it will do nothing and return false.

The following rules apply:

If the record could not be retrieved, the result is positioned after the last record and false is returned. If the record is successfully retrieved, true is returned.

See also:
previous(), first(), last(), seek(), at(), isActive(), and isValid().


nextResult

public final boolean nextResult()
Discards the current result set and navigates to the next if available.

Some databases are capable of returning multiple result sets for stored procedures or SQL batches (a query strings that contains multiple statements). If multiple result sets are available after executing a query this function can be used to navigate to the next result set(s).

If a new result set is available this function will return true. The query will be repositioned on an invalid record in the new result set and must be navigated to a valid record before data values can be retrieved. If a new result set isn't available the function returns false and the the query is set to inactive. In any case the old result set will be discarded.

When one of the statements is a non-select statement a count of affected rows may be available instead of a result set.

Note that some databases, i.e. Microsoft SQL Server, requires non-scrollable cursors when working with multiple result sets. Some databases may execute all statements at once while others may delay the execution until the result set is actually accessed, and some databases may have restrictions on which statements are allowed to be used in a SQL batch.

See also:
QSqlDriver::hasFeature(), setForwardOnly(), next(), isSelect(), numRowsAffected(), isActive(), and lastError().


numRowsAffected

public final int numRowsAffected()
Returns the number of rows affected by the result's SQL statement, or -1 if it cannot be determined. Note that for SELECT statements, the value is undefined; use size() instead. If the query is not active, -1 is returned.

See also:
size(), and QSqlDriver::hasFeature().


numericalPrecisionPolicy

public final QSql.NumericalPrecisionPolicy numericalPrecisionPolicy()
Returns the current precision policy.

See also:
QSql::NumericalPrecisionPolicy , and setNumericalPrecisionPolicy().


prepare

public final boolean prepare(java.lang.String query)
Prepares the SQL query query for execution. Returns true if the query is prepared successfully; otherwise returns false.

The query may contain placeholders for binding values. Both Oracle style colon-name (e.g., :surname), and ODBC style (?) placeholders are supported; but they cannot be mixed in the same query. See the Detailed Description for examples.

Portability note: Some databases choose to delay preparing a query until it is executed the first time. In this case, preparing a syntactically wrong query succeeds, but every consecutive exec() will fail.

Example:

        QSqlQuery query = new QSqlQuery();
        query.prepare("INSERT INTO person (id, forename, surname) " +
                      "VALUES (:id, :forename, :surname)");
        query.bindValue(":id", 1001);
        query.bindValue(":forename", "Bart");
        query.bindValue(":surname", "Simpson");
        query.exec();
    

See also:
exec(), bindValue(), and addBindValue().


previous

public final boolean previous()
Retrieves the previous record in the result, if available, and positions the query on the retrieved record. Note that the result must be in the active state and isSelect() must return true before calling this function or it will do nothing and return false.

The following rules apply:

If the record could not be retrieved, the result is positioned before the first record and false is returned. If the record is successfully retrieved, true is returned.

See also:
next(), first(), last(), seek(), at(), isActive(), and isValid().


record

public final QSqlRecord record()
Returns a QSqlRecord containing the field information for the current query. If the query points to a valid row (isValid() returns true), the record is populated with the row's values. An empty record is returned when there is no active query (isActive() returns false).

To retrieve values from a query, value() should be used since its index-based lookup is faster.

In the following example, a SELECT * FROM query is executed. Since the order of the columns is not defined, QSqlRecord::indexOf() is used to obtain the index of a column.

    QSqlQuery q = new QSqlQuery("select * from employees");
    QSqlRecord rec = q.record();

    System.out.println("Number of columns: " + rec.count());

    int nameCol = rec.indexOf("name"); // index of the field "name"
    while (q.next())
        System.out.println(q.value(nameCol).toString()); // output all names

See also:
value().


result

public final QSqlResult result()
Returns the result associated with the query.


seek

public final boolean seek(int i)
Retrieves the record at position index, if available, and positions the query on the retrieved record. The first record is at position 0. Note that the query must be in an active state and isSelect() must return true before calling this function.

If relative is false (the default), the following rules apply:

If relative is true, the following rules apply:

See also:
next(), previous(), first(), last(), at(), isActive(), and isValid().


seek

public final boolean seek(int i,
                          boolean relative)
Retrieves the record at position index, if available, and positions the query on the retrieved record. The first record is at position 0. Note that the query must be in an active state and isSelect() must return true before calling this function.

If relative is false (the default), the following rules apply:

If relative is true, the following rules apply:

See also:
next(), previous(), first(), last(), at(), isActive(), and isValid().


setForwardOnly

public final void setForwardOnly(boolean forward)
Sets forward only mode to forward. If forward is true, only next() and seek() with positive values, are allowed for navigating the results.

Forward only mode can be (depending on the driver) more memory efficient since results do not need to be cached. It will also improve performance on some databases. For this to be true, you must call setForwardMode() before the query is prepared or executed. Note that the constructor that takes a query and a database may execute the query.

Forward only mode is off by default.

See also:
isForwardOnly(), next(), and seek().


setNumericalPrecisionPolicy

public final void setNumericalPrecisionPolicy(QSql.NumericalPrecisionPolicy precisionPolicy)
Instruct the database driver to return numerical values with a precision specified by precisionPolicy.

The Oracle driver, for example, retrieves numerical values as strings by default to prevent the loss of precision. If the high precision doesn't matter, use this method to increase execution speed by bypassing string conversions.

Note: Drivers that don't support fetching numerical values with low precision will ignore the precision policy. You can use QSqlDriver::hasFeature() to find out whether a driver supports this feature.

Note: Setting the precision policy doesn't affect the currently active query. Call exec(QString) or prepare() in order to activate the policy.

See also:
QSql::NumericalPrecisionPolicy , and numericalPrecisionPolicy().


size

public final int size()
Returns the size of the result (number of rows returned), or -1 if the size cannot be determined or if the database does not support reporting information about query sizes. Note that for non-SELECT statements (isSelect() returns false), size() will return -1. If the query is not active (isActive() returns false), -1 is returned.

To determine the number of rows affected by a non-SELECT statement, use numRowsAffected().

See also:
isActive(), numRowsAffected(), and QSqlDriver::hasFeature().


value

public final java.lang.Object value(int i)
Returns the value of field index in the current record.

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

        SELECT forename, surname FROM people;
field 0 is forename and field 1 is surname. Using SELECT * is not recommended because the order of the fields in the query is undefined.

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

See also:
previous(), next(), first(), last(), seek(), isActive(), and isValid().


clone

public QSqlQuery clone()
This method is reimplemented for internal reasons

Overrides:
clone in class java.lang.Object