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python-cx_Oracle/doc/src/api_manual/cursor.rst
Anthony Tuininga 4ed562c205 Documentation updates, including changes for PEP 8 compliance, to take 
into account the fact that the default branch has changed to main, etc.
2021-05-18 16:53:31 -06:00

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.. _cursorobj:
*************
Cursor Object
*************
.. method:: Cursor.__enter__()
The entry point for the cursor as a context manager. It returns itself.
.. note::
This method is an extension to the DB API definition.
.. method:: Cursor.__exit__()
The exit point for the cursor as a context manager. It closes the cursor.
.. note::
This method is an extension to the DB API definition.
.. attribute:: Cursor.arraysize
This read-write attribute can be used to tune the number of rows internally
fetched and buffered by internal calls to the database when fetching rows
from SELECT statements and REF CURSORS. The value can drastically affect
the performance of a query since it directly affects the number of network
round trips between Python and the database. For methods like
:meth:`~Cursor.fetchone()` and :meth:`~Cursor.fetchall()` it does not change
how many rows are returned to the application. For
:meth:`~Cursor.fetchmany()` it is the default number of rows to fetch.
Due to the performance benefits, the default ``Cursor.arraysize`` is 100
instead of the 1 that the DB API recommends. This value means that 100 rows
are fetched by each internal call to the database.
See :ref:`Tuning Fetch Performance <tuningfetch>` for more information.
.. attribute:: Cursor.bindarraysize
This read-write attribute specifies the number of rows to bind at a time
and is used when creating variables via :meth:`~Cursor.setinputsizes()` or
:meth:`~Cursor.var()`. It defaults to 1 meaning to bind a single row at a
time.
.. note::
The DB API definition does not define this attribute.
.. method:: Cursor.arrayvar(typ, value, [size])
Create an array variable associated with the cursor of the given type and
size and return a :ref:`variable object <varobj>`. The value is either an
integer specifying the number of elements to allocate or it is a list and
the number of elements allocated is drawn from the size of the list. If the
value is a list, the variable is also set with the contents of the list. If
the size is not specified and the type is a string or binary, 4000 bytes
is allocated. This is needed for passing arrays to PL/SQL (in cases where
the list might be empty and the type cannot be determined automatically) or
returning arrays from PL/SQL.
Array variables can only be used for PL/SQL associative arrays with
contiguous keys. For PL/SQL associative arrays with sparsely populated keys
or for varrays and nested tables, the approach shown in this
`example <https://github.com/oracle/python-cx_Oracle/blob/main/
samples/plsql_collection.py>`__ needs to be used.
.. note::
The DB API definition does not define this method.
.. method:: Cursor.bindnames()
Return the list of bind variable names bound to the statement. Note that a
statement must have been prepared first.
.. note::
The DB API definition does not define this method.
.. attribute:: Cursor.bindvars
This read-only attribute provides the bind variables used for the last
execute. The value will be either a list or a dictionary depending on
whether binding was done by position or name. Care should be taken when
referencing this attribute. In particular, elements should not be removed
or replaced.
.. note::
The DB API definition does not define this attribute.
.. method:: Cursor.callfunc(name, returnType, parameters=[], \
keyword_parameters={})
Call a function with the given name. The return type is specified in the
same notation as is required by :meth:`~Cursor.setinputsizes()`. The
sequence of parameters must contain one entry for each parameter that the
function expects. Any keyword parameters will be included after the
positional parameters. The result of the call is the return value of the
function.
See :ref:`plsqlfunc` for an example.
.. versionchanged:: 8.2
For consistency and compliance with the PEP 8 naming style, the
parameter `keywordParameters` was renamed to `keyword_parameters`. The
old name will continue to work as a keyword parameter for a period of
time.
.. note::
The DB API definition does not define this method.
.. note::
If you intend to call :meth:`Cursor.setinputsizes()` on the cursor
prior to making this call, then note that the first item in the
parameter list refers to the return value of the function.
.. method:: Cursor.callproc(name, parameters=[], keyword_parameters={})
Call a procedure with the given name. The sequence of parameters must
contain one entry for each parameter that the procedure expects. The result
of the call is a modified copy of the input sequence. Input parameters are
left untouched; output and input/output parameters are replaced with
possibly new values. Keyword parameters will be included after the
positional parameters and are not returned as part of the output sequence.
See :ref:`plsqlproc` for an example.
.. versionchanged:: 8.2
For consistency and compliance with the PEP 8 naming style, the
parameter `keywordParameters` was renamed to `keyword_parameters`. The
old name will continue to work as a keyword parameter for a period of
time.
.. note::
The DB API definition does not allow for keyword parameters.
.. method:: Cursor.close()
Close the cursor now, rather than whenever __del__ is called. The cursor
will be unusable from this point forward; an Error exception will be raised
if any operation is attempted with the cursor.
.. attribute:: Cursor.connection
This read-only attribute returns a reference to the connection object on
which the cursor was created.
.. note::
This attribute is an extension to the DB API definition but it is
mentioned in PEP 249 as an optional extension.
.. data:: Cursor.description
This read-only attribute is a sequence of 7-item sequences. Each of these
sequences contains information describing one result column: (name, type,
display_size, internal_size, precision, scale, null_ok). This attribute
will be None for operations that do not return rows or if the cursor has
not had an operation invoked via the :meth:`~Cursor.execute()` method yet.
The type will be one of the :ref:`database type constants <dbtypes>`
defined at the module level.
.. method:: Cursor.execute(statement, parameters=[], ** keyword_parameters)
Execute a statement against the database. See :ref:`sqlexecution`.
Parameters may be passed as a dictionary or sequence or as keyword
parameters. If the parameters are a dictionary, the values will be bound by
name and if the parameters are a sequence the values will be bound by
position. Note that if the values are bound by position, the order of the
variables is from left to right as they are encountered in the statement
and SQL statements are processed differently than PL/SQL statements. For
this reason, it is generally recommended to bind parameters by name instead
of by position.
Parameters passed as a dictionary are name and value pairs. The name maps
to the bind variable name used by the statement and the value maps to the
Python value you wish bound to that bind variable.
A reference to the statement will be retained by the cursor. If None or the
same string object is passed in again, the cursor will execute that
statement again without performing a prepare or rebinding and redefining.
This is most effective for algorithms where the same statement is used, but
different parameters are bound to it (many times). Note that parameters
that are not passed in during subsequent executions will retain the value
passed in during the last execution that contained them.
For maximum efficiency when reusing an statement, it is best to use the
:meth:`~Cursor.setinputsizes()` method to specify the parameter types and
sizes ahead of time; in particular, None is assumed to be a string of
length 1 so any values that are later bound as numbers or dates will raise
a TypeError exception.
If the statement is a query, the cursor is returned as a convenience to the
caller (so it can be used directly as an iterator over the rows in the
cursor); otherwise, ``None`` is returned.
.. note::
The DB API definition does not define the return value of this method.
.. method:: Cursor.executemany(statement, parameters, batcherrors=False, \
arraydmlrowcounts=False)
Prepare a statement for execution against a database and then execute it
against all parameter mappings or sequences found in the sequence
parameters. See :ref:`batchstmnt`.
The statement is managed in the same way as the :meth:`~Cursor.execute()`
method manages it. If the size of the buffers allocated for any of the
parameters exceeds 2 GB, you will receive the error "DPI-1015: array size
of <n> is too large", where <n> varies with the size of each element being
allocated in the buffer. If you receive this error, decrease the number of
elements in the sequence parameters.
If there are no parameters, or parameters have previously been bound, the
number of iterations can be specified as an integer instead of needing to
provide a list of empty mappings or sequences.
When true, the batcherrors parameter enables batch error support within
Oracle and ensures that the call succeeds even if an exception takes place
in one or more of the sequence of parameters. The errors can then be
retrieved using :meth:`~Cursor.getbatcherrors()`.
When true, the arraydmlrowcounts parameter enables DML row counts to be
retrieved from Oracle after the method has completed. The row counts can
then be retrieved using :meth:`~Cursor.getarraydmlrowcounts()`.
Both the batcherrors parameter and the arraydmlrowcounts parameter can only
be true when executing an insert, update, delete or merge statement; in all
other cases an error will be raised.
For maximum efficiency, it is best to use the
:meth:`~Cursor.setinputsizes()` method to specify the parameter types and
sizes ahead of time; in particular, None is assumed to be a string of
length 1 so any values that are later bound as numbers or dates will raise
a TypeError exception.
.. method:: Cursor.executemanyprepared(num_iters)
Execute the previously prepared and bound statement the given number of
times. The variables that are bound must have already been set to their
desired value before this call is made. This method was designed for the
case where optimal performance is required as it comes at the expense of
compatibility with the DB API.
.. note::
The DB API definition does not define this method.
.. deprecated:: 6.4
Use :meth:`~Cursor.executemany()` instead with None for the statement
argument and an integer for the parameters argument.
.. method:: Cursor.fetchall()
Fetch all (remaining) rows of a query result, returning them as a list of
tuples. An empty list is returned if no more rows are available. Note that
the cursor's arraysize attribute can affect the performance of this
operation, as internally reads from the database are done in batches
corresponding to the arraysize.
An exception is raised if the previous call to :meth:`~Cursor.execute()`
did not produce any result set or no call was issued yet.
See :ref:`fetching` for an example.
.. method:: Cursor.fetchmany(num_rows=cursor.arraysize)
Fetch the next set of rows of a query result, returning a list of tuples.
An empty list is returned if no more rows are available. Note that the
cursor's arraysize attribute can affect the performance of this operation.
The number of rows to fetch is specified by the parameter. If it is not
given, the cursor's arraysize attribute determines the number of rows to be
fetched. If the number of rows available to be fetched is fewer than the
amount requested, fewer rows will be returned.
An exception is raised if the previous call to :meth:`~Cursor.execute()`
did not produce any result set or no call was issued yet.
See :ref:`fetching` for an example.
.. method:: Cursor.fetchone()
Fetch the next row of a query result set, returning a single tuple or None
when no more data is available.
An exception is raised if the previous call to :meth:`~Cursor.execute()`
did not produce any result set or no call was issued yet.
See :ref:`fetching` for an example.
.. method:: Cursor.fetchraw(num_rows=cursor.arraysize)
Fetch the next set of rows of a query result into the internal buffers of
the defined variables for the cursor. The number of rows actually fetched
is returned.
An exception is raised if the previous call to :meth:`~Cursor.execute()`
did not produce any result set or no call was issued yet.
.. deprecated:: 8.2
Use :meth:`Cursor.fetchmany()` instead.
.. note::
The DB API definition does not define this method.
.. attribute:: Cursor.fetchvars
This read-only attribute specifies the list of variables created for the
last query that was executed on the cursor. Care should be taken when
referencing this attribute. In particular, elements should not be removed
or replaced.
.. note::
The DB API definition does not define this attribute.
.. method:: Cursor.getarraydmlrowcounts()
Retrieve the DML row counts after a call to :meth:`~Cursor.executemany()`
with arraydmlrowcounts enabled. This will return a list of integers
corresponding to the number of rows affected by the DML statement for each
element of the array passed to :meth:`~Cursor.executemany()`.
.. note::
The DB API definition does not define this method and it is only
available for Oracle 12.1 and higher.
.. method:: Cursor.getbatcherrors()
Retrieve the exceptions that took place after a call to
:meth:`~Cursor.executemany()` with batcherrors enabled. This will return a
list of Error objects, one error for each iteration that failed. The offset
can be determined by looking at the offset attribute of the error object.
.. note::
The DB API definition does not define this method.
.. method:: Cursor.getimplicitresults()
Return a list of cursors which correspond to implicit results made
available from a PL/SQL block or procedure without the use of OUT ref
cursor parameters. The PL/SQL block or procedure opens the cursors and
marks them for return to the client using the procedure
dbms_sql.return_result. Cursors returned in this fashion should not be
closed. They will be closed automatically by the parent cursor when it is
closed. Closing the parent cursor will invalidate the cursors returned by
this method.
.. versionadded:: 5.3
.. note::
The DB API definition does not define this method and it is only
available for Oracle Database 12.1 (both client and server must be at
this level or higher). It is most like the DB API method nextset(), but
unlike that method (which requires that the next result set overwrite
the current result set), this method returns cursors which can be
fetched independently of each other.
.. attribute:: Cursor.inputtypehandler
This read-write attribute specifies a method called for each value that is
bound to a statement executed on the cursor and overrides the attribute
with the same name on the connection if specified. The method signature is
handler(cursor, value, arraysize) and the return value is expected to be a
variable object or None in which case a default variable object will be
created. If this attribute is None, the value of the attribute with the
same name on the connection is used.
.. note::
This attribute is an extension to the DB API definition.
.. method:: Cursor.__iter__()
Returns the cursor itself to be used as an iterator.
.. note::
This method is an extension to the DB API definition but it is
mentioned in PEP 249 as an optional extension.
.. data:: Cursor.lastrowid
This read-only attribute returns the rowid of the last row modified by the
cursor. If no row was modified by the last operation performed on the
cursor, the value None is returned.
.. versionadded:: 7.3
.. attribute:: Cursor.outputtypehandler
This read-write attribute specifies a method called for each column that is
to be fetched from this cursor. The method signature is
handler(cursor, name, defaultType, length, precision, scale) and the return
value is expected to be a variable object or None in which case a default
variable object will be created. If this attribute is None, the value of
the attribute with the same name on the connection is used instead.
See :ref:`outputtypehandlers`.
.. note::
This attribute is an extension to the DB API definition.
.. method:: Cursor.parse(statement)
This can be used to parse a statement without actually executing it (this
step is done automatically by Oracle when a statement is executed).
.. note::
The DB API definition does not define this method.
.. note::
You can parse any DML or DDL statement. DDL statements are executed
immediately and an implied commit takes place.
.. attribute:: Cursor.prefetchrows
This read-write attribute can be used to tune the number of rows that the
Oracle Client library fetches when a SELECT statement is executed. This
value can reduce the number of round-trips to the database that are required
to fetch rows but at the cost of additional memory. Setting this value to 0
can be useful when the timing of fetches must be explicitly controlled.
See :ref:`Tuning Fetch Performance <tuningfetch>` for more information.
.. note::
The DB API definition does not define this method.
.. method:: Cursor.prepare(statement, [tag])
This can be used before a call to :meth:`~Cursor.execute()` to define the
statement that will be executed. When this is done, the prepare phase will
not be performed when the call to :meth:`~Cursor.execute()` is made with
None or the same string object as the statement. If specified the
statement will be returned to the statement cache with the given tag. See
the Oracle documentation for more information about the statement cache.
See :ref:`Statement Caching <stmtcache>` for more information.
.. note::
The DB API definition does not define this method.
.. attribute:: Cursor.rowcount
This read-only attribute specifies the number of rows that have currently
been fetched from the cursor (for select statements), that have been
affected by the operation (for insert, update, delete and merge
statements), or the number of successful executions of the statement
(for PL/SQL statements).
.. attribute:: Cursor.rowfactory
This read-write attribute specifies a method to call for each row that is
retrieved from the database. Ordinarily a tuple is returned for each row
but if this attribute is set, the method is called with the tuple that
would normally be returned, and the result of the method is returned
instead.
See :ref:`rowfactories`.
.. note::
The DB API definition does not define this attribute.
.. method:: Cursor.scroll(value=0, mode="relative")
Scroll the cursor in the result set to a new position according to the
mode.
If mode is "relative" (the default value), the value is taken as an offset
to the current position in the result set. If set to "absolute", value
states an absolute target position. If set to "first", the cursor is
positioned at the first row and if set to "last", the cursor is set to the
last row in the result set.
An error is raised if the mode is "relative" or "absolute" and the scroll
operation would position the cursor outside of the result set.
.. versionadded:: 5.3
.. note::
This method is an extension to the DB API definition but it is
mentioned in PEP 249 as an optional extension.
.. attribute:: Cursor.scrollable
This read-write boolean attribute specifies whether the cursor can be
scrolled or not. By default, cursors are not scrollable, as the server
resources and response times are greater than nonscrollable cursors. This
attribute is checked and the corresponding mode set in Oracle when calling
the method :meth:`~Cursor.execute()`.
.. versionadded:: 5.3
.. note::
The DB API definition does not define this attribute.
.. method:: Cursor.setinputsizes(\*args, \*\*keywordArgs)
This can be used before a call to :meth:`~Cursor.execute()`,
:meth:`~Cursor.callfunc()` or :meth:`~Cursor.callproc()` to predefine
memory areas for the operation's parameters. Each parameter should be a
type object corresponding to the input that will be used or it should be an
integer specifying the maximum length of a string parameter. Use keyword
parameters when binding by name and positional parameters when binding by
position. The singleton None can be used as a parameter when using
positional parameters to indicate that no space should be reserved for that
position.
.. note::
If you plan to use :meth:`~Cursor.callfunc()` then be aware that the
first parameter in the list refers to the return value of the function.
.. method:: Cursor.setoutputsize(size, [column])
This method does nothing and is retained solely for compatibility with the
DB API. The module automatically allocates as much space as needed to fetch
LONG and LONG RAW columns (or CLOB as string and BLOB as bytes).
.. attribute:: Cursor.statement
This read-only attribute provides the string object that was previously
prepared with :meth:`~Cursor.prepare()` or executed with
:meth:`~Cursor.execute()`.
.. note::
The DB API definition does not define this attribute.
.. method:: Cursor.var(typ, [size, arraysize, inconverter, outconverter, \
typename, encoding_errors, bypass_decode])
Create a variable with the specified characteristics. This method was
designed for use with PL/SQL in/out variables where the length or type
cannot be determined automatically from the Python object passed in or for
use in input and output type handlers defined on cursors or connections.
The typ parameter specifies the type of data that should be stored in the
variable. This should be one of the :ref:`database type constants
<dbtypes>`, :ref:`DB API constants <types>`, an object type returned from
the method :meth:`Connection.gettype()` or one of the following Python
types:
.. list-table::
:header-rows: 1
* - Python Type
- Database Type
* - bool
- :attr:`cx_Oracle.DB_TYPE_BOOLEAN`
* - bytes
- :attr:`cx_Oracle.DB_TYPE_RAW`
* - datetime.date
- :attr:`cx_Oracle.DB_TYPE_DATE`
* - datetime.datetime
- :attr:`cx_Oracle.DB_TYPE_DATE`
* - datetime.timedelta
- :attr:`cx_Oracle.DB_TYPE_INTERVAL_DS`
* - decimal.Decimal
- :attr:`cx_Oracle.DB_TYPE_NUMBER`
* - float
- :attr:`cx_Oracle.DB_TYPE_NUMBER`
* - int
- :attr:`cx_Oracle.DB_TYPE_NUMBER`
* - str
- :attr:`cx_Oracle.DB_TYPE_VARCHAR`
The size parameter specifies the length of string and raw variables and is
ignored in all other cases. If not specified for string and raw variables,
the value 4000 is used.
The arraysize parameter specifies the number of elements the variable will
have. If not specified the bind array size (usually 1) is used. When a
variable is created in an output type handler this parameter should be set
to the cursor's array size.
The inconverter and outconverter parameters specify methods used for
converting values to/from the database. More information can be found in
the section on :ref:`variable objects<varobj>`.
The typename parameter specifies the name of a SQL object type and must be
specified when using type :data:`cx_Oracle.OBJECT` unless the type object
was passed directly as the first parameter.
The encoding_errors parameter specifies what should happen when decoding
byte strings fetched from the database into strings. It should be one of
the values noted in the builtin
`decode <https://docs.python.org/3/library/stdtypes.html#bytes.decode>`__
function.
The bypass_decode parameter, if specified, should be passed as a
boolean value. Passing a `True` value causes values of database types
:data:`~cx_Oracle.DB_TYPE_VARCHAR`, :data:`~cx_Oracle.DB_TYPE_CHAR`,
:data:`~cx_Oracle.DB_TYPE_NVARCHAR`, :data:`~cx_Oracle.DB_TYPE_NCHAR` and
:data:`~cx_Oracle.DB_TYPE_LONG` to be returned as `bytes` instead of `str`,
meaning that cx_Oracle doesn't do any decoding. See :ref:`Fetching raw
data <fetching-raw-data>` for more information.
.. versionadded:: 8.2
The parameter `bypass_decode` was added.
.. versionchanged:: 8.2
For consistency and compliance with the PEP 8 naming style, the
parameter `encodingErrors` was renamed to `encoding_errors`. The old
name will continue to work as a keyword parameter for a period of time.
.. note::
The DB API definition does not define this method.
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