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Better docs for fast executemany functions.

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Issue #502.
This commit is contained in:
Daniele Varrazzo 2017-02-02 16:02:33 +00:00
parent 27652ed3b0
commit d2fdc5ca9f
1 changed files with 31 additions and 15 deletions
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46
lib/extras.py
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@ -1168,11 +1168,15 @@ def execute_batch(cur, sql, argslist, page_size=100):
Execute *sql* several times, against all parameters set (sequences or Execute *sql* several times, against all parameters set (sequences or
mappings) found in *argslist*. mappings) found in *argslist*.
The function is semantically similar to `~cursor.executemany()`, but has a The function is semantically similar to
different implementation: Psycopg will join the statements into fewer
multi-statement commands, reducing the number of server roundtrips, .. parsed-literal::
resulting in better performances. Every command contains at most
*page_size* statements. *cur*\.\ `~cursor.executemany`\ (\ *sql*\ , *argslist*\ )
but has a different implementation: Psycopg will join the statements into
fewer multi-statement commands, each one containing at most *page_size*
statements, resulting in a reduced number of server roundtrips.
""" """
for page in _paginate(argslist, page_size=page_size): for page in _paginate(argslist, page_size=page_size):
@ -1183,19 +1187,31 @@ def execute_batch(cur, sql, argslist, page_size=100):
def execute_values(cur, sql, argslist, template=None, page_size=100): def execute_values(cur, sql, argslist, template=None, page_size=100):
'''Execute a statement using :sql:`VALUES` with a sequence of parameters. '''Execute a statement using :sql:`VALUES` with a sequence of parameters.
*sql* must contain a single ``%s`` placeholder, which will be replaced by a :param cur: the cursor to use to execute the query.
`VALUES list`__. Every statement will contain at most *page_size* sets of
arguments. :param sql: the query to execute. It must contain a single ``%s``
placeholder, which will be replaced by a `VALUES list`__.
Example: ``"INSERT INTO mytable (id, f1, f2) VALUES %s"``.
:param argslist: sequence of sequences or dictionaries with the arguments
to send to the query. The type and content must be consistent with
*template*.
:param template: the snippet to merge to every item in *argslist* to
compose the query. If *argslist* items are sequences it should contain
positional placeholders (e.g. ``"(%s, %s, %s)"``, or ``"(%s, %s, 42)``"
if there are constants value...); If *argslist* is items are mapping
it should contain named placeholders (e.g. ``"(%(id)s, %(f1)s, 42)"``).
If not specified, assume the arguments are sequence and use a simple
positional template (i.e. ``(%s, %s, ...)``), with the number of
placeholders sniffed by the first element in *argslist*.
:param page_size: maximum number of *argslist* items to include in every
statement. If there are more items the function will execute more than
one statement.
.. __: https://www.postgresql.org/docs/current/static/queries-values.html .. __: https://www.postgresql.org/docs/current/static/queries-values.html
*template* is the part merged to the arguments, so it should be compatible
with the content of *argslist* (it should contain the right number of
arguments if *argslist* is a sequence of sequences, or compatible names if
*argslist* is a sequence of mappings). If not specified, assume the
arguments are sequence and use a simple positional template (i.e.
``(%s, %s, ...)``).
While :sql:`INSERT` is an obvious candidate for this function it is While :sql:`INSERT` is an obvious candidate for this function it is
possible to use it with other statements, for example:: possible to use it with other statements, for example::