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All the FAQ have they own id that can be used in URLs to refer to
This commit is contained in:
Daniele Varrazzo
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5473d50a09
commit
67064f8e03
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@ -10,6 +10,7 @@ suggest new entries!
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Problems with transactions handling
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-----------------------------------
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.. _faq-idle-in-transaction:
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.. cssclass:: faq
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Why does `!psycopg2` leave database sessions "idle in transaction"?
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@ -25,6 +26,10 @@ Why does `!psycopg2` leave database sessions "idle in transaction"?
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connection in `~connection.autocommit` mode to avoid a new transaction to
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be started at the first command.
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.. _faq-transaction-aborted:
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.. cssclass:: faq
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I receive the error *current transaction is aborted, commands ignored until end of transaction block* and can't do anything else!
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There was a problem *in the previous* command to the database, which
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resulted in an error. The database will not recover automatically from
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@ -35,6 +40,10 @@ I receive the error *current transaction is aborted, commands ignored until end
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.. |SAVEPOINT| replace:: :sql:`SAVEPOINT`
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.. _SAVEPOINT: http://www.postgresql.org/docs/current/static/sql-savepoint.html
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.. _faq-transaction-aborted-multiprocess:
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.. cssclass:: faq
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Why do I get the error *current transaction is aborted, commands ignored until end of transaction block* when I use `!multiprocessing` (or any other forking system) and not when use `!threading`?
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Psycopg's connections can't be shared across processes (but are thread
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safe). If you are forking the Python process make sure to create a new
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@ -45,6 +54,7 @@ Why do I get the error *current transaction is aborted, commands ignored until e
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Problems with type conversions
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------------------------------
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.. _faq-cant-adapt:
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.. cssclass:: faq
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Why does `!cursor.execute()` raise the exception *can't adapt*?
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@ -53,6 +63,10 @@ Why does `!cursor.execute()` raise the exception *can't adapt*?
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as query parameter an object for which there is no adapter registered for
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its class. See :ref:`adapting-new-types` for informations.
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.. _faq-number-required:
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.. cssclass:: faq
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I can't pass an integer or a float parameter to my query: it says *a number is required*, but *it is* a number!
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In your query string, you always have to use ``%s`` placeholders,
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event when passing a number. All Python objects are converted by Psycopg
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@ -62,6 +76,10 @@ I can't pass an integer or a float parameter to my query: it says *a number is r
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>>> cur.execute("INSERT INTO numbers VALUES (%d)", (42,)) # WRONG
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>>> cur.execute("INSERT INTO numbers VALUES (%s)", (42,)) # correct
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.. _faq-not-all-arguments-converted:
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.. cssclass:: faq
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I try to execute a query but it fails with the error *not all arguments converted during string formatting* (or *object does not support indexing*). Why?
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Psycopg always require positional arguments to be passed as a sequence, even
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when the query takes a single parameter. And remember that to make a
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@ -73,6 +91,10 @@ I try to execute a query but it fails with the error *not all arguments converte
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>>> cur.execute("INSERT INTO foo VALUES (%s)", ("bar",)) # correct
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>>> cur.execute("INSERT INTO foo VALUES (%s)", ["bar"]) # correct
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.. _faq-unicode:
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.. cssclass:: faq
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My database is Unicode, but I receive all the strings as UTF-8 `!str`. Can I receive `!unicode` objects instead?
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The following magic formula will do the trick::
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@ -81,6 +103,10 @@ My database is Unicode, but I receive all the strings as UTF-8 `!str`. Can I rec
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See :ref:`unicode-handling` for the gory details.
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.. _faq-float:
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.. cssclass:: faq
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Psycopg converts :sql:`decimal`\/\ :sql:`numeric` database types into Python `!Decimal` objects. Can I have `!float` instead?
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You can register a customized adapter for PostgreSQL decimal type::
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@ -94,6 +120,10 @@ Psycopg converts :sql:`decimal`\/\ :sql:`numeric` database types into Python `!D
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documentation. If you find `!psycopg2.extensions.DECIMAL` not avalable, use
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`!psycopg2._psycopg.DECIMAL` instead.
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.. _faq-bytea-9.0:
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.. cssclass:: faq
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Transferring binary data from PostgreSQL 9.0 doesn't work.
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PostgreSQL 9.0 uses by default `the "hex" format`__ to transfer
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:sql:`bytea` data: the format can't be parsed by the libpq 8.4 and
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@ -109,6 +139,10 @@ Transferring binary data from PostgreSQL 9.0 doesn't work.
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.. __: http://www.postgresql.org/docs/current/static/datatype-binary.html
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.. __: http://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-BYTEA-OUTPUT
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.. _faq-array:
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.. cssclass:: faq
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Arrays of *TYPE* are not casted to list.
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Arrays are only casted to list when their oid is known, and an array
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typecaster is registered for them. If there is no typecaster, the array is
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@ -120,6 +154,7 @@ Arrays of *TYPE* are not casted to list.
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Best practices
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--------------
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.. _faq-reuse-cursors:
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.. cssclass:: faq
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When should I save and re-use a cursor as opposed to creating a new one as needed?
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@ -131,6 +166,10 @@ When should I save and re-use a cursor as opposed to creating a new one as neede
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them.) The only exception are tight loops where one usually use the same
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cursor for a whole bunch of :sql:`INSERT`\s or :sql:`UPDATE`\s.
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.. _faq-reuse-connections:
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.. cssclass:: faq
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When should I save and re-use a connection as opposed to creating a new one as needed?
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Creating a connection can be slow (think of SSL over TCP) so the best
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practice is to create a single connection and keep it open as long as
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@ -139,6 +178,10 @@ When should I save and re-use a connection as opposed to creating a new one as n
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left "idle in transaction". See also `psycopg2.pool` for lightweight
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connection pooling.
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.. _faq-named-cursors:
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.. cssclass:: faq
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What are the advantages or disadvantages of using named cursors?
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The only disadvantages is that they use up resources on the server and
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that there is a little overhead because a at least two queries (one to
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@ -151,16 +194,22 @@ What are the advantages or disadvantages of using named cursors?
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Problems compiling and deploying psycopg2
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-----------------------------------------
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.. _faq-python-h:
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.. cssclass:: faq
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I can't compile `!psycopg2`: the compiler says *error: Python.h: No such file or directory*. What am I missing?
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You need to install a Python development package: it is usually called
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``python-dev``.
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.. _faq-libpq-fe-h:
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.. cssclass:: faq
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I can't compile `!psycopg2`: the compiler says *error: libpq-fe.h: No such file or directory*. What am I missing?
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You need to install the development version of the libpq: the package is
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usually called ``libpq-dev``.
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.. _faq-lo_truncate:
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.. cssclass:: faq
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@ -179,6 +228,10 @@ I can't compile `!psycopg2`: the compiler says *error: libpq-fe.h: No such file
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.. |lo_truncate| replace:: `!lo_truncate()`
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.. _lo_truncate: http://www.postgresql.org/docs/current/static/lo-interfaces.html#LO-TRUNCATE
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.. _faq-import-mod_wsgi:
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.. cssclass:: faq
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Psycopg raises *ImportError: cannot import name tz* on import in mod_wsgi / ASP, but it works fine otherwise.
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If `!psycopg2` is installed in an egg_ (e.g. because installed by
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:program:`easy_install`), the user running the program may be unable to
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