Added doc notes about how to avoid JSON parsing

Added FAQ too as it has bitten more than one user
(see tickets #172, #190).
This commit is contained in:
Daniele Varrazzo 2014-01-14 18:30:41 +00:00
parent 3f6497d587
commit 9e8923b884
2 changed files with 27 additions and 1 deletions

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@ -189,6 +189,20 @@ the `Json` adapter::
Reading from the database, |pgjson| values will be automatically converted to Reading from the database, |pgjson| values will be automatically converted to
Python objects. Python objects.
.. note::
If you are using the PostgreSQL :sql:`json` data type but you want to read
it as string in Python instead of having it parsed, your can either cast
the column to :sql:`text` in the query (it is an efficient operation, that
doesn't involve a copy)::
cur.execute("select jsondata::text from mytable")
or you can register a no-op `!loads()` function with
`register_default_json()`::
psycopg2.extras.register_default_json(loads=lambda x: x)
.. note:: .. note::
You can use `~psycopg2.extensions.register_adapter()` to adapt any Python You can use `~psycopg2.extensions.register_adapter()` to adapt any Python
@ -204,7 +218,7 @@ Python objects.
effects. effects.
If you want to customize the adaptation from Python to PostgreSQL you can If you want to customize the adaptation from Python to PostgreSQL you can
either provide a custom `!dumps()` function to `!Json`:: either provide a custom `!dumps()` function to `Json`::
curs.execute("insert into mytable (jsondata) values (%s)", curs.execute("insert into mytable (jsondata) values (%s)",
[Json({'a': 100}, dumps=simplejson.dumps)]) [Json({'a': 100}, dumps=simplejson.dumps)])

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@ -125,6 +125,18 @@ Psycopg converts :sql:`decimal`\/\ :sql:`numeric` database types into Python `!D
`!psycopg2._psycopg.DECIMAL` instead. `!psycopg2._psycopg.DECIMAL` instead.
.. _faq-json-adapt:
.. cssclass:: faq
Psycopg automatically converts PostgreSQL :sql:`json` data into Python objects. How can I receive strings instead?
The easiest way to avoid JSON parsing is to register a no-op function with
`~psycopg2.extras.register_default_json()`::
psycopg2.extras.register_default_json(loads=lambda x: x)
See :ref:`adapt-json` for further details.
.. _faq-bytea-9.0: .. _faq-bytea-9.0:
.. cssclass:: faq .. cssclass:: faq