Обсуждение: Adaptation in psycopg3
Hello, I wrote a description of the psycopg3 adaptation system and the main differences compared to psycopg2: available at https://www.psycopg.org/articles/2020/11/24/psycopg3-adaptation/ Initial API docs are available at https://www.psycopg.org/psycopg3/docs/adaptation.html Feedback is welcome. Cheers! -- Daniele
El 24/11/20 a las 17:52, Daniele Varrazzo escribió: > Hello, > > I wrote a description of the psycopg3 adaptation system and the main > differences compared to psycopg2: available at > https://www.psycopg.org/articles/2020/11/24/psycopg3-adaptation/ > > Initial API docs are available at > https://www.psycopg.org/psycopg3/docs/adaptation.html > > Feedback is welcome. Cheers! > > -- Daniele > Hi Daniele, thanks for your effort. After reading the docs i have a question about the parameters in the 'in' clause. In psycopg2 i do: params = (1,2,3,4) cursor.execute("select * from mytable where field1 in %s", (params,)) or params = ('black','red','green') cursor.execute("select * from mytable where field2 in %s", (params,)) What will it be like in psycopg3, will it be the same?, will I have to create a special adapter? Thanks -- Oswaldo Hernández
On 11/25/20 4:29 AM, listas wrote: > El 24/11/20 a las 17:52, Daniele Varrazzo escribió: >> Hello, >> >> I wrote a description of the psycopg3 adaptation system and the main >> differences compared to psycopg2: available at >> https://www.psycopg.org/articles/2020/11/24/psycopg3-adaptation/ >> >> Initial API docs are available at >> https://www.psycopg.org/psycopg3/docs/adaptation.html >> >> Feedback is welcome. Cheers! >> >> -- Daniele >> > > Hi Daniele, thanks for your effort. > > After reading the docs i have a question about the parameters in the > 'in' clause. > > In psycopg2 i do: > > params = (1,2,3,4) > cursor.execute("select * from mytable where field1 in %s", (params,)) > > or > > params = ('black','red','green') > cursor.execute("select * from mytable where field2 in %s", (params,)) > > What will it be like in psycopg3, will it be the same?, will I have to > create a special adapter? From the link: "cannot use the IN (...) construct: # Must use "AND nation = any (%s)" cur.execute("... AND nation in %s", [("IT", "FR", "DE")]) " > > Thanks > -- > Oswaldo Hernández > > -- Adrian Klaver adrian.klaver@aklaver.com
On Wed, 25 Nov 2020 at 12:29, listas <listas@soft-com.es> wrote:
> After reading the docs i have a question about the parameters in the
> 'in' clause.
>
> In psycopg2 i do:
>
> params = (1,2,3,4)
> cursor.execute("select * from mytable where field1 in %s", (params,))
>
> or
>
> params = ('black','red','green')
> cursor.execute("select * from mytable where field2 in %s", (params,))
>
> What will it be like in psycopg3, will it be the same?, will I have to
> create a special adapter?
Hollo Oswaldo,
"IN" cannot be used, because it's a SQL construct, so "(1, 2, 3)" is
not something that postgres will understand as a parameter.
You can use "= any (%s)" and pass a list. This is something you can do
in psycopg2 too, and it's actually a better choice, because it works
with empty lists too, unless `IN ()`, which is a syntax error for
Postgres.
What you can do is:
params = ['black','red','green']
cursor.execute("select * from mytable where field2 = any(%s)", (params,))
interesting fact: "= any" is what postgres really uses internally,
even if you use the "IN ()" syntax:
piro=# explain select * from mytable where myint in (1,2,3);
QUERY PLAN
---------------------------------------------------------
Seq Scan on mytable (cost=0.00..45.06 rows=38 width=4)
Filter: (myint = ANY ('{1,2,3}'::integer[]))
(2 rows)
-- Daniele
El 25/11/20 a las 15:45, Daniele Varrazzo escribió:
> On Wed, 25 Nov 2020 at 12:29, listas <listas@soft-com.es> wrote:
>
>> After reading the docs i have a question about the parameters in the
>> 'in' clause.
>>
>> In psycopg2 i do:
>>
>> params = (1,2,3,4)
>> cursor.execute("select * from mytable where field1 in %s", (params,))
>>
>> or
>>
>> params = ('black','red','green')
>> cursor.execute("select * from mytable where field2 in %s", (params,))
>>
>> What will it be like in psycopg3, will it be the same?, will I have to
>> create a special adapter?
>
> Hollo Oswaldo,
>
> "IN" cannot be used, because it's a SQL construct, so "(1, 2, 3)" is
> not something that postgres will understand as a parameter.
>
> You can use "= any (%s)" and pass a list. This is something you can do
> in psycopg2 too, and it's actually a better choice, because it works
> with empty lists too, unless `IN ()`, which is a syntax error for
> Postgres.
>
> What you can do is:
>
> params = ['black','red','green']
> cursor.execute("select * from mytable where field2 = any(%s)", (params,))
>
> interesting fact: "= any" is what postgres really uses internally,
> even if you use the "IN ()" syntax:
>
> piro=# explain select * from mytable where myint in (1,2,3);
> QUERY PLAN
> ---------------------------------------------------------
> Seq Scan on mytable (cost=0.00..45.06 rows=38 width=4)
> Filter: (myint = ANY ('{1,2,3}'::integer[]))
> (2 rows)
>
> -- Daniele
>
Thank for your replies, I will use "=any(params list)" in psycopg3
The second question is: if psycopg3 is going to do the automatic cast of
the types, will it be able to distinguish between a json and a list of
values?.
Example:
data = ["a", "b", "c"]
idList = [4,7,2]
cursor.execute("update mytable set jsfield=%s where id = any(%s)",
(data, idList))
What will be the correct syntax in this case?
Thanks,
--
Oswaldo Hernández
On Wed, 25 Nov 2020 at 18:00, listas <listas@soft-com.es> wrote:
> Thank for your replies, I will use "=any(params list)" in psycopg3
No problem. But if it was not clear, this is something that works
already in psycopg2 too: it could be useful if you want to port code
later.
> The second question is: if psycopg3 is going to do the automatic cast of
> the types, will it be able to distinguish between a json and a list of
> values?.
> Example:
>
> data = ["a", "b", "c"]
> idList = [4,7,2]
>
> cursor.execute("update mytable set jsfield=%s where id = any(%s)",
> (data, idList))
>
> What will be the correct syntax in this case?
You would do like in psycopg2. There isn't a single json type in
python (it could be a list, dict, number, None...) so there is a
"Json" wrapper to tell psycopg to pass e.g. a json number rather than
a number-number:
https://www.psycopg.org/docs/extras.html?highlight=json#json-adaptation
What you would do, both in psycopg2 and 3, would be something like:
cursor.execute("update mytable set jsfield=%s where id = any(%s)",
(Json(data), idList))
Code like this should work in both versions.
Cheers
-- Daniele
...
>
> What you would do, both in psycopg2 and 3, would be something like:
>
> cursor.execute("update mytable set jsfield=%s where id = any(%s)",
> (Json(data), idList))
>
> Code like this should work in both versions.
>
perfect :) thank you very much
--
Oswaldo Hernández