Обсуждение: Adaptation in psycopg3

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Adaptation in psycopg3

От
Daniele Varrazzo
Дата:
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



Re: Adaptation in psycopg3

От
listas
Дата:
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



Re: Adaptation in psycopg3

От
Adrian Klaver
Дата:
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



Re: Adaptation in psycopg3

От
Daniele Varrazzo
Дата:
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



Re: Adaptation in psycopg3

От
listas
Дата:
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




Re: Adaptation in psycopg3

От
Daniele Varrazzo
Дата:
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



Re: Adaptation in psycopg3

От
listas
Дата:
...
> 
> 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