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