Random thoughts. Need mode opinions. def main(): conn

Question

Random thoughts. Need mode opinions. def main(): conn

= psycopg.connect(user="postgres", password="example", host="localhost", port=5432, dbname="postgres")
with conn.cursor() as cursor, conn.cursor() as cursor2:
# both cursor and cursor2 will use the same connection,
# so any way queries are sequential
cursor.execute("insert into test1 (id) values (uuid_generate_v4());")
cursor2.execute("insert into test1 (id) values (uuid_generate_v4());")
cursor2.rollback() # this will fail because Cursor does not have rollback method
conn.commit() # this will commit any changes made by cursor and cursor2
conn.close()

so what is the perpose of Cursor (not ServerCursor) in psycopg as it gives allmost nothing special conpared to connection?
compared to asyncpg which makes all the same without extra abstraction

0

02.06.2024

13 ответов

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Artem Автор вопроса

Muflone
They are used to read the data

yes. but question is more about why not they use connection without this confusing abstraction imho: if we compare Cursor behavior to real ServerCursor it's really confusing

0

5 месяцев назад

Muflone

Artem
yes. but question is more about why not they use c...

The cursor have the records positioning If you'd remove the cursor you couldn't read partially the data and every selection would void the previous selection

0

5 месяцев назад

Artem Автор вопроса

Muflone
The cursor have the records positioning If you'd ...

in case or Cursor data is already transferd to client from db server. you are free to do anything you like with it only ServerCursor gives power of postgres cursor with chunk reads

0

5 месяцев назад

Muflone

Artem
in case or Cursor data is already transferd to cli...

This isn't relevant Cursors have positioning, the above's still valid

0

5 месяцев назад

Artem Автор вопроса

Muflone
This isn't relevant Cursors have positioning, the...

cursor has positioning but in case of usual (not server) cursor they could just give it to user without any coursor data is already in memory user could iterate it any way he likes to be more clear this code will work without any problems def main(): conn = psycopg.connect(user="postgres", password="example", host="localhost", port=5432, dbname="postgres") with conn.cursor() as cursor: cursor.execute("insert into test1 (id) values (uuid_generate_v4()) returning id;") cursor.connection.commit() time.sleep(30) # stop database container print(cursor.fetchall()) # -> [(UUID('98b26338-61ba-448a-8953-d1bc49e86f93'),)]

0

5 месяцев назад

Muflone

Artem
cursor has positioning but in case of usual (not s...

This code don't use positioning

0

5 месяцев назад

Artem Автор вопроса

Muflone
This code don't use positioning

same def main(): conn = psycopg.connect(user="postgres", password="example", host="localhost", port=5432, dbname="postgres") with conn.cursor() as cursor: cursor.execute("select * from test1;") time.sleep(20) # stop database container cursor.scroll(2) print(cursor.fetchmany(2)) # -> [(UUID('3eaeccf6-aa60-493d-9f1a-219a600edba6'),), (UUID('98b26338-61ba-448a-8953-d1bc49e86f93'),)]

0

5 месяцев назад

Muflone

Artem
same def main(): conn = psycopg.connect(user=...

Ok now do two queries Read a record from the first query and compare the result from the 2nd query, one record per time

0

5 месяцев назад

Artem Автор вопроса

Muflone
Ok now do two queries Read a record from the firs...

and what should it show to me? what I'm talking about is that Cursor abstraction is useless here just return to the user (one, N, all) as everything already in memory query by query and let user process data in any way just compare psycopg and asyncpg approaches and you'll understand what I'm takking about

0

5 месяцев назад

CHRS

Artem
same def main(): conn = psycopg.connect(user=...

why cursor.scroll() ?

0

5 месяцев назад

Muflone

Artem
and what should it show to me? what I'm talking ab...

I doubt you read the answers Your code has no positioning and it will not be possible without cursors Also I explained the Google example Also that's part of dbapi2

0

5 месяцев назад

Artem Автор вопроса

Muflone
I doubt you read the answers Your code has no pos...

seems like dbapi2 spec is the only argument here relevant for me cause everything else works fine without it thanks

0

5 месяцев назад

Muflone · Accepted Answer

Muflone

They are used to read the data

0

5 месяцев назад

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Random thoughts. Need mode opinions. def main(): conn

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