So I’m using sqlalchemy
for a project I’m working on. I’ve got an issue where I will eventually have thousands of records that need to be saved every hour. These records may be inserted or updated. I’ve been using bulk_save_objects
for this and it’s worked great. However now I have to introduce a history to these records being saved, which means I need the IDs returned so I can link these entries to an entry in a history table. I know about using return_defaults
, and that works. However, it introduces a problem that my bulk_save_objects
inserts and updates one entry at a time, instead of in bulk, which removes the purpose. Is there another option, where I can bulk insert and update at the same time, but retain the IDs?
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Answer
The desired result can be achieved using a technique similar to the one described in the answer here by uploading the rows to a temporary table and then performing an UPDATE followed by an INSERT that returns the inserted ID values. For SQL Server, that would be an OUTPUT clause on the INSERT statement:
main_table = "team"
# <set up test environment>
with engine.begin() as conn:
conn.execute(sa.text(f"DROP TABLE IF EXISTS [{main_table}]"))
conn.execute(
sa.text(
f"""
CREATE TABLE [dbo].[{main_table}](
[id] [int] IDENTITY(1,1) NOT NULL,
[prov] [varchar](2) NOT NULL,
[city] [varchar](50) NOT NULL,
[name] [varchar](50) NOT NULL,
[comments] [varchar](max) NULL,
CONSTRAINT [PK_team] PRIMARY KEY CLUSTERED
(
[id] ASC
)
)
"""
)
)
conn.execute(
sa.text(
f"""
CREATE UNIQUE NONCLUSTERED INDEX [UX_team_prov_city] ON [dbo].[{main_table}]
(
[prov] ASC,
[city] ASC
)
"""
)
)
conn.execute(
sa.text(
f"""
INSERT INTO [{main_table}] ([prov], [city], [name])
VALUES ('AB', 'Calgary', 'Flames')
"""
)
)
# <data for upsert>
df = pd.DataFrame(
[
("AB", "Calgary", "Flames", "hard-working, handsome lads"),
("AB", "Edmonton", "Oilers", "ruffians and scalawags"),
],
columns=["prov", "city", "name", "comments"],
)
# <perform upsert, returning IDs>
temp_table = "#so65525098"
with engine.begin() as conn:
df.to_sql(temp_table, conn, index=False, if_exists="replace")
conn.execute(
sa.text(
f"""
UPDATE main SET main.name = temp.name,
main.comments = temp.comments
FROM [{main_table}] main INNER JOIN [{temp_table}] temp
ON main.prov = temp.prov AND main.city = temp.city
"""
)
)
inserted = conn.execute(
sa.text(
f"""
INSERT INTO [{main_table}] (prov, city, name, comments)
OUTPUT INSERTED.prov, INSERTED.city, INSERTED.id
SELECT prov, city, name, comments FROM [{temp_table}] temp
WHERE NOT EXISTS (
SELECT * FROM [{main_table}] main
WHERE main.prov = temp.prov AND main.city = temp.city
)
"""
)
).fetchall()
print(inserted)
"""console output:
[('AB', 'Edmonton', 2)]
"""
# <check results>
with engine.begin() as conn:
pprint(conn.execute(sa.text(f"SELECT * FROM {main_table}")).fetchall())
"""console output:
[(1, 'AB', 'Calgary', 'Flames', 'hard-working, handsome lads'),
(2, 'AB', 'Edmonton', 'Oilers', 'ruffians and scalawags')]
"""