SqlAlchemy: getting the id of the last record inserted

问题

I am using SQLAlchemy without the ORM, i.e. using hand crafted SQL statememts to directly interact with the backend db. I am using PG as my backend db (psycopg2 as DB driver) in this instance - I don't know if that affects the answer.

I have statements like this (for brevity, assume that conn is a valid connection to the db):

conn.execute("INSERT INTO user (name, country_id) VALUES ('Homer', 123)")

Assume also that the user table consists of the columns (id [SERIAL PRIMARY KEY], name, country_id)

How may I obtain the id of the new user (ideally, without hitting the db again?)

回答1:

You might be able to use the RETURNING clause of the INSERT statement like this:

result = conn.execute("INSERT INTO user (name, country_id) VALUES ('Homer', 123)
                       RETURNING *")

If you only want the resulting id:

rslt_id = conn.execute("INSERT INTO user (name, country_id) VALUES ('Homer', 123)
                        RETURNING id")

回答2:

User lastrowid

result = conn.execute("INSERT INTO user (name, country_id) VALUES ('Homer', 123)")
result.lastrowid

回答3:

Current SQLAlchemy documentation suggests

result.inserted_primary_key should work!

回答4:

this question has been asked many times on stackoverflow and no answer I have seen is comprehensive. Googling 'sqlalchemy insert get id of new row' brings up a lot of them.

There are three levels to SQLAlchemy. Top: the ORM. Middle: Database abstraction (DBA) with Table classes etc. Bottom: SQL using the text function.

To an OO programmer the ORM level looks natural, but to a database programmer it looks ugly and the ORM gets in the way. The DBA layer is an OK compromise. The SQL layer looks natural to database programmers and would look alien to an OO-only programmer.

Each level has it own syntax, similar but different enough to be frustrating. On top of this there is almost too much documentation online, very hard to find the answer.

I will describe how to get the inserted id AT THE SQL LAYER for the RDBMS I use.

Table: User(user_id integer primary autoincrement key, user_name string)
conn: Is a Connection obtained within SQLAlchemy to the DBMS you are using.


SQLite
======
insstmt = text(
    '''INSERT INTO user (user_name)
    VALUES (:usernm) ''' )
# Execute within a transaction (optional)
txn = conn.begin()
result = conn.execute(insstmt, usernm='Jane Doe')
# The id!
recid = result.lastrowid
txn.commit()


MS SQL Server
=============
insstmt = text(
    '''INSERT INTO user (user_name) 
    OUTPUT inserted.record_id
    VALUES (:usernm) ''' )
txn = conn.begin()
result = conn.execute(insstmt, usernm='Jane Doe')
# The id!
recid = result.fetchone()[0]
txn.commit()


MariaDB/MySQL
=============
insstmt = text(
    '''INSERT INTO user (user_name)
    VALUES (:usernm) ''' )
txn = conn.begin()
result = conn.execute(insstmt, usernm='Jane Doe')
# The id!
recid = conn.execute(text('SELECT LAST_INSERT_ID()')).fetchone()[0]
txn.commit()


Postgres
========
insstmt = text(
    '''INSERT INTO user (user_name)
    VALUES (:usernm) 
    RETURNING user_id ''' )
txn = conn.begin()
result = conn.execute(insstmt, usernm='Jane Doe')
# The id!
recid = result.fetchone()[0]
txn.commit()

回答5:

result.inserted_primary_key

Worked for me. The only thing to note is that this returns a list that contains that last_insert_id.

回答6:

Make sure you use fetchrow/fetch to receive the returning object

insert_stmt = user.insert().values(name="homer", country_id="123").returning(user.c.id)

row_id = await conn.fetchrow(insert_stmt)

来源：https://stackoverflow.com/questions/8589674/sqlalchemy-getting-the-id-of-the-last-record-inserted

标签

python

postgresql

sqlalchemy

psycopg2