Can I add a new item based on another database row in SQLAlchemy?

Question

As the title suggests, I want to add a row with an id based on another row in SQLALchemy. Currently, I'm adding an extra select, but I'd like to get rid of this. I know this is possible in MySQL, so I'm just trying to figure out the SQLAlchemy version. Here's what I currently have:

keywords = ['a', 'b', 'c']
prefix_id = session.query(Prefix.id)\
    .filter_by(name=some_prefix).first()[0]
inventory_item = InventoryItem(
    item=some_item, prefix_id=prefix_id, address=some_address)
inventory_item_metas = [InventoryItemMeta(
    inventory_item=inventory_item,
    type='keyword',
    value=keyword) for keyword in keywords]

Note that I'm adding more items based off the id returned, so I'd like to do everything in one transaction as efficiently as possible.

Look at this: SO answer It might give you some ideas.

user734094
– user734094

2015-06-02 07:11:01 +00:00
Commented Jun 2, 2015 at 7:11 — user734094
– user734094, Commented Jun 2, 2015 at 7:11

user554538 · Accepted Answer · 2015-05-31 02:43:14Z

2

+25

If i0 is the object you want to copy, you can remove it from the session to make it transient:

i0 = select
session.expunge(i0)

Then you set it's id to None so that it's no longer referencing any real database row:

i0.id = None

Then you can modify the object:

i0.a = 1
i0.b = 2

And finally, you add the transient object back to the session and flush it to get a new id for it:

session.add(i0)
session.flush()

You'll find that the object is now a new row:

print i0.id #New ID

And if you look things up by the old ID, you'll have another object that's the same as before the changes, with the original ID, too.

answered May 31, 2015 at 2:43

user554538

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1 Comment

Eli Over a year ago

How does this answer my question? I don't want to copy any objects.

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