mirror of
https://github.com/fastapi/sqlmodel.git
synced 2025-11-04 14:47:08 +08:00
151 lines
3.2 KiB
Markdown
151 lines
3.2 KiB
Markdown
# Remove Data Connections
|
|
|
|
We currently have a `team` table:
|
|
|
|
<table>
|
|
<tr>
|
|
<th>id</th><th>name</th><th>headquarters</th>
|
|
</tr>
|
|
<tr>
|
|
<td>1</td><td>Preventers</td><td>Sharp Tower</td>
|
|
</tr>
|
|
<tr>
|
|
<td>2</td><td>Z-Force</td><td>Sister Margaret's Bar</td>
|
|
</tr>
|
|
</table>
|
|
|
|
And a `hero` table:
|
|
|
|
<table>
|
|
<tr>
|
|
<th>id</th><th>name</th><th>secret_name</th><th>age</th><th>team_id</th>
|
|
</tr>
|
|
<tr>
|
|
<td>1</td><td>Deadpond</td><td>Dive Wilson</td><td>null</td><td>2</td>
|
|
</tr>
|
|
<tr>
|
|
<td>2</td><td>Rusty-Man</td><td>Tommy Sharp</td><td>48</td><td>1</td>
|
|
</tr>
|
|
<tr>
|
|
<td>3</td><td>Spider-Boy</td><td>Pedro Parqueador</td><td>null</td><td>1</td>
|
|
</tr>
|
|
</table>
|
|
|
|
Let's see how to **remove** connections between rows in tables.
|
|
|
|
We will continue with the code from the previous chapter.
|
|
|
|
/// details | 👀 Full file preview
|
|
|
|
//// tab | Python 3.10+
|
|
|
|
```Python
|
|
{!./docs_src/tutorial/connect/update/tutorial001_py310.py!}
|
|
```
|
|
|
|
////
|
|
|
|
//// tab | Python 3.7+
|
|
|
|
```Python
|
|
{!./docs_src/tutorial/connect/update/tutorial001.py!}
|
|
```
|
|
|
|
////
|
|
|
|
///
|
|
|
|
## Break a Connection
|
|
|
|
We don't really have to delete anything to break a connection. We can just assign `None` to the foreign key, in this case, to the `team_id`.
|
|
|
|
Let's say **Spider-Boy** is tired of the lack of friendly neighbors and wants to get out of the **Preventers**.
|
|
|
|
We can simply set the `team_id` to `None`, and now it doesn't have a connection with the team:
|
|
|
|
//// tab | Python 3.10+
|
|
|
|
```Python hl_lines="8"
|
|
# Code above omitted 👆
|
|
|
|
{!./docs_src/tutorial/connect/delete/tutorial001_py310.py[ln:29-30]!}
|
|
|
|
# Previous code here omitted 👈
|
|
|
|
{!./docs_src/tutorial/connect/delete/tutorial001_py310.py[ln:66-70]!}
|
|
|
|
# Code below omitted 👇
|
|
```
|
|
|
|
////
|
|
|
|
//// tab | Python 3.7+
|
|
|
|
```Python hl_lines="8"
|
|
# Code above omitted 👆
|
|
|
|
{!./docs_src/tutorial/connect/delete/tutorial001.py[ln:31-32]!}
|
|
|
|
# Previous code here omitted 👈
|
|
|
|
{!./docs_src/tutorial/connect/delete/tutorial001.py[ln:68-72]!}
|
|
|
|
# Code below omitted 👇
|
|
```
|
|
|
|
////
|
|
|
|
/// details | 👀 Full file preview
|
|
|
|
//// tab | Python 3.10+
|
|
|
|
```Python
|
|
{!./docs_src/tutorial/connect/delete/tutorial001_py310.py!}
|
|
```
|
|
|
|
////
|
|
|
|
//// tab | Python 3.7+
|
|
|
|
```Python
|
|
{!./docs_src/tutorial/connect/delete/tutorial001.py!}
|
|
```
|
|
|
|
////
|
|
|
|
///
|
|
|
|
Again, we just **assign** a value to that field attribute `team_id`, now the value is `None`, which means `NULL` in the database. Then we `add()` the hero to the session, and then `commit()`.
|
|
|
|
Next we `refresh()` it to get the recent data, and we print it.
|
|
|
|
Running that in the command line will output:
|
|
|
|
<div class="termy">
|
|
|
|
```console
|
|
$ python app.py
|
|
|
|
// Previous output omitted 😉
|
|
|
|
// Update the hero
|
|
INFO Engine UPDATE hero SET team_id=? WHERE hero.id = ?
|
|
INFO Engine [cached since 0.07753s ago] (None, 3)
|
|
// Commit the session
|
|
INFO Engine COMMIT
|
|
// Automatically start a new transaction
|
|
INFO Engine BEGIN (implicit)
|
|
// Refresh the hero
|
|
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age, hero.team_id
|
|
FROM hero
|
|
WHERE hero.id = ?
|
|
INFO Engine [cached since 0.1661s ago] (3,)
|
|
|
|
// Print the hero without a team
|
|
No longer Preventer: id=3 secret_name='Pedro Parqueador' team_id=None name='Spider-Boy' age=None
|
|
```
|
|
|
|
</div>
|
|
|
|
That's it, we now removed a connection between rows in different tables by unsetting the foreign key column. 💥
|