mirror of
https://github.com/PaiGramTeam/sqlmodel.git
synced 2024-11-23 08:10:57 +00:00
109 lines
2.7 KiB
Markdown
109 lines
2.7 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>
|
||
<summary>👀 Full file preview</summary>
|
||
|
||
```Python
|
||
{!./docs_src/tutorial/connect/update/tutorial001.py!}
|
||
```
|
||
|
||
</details>
|
||
|
||
## 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:
|
||
|
||
```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>
|
||
<summary>👀 Full file preview</summary>
|
||
|
||
```Python
|
||
{!./docs_src/tutorial/connect/delete/tutorial001.py!}
|
||
```
|
||
|
||
</details>
|
||
|
||
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. 💥
|