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83 lines
2.3 KiB
Markdown
83 lines
2.3 KiB
Markdown
# Remove Data Connections
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We currently have a `team` table:
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<table>
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<tr>
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<th>id</th><th>name</th><th>headquarters</th>
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</tr>
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<tr>
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<td>1</td><td>Preventers</td><td>Sharp Tower</td>
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</tr>
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<tr>
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<td>2</td><td>Z-Force</td><td>Sister Margaret's Bar</td>
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</tr>
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</table>
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And a `hero` table:
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<table>
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<tr>
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<th>id</th><th>name</th><th>secret_name</th><th>age</th><th>team_id</th>
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</tr>
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<tr>
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<td>1</td><td>Deadpond</td><td>Dive Wilson</td><td>null</td><td>2</td>
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</tr>
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<tr>
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<td>2</td><td>Rusty-Man</td><td>Tommy Sharp</td><td>48</td><td>1</td>
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</tr>
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<tr>
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<td>3</td><td>Spider-Boy</td><td>Pedro Parqueador</td><td>null</td><td>1</td>
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</tr>
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</table>
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Let's see how to **remove** connections between rows in tables.
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We will continue with the code from the previous chapter.
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{* ./docs_src/tutorial/connect/update/tutorial001_py310.py ln[0] *}
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## Break a Connection
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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`.
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Let's say **Spider-Boy** is tired of the lack of friendly neighbors and wants to get out of the **Preventers**.
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We can simply set the `team_id` to `None`, and now it doesn't have a connection with the team:
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{* ./docs_src/tutorial/connect/delete/tutorial001_py310.py ln[29:30,66:70] hl[66] *}
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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()`.
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Next we `refresh()` it to get the recent data, and we print it.
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Running that in the command line will output:
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<div class="termy">
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```console
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$ python app.py
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// Previous output omitted 😉
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// Update the hero
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INFO Engine UPDATE hero SET team_id=? WHERE hero.id = ?
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INFO Engine [cached since 0.07753s ago] (None, 3)
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// Commit the session
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INFO Engine COMMIT
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// Automatically start a new transaction
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INFO Engine BEGIN (implicit)
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// Refresh the hero
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INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age, hero.team_id
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FROM hero
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WHERE hero.id = ?
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INFO Engine [cached since 0.1661s ago] (3,)
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// Print the hero without a team
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No longer Preventer: id=3 secret_name='Pedro Parqueador' team_id=None name='Spider-Boy' age=None
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```
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</div>
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That's it, we now removed a connection between rows in different tables by unsetting the foreign key column. 💥
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