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211 lines
7.1 KiB
Markdown
211 lines
7.1 KiB
Markdown
# Create and Connect Rows
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We will now **create rows** for each table. ✨
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The `team` table will look like this:
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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 after we finish working with the data in this chapter, the `hero` table will look like this:
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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>null</td>
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</tr>
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</table>
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Each row in the table `hero` will point to a row in the table `team`:
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<img alt="table relationships" src="/img/tutorial/relationships/select/relationships2.svg">
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/// info
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We will later update **Spider-Boy** to add him to the **Preventers** team too, but not yet.
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///
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We will continue with the code in the previous example and we will add more things to it.
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{* ./docs_src/tutorial/connect/create_tables/tutorial001_py310.py ln[0] *}
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Make sure you remove the `database.db` file before running the examples to get the same results.
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## Create Rows for Teams with **SQLModel**
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Let's do the same we did before and define a `create_heroes()` function where we create our heroes.
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And now we will also create the teams there. 🎉
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Let's start by creating two teams:
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{* ./docs_src/tutorial/connect/insert/tutorial001_py310.py ln[29:35] hl[29:35] *}
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This would hopefully look already familiar.
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We start a **session** in a `with` block using the same **engine** we created above.
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Then we create two instances of the model class (in this case `Team`).
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Next we add those objects to the **session**.
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And finally we **commit** the session to save the changes to the database.
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## Add It to Main
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Let's not forget to add this function `create_heroes()` to the `main()` function so that we run it when calling the program from the command line:
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{* ./docs_src/tutorial/connect/insert/tutorial001_py310.py ln[61:63] hl[63] *}
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## Run it
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If we run that code we have up to now, it 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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// Automatically start a transaction
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INFO Engine BEGIN (implicit)
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// Add the teams to the database
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INFO Engine INSERT INTO team (name, headquarters) VALUES (?, ?)
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INFO Engine [generated in 0.00050s] ('Preventers', 'Sharp Tower')
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INFO Engine INSERT INTO team (name, headquarters) VALUES (?, ?)
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INFO Engine [cached since 0.002324s ago] ('Z-Force', 'Sister Margaret's Bar')
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INFO Engine COMMIT
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```
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</div>
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You can see in the output that it uses common SQL `INSERT` statements to create the rows.
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## Create Rows for Heroes in Code
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Now let's create one hero object to start.
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As the `Hero` class model now has a field (column, attribute) `team_id`, we can set it by using the ID field from the `Team` objects we just created before:
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{* ./docs_src/tutorial/connect/insert/tutorial001_py310.py ln[29:39] hl[38] *}
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We haven't committed this hero to the database yet, but there are already a couple of things to pay **attention** to.
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If the database already had some teams, we wouldn't even know **what is the ID** that is going to be automatically assigned to each team by the database, for example, we couldn't just guess `1` or `2`.
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But once the team is created and committed to the database, we can access the object's `id` field to get that ID.
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Accessing an attribute in a model that was just committed, for example with `team_z_force.id`, automatically **triggers a refresh** of the data from the DB in the object, and then exposes the value for that field.
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So, even though we are not committing this hero yet, just because we are using `team_z_force.id`, that will trigger some SQL sent to the database to fetch the data for this team.
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That line alone would generate an output of:
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```
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INFO Engine BEGIN (implicit)
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INFO Engine SELECT team.id AS team_id, team.name AS team_name, team.headquarters AS team_headquarters
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FROM team
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WHERE team.id = ?
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INFO Engine [generated in 0.00025s] (2,)
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```
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Let's now create two more heroes:
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{* ./docs_src/tutorial/connect/insert/tutorial001_py310.py ln[29:50] hl[40:46] *}
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When creating `hero_rusty_man`, we are accessing `team_preventers.id`, so that will also trigger a refresh of its data, generating an output of:
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```
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INFO Engine SELECT team.id AS team_id, team.name AS team_name, team.headquarters AS team_headquarters
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FROM team
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WHERE team.id = ?
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INFO Engine [cached since 0.001795s ago] (1,)
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```
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There's something else to note. We marked `team_id` as `Optional[int]`, meaning that this could be `NULL` on the database (and `None` in Python).
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That means that a hero doesn't have to have a team. And in this case, **Spider-Boy** doesn't have one.
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Next we just commit the changes to save them to the database, and that will generate the output:
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```
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INFO Engine INSERT INTO hero (name, secret_name, age, team_id) VALUES (?, ?, ?, ?)
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INFO Engine [generated in 0.00022s] ('Deadpond', 'Dive Wilson', None, 2)
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INFO Engine INSERT INTO hero (name, secret_name, age, team_id) VALUES (?, ?, ?, ?)
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INFO Engine [cached since 0.0007987s ago] ('Rusty-Man', 'Tommy Sharp', 48, 1)
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INFO Engine INSERT INTO hero (name, secret_name, age, team_id) VALUES (?, ?, ?, ?)
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INFO Engine [cached since 0.001095s ago] ('Spider-Boy', 'Pedro Parqueador', None, None)
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INFO Engine COMMIT
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```
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## Refresh and Print Heroes
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Now let's refresh and print those new heroes to see their new ID pointing to their teams:
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{* ./docs_src/tutorial/connect/insert/tutorial001_py310.py ln[29:58] hl[52:54,56:58] *}
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If we execute that in the command line, it 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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// Automatically start a transaction
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INFO Engine BEGIN (implicit)
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// Refresh the first 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 [generated in 0.00021s] (1,)
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// Refresh the second 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 0.001575s ago] (2,)
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// Refresh the third 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 0.002518s ago] (3,)
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// Print the heroes
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Created hero: id=1 secret_name='Dive Wilson' team_id=2 name='Deadpond' age=None
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Created hero: id=2 secret_name='Tommy Sharp' team_id=1 name='Rusty-Man' age=48
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Created hero: 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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They now have their `team_id`s, nice!
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## Relationships
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Relationships in SQL databases are just made by having **columns in one table** referencing the values in **columns on other tables**.
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And here we have treated them just like that, more **column fields**, which is what they actually are behind the scenes in the SQL database.
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But later in this tutorial, in the next group of chapters, you will learn about **Relationship Attributes** to make it all a lot easier to work with in code. ✨
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