8.2 KiB
Create and Connect Rows
We will now create rows for each table. ✨
The team table will look like this:
| id | name | headquarters |
|---|---|---|
| 1 | Preventers | Sharp Tower |
| 2 | Z-Force | Sister Margaret’s Bar |
And after we finish working with the data in this chapter, the hero table will look like this:
| id | name | secret_name | age | team_id |
|---|---|---|---|---|
| 1 | Deadpond | Dive Wilson | null | 2 |
| 2 | Rusty-Man | Tommy Sharp | 48 | 1 |
| 3 | Spider-Boy | Pedro Parqueador | null | null |
Each row in the table hero will point to a row in the table team:
!!! info We will later update Spider-Boy to add him to the Preventers team too, but not yet.
We will continue with the code in the previous example and we will add more things to it.
👀 Full file preview
{!./docs_src/tutorial/connect/create_tables/tutorial001.py!}
Make sure you remove the database.db file before running the examples to get the same results.
Create Rows for Teams with SQLModel
Let's do the same we did before and define a create_heroes() function where we create our heroes.
And now we will also create the teams there. 🎉
Let's start by creating two teams:
# Code above omitted 👆
{!./docs_src/tutorial/connect/insert/tutorial001.py[ln:31-37]!}
# Code below omitted 👇
👀 Full file preview
{!./docs_src/tutorial/connect/insert/tutorial001.py!}
This would hopefully look already familiar.
We start a session in a with block using the same engine we created above.
Then we create two instances of the model class (in this case Team).
Next we add those objects to the session.
And finally we commit the session to save the changes to the database.
Add It to Main
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:
# Code above omitted 👆
{!./docs_src/tutorial/connect/insert/tutorial001.py[ln:63-65]!}
# Code below omitted 👇
👀 Full file preview
{!./docs_src/tutorial/connect/insert/tutorial001.py!}
Run it
If we run that code we have up to now, it will output:
$ python app.py
// Previous output omitted 😉
// Automatically start a transaction
INFO Engine BEGIN (implicit)
// Add the teams to the database
INFO Engine INSERT INTO team (name, headquarters) VALUES (?, ?)
INFO Engine [generated in 0.00050s] ('Preventers', 'Sharp Tower')
INFO Engine INSERT INTO team (name, headquarters) VALUES (?, ?)
INFO Engine [cached since 0.002324s ago] ('Z-Force', 'Sister Margaret’s Bar')
INFO Engine COMMIT
You can see in the output that it uses common SQL INSERT statements to create the rows.
Create Rows for Heroes in Code
Now let's create one hero object to start.
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:
# Code above omitted 👆
{!./docs_src/tutorial/connect/insert/tutorial001.py[ln:31-41]!}
# Code below omitted 👇
👀 Full file preview
{!./docs_src/tutorial/connect/insert/tutorial001.py!}
We haven't committed this hero to the database yet, but there are already a couple of things to pay attention to.
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.
But once the team is created and committed to the database, we can access the object's id field to get that ID.
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.
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.
That line alone would generate an output of:
INFO Engine BEGIN (implicit)
INFO Engine SELECT team.id AS team_id, team.name AS team_name, team.headquarters AS team_headquarters
FROM team
WHERE team.id = ?
INFO Engine [generated in 0.00025s] (2,)
Let's now create two more heroes:
# Code above omitted 👆
{!./docs_src/tutorial/connect/insert/tutorial001.py[ln:31-52]!}
# Code below omitted 👇
👀 Full file preview
{!./docs_src/tutorial/connect/insert/tutorial001.py!}
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:
INFO Engine SELECT team.id AS team_id, team.name AS team_name, team.headquarters AS team_headquarters
FROM team
WHERE team.id = ?
INFO Engine [cached since 0.001795s ago] (1,)
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).
That means that a hero doesn't have to have a team. And in this case, Spider-Boy doesn't have one.
Next we just commit the changes to save them to the database, and that will generate the output:
INFO Engine INSERT INTO hero (name, secret_name, age, team_id) VALUES (?, ?, ?, ?)
INFO Engine [generated in 0.00022s] ('Deadpond', 'Dive Wilson', None, 2)
INFO Engine INSERT INTO hero (name, secret_name, age, team_id) VALUES (?, ?, ?, ?)
INFO Engine [cached since 0.0007987s ago] ('Rusty-Man', 'Tommy Sharp', 48, 1)
INFO Engine INSERT INTO hero (name, secret_name, age, team_id) VALUES (?, ?, ?, ?)
INFO Engine [cached since 0.001095s ago] ('Spider-Boy', 'Pedro Parqueador', None, None)
INFO Engine COMMIT
Refresh and Print Heroes
Now let's refresh and print those new heroes to see their new ID pointing to their teams:
# Code above omitted 👆
{!./docs_src/tutorial/connect/insert/tutorial001.py[ln:31-60]!}
# Code below omitted 👇
👀 Full file preview
{!./docs_src/tutorial/connect/insert/tutorial001.py!}
If we execute that in the command line, it will output:
$ python app.py
// Previous output omitted 😉
// Automatically start a transaction
INFO Engine BEGIN (implicit)
// Refresh the first hero
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age, hero.team_id
FROM hero
WHERE hero.id = ?
INFO Engine [generated in 0.00021s] (1,)
// Refresh the second 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 0.001575s ago] (2,)
// Refresh the third 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 0.002518s ago] (3,)
// Print the heroes
Created hero: id=1 secret_name='Dive Wilson' team_id=2 name='Deadpond' age=None
Created hero: id=2 secret_name='Tommy Sharp' team_id=1 name='Rusty-Man' age=48
Created hero: id=3 secret_name='Pedro Parqueador' team_id=None name='Spider-Boy' age=None
They now have their team_ids, nice!
Relationships
Relationships in SQL databases are just made by having columns in one table referencing the values in columns on other tables.
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.
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. ✨