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131 lines
5.0 KiB
Markdown
131 lines
5.0 KiB
Markdown
# Create Data with Many-to-Many Relationships
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Let's continue from where we left and create some data.
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We'll create data for this same **many-to-many** relationship with a link table:
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<img alt="many-to-many table relationships" src="/img/tutorial/many-to-many/many-to-many.drawio.svg">
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We'll continue from where we left off with the previous code.
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{* ./docs_src/tutorial/many_to_many/tutorial001_py310.py ln[0] *}
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## Create Heroes
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As we have done before, we'll create a function `create_heroes()` and we'll create some teams and heroes in it:
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{* ./docs_src/tutorial/many_to_many/tutorial001_py310.py ln[36:54] hl[44] *}
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This is very similar to what we have done before.
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We create a couple of teams, and then three heroes.
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The only new detail is that instead of using an argument `team` we now use `teams`, because that is the name of the new **relationship attribute**. And more importantly, we pass a **list of teams** (even if it contains a single team).
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See how **Deadpond** now belongs to the two teams?
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## Commit, Refresh, and Print
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Now let's do as we have done before, `commit` the **session**, `refresh` the data, and print it:
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{* ./docs_src/tutorial/many_to_many/tutorial001_py310.py ln[36:69] hl[55:58,60:62,64:69] *}
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## Add to Main
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As before, add the `create_heroes()` function to the `main()` function to make sure it is called when running this program from the command line:
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{* ./docs_src/tutorial/many_to_many/tutorial001_py310.py ln[72:74] *}
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## Run the Program
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If we run the program from the command line, it would 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 new transaction
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INFO Engine BEGIN (implicit)
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// Insert the hero data first
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INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
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INFO Engine [generated in 0.00041s] ('Deadpond', 'Dive Wilson', None)
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INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
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INFO Engine [cached since 0.001942s ago] ('Rusty-Man', 'Tommy Sharp', 48)
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INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
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INFO Engine [cached since 0.002541s ago] ('Spider-Boy', 'Pedro Parqueador', None)
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// Insert the team data second
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INFO Engine INSERT INTO team (name, headquarters) VALUES (?, ?)
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INFO Engine [generated in 0.00037s] ('Z-Force', 'Sister Margaret's Bar')
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INFO Engine INSERT INTO team (name, headquarters) VALUES (?, ?)
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INFO Engine [cached since 0.001239s ago] ('Preventers', 'Sharp Tower')
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// Insert the link data last, to be able to re-use the created IDs
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INFO Engine INSERT INTO heroteamlink (team_id, hero_id) VALUES (?, ?)
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INFO Engine [generated in 0.00026s] ((2, 3), (1, 1), (2, 1), (2, 2))
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// Commit and save the data in the database
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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 data
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INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
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FROM hero
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WHERE hero.id = ?
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INFO Engine [generated in 0.00019s] (1,)
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INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
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FROM hero
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WHERE hero.id = ?
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INFO Engine [cached since 0.001959s ago] (2,)
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INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
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FROM hero
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WHERE hero.id = ?
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INFO Engine [cached since 0.003215s ago] (3,)
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// Print Deadpond
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Deadpond: name='Deadpond' age=None id=1 secret_name='Dive Wilson'
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// Accessing the .team attribute triggers a refresh
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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, heroteamlink
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WHERE ? = heroteamlink.hero_id AND team.id = heroteamlink.team_id
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INFO Engine [generated in 0.00025s] (1,)
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// Print Deadpond's teams, 2 teams! 🎉
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Deadpond teams: [Team(id=1, name='Z-Force', headquarters='Sister Margaret's Bar'), Team(id=2, name='Preventers', headquarters='Sharp Tower')]
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// Print Rusty-Man
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Rusty-Man: name='Rusty-Man' age=48 id=2 secret_name='Tommy Sharp'
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// Accessing the .team attribute triggers a refresh
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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, heroteamlink
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WHERE ? = heroteamlink.hero_id AND team.id = heroteamlink.team_id
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INFO Engine [cached since 0.001716s ago] (2,)
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// Print Rusty-Man teams, just one, but still a list
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Rusty-Man Teams: [Team(id=2, name='Preventers', headquarters='Sharp Tower')]
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// Print Spider-Boy
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Spider-Boy: name='Spider-Boy' age=None id=3 secret_name='Pedro Parqueador'
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// Accessing the .team attribute triggers a refresh
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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, heroteamlink
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WHERE ? = heroteamlink.hero_id AND team.id = heroteamlink.team_id
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INFO Engine [cached since 0.002739s ago] (3,)
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// Print Spider-Boy's teams, just one, but still a list
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Spider-Boy Teams: [Team(id=2, name='Preventers', headquarters='Sharp Tower')]
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// Automatic roll back any previous automatic transaction, at the end of the with block
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INFO Engine ROLLBACK
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```
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</div>
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## Recap
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After setting up the model link, using it with **relationship attributes** is fairly straightforward, just Python objects. ✨
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