mirror of
https://github.com/PaiGramTeam/sqlmodel.git
synced 2024-11-28 18:19:21 +00:00
201 lines
4.9 KiB
Markdown
201 lines
4.9 KiB
Markdown
# Create Models with a Many-to-Many Link
|
|
|
|
We'll now support **many-to-many** relationships using a **link table** like this:
|
|
|
|
<img alt="many-to-many table relationships" src="/img/tutorial/many-to-many/many-to-many.svg">
|
|
|
|
Let's start by defining the class models, including the **link table** model.
|
|
|
|
## Link Table Model
|
|
|
|
As we want to support a **many-to-many** relationship, now we need a **link table** to connect them.
|
|
|
|
We can create it just as any other **SQLModel**:
|
|
|
|
```Python hl_lines="6-12"
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py[ln:1-12]!}
|
|
|
|
# Code below omitted 👇
|
|
```
|
|
|
|
<details>
|
|
<summary>👀 Full file preview</summary>
|
|
|
|
```Python
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py!}
|
|
```
|
|
|
|
</details>
|
|
|
|
This is a **SQLModel** class model table like any other.
|
|
|
|
It has two fields, `team_id` and `hero_id`.
|
|
|
|
They are both **foreign keys** to their respective tables. We'll create those models in a second, but you already know how that works.
|
|
|
|
And **both fields are primary keys**. We hadn't used this before. 🤓
|
|
|
|
## Team Model
|
|
|
|
Let's see the `Team` model, it's almost identical as before, but with a little change:
|
|
|
|
```Python hl_lines="8"
|
|
# Code above omitted 👆
|
|
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py[ln:15-20]!}
|
|
|
|
# Code below omitted 👇
|
|
```
|
|
|
|
<details>
|
|
<summary>👀 Full file preview</summary>
|
|
|
|
```Python
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py!}
|
|
```
|
|
|
|
</details>
|
|
|
|
The **relationship attribute `heroes`** is still a list of heroes, annotated as `List["Hero"]`. Again, we use `"Hero"` in quotes because we haven't declared that class yet by this point in the code (but as you know, editors and **SQLModel** understand that).
|
|
|
|
We use the same **`Relationship()`** function.
|
|
|
|
We use **`back_populates="teams"`**. Before we referenced an attribute `team`, but as now we can have many, we'll rename it to `teams` when creating the `Hero` model.
|
|
|
|
And here's the important part to allow the **many-to-many** relationship, we use **`link_model=HeroTeamLink`**. That's it. ✨
|
|
|
|
## Hero Model
|
|
|
|
Let's see the other side, here's the `Hero` model:
|
|
|
|
```Python hl_lines="9"
|
|
# Code above omitted 👆
|
|
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py[ln:23-29]!}
|
|
|
|
# Code below omitted 👇
|
|
```
|
|
|
|
<details>
|
|
<summary>👀 Full file preview</summary>
|
|
|
|
```Python
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py!}
|
|
```
|
|
|
|
</details>
|
|
|
|
We **removed** the previous `team_id` field (column) because now the relationship is done via the link table. 🔥
|
|
|
|
The relationship attribute is now named **`teams`** instead of `team`, as now we support multiple teams.
|
|
|
|
It is no longer an `Optional[Team]` but a list of teams, annotated as **`List[Team]`**.
|
|
|
|
We are using the **`Relationship()`** here too.
|
|
|
|
We still have **`back_populates="heroes"`** as before.
|
|
|
|
And now we have a **`link_model=HeroTeamLink`**. ✨
|
|
|
|
## Create the Tables
|
|
|
|
The same as before, we will have the rest of the code to create the **engine**, and a function to create all the tables `create_db_and_tables()`.
|
|
|
|
```Python hl_lines="9"
|
|
# Code above omitted 👆
|
|
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py[ln:32-39]!}
|
|
|
|
# Code below omitted 👇
|
|
```
|
|
|
|
<details>
|
|
<summary>👀 Full file preview</summary>
|
|
|
|
```Python
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py!}
|
|
```
|
|
|
|
</details>
|
|
|
|
|
|
And as in previous examples, we will add that function to a function `main()`, and we will call that `main()` function in the main block:
|
|
|
|
```Python hl_lines="4"
|
|
# Code above omitted 👆
|
|
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py[ln:78-79]!}
|
|
# We will do more stuff here later 👈
|
|
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py[ln:83-84]!}
|
|
```
|
|
|
|
<details>
|
|
<summary>👀 Full file preview</summary>
|
|
|
|
```Python
|
|
{!./docs_src/tutorial/many_to_many/tutorial001.py!}
|
|
```
|
|
|
|
</details>
|
|
|
|
|
|
## Run the Code
|
|
|
|
If you run the code in the command line, it would output:
|
|
|
|
<div class="termy">
|
|
|
|
```console
|
|
$ python app.py
|
|
|
|
// Boilerplate omitted 😉
|
|
|
|
INFO Engine
|
|
CREATE TABLE team (
|
|
id INTEGER,
|
|
name VARCHAR NOT NULL,
|
|
headquarters VARCHAR NOT NULL,
|
|
PRIMARY KEY (id)
|
|
)
|
|
|
|
|
|
INFO Engine [no key 0.00033s] ()
|
|
INFO Engine
|
|
CREATE TABLE hero (
|
|
id INTEGER,
|
|
name VARCHAR NOT NULL,
|
|
secret_name VARCHAR NOT NULL,
|
|
age INTEGER,
|
|
PRIMARY KEY (id)
|
|
)
|
|
|
|
|
|
INFO Engine [no key 0.00016s] ()
|
|
INFO Engine
|
|
|
|
// Our shinny new link table ✨
|
|
CREATE TABLE heroteamlink (
|
|
team_id INTEGER,
|
|
hero_id INTEGER,
|
|
PRIMARY KEY (team_id, hero_id),
|
|
FOREIGN KEY(team_id) REFERENCES team (id),
|
|
FOREIGN KEY(hero_id) REFERENCES hero (id)
|
|
)
|
|
|
|
|
|
INFO Engine [no key 0.00031s] ()
|
|
INFO Engine COMMIT
|
|
|
|
```
|
|
|
|
</div>
|
|
|
|
## Recap
|
|
|
|
We can support **many-to-many** relationships between tables by declaring a link table.
|
|
|
|
We can create it the same way as with other **SQLModel** classes, and then use it in the `link_model` parameter to `Relationship()`.
|
|
|
|
Now let's work with data using these models in the next chapters. 🤓
|