mirror of
https://github.com/PaiGramTeam/sqlmodel.git
synced 2024-11-23 08:10:57 +00:00
262 lines
7.4 KiB
Markdown
262 lines
7.4 KiB
Markdown
# Create Connected Tables
|
||
|
||
Now we will deal with **connected** data put in different tables.
|
||
|
||
So, the first step is to create more than one table and connect them, so that each row in one table can reference another row in the other table.
|
||
|
||
We have been working with heroes in a single table `hero`. Let's now add a table `team`.
|
||
|
||
The team table will look like this:
|
||
|
||
<table>
|
||
<tr>
|
||
<th>id</th><th>name</th><th>headquarters</th>
|
||
</tr>
|
||
<tr>
|
||
<td>1</td><td>Preventers</td><td>Sharp Tower</td>
|
||
</tr>
|
||
<tr>
|
||
<td>2</td><td>Z-Force</td><td>Sister Margaret’s Bar</td>
|
||
</tr>
|
||
</table>
|
||
|
||
To connect them, we will add another column to the hero table to point to each team by the ID with the `team_id`:
|
||
|
||
<table>
|
||
<tr>
|
||
<th>id</th><th>name</th><th>secret_name</th><th>age</th><th>team_id ✨</th>
|
||
</tr>
|
||
<tr>
|
||
<td>1</td><td>Deadpond</td><td>Dive Wilson</td><td>null</td><td>2 ✨</td>
|
||
</tr>
|
||
<tr>
|
||
<td>2</td><td>Spider-Boy</td><td>Pedro Parqueador</td><td>null</td><td>1 ✨</td>
|
||
</tr>
|
||
<tr>
|
||
<td>3</td><td>Rusty-Man</td><td>Tommy Sharp</td><td>48</td><td>1 ✨</td>
|
||
</tr>
|
||
</table>
|
||
|
||
This way each row in the table `hero` can point to a row in the table `team`:
|
||
|
||
<img alt="table relationships" src="/img/databases/relationships.svg">
|
||
|
||
## One-to-Many and Many-to-One
|
||
|
||
Here we are creating connected data in a relationship where **one** team could have **many** heroes. So it is commonly called a **one-to-many** or **many-to-one** relationship.
|
||
|
||
The **many-to-one** part can be seen if we start from the heroes, **many** heroes could be part of **one** team.
|
||
|
||
This is probably the most popular type of relationship, so we'll start with that. But there's also **many-to-many** and **one-to-one** relationships.
|
||
|
||
## Create Tables in Code
|
||
|
||
### Create the `team` Table
|
||
|
||
Let's start by creating the tables in code.
|
||
|
||
Import the things we need from `sqlmodel` and create a new `Team` model:
|
||
|
||
```Python hl_lines="6-9"
|
||
{!./docs_src/tutorial/connect/create_tables/tutorial001.py[ln:1-9]!}
|
||
|
||
# Code below omitted 👇
|
||
```
|
||
|
||
<details>
|
||
<summary>👀 Full file preview</summary>
|
||
|
||
```Python
|
||
{!./docs_src/tutorial/connect/create_tables/tutorial001.py!}
|
||
```
|
||
|
||
</details>
|
||
|
||
This is very similar to what we have been doing with the `Hero` model.
|
||
|
||
The `Team` model will be in a table automatically named `"team"`, and it will have the columns:
|
||
|
||
* `id`, the primary key, automatically generated by the database
|
||
* `name`, the name of the team
|
||
* We also tell **SQLModel** to create an index for this column
|
||
* `headquarters`, the headquarters of the team
|
||
|
||
And finally we mark it as a table in the config.
|
||
|
||
### Create the New `hero` Table
|
||
|
||
Now let's create the `hero` table.
|
||
|
||
This is the same model we have been using up to now, we are just adding the new column `team_id`:
|
||
|
||
```Python hl_lines="18"
|
||
{!./docs_src/tutorial/connect/create_tables/tutorial001.py[ln:1-18]!}
|
||
|
||
# Code below omitted 👇
|
||
```
|
||
|
||
<details>
|
||
<summary>👀 Full file preview</summary>
|
||
|
||
```Python
|
||
{!./docs_src/tutorial/connect/create_tables/tutorial001.py!}
|
||
```
|
||
|
||
</details>
|
||
|
||
Most of that should look familiar:
|
||
|
||
The column will be named `team_id`. It will be an integer, and it could be `NULL` in the database (or `None` in Python), becase there could be some heroes that don't belong to any team.
|
||
|
||
We add a default of `None` to the `Field()` so we don't have to explicitly pass `team_id=None` when creating a hero.
|
||
|
||
Now, here's the new part:
|
||
|
||
In `Field()` we pass the argument `foreign_key="team.id"`. This tells the database that this column `team_id` is a foreign key to the table `team`. A "**foreign key**" just means that this column will have the **key** to identify a row in a **foreign** table.
|
||
|
||
The value in this column `team_id` will be the same integer that is in some row in the `id` column on the `team` table. That is what connects the two tables.
|
||
|
||
#### The Value of `foreign_key`
|
||
|
||
Notice that the `foreign_key` is a string.
|
||
|
||
Inside it has the name of the **table**, then a dot, and then the name of the **column**.
|
||
|
||
This is the name of the **table** in the database, so it is `"team"`, not the name of the **model** class `Team` (with a capital `T`).
|
||
|
||
If you had a custom table name, you would use that custom table name.
|
||
|
||
!!! info
|
||
You can learn about setting a custom table name for a model in the Advanced User Guide.
|
||
|
||
### Create the Tables
|
||
|
||
Now we can add the same code as before to create the engine and the function to create the tables:
|
||
|
||
```Python hl_lines="3-4 6 9-10"
|
||
# Code above omitted 👆
|
||
|
||
{!./docs_src/tutorial/connect/create_tables/tutorial001.py[ln:21-28]!}
|
||
```
|
||
|
||
<details>
|
||
<summary>👀 Full file preview</summary>
|
||
|
||
```Python
|
||
{!./docs_src/tutorial/connect/create_tables/tutorial001.py!}
|
||
```
|
||
|
||
</details>
|
||
|
||
And as before, we'll call this function from another function `main()`, and we'll add that function `main()` to the main block of the file:
|
||
|
||
```Python hl_lines="3-4 7-8"
|
||
# Code above omitted 👆
|
||
|
||
{!./docs_src/tutorial/connect/create_tables/tutorial001.py[ln:31-36]!}
|
||
```
|
||
|
||
<details>
|
||
<summary>👀 Full file preview</summary>
|
||
|
||
```Python
|
||
{!./docs_src/tutorial/connect/create_tables/tutorial001.py!}
|
||
```
|
||
|
||
</details>
|
||
|
||
## Run the Code
|
||
|
||
!!! tip
|
||
Before running the code, make sure you delete the file `database.db` to make sure you start from scratch.
|
||
|
||
If we run the code we have up to now, it will go and create the database file `database.db` and the tables in it we just defined, `team` and `hero`:
|
||
|
||
<div class="termy">
|
||
|
||
```console
|
||
$ python app.py
|
||
|
||
// Automatically start a new transaction
|
||
INFO Engine BEGIN (implicit)
|
||
|
||
// Check if the tables exist already
|
||
INFO Engine PRAGMA main.table_info("team")
|
||
INFO Engine [raw sql] ()
|
||
INFO Engine PRAGMA temp.table_info("team")
|
||
INFO Engine [raw sql] ()
|
||
INFO Engine PRAGMA main.table_info("hero")
|
||
INFO Engine [raw sql] ()
|
||
INFO Engine PRAGMA temp.table_info("hero")
|
||
INFO Engine [raw sql] ()
|
||
|
||
// Create the tables
|
||
INFO Engine
|
||
CREATE TABLE team (
|
||
id INTEGER,
|
||
name VARCHAR NOT NULL,
|
||
headquarters VARCHAR NOT NULL,
|
||
PRIMARY KEY (id)
|
||
)
|
||
|
||
|
||
INFO Engine [no key 0.00010s] ()
|
||
INFO Engine
|
||
CREATE TABLE hero (
|
||
id INTEGER,
|
||
name VARCHAR NOT NULL,
|
||
secret_name VARCHAR NOT NULL,
|
||
age INTEGER,
|
||
team_id INTEGER,
|
||
PRIMARY KEY (id),
|
||
FOREIGN KEY(team_id) REFERENCES team (id)
|
||
)
|
||
|
||
|
||
INFO Engine [no key 0.00026s] ()
|
||
INFO Engine COMMIT
|
||
```
|
||
|
||
</div>
|
||
|
||
## Create Tables in SQL
|
||
|
||
Let's see that same generated SQL code.
|
||
|
||
As we saw before, those `VARCHAR` columns are converted to `TEXT` in SQLite, which is the database we are using for these experiments.
|
||
|
||
So, the first SQL could also be written as:
|
||
|
||
```SQL
|
||
CREATE TABLE team (
|
||
id INTEGER,
|
||
name TEXT NOT NULL,
|
||
headquarters TEXT NOT NULL,
|
||
PRIMARY KEY (id)
|
||
)
|
||
```
|
||
|
||
And the second table could be written as:
|
||
|
||
```SQL hl_lines="8"
|
||
CREATE TABLE hero (
|
||
id INTEGER,
|
||
name TEXT NOT NULL,
|
||
secret_name TEXT NOT NULL,
|
||
age INTEGER,
|
||
team_id INTEGER,
|
||
PRIMARY KEY (id),
|
||
FOREIGN KEY(team_id) REFERENCES team (id)
|
||
)
|
||
```
|
||
|
||
The only new is the `FOREIGN KEY` line, and as you can see, it tells the database what column in this table is a foreign key (`team_id`), which other (foreign) table it references (`team`) and which column in that table is the key to define which row to connect (`id`).
|
||
|
||
Feel free to experiment with it in **DB Browser for SQLite**.
|
||
|
||
## Recap
|
||
|
||
Using **SQLModel**, in most of the cases you only need a field (column) with a `foreign_key` in the `Field()` with a string pointing to another table and column to connect two tables.
|
||
|
||
Now that we have the tables created and connected, let's create some rows in the next chapter. 🚀
|