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338 lines
11 KiB
Markdown
338 lines
11 KiB
Markdown
# Models with Relationships in FastAPI
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If we go right now and read a single **hero** by ID, we get the hero data with the team ID.
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But we don't get any data about the particular team:
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<img class="shadow" alt="Interactive API docs UI getting a single hero" src="/img/tutorial/fastapi/relationships/image01.png">
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We get a response of:
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```JSON hl_lines="5"
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{
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"name": "Deadpond",
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"secret_name": "Dive Wilson",
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"age": null,
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"team_id": 1,
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"id": 1,
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}
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```
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And the same way, if we get a **team** by ID, we get the team data, but we don't get any information about this team's heroes:
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<img class="shadow" alt="Interactive API docs UI getting a single team" src="/img/tutorial/fastapi/relationships/image02.png">
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Here we get a response of:
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```JSON
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{
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"name": "Preventers",
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"headquarters": "Sharp Tower",
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"id": 2
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}
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```
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...but no information about the heroes.
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Let's update that. 🤓
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## Why Aren't We Getting More Data
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First, why is it that we are not getting the related data for each hero and for each team?
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It's because we declared the `HeroRead` with only the same base fields of the `HeroBase` plus the `id`. But it doesn't include a field `team` for the **relationship attribute**.
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And the same way, we declared the `TeamRead` with only the same base fields of the `TeamBase` plus the `id`. But it doesn't include a field `heroes` for the **relationship attribute**.
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```Python hl_lines="3-5 9-10 14-19 23-24"
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# Code above omitted 👆
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{!./docs_src/tutorial/fastapi/teams/tutorial001.py[ln:7-9]!}
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# Code here omitted 👈
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{!./docs_src/tutorial/fastapi/teams/tutorial001.py[ln:22-23]!}
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# Code here omitted 👈
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{!./docs_src/tutorial/fastapi/teams/tutorial001.py[ln:31-36]!}
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# Code here omitted 👈
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{!./docs_src/tutorial/fastapi/teams/tutorial001.py[ln:45-46]!}
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# Code below omitted 👇
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```
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<details>
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<summary>👀 Full file preview</summary>
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```Python
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{!./docs_src/tutorial/fastapi/teams/tutorial001.py!}
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```
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</details>
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Now, remember that <a href="https://fastapi.tiangolo.com/tutorial/response-model/" class="external-link" target="_blank">FastAPI uses the `response_model` to validate and **filter** the response data</a>?
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In this case, we used `response_model=TeamRead` and `response_model=HeroRead`, so FastAPI will use them to filter the response data, even if we return a **table model** that includes **relationship attributes**:
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```Python hl_lines="3 8 12 17"
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# Code above omitted 👆
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{!./docs_src/tutorial/fastapi/teams/tutorial001.py[ln:104-109]!}
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# Code here omitted 👈
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{!./docs_src/tutorial/fastapi/teams/tutorial001.py[ln:159-164]!}
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# Code below omitted 👇
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```
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<details>
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<summary>👀 Full file preview</summary>
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```Python
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{!./docs_src/tutorial/fastapi/teams/tutorial001.py!}
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```
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</details>
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## Don't Include All the Data
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Now let's stop for a second and think about it.
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We cannot simply include *all* the data, including all the internal relationships, because each **hero** has an attribute `team` with their team, and then that **team** also has an attribute `heroes` with all the **heroes** in the team, including this one.
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If we tried to include everything, we could make the server application **crash** trying to extract **infinite data**, going through the same hero and team over and over again internally, something like this:
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```JSON hl_lines="2 13 24 34"
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{
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"name": "Rusty-Man",
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"secret_name": "Tommy Sharp",
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"age": 48,
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"team_id": 1,
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"id": 1,
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"team": {
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"name": "Preventers",
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"headquarters": "Sharp Tower",
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"id": 2,
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"heroes": [
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{
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"name": "Rusty-Man",
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"secret_name": "Tommy Sharp",
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"age": 48,
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"team_id": 1,
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"id": 1,
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"team": {
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"name": "Preventers",
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"headquarters": "Sharp Tower",
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"id": 2,
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"heroes": [
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{
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"name": "Rusty-Man",
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"secret_name": "Tommy Sharp",
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"age": 48,
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"team_id": 1,
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"id": 1,
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"team": {
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"name": "Preventers",
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"headquarters": "Sharp Tower",
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"id": 2,
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"heroes": [
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...with infinite data here... 😱
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]
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}
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}
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]
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}
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}
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]
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}
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}
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```
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As you can see, in this example, we would get the hero **Rusty-Man**, and from this hero we would get the team **Preventers**, and then from this team we would get its heroes, of course, including **Rusty-Man**... 😱
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So we start again, and in the end, the server would just crash trying to get all the data with a `"Maximum recursion error"`, we would not even get a response like the one above.
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So, we need to carefully choose in which cases we want to include data and in which not.
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## What Data to Include
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This is a decision that will depend on **each application**.
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In our case, let's say that if we get a **list of heroes**, we don't want to also include each of their teams in each one.
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And if we get a **list of teams**, we don't want to get a list of the heroes for each one.
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But if we get a **single hero**, we want to include the team data (without the team's heroes).
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And if we get a **single team**, we want to include the list of heroes (without each hero's team).
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Let's add a couple more **data models** that declare that data so we can use them in those two specific *path operations*.
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## Models with Relationships
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Let's add the models `HeroReadWithTeam` and `TeamReadWithHeroes`.
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We'll add them **after** the other models so that we can easily reference the previous models.
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```Python hl_lines="3-4 7-8"
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# Code above omitted 👆
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{!./docs_src/tutorial/fastapi/relationships/tutorial001.py[ln:61-66]!}
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# Code below omitted 👇
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```
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<details>
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<summary>👀 Full file preview</summary>
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```Python
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{!./docs_src/tutorial/fastapi/relationships/tutorial001.py!}
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```
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</details>
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These two models are very **simple in code**, but there's a lot happening here. Let's check it out.
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### Inheritance and Type Annotations
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The `HeroReadWithTeam` **inherits** from `HeroRead`, which means that it will have the **normal fields for reading**, including the required `id` that was declared in `HeroRead`.
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And then it adds the **new field** `team`, which could be `None`, and is declared with the type `TeamRead` with the base fields for reading a team.
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Then we do the same for the `TeamReadWithHeroes`, it **inherits** from `TeamRead`, and declares the **new field** `heroes`, which is a list of `HeroRead`.
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### Data Models Without Relationship Attributes
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Now, notice that these new fields `team` and `heroes` are not declared with `Relationship()`, because these are not **table models**, they cannot have **relationship attributes** with the magic access to get that data from the database.
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Instead, here these are only **data models** that will tell FastAPI **which attributes** to get data from and **which data** to get from them.
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### Reference to Other Models
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Also, notice that the field `team` is not declared with this new `TeamReadWithHeroes`, because that would again create that infinite recursion of data. Instead, we declare it with the normal `TeamRead` model.
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And the same for `TeamReadWithHeroes`, the model used for the new field `heroes` uses `HeroRead` to get only each hero's data.
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This also means that, even though we have these two new models, **we still need the previous ones**, `HeroRead` and `TeamRead`, because we need to reference them here (and we are also using them in the rest of the *path operations*).
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## Update the Path Operations
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Now we can update the *path operations* to use the new models.
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This will tell **FastAPI** to take the object that we return from the *path operation function* (a **table model**) and **access the additional attributes** from them to extract their data.
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In the case of the hero, this tells FastAPI to extract the `team` too. And in the case of the team, to extract the list of `heroes` too.
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```Python hl_lines="3 8 12 17"
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# Code above omitted 👆
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{!./docs_src/tutorial/fastapi/relationships/tutorial001.py[ln:113-118]!}
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# Code here omitted 👈
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{!./docs_src/tutorial/fastapi/relationships/tutorial001.py[ln:168-173]!}
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# Code below omitted 👇
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```
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<details>
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<summary>👀 Full file preview</summary>
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```Python
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{!./docs_src/tutorial/fastapi/relationships/tutorial001.py!}
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```
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</details>
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## Check It Out in the Docs UI
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Now let's try it out again in the **docs UI**.
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Let's try again with the same **hero** with ID `1`:
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<img class="shadow" alt="Interactive API docs UI getting a single hero with team" src="/img/tutorial/fastapi/relationships/image03.png">
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Now we get the **team** data included:
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```JSON hl_lines="7-11"
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{
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"name": "Deadpond",
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"secret_name": "Dive Wilson",
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"age": null,
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"team_id": 1,
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"id": 1,
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"team": {
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"name": "Z-Force",
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"headquarters": "Sister Margaret’s Bar",
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"id": 1
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}
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}
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```
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And if we get now the **team** with ID `2`:
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<img class="shadow" alt="Interactive API docs UI getting a single team with the list of heroes" src="/img/tutorial/fastapi/relationships/image04.png">
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Now we get the list of **heroes** included:
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```JSON hl_lines="5-41"
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{
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"name": "Preventers",
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"headquarters": "Sharp Tower",
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"id": 2,
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"heroes": [
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{
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"name": "Rusty-Man",
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"secret_name": "Tommy Sharp",
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"age": 48,
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"team_id": 2,
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"id": 2
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},
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{
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"name": "Spider-Boy",
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"secret_name": "Pedro Parqueador",
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"age": null,
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"team_id": 2,
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"id": 3
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},
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{
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"name": "Tarantula",
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"secret_name": "Natalia Roman-on",
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"age": 32,
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"team_id": 2,
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"id": 6
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},
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{
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"name": "Dr. Weird",
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"secret_name": "Steve Weird",
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"age": 36,
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"team_id": 2,
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"id": 7
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},
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{
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"name": "Captain North America",
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"secret_name": "Esteban Rogelios",
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"age": 93,
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"team_id": 2,
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"id": 8
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}
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]
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}
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```
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## Recap
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Using the same techniques to declare additional **data models**, we can tell FastAPI what data to return in the responses, even when we return **table models**.
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Here we almost **didn't have to change the FastAPI app** code, but of course, there will be cases where you need to get the data and process it in different ways in the *path operation function* before returning it.
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But even in those cases, you will be able to define the **data models** to use in `response_model` to tell FastAPI how to validate and filter the data.
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By this point, you already have a very robust API to handle data in a SQL database combining **SQLModel** with **FastAPI**, and implementing **best practices**, like data validation, conversion, filtering, and documentation. ✨
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In the next chapter, I'll tell you how to implement automated **testing** for your application using FastAPI and SQLModel. ✅
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