If we go right now and read a single **hero** by ID, we get the hero data with the team ID.
But we don't get any data about the particular team:
<imgclass="shadow"alt="Interactive API docs UI getting a single hero"src="/img/tutorial/fastapi/relationships/image01.png">
We get a response of:
```JSON hl_lines="5"
{
"name": "Deadpond",
"secret_name": "Dive Wilson",
"age": null,
"team_id": 1,
"id": 1,
}
```
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:
<imgclass="shadow"alt="Interactive API docs UI getting a single team"src="/img/tutorial/fastapi/relationships/image02.png">
Here we get a response of:
```JSON
{
"name": "Preventers",
"headquarters": "Sharp Tower",
"id": 2
}
```
...but no information about the heroes.
Let's update that. 🤓
## Why Aren't We Getting More Data
First, why is it that we are not getting the related data for each hero and for each team?
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**.
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**.
Now, remember that <ahref="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>?
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**:
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.
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:
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**... 😱
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.
So, we need to carefully choose in which cases we want to include data and in which not.
## What Data to Include
This is a decision that will depend on **each application**.
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.
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`.
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.
Then we do the same for the `TeamReadWithHeroes`, it **inherits** from `TeamRead`, and declares the **new field**`heroes`, which is a list of `HeroRead`.
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.
Instead, here these are only **data models** that will tell FastAPI **which attributes** to get data from and **which data** to get from them.
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.
And the same for `TeamReadWithHeroes`, the model used for the new field `heroes` uses `HeroRead` to get only each hero's data.
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*).
## Update the Path Operations
Now we can update the *path operations* to use the new models.
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.
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.
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**.
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.
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.
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. ✨
