# SQL (Relational) Databases { #sql-relational-databases }

**FastAPI** doesn't require you to use a SQL (relational) database. But you can use **any database** that you want.

Here we'll see an example using [SQLModel](https://sqlmodel.tiangolo.com/).

**SQLModel** is built on top of [SQLAlchemy](https://www.sqlalchemy.org/) and Pydantic. It was made by the same author of **FastAPI** to be the perfect match for FastAPI applications that need to use **SQL databases**.

    duplex request bodies. Such interceptors should check `RequestBody.isDuplex()` and avoid
    accessing the request body when it is.

    Duplex calls require HTTP/2. If HTTP/1 is established instead the duplex call will fail. The
    most common use of duplex calls is [gRPC][grpc_http2].

Available JDKs on your machine are automatically detected and wired for the various compile and test tasks.
Some tests require multiple JDKs to be installed on your computer, be aware of this if you make changes related to anything toolchains related.

        if (stream.isOpen) {
          streams[streamId] = stream
        }
      }
      if (associatedStreamId == 0) {
        writer.headers(outFinished, streamId, requestHeaders)
      } else {
        require(!client) { "client streams shouldn't have associated stream IDs" }
        // HTTP/2 has a PUSH_PROMISE frame.
        writer.pushPromise(associatedStreamId, streamId, requestHeaders)
      }
    }

   * type. That said, we could *accept* a `@Nullable T[]` (which, given that we treat arrays as
   * covariant, would still permit a plain `T[]`) and return a plain `T[]`. But of course that would
   * require its own suppression, since it is also unsound. toArray(T[]) is just a mess from a
   * nullness perspective. The signature below at least has the virtue of being relatively simple.
   */
  @SuppressWarnings("nullness")

   * available for all platforms and configurations. If that implementation is unavailable, this
   * method falls back to {@code getStackTrace}. Callers that require the special implementation can
   * check its availability with {@link #lazyStackTraceIsLazy()}.
   *
   * <p>The expected (but not guaranteed) performance of the special implementation differs from

   * type. That said, we could *accept* a `@Nullable T[]` (which, given that we treat arrays as
   * covariant, would still permit a plain `T[]`) and return a plain `T[]`. But of course that would
   * require its own suppression, since it is also unsound. toArray(T[]) is just a mess from a
   * nullness perspective. The signature below at least has the virtue of being relatively simple.
   */
  @SuppressWarnings("nullness")

    * You can also add [`Security` dependencies with `scopes`](../advanced/security/oauth2-scopes.md).

/// tip

Having `dependencies` in the `APIRouter` can be used, for example, to require authentication for a whole group of *path operations*. Even if the dependencies are not added individually to each one of them.

///

/// check

*   Include unit tests when you contribute new features, as they help to a)
    prove that your code works correctly, and b) guard against future breaking
    changes to lower the maintenance cost.
*   Bug fixes also generally require unit tests, because the presence of bugs
    usually indicates insufficient test coverage.
*   Keep API compatibility in mind when you change code in core TensorFlow,
    e.g., code in

                            && !conn.getNegotiateResponse().isSigningRequired()) {
                        // if signing is not enforced, dont use connections that have signing enforced
                        // for purposes that dont require it.
                        if (log.isTraceEnabled()) {
                            log.debug("Cannot reuse, signing enforced on connection " + conn);
                        }
                        continue;