# 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 <a href="https://sqlmodel.tiangolo.com/" class="external-link" target="_blank">SQLModel</a>.

        // there are bugs in various JVM that have problems doing this across
        // different filesystem. So we'll incur the small hit to actually copy
        // here and be safe. jvz.
        // ----------------------------------------------------------------------------

        try {
            Files.createDirectories(destination.toPath().getParent());

        Activation activation = profile.getActivation();

        String jdk = activation.getJdk();

        // null case is covered by canDetermineActivation(), so we can do a straight startsWith() here.
        if (jdk.startsWith("[") || jdk.startsWith("(")) {
            try {
                return matchJdkVersionRange(jdk);
            } catch (InvalidVersionSpecificationException e) {

         */
        FILE_MODIFIED,
        /**
         * Directory was renamed
         */
        DIRECTORY_RENAMED,
        /**
         * File or directory attributes were changed
         */
        ATTRIBUTES_CHANGED
    }

    /**
     * SMB2 File Action constants
     */
    private static final int FILE_ACTION_ADDED = 0x00000001;

 *       APIs are offered that don't).
 *   <li>Can't be passed directly to methods that expect {@code long[]} (though the most common
 *       utilities do have replacements here).
 *   <li>Dependency on {@code com.google.common} / Guava.
 * </ul>
 *
 * <p>Advantages compared to {@link com.google.common.collect.ImmutableList ImmutableList}{@code
 * <Long>}:
 *
 * <ul>

 *       APIs are offered that don't).
 *   <li>Can't be passed directly to methods that expect {@code int[]} (though the most common
 *       utilities do have replacements here).
 *   <li>Dependency on {@code com.google.common} / Guava.
 * </ul>
 *
 * <p>Advantages compared to {@link com.google.common.collect.ImmutableList ImmutableList}{@code
 * <Integer>}:
 *
 * <ul>

	setRequestValidityMiddleware,
	// Add upload forwarding middleware for site replication
	setUploadForwardingMiddleware,
	// Add bucket forwarding middleware
	setBucketForwardingMiddleware,
	// Add new middlewares here.
}

// configureServer handler returns final handler for the http server.
func configureServerHandler(endpointServerPools EndpointServerPools) (http.Handler, error) {

		}()
		time.Sleep(1 * time.Millisecond) // wait for goroutine to advance; ref=2

		// Unlock the 1st lock; ref=1 after this line
		nsLk.unlock("volume", "path", false)

		// Taking another lockMapMutex here allows queuing up additional lockers. This should
		// not be required but makes reproduction much easier.
		nsLk.lockMapMutex.Lock()

		// lk3 blocks.
		lk3ch := make(chan bool)
		go func() {

have to make sure that it's a single process running those previous steps *even* if afterwards, you start **multiple processes** (multiple workers) for the application itself. If those steps were run by **multiple processes**, they would **duplicate** the work by running it in **parallel**, and if the steps were something delicate like a database migration, they could cause conflicts with each other.

Of course, there are some cases where there's no problem in running the previous steps multiple...

    return Ordering.explicit(new ArrayList<>(elementsPlus));
  }

  /*
   * All the ContiguousSet generators below manually reject nulls here. In principle, we'd like to
   * defer that to Range, since it's ContiguousSet.create() that's used to create the sets. However,
   * that gets messy here, and we already have null tests for Range.
   */

  /*