<img src="/img/tutorial/dependencies/image02.png">

## Shortcut { #shortcut }

But you see that we are having some code repetition here, writing `CommonQueryParams` twice:

//// tab | Python 3.8+

```Python
commons: Annotated[CommonQueryParams, Depends(CommonQueryParams)]
```

////

//// tab | Python 3.8+ non-Annotated

* Have shared logic (the same code logic again and again).
* Share database connections.
* Enforce security, authentication, role requirements, etc.
* And many other things...

All these, while minimizing code repetition.

## First Steps { #first-steps }

Let's see a very simple example. It will be so simple that it is not very useful, for now.

But this way we can focus on how the **Dependency Injection** system works.

It has an integrated dependency injection system, inspired by Angular 2. It requires pre-registering the "injectables" (like all the other dependency injection systems I know), so, it adds to the verbosity and code repetition.

As the parameters are described with TypeScript types (similar to Python type hints), editor support is quite good.

 * </ul>
 *
 * @author Jim McMaster
 * @author Jige Yu
 * @since 10.0
 */
@GwtCompatible
@NullMarked
public final class EqualsTester {
  private static final int REPETITIONS = 3;

  private final List<List<Object>> equalityGroups = new ArrayList<>();
  private final RelationshipTester.ItemReporter itemReporter;

  /** Constructs an empty EqualsTester instance */
  public EqualsTester() {

 * to explicitly add another equivalence group.
 *
 * @author Gregory Kick
 * @since 10.0
 */
@GwtCompatible
@NullMarked
public final class EquivalenceTester<T> {
  private static final int REPETITIONS = 3;

  private final Equivalence<? super T> equivalence;
  private final RelationshipTester<T> delegate;
  private final List<T> items = new ArrayList<>();

 * </ul>
 *
 * @author Jim McMaster
 * @author Jige Yu
 * @since 10.0
 */
@GwtCompatible
@NullMarked
public final class EqualsTester {
  private static final int REPETITIONS = 3;

  private final List<List<Object>> equalityGroups = new ArrayList<>();
  private final RelationshipTester.ItemReporter itemReporter;

  /** Constructs an empty EqualsTester instance */
  public EqualsTester() {

* Update [SQL tutorial with SQLAlchemy, using `Depends` to improve editor support and reduce code repetition](https://fastapi.tiangolo.com/tutorial/sql-databases/). PR [#52](https://github.com/tiangolo/fastapi/pull/52).