**`Session`** хранит **объекты в памяти** и отслеживает необходимые изменения в данных, затем **использует `engine`** для общения с базой данных.

Мы создадим **зависимость** FastAPI с `yield`, которая будет предоставлять новую `Session` для каждого запроса. Это и обеспечивает использование одной сессии на запрос. 🤓

  /**
   * Divides an iterator into unmodifiable sublists of the given size (the final list may be
   * smaller). For example, partitioning an iterator containing {@code [a, b, c, d, e]} with a
   * partition size of 3 yields {@code [[a, b, c], [d, e]]} -- an outer iterator containing two
   * inner lists of three and two elements, all in the original order.
   *
   * <p>The returned lists implement {@link java.util.RandomAccess}.
   *

   *
   *  * A `SYN_RESET` frame abnormally terminates the stream.
   *  * Both input and output streams have transmitted all data and headers.
   *
   * Note that the input stream may continue to yield data even after a stream reports itself as
   * not open. This is because input data is buffered.
   */
  val isOpen: Boolean
    get() {
      withLock {
        if (errorCode != null) {
          return false

  void awaitTimedWaiting(Thread thread) {
    while (true) {
      switch (thread.getState()) {
        case BLOCKED:
        case NEW:
        case RUNNABLE:
        case WAITING:
          Thread.yield();
          break;
        case TIMED_WAITING:
          return;
        case TERMINATED:
          throw new AssertionError();
      }
    }
  }

                }
              });
      expectedKeys.add(s);
    }

    computationLatch.countDown();
    // let some computations complete
    while (computedCount.get() < nThreads) {
      Thread.yield();
    }
    cache.invalidateAll();
    tasksFinished.await();

    // Check all of the removal notifications we received: they should have had correctly-associated

Crearemos una **dependencia de FastAPI** con `yield` que proporcionará una nueva `Session` para cada request. Esto es lo que asegura que usemos una sola session por request. 🤓

     * the encoded path will have a trailing '/'.
     *
     * Popping "/a/b/c/" yields "/a/b/". In this case the list of path segments goes from ["a",
     * "b", "c", ""] to ["a", "b", ""].
     *
     * Popping "/a/b/c" also yields "/a/b/". The list of path segments goes from ["a", "b", "c"]
     * to ["a", "b", ""].
     */
    private fun pop() {

    sink.writeUtf8(content)
    sink.close()
  }

  /**
   * @param delta the offset from the current date to use. Negative values yield dates in the past;
   * positive values yield dates in the future.
   */
  private fun formatDate(
    delta: Long,
    timeUnit: TimeUnit,
  ): String = formatDate(Date(System.currentTimeMillis() + timeUnit.toMillis(delta)))

   * {@link Predicate#apply}), the returned predicate may not be <i>consistent with equals</i>. For
   * example, {@code instanceOf(ArrayList.class)} will yield different results for the two equal
   * instances {@code Lists.newArrayList(1)} and {@code Arrays.asList(1)}.
   *
   * <p><b>Discouraged:</b> Prefer using {@code clazz::isInstance} or {@code x -> x instanceof

{* ../../docs_src/sql_databases/tutorial001_an_py310.py ln[21:22] hl[21:22] *}

### 创建会话（Session）依赖项

**`Session`** 会存储**内存中的对象**并跟踪数据中所需更改的内容，然后它**使用 `engine`** 与数据库进行通信。

我们会使用 `yield` 创建一个 FastAPI **依赖项**，为每个请求提供一个新的 `Session` 。这确保我们每个请求使用一个单独的会话。🤓

然后我们创建一个 `Annotated` 的依赖项 `SessionDep` 来简化其他也会用到此依赖的代码。

{* ../../docs_src/sql_databases/tutorial001_an_py310.py ln[25:30]  hl[25:27,30] *}