注: プライマリキーのフィールドには `int | None` を使っています。これは Python コード内で `id=None` のように「`id` なしでオブジェクトを作成」し、保存時にデータベースが生成することを想定するためです。SQLModel はデータベースが `id` を提供することを理解し、スキーマでは「NULL 不可の `INTEGER` 列」を定義します。詳細は [SQLModel のプライマリキーに関するドキュメント](https://sqlmodel.tiangolo.com/tutorial/create-db-and-table/#primary-key-id) を参照してください。

* `Field(index=True)` は、この列に対して SQL のインデックスを作成するよう SQLModel に指示します。これにより、この列でフィルタしてデータを読む場合に検索が高速になります。

   * timeouts (due to a problem with the transport). When a stream times out we don't know whether
   * the problem impacts just one stream or the entire connection.
   *
   * To differentiate the two cases we ping the server when a stream times out. If the overall
   * connection is fine the ping will receive a pong; otherwise it won't.
   *

  /** Counts the bytes in the given input stream using skip if possible. */
  private static long countBySkipping(InputStream in) throws IOException {
    long count = 0;
    long skipped;
    while ((skipped = skipUpTo(in, Integer.MAX_VALUE)) > 0) {
      count += skipped;
    }
    return count;
  }

  /**
   * Copies the contents of this byte source to the given {@code OutputStream}. Does not close
   * {@code output}.
   *

        this.flags = WITNESS_REGISTER_IP_NOTIFICATION;
    }
    
    private String generateRegistrationId() {
        return "REG-" + System.currentTimeMillis() + "-" + 
               Integer.toHexString(System.identityHashCode(this));
    }
    
    public long getNextSequenceNumber() {
        return sequenceNumber.incrementAndGet();
    }
    
    public void updateHeartbeat() {

      }

      // adding count to me!  No rebalance possible.
      result[0] = elemCount;
      long resultCount = (long) elemCount + count;
      checkArgument(resultCount <= Integer.MAX_VALUE);
      this.elemCount += count;
      this.totalCount += count;
      return this;
    }

    @Nullable AvlNode<E> remove(

Ele também foi um dos primeiros frameworks a gerar um schema personalizado declarando a API inteira em JSON.

Ele não era baseado em um padrão como OpenAPI e JSON Schema. Então não seria simples integrá-lo com outras ferramentas, como Swagger UI. Mas novamente, era uma ideia muito inovadora.

Ele tem um recurso interessante e incomum: usando o mesmo framework, é possível criar APIs e também CLIs.

    long[] array = {0L, 1L, 2L};

    List<Byte> bytes = Arrays.asList((byte) 0, (byte) 1, (byte) 2);
    List<Short> shorts = Arrays.asList((short) 0, (short) 1, (short) 2);
    List<Integer> ints = Arrays.asList(0, 1, 2);
    List<Float> floats = Arrays.asList(0.0f, 1.0f, 2.0f);
    List<Long> longs = Arrays.asList(0L, 1L, 2L);
    List<Double> doubles = Arrays.asList(0.0, 1.0, 2.0);

    short[] array = {(short) 0, (short) 1, (short) 2};

    List<Byte> bytes = Arrays.asList((byte) 0, (byte) 1, (byte) 2);
    List<Short> shorts = Arrays.asList((short) 0, (short) 1, (short) 2);
    List<Integer> ints = Arrays.asList(0, 1, 2);
    List<Float> floats = Arrays.asList(0.0f, 1.0f, 2.0f);
    List<Long> longs = Arrays.asList(0L, 1L, 2L);
    List<Double> doubles = Arrays.asList(0.0, 1.0, 2.0);

    **注意：** 我们为主键字段使用 `int | None`，这样在 Python 代码中我们可以在没有 `id`（`id=None`）的情况下创建对象，并假定数据库在保存时会生成它。SQLModel 会理解数据库会提供 `id`，并在数据库模式中将该列定义为非空的 `INTEGER`。详见 [SQLModel 关于主键的文档](https://sqlmodel.tiangolo.com/tutorial/create-db-and-table/#primary-key-id)。

* `Field(index=True)` 会告诉 SQLModel 应该为此列创建一个 **SQL 索引**，这样在读取按此列过滤的数据时，程序能在数据库中进行更快的查找。

<div class="termy">

```console
// Go to the home directory
$ cd
// Create a directory for all your code projects
$ mkdir code
// Enter into that code directory
$ cd code
// Create a directory for this project
$ mkdir awesome-project
// Enter into that project directory
$ cd awesome-project
```

</div>

## Create a Virtual Environment { #create-a-virtual-environment }