}

  /** A factory that chooses the most space-efficient representation of the table. */
  static <R, C, V> RegularImmutableTable<R, C, V> forOrderedComponents(
      ImmutableList<Cell<R, C, V>> cellList,
      ImmutableSet<R> rowSpace,
      ImmutableSet<C> columnSpace) {
    // use a dense table if more than half of the cells have values
    // TODO(gak): tune this condition based on empirical evidence

            if (elementName.equals("table")) {
                if (currentTable != null) {
                    throw new UnsupportedOperationException("A table within a table is not supported.");
                }
                currentTable = document.createElement("table");
                nodes.push(currentTable);
                return true;
            }

  }

  /** A factory that chooses the most space-efficient representation of the table. */
  static <R, C, V> RegularImmutableTable<R, C, V> forOrderedComponents(
      ImmutableList<Cell<R, C, V>> cellList,
      ImmutableSet<R> rowSpace,
      ImmutableSet<C> columnSpace) {
    // use a dense table if more than half of the cells have values
    // TODO(gak): tune this condition based on empirical evidence

@GwtCompatible
@NullMarked
public class HashBasedTableColumnMapTest extends ColumnMapTests {
  public HashBasedTableColumnMapTest() {
    super(false, true, true, false);
  }

  @Override
  Table<Integer, String, Character> makeTable() {
    return HashBasedTable.create();
  }

@GwtCompatible
@NullMarked
public class HashBasedTableRowMapTest extends RowMapTests {
  public HashBasedTableRowMapTest() {
    super(false, true, true, true);
  }

  @Override
  Table<String, Integer, Character> makeTable() {
    return HashBasedTable.create();
  }

@GwtCompatible
@NullMarked
public class TreeBasedTableRowTest extends RowTests {
  public TreeBasedTableRowTest() {
    super(false, true, true, true, true);
  }

  @Override
  Table<Character, String, Integer> makeTable() {
    return TreeBasedTable.create();
  }

      Table<R, C, V> table(Table<R, C, V> table, @Nullable Object mutex) {
    return new SynchronizedTable<>(table, mutex);
  }

  static final class SynchronizedTable<
          R extends @Nullable Object, C extends @Nullable Object, V extends @Nullable Object>
      extends SynchronizedObject implements Table<R, C, V> {

    SynchronizedTable(Table<R, C, V> delegate, @Nullable Object mutex) {

// First finds the first record ordered by primary key, matching given conditions conds
func (db *DB) First(dest interface{}, conds ...interface{}) (tx *DB) {
	tx = db.Limit(1).Order(clause.OrderByColumn{
		Column: clause.Column{Table: clause.CurrentTable, Name: clause.PrimaryKey},
	})
	if len(conds) > 0 {
		if exprs := tx.Statement.BuildCondition(conds[0], conds[1:]...); len(exprs) > 0 {
			tx.Statement.AddClause(clause.Where{Exprs: exprs})
		}

匯入 `SQLModel` 並建立一個資料庫模型：

{* ../../docs_src/sql_databases/tutorial001_an_py310.py ln[1:11] hl[7:11] *}

`Hero` 類別與 Pydantic 模型非常相似（事實上，在底層它就是一個 Pydantic 模型）。

有幾點差異：

* `table=True` 告訴 SQLModel 這是一個「資料表模型」（table model），它應該代表 SQL 資料庫中的一個資料表，而不僅僅是「資料模型」（就像一般的 Pydantic 類別）。

* `Field(primary_key=True)` 告訴 SQLModel，`id` 是 SQL 資料庫中的「主鍵」。 （你可以在 SQLModel 文件中進一步了解 SQL 主鍵）

@GwtIncompatible // TODO(hhchan): ArrayTable
@NullUnmarked
public class ArrayTableColumnMapTest extends ColumnMapTests {
  public ArrayTableColumnMapTest() {
    super(true, false, false, false);
  }

  @Override
  Table<Integer, String, Character> makeTable() {
    return ArrayTable.create(asList(1, 2, 3), asList("foo", "bar", "dog"));
  }

  @Override
  protected Map<String, Map<Integer, Character>> makeEmptyMap() {