Apache Calcite CalciteConnection 执行linq4j

org.apache.calcite.test.LinqFrontJdbcBackTest

/**
 * Tests for a linq4j front-end and JDBC back-end.
 */
public class LinqFrontJdbcBackTest {
  @Test public void testTableWhere() throws SQLException,
      ClassNotFoundException {
    final Connection connection =
        CalciteAssert.that(CalciteAssert.Config.JDBC_FOODMART).connect();
    final CalciteConnection calciteConnection =
        connection.unwrap(CalciteConnection.class);
    final SchemaPlus rootSchema = calciteConnection.getRootSchema();
    ParameterExpression c =
        Expressions.parameter(JdbcTest.Customer.class, "c");
    String s =
        Schemas.queryable(Schemas.createDataContext(connection, rootSchema),
            rootSchema.getSubSchema("foodmart"),
            JdbcTest.Customer.class, "customer")
            .where(
                Expressions.lambda(
                    Expressions.lessThan(
                        Expressions.field(c, "customer_id"),
                        Expressions.constant(5)),
                    c))
            .toList()
            .toString();
    Util.discard(s);
  }
}

 

本质上是获取

  QueryableTable table = (QueryableTable) schema.getTable(tableName);
    return table.asQueryable(root.getQueryProvider(), schema, tableName);

QueryableTable 就是自定义的table实现