Method GetSchema

cpp/src/arrow/flight/sql/example/sqlite_statement.cc:108–145

}

arrow::Result<std::shared_ptr<Schema>> SqliteStatement::GetSchema() const {
  std::vector<std::shared_ptr<Field>> fields;
  int column_count = sqlite3_column_count(stmt_);
  for (int i = 0; i < column_count; i++) {
    const char* column_name = sqlite3_column_name(stmt_, i);

    // SQLite does not always provide column types, especially when the statement has not
    // been executed yet. Because of this behaviour this method tries to get the column
    // types in two attempts:
    // 1. Use sqlite3_column_type(), which return SQLITE_NULL if the statement has not
    //    been executed yet
    // 2. Use sqlite3_column_decltype(), which returns correctly if given column is
    //    declared in the table.
    // Because of this limitation, it is not possible to know the column types for some
    // prepared statements, in this case it returns a dense_union type covering any type
    // SQLite supports.
    const int column_type = sqlite3_column_type(stmt_, i);
    const char* table = sqlite3_column_table_name(stmt_, i);
    std::shared_ptr<DataType> data_type = GetDataTypeFromSqliteType(column_type);
    if (data_type->id() == Type::NA) {
      // Try to retrieve column type from sqlite3_column_decltype
      const char* column_decltype = sqlite3_column_decltype(stmt_, i);
      if (column_decltype != NULLPTR) {
        ARROW_ASSIGN_OR_RAISE(data_type, GetArrowType(column_decltype));
      } else {
        // If it cannot determine the actual column type, return a dense_union type
        // covering any type SQLite supports.
        data_type = GetUnknownColumnDataType();
      }
    }
    ColumnMetadata column_metadata = GetColumnMetadata(column_type, table);

    fields.push_back(
        arrow::field(column_name, data_type, column_metadata.metadata_map()));
  }

  return arrow::schema(fields);
}

SqliteStatement::~SqliteStatement() { sqlite3_finalize(stmt_); }