sql_exec_context.h

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/*
  Copyright (c) 2022, 2025, Oracle and/or its affiliates.
 
  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License, version 2.0,
  as published by the Free Software Foundation.
 
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  as designated in a particular file or component or in included license
  documentation.  The authors of MySQL hereby grant you an additional
  permission to link the program and your derivative works with the
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  the program or referenced in the documentation.
 
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
 
  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/
 
#ifndef ROUTING_SQL_EXEC_CONTEXT_INCLUDED
#define ROUTING_SQL_EXEC_CONTEXT_INCLUDED
 
#include <map>
#include <optional>
#include <string>
#include <vector>
 
#include "mysql/harness/stdx/expected.h"
#include "sql_value.h"
 
/**
 * execution context for SQL.
 *
 * - system-variables
 * - diagnostics area
 */
class ExecutionContext {
 public:
  /**
   * system-variables as returned by the server.
   *
   * can be queried from the server with:
   *
   * - SELECT @@SESSION.{k}
   * - SELECT @@LOCAL.{k}
   *
   * can be set on the server with:
   *
   * - SET k = v;
   * - SET @@SESSION.k = v;
   * - SET @@LOCAL.k = v;
   * - SET SESSION k = v;
   * - SET LOCAL k = v;
   *
   * changes to system-vars on the server are returned via
   * the sesssion-tracker for system-variables.
   */
  class SystemVariables {
   public:
    using key_type = std::string;
    using value_type = Value;  // aka std::optional<std::string>
 
    /**
     * set k to v.
     *
     * if k doesn't exist in the system-vars yet, it gets inserted.
     */
    void set(key_type k, value_type v) {
      vars_.insert_or_assign(std::move(k), std::move(v));
    }
 
    /**
     * find 'k' in sytem-vars.
     *
     * @param k key
     *
     * if 'k' does not exist in system-vars, a NULL-like value is returned.
     * otherwise return the value for the system-var referenced by 'k'
     *
     * @returns std::nullopt if key is not found, the found value otherwise.
     */
    std::optional<value_type> find(const key_type &k) const {
      const auto it = vars_.find(k);
      if (it == vars_.end()) return {std::nullopt};
 
      return it->second;
    }
 
    /**
     * get 'k' from system-vars.
     *
     * @param k key
     *
     * if 'k' does not exist in system-vars, a NULL-like value is returned.
     * otherwise return the value for the system-var referenced by 'k' which may
     * be NULL-like or a string.
     *
     * @returns std::nullopt if key is not found or value is NULL-like, the
     * found value otherwise
     */
    value_type get(const key_type &k) const {
      const auto res = find(k);
      if (!res) return {std::nullopt};
 
      return *res;
    }
 
    using iterator = std::map<key_type, value_type>::iterator;
    using const_iterator = std::map<key_type, value_type>::const_iterator;
 
    iterator begin() { return vars_.begin(); }
    const_iterator begin() const { return vars_.begin(); }
    iterator end() { return vars_.end(); }
    const_iterator end() const { return vars_.end(); }
 
    /**
     * check if their is a no system-var.
     */
    bool empty() const { return vars_.empty(); }
 
   private:
    std::map<key_type, value_type> vars_;
  };
 
  /**
   * diagnostics area.
   *
   * - warnings, errors and notes.
   *
   * used by:
   *
   * - SHOW WARNINGS
   * - SHOW ERRORS
   * - SHOW COUNT(*) WARNINGS
   * - SHOW COUNT(*) ERRORS
   * - SELECT @@warning_count
   * - SELECT @@error_count
   */
  class DiagnosticsArea {
   public:
    class Warning {
     public:
      Warning(std::string level, uint64_t code, std::string msg)
          : level_(std::move(level)), code_(code), msg_{std::move(msg)} {}
 
      std::string level() const { return level_; }
      uint64_t code() const { return code_; }
      std::string message() const { return msg_; }
 
     private:
      std::string level_;
      uint64_t code_;
      std::string msg_;
    };
 
    std::vector<Warning> &warnings() { return warnings_; }
    const std::vector<Warning> &warnings() const { return warnings_; }
 
   private:
    std::vector<Warning> warnings_;
  };
 
  DiagnosticsArea &diagnostics_area() { return diagnostics_area_; }
 
  const DiagnosticsArea &diagnostics_area() const { return diagnostics_area_; }
 
  SystemVariables &system_variables() { return system_variables_; }
 
  const SystemVariables &system_variables() const { return system_variables_; }
 
 private:
  SystemVariables system_variables_;
 
  DiagnosticsArea diagnostics_area_;
};
 
#endif