set_variables_helper.h

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#ifndef SET_VARIABLES_HELPER_H
#define SET_VARIABLES_HELPER_H
 
#include <sql/set_var.h>   // set_var_base, enum_var_type
#include <sql/sql_lex.h>   // LEX
#include <sql/sql_list.h>  // List
 
class THD;
class Storing_auto_THD;
 
/**
  A helper class to fascilitate executing SET on system variables.
 
  Runs in the current @ref THD, but in a temp @ref LEX to avoid
  polluting the THD::lex with the changes.
 
  Useful for service implementations looking to set values
  to system variables.
 
  Should be used in a single THD.
 
  A proper usage is something of the sort:
 
  <code>
  THD *curr_thd = ...;
  Item *value1 = Item_int(20), *val2= Item_int(30);
 
  Set_variables_helper hlp(curr_thd);
 
  if (hlp.add_variable(nullptr, 0, "foo", 3, enum_var_type::PERSIST_ONLY,
  value1)) return true;
 
  if (hlp.add_variable("bar", 3, "baz", 3, enum_var_type::PERSIST, val2))
    return true;
 
  ...
 
  if (hlp->execute())
    return true;
  </code>
 
  The above executes the following command
  <code>
  SET PERSIST_ONLY foo = 20, PERSIST bar.baz = 30;
  </code>
 
  @sa @ref sql_set_variables
*/
class Set_variables_helper {
  List<set_var_base> m_sysvar_list;
  THD *m_thd;
  LEX *m_lex_save, m_lex_tmp;
  Storing_auto_THD *m_thd_auto;
 
 public:
  /**
    Initializes the helper and switches to the canned temp @ref LEX
    @param existing_thd the THD to execute on.
  */
  Set_variables_helper(THD *existing_thd);
 
  ~Set_variables_helper();
 
  /**
    Adds setting one variable instruction.
 
    Adds a:
    @code
      <var_type> [prefix.]suffix = variable_value
    @endcode
    to the SET command being constructed.
 
    @param prefix the prefix for the variable name or nullptr if none
    @param prefix_length length of prefix, 0 if empty
    @param suffix the name of the variable to set. Must be nonnull
    @param suffix_length the length of suffix
    @param variable_value the value to set
    @param var_type how to set: PERSIST, PERSIST_ONLY etc
    @retval true failure
    @retval false success
  */
  bool add_variable(const char *prefix, size_t prefix_length,
                    const char *suffix, size_t suffix_length,
                    Item *variable_value, enum_var_type var_type);
 
  /**
    Executes the SET command for all variables added.
 
    @retval true failure
    @retval false success
 
  */
  bool execute();
 
  /* gets the current thread to execute the SET in */
  THD *get_thd() { return m_thd; }
 
  /* returns true if it's running on a local session */
  bool is_auto_thd() { return m_thd_auto != nullptr; }
 
  /**
    @brief Checks the update type for the system variable and throws error if
    any found
    @param prefix the prefix for the variable name or nullptr if none
    @param prefix_length length of prefix, 0 if empty
    @param suffix the name of the variable to set. Must be nonnull
    @param suffix_length the length of suffix
    @param variable_value the value to set
    @retval true failure
    @retval false success
  */
  bool check_variable_update_type(const char *prefix, size_t prefix_length,
                                  const char *suffix, size_t suffix_length,
                                  Item *variable_value);
};
 
#endif /* SET_VARIABLES_HELPER_H */