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关于一个配置项的设计

 
  • Jun 28, 2014

有个需求需要配置每张表的备份SQL语句，我开始想实现如下的效果：

struct TableBackupSQL
{
  uint64_t table_id_;
  const char* sql_;
  const char * table_name_;
  TableBackupSQL()
  {
    sql_ = NULL;
    table_name_ = NULL;
    table_id_ = OB_INVALID_ID;
  }
  TableBackupSQL(uint64_t table_id, const char* table_name, const char* sql)
  {
    sql_ = sql;
    table_name_ = table_name;
    table_id_ = table_id;
  }
};

struct TableBackupTransaction
{
  static const int OB_MAX_SQL_PER_TRANS = 5;
  TableBackupSQL sql_list_[OB_MAX_SQL_PER_TRANS];
};


TableBackupTransaction table_backup_list_[] =
{
  {
    TableBackupSQL(1, "name", "select * from cs"),
    TableBackupSQL(2, "name2", "select 2* from cs")
  },
  {
    TableBackupSQL(1, "name", "select * from cs")
  }
};

然后用宏美化一下就成这样了： 

#define TABLE_BACKUP_SINGLE(table_prefix, sql)\
  { TableBackupSQL(table_prefix##_TID, table_prefix##_TABLE_NAME, sql) }
#define TABLE_BACKUP(table_prefix, sql)\
   TableBackupSQL(table_prefix##_TID, table_prefix##_TABLE_NAME, sql)
#define TABLE_BACKUP_MULTIPLE

ObInnerTableBackupGuard::TableBackupSQL ObInnerTableBackupGuard::table_backup_list_[][MAX_SQL_PER_TRANS] =
{
  TABLE_BACKUP_SINGLE(OB_FIRST_ROOT_TABLE, "select * from %s"),

  TABLE_BACKUP_MULTIPLE
  {
    TABLE_BACKUP(OB_ALL_TABLE, "select * from %s"),
    TABLE_BACKUP(OB_ALL_COLUMN, "select * from %s"),
    TABLE_BACKUP(OB_ALL_JOIN_INFO, "select * from %s"),
    TABLE_BACKUP(OB_ALL_DDL_OPERATION, "select max(schema_version) from %s "),
  },

  TABLE_BACKUP_SINGLE(OB_ALL_SYS_STAT, "select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_SYS_PARAM, "select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_USER, "select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_TABLE_PRIVILEGE,  "select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_CLUSTER, "select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_TRIGGER_EVENT, "select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_CLIENT, "select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_SYS_CONFIG,"select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_SYS_CONFIG_STAT, "select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_SERVER, "select * from %s"),
  TABLE_BACKUP_SINGLE(OB_ALL_CLUSTER_STAT, "select * from %s")
};

无奈想法很美好，实际上行不通，至少不开C++11新特性的情况下，不允许这样初始化，退而求其次：

struct TableBackupTransaction
{
  static const int OB_MAX_SQL_PER_TRANS = 5;
  int sql_count_;
  TableBackupSQL sql_list_[OB_MAX_SQL_PER_TRANS];
  TableBackupTransaction(const TableBackupSQL * sql_list, int count)
  {
    //assert, length sql_list
    for(int i = 0; i < count; i++)
    {
      sql_list_[i] = sql_list[i];
    }//or memcpy
    sql_count_ = count;
  }
  TableBackupTransaction(const TableBackupSQL & sql_list)
  {
    sql_list_[0] = sql_list;
    sql_count_ = 1;
  }
};

TableBackupTransaction table_backup_list_[] =
{
  TableBackupTransaction({
    TableBackupSQL(1, "name", "select * from cs"),
    TableBackupSQL(2, "name2", "select 2* from cs")
  }),
  TableBackupTransaction({
    TableBackupSQL(1, "name", "select * from cs")
  })
};

多了一次复制，但是初始化列表{a,b,c…}在不开C++11的时候不能作为函数参数传递，只能这样

TableBackupSQL table_backup_[] =
{
    TableBackupSQL(1, "name", "select * from cs"),
    TableBackupSQL(2, "name2", "select 2* from cs")
};
TableBackupTransaction table_backup_list_[] =
{
  TableBackupTransaction(table_backup_, sizeof(table_backup_)/sizeof(TableBackupSQL)),
  TableBackupTransaction(TableBackupSQL(1, "name", "select * from cs"))
};

弱爆了，最后改成二位数组好了：

struct TableBackupSQL
{
  uint64_t table_id_;
  const char* sql_;
  const char * table_name_;
  TableBackupSQL()
  {
    sql_ = NULL;
    table_name_ = NULL;
    table_id_ = OB_INVALID_ID;
  }
  TableBackupSQL(uint64_t table_id, const char* table_name, const char* sql)
  {
    sql_ = sql;
    table_name_ = table_name;
    table_id_ = table_id;
  }
  bool is_valid() const
  {
    return sql_ != NULL && table_name_ != NULL && table_id_ != OB_INVALID_ID;
  }
};

TableBackupSQL table_backup_list_[][5] =
{
  {
    TableBackupSQL(1, "name", "select * from cs"),
    TableBackupSQL(2, "name2", "select 2* from cs")
  },
  {
    TableBackupSQL(1, "name", "select * from cs")
  }
};

只不过二维数组每个维度只是数组，没有额外的信息，不能扩展，访问只能这样：

int main(void)
{
  TableBackupSQL (*trans)[5] = table_backup_list_;
  for (int i = 0; i < sizeof(table_backup_list_)/(sizeof(TableBackupSQL)*5); i++, trans++)
  {
    for (int j = 0; j < 5; j++)
    {
      const TableBackupSQL& desc = *trans[j];
      if (!desc.is_valid())
      {
        break;
      }
      printf("%d, %d: %d, %s, %s\n",i ,j , desc.table_id_, desc.table_name_, desc.sql_);
    }
  }
}

或者

int main(void)
{
  for (int i = 0; i < sizeof(table_backup_list_)/(sizeof(TableBackupSQL)*5); i++)
  {
    const TableBackupSQL (&trans)[5] = table_backup_list_[i];
    for (int j = 0; j < 5; j++)
    {
      const TableBackupSQL desc = trans[j];
      if (!desc.is_valid())
      {
        break;
      }
      printf("%d, %d: %d, %s, %s\n",i ,j , desc.table_id_, desc.table_name_, desc.sql_);
    }
  }
}

弱爆了….所以我最后决定把Transaction和单条事务直接分开了….

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