//已知表名，要获得该表信息
void Table::getTableInfo()
{
ifstream infile;
string filename;
filename = table_name + "_tableinfo.txt";
if (!isTableExist()){
//表不存在
throw Table_Index_Error("table", table_name);
}
infile.open(filename.c_str(), ios::in);
if (!infile) throw File_openfail(filename.c_str());
int i = 0;
while (!infile.eof()){
infile >> attrs[i].attr_name;
infile >> attrs[i].attr_def_type;
infile >> attrs[i].attr_type;
infile >> attrs[i].attr_id;
infile >> attrs[i].attr_len;
i++;
}
attr_num = i - 1;
CalcRecordLen();
}
void DatabaseDictionary::removeTable(
const Context & context,
const String & table_name)
{
if (!isTableExist(context, table_name))
throw Exception("Table " + name + "." + table_name + " doesn't exist.", ErrorCodes::UNKNOWN_TABLE);
auto objects_map = external_dictionaries.getObjectsMap();
deleted_tables.insert(table_name);
}
bool Table::dropTable()
{
string filename;
string newTableList = "";
ifstream infile;
ofstream outfile;
if (!isTableExist()){ //该表不存在
cerr << "The table doesn't exist!" << endl;
return false; //删除失败，返回false
}
//表存在，则删除或更新相关文件
//删除tablelist.txt中表名
infile.open("tablelist.txt", ios::in); //以只读模式打开文件，读取其中信息
if (!infile) throw File_openfail("tablelist.txt");
string tablename;
while (!infile.eof()){
getline(infile, tablename); //每行只储存一个表名信息
if (tablename != "" && tablename != table_name){
//过滤掉要删除的表名，保留其余的表名信息，存在newTableList中
newTableList = newTableList + tablename + '\n';
}
}
outfile.open("tablelist.txt", ios::out); //打开tablelist.txt并清空
if (!outfile) throw File_openfail("tablelist.txt");
outfile << newTableList; //将保留的表名信息存入文件中
outfile.close();
//删除记录表的字段的文件
filename = table_name + "_tableinfo.txt";
remove(filename.c_str()); //移除文件
//删除记录表中所有索引信息的文件
filename = table_name + "_tableindexinfo.txt";
remove(filename.c_str());
//删除记录表中记录的文件
filename = table_name + "_tablereco";
remove(filename.c_str()); //移除文件
return true;
}
//建表，更新或创建相关文件
bool Table::createTable()
{
string filename;
ofstream outfile;
if (isTableExist()){ //该表在数据库中已存在
cerr << "The table has already been existed!" << endl;
return false; //建表失败，返回false
}
//表不存在，则建立新表
//更新储存表名的文件
outfile.open("tablelist.txt", ios::app); //以追加模式打开
if (!outfile) throw File_openfail("tablelist");
outfile << table_name << endl; //向文件中输出表名
outfile.close();
//新建储存该表的字段信息的文件
filename = table_name + "_tableinfo.txt";
outfile.open(filename.c_str(), ios::out);
if (!outfile) throw File_openfail(filename.c_str());
for (int i = 0; i < attr_num; i++){ //将表的字段信息存在文件中
outfile << attrs[i].attr_name << " ";
outfile << attrs[i].attr_def_type << " ";
outfile << attrs[i].attr_type << " ";
outfile << i << " ";
outfile << attrs[i].attr_len << endl;
}
outfile.close();
//新建储存该表的记录信息的文件
filename = table_name + "_tablereco";
outfile.open(filename.c_str(), ios::out);
if (!outfile) throw File_openfail(filename.c_str());
outfile.close(); //建立即可，此时不需要插入任何记录
return true;
}
