Question

示例代码：

pqxx::connection c("user=postgres");
pqxx::work txn(c);
pqxx::result r = txn.exec("SELECT d.datname as \"Name\","
       "pg_catalog.pg_get_userbyid(d.datdba) as \"Owner\","
       "pg_catalog.pg_encoding_to_char(d.encoding) as \"Encoding\","
       "d.datcollate as \"Collate\","
       "d.datctype as \"Ctype\","
       "pg_catalog.array_to_string(d.datacl, E'\\n') AS \"Access privileges\""
       "   FROM pg_catalog.pg_database d"
       "   ORDER BY 1");
try {
  for(int rownum=0; rownum<r.size(); ++rownum ) {
    const pqxx::result::tuple row = r[rownum];
    std::cout << "Column 0 Name: \'" << row[0].name() << "\': " << row[0].c_str() << std::endl;
    const std::string s = "Name";
    std::cout << (row[0].name() == s) << std::endl;
    std::cout << "dbname: \'" << row[s].c_str() << "\'" << std::endl; // Exception here
  }
} catch(const pqxx::argument_error &e) {
  std::cout << "Argument Error: " << e.what() << std::endl;
}

我的输出如下

Column 0 Name: 'Name': mydb
1
Argument Error: Unknown column name: 'Name'

第一列名称为“Name”，并根据字符串“Name”测试行名称会生成一个true语句。但是当我通过该字符串访问它时，我得到一个例外。

Answer 1

好的，完全是asinine。如果你想要像大写这样的东西，你必须引用这个名字。

如此改变

const std::string s = "Name";

到

const std::string s = "\"Name\"";

解决了这个问题。显然，C接口会降低您所称的内容，但不会低估其测试的字段。 ARG！我不得不通过libpqxx代码来解决这个问题。

为什么我不能按名称访问列？

1 个答案: