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97 lines
2.1 KiB
C++
97 lines
2.1 KiB
C++
#pragma once
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#include <mysqlxx/Exception.h>
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namespace mysqlxx
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{
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struct NullType {};
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const NullType null = {};
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/** Store NULL-able types from MySQL.
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* Usage example:
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* mysqlxx::Null<int> x = mysqlxx::null;
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* std::cout << (x.isNull() ? "Ok." : "Fail.") << std::endl;
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* x = 10;
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*/
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template <typename T>
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class Null
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{
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public:
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T data {};
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bool is_null = true;
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Null() : is_null(true) {}
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Null(const Null<T> &) = default;
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Null(Null<T> &&) noexcept = default;
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Null(NullType) : is_null(true) {}
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explicit Null(const T & data_) : data(data_), is_null(false) {}
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operator T & ()
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{
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if (is_null)
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throw Exception("Value is NULL");
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return data;
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}
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operator const T & () const
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{
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if (is_null)
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throw Exception("Value is NULL");
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return data;
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}
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Null<T> & operator= (Null<T> &&) noexcept = default;
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Null<T> & operator= (const Null<T> &) = default;
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Null<T> & operator= (const T & data_) { is_null = false; data = data_; return *this; }
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Null<T> & operator= (const NullType) { is_null = true; data = T(); return *this; }
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bool isNull() const { return is_null; }
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bool operator< (const Null<T> & other) const
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{
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return is_null < other.is_null
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|| (is_null == other.is_null && data < other.data);
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}
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bool operator< (const NullType) const { return false; }
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bool operator== (const Null<T> & other) const
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{
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return is_null == other.is_null && data == other.data;
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}
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bool operator== (const T & other) const
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{
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return !is_null && data == other;
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}
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bool operator== (const NullType) const { return is_null; }
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bool operator!= (const Null<T> & other) const
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{
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return !(*this == other);
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}
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bool operator!= (const NullType) const { return !is_null; }
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bool operator!= (const T & other) const
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{
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return is_null || data != other;
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}
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};
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template<typename T>
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T getValueFromNull(const Null<T> & maybe)
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{
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if (maybe.isNull())
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return {};
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return maybe;
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}
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}
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