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Reflection-based aliases (#101)
* Add reflection-based aliases usable via `<column/table/expression>.as<"my_alias">()` (requires reflection-capable compiler) * Add macro for checking if reflection functionalities should be included and add test code that uses the generated member
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‎include/sqlpp23/core/basic/table.h‎

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#include <sqlpp23/core/detail/type_set.h>
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#include <sqlpp23/core/type_traits.h>
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#include <sqlpp23/core/name/create_reflection_name_tag.h>
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namespace sqlpp {
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template <typename TableSpec>
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struct table_t : public TableSpec::template _table_columns<table_t<TableSpec>>,
@@ -44,6 +46,15 @@ struct table_t : public TableSpec::template _table_columns<table_t<TableSpec>>,
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-> table_as_t<TableSpec, name_tag_of_t<NameTagProvider>> {
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return {};
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}
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#if SQLPP_INCLUDE_REFLECTION == 1
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template <::sqlpp::detail::fixed_string Alias>
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constexpr auto as() const -> table_as_t<
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TableSpec,
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name_tag_of_t<decltype(::sqlpp::meta::make_alias<Alias>())>> {
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return {};
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}
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#endif
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};
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template <typename TableSpec>

‎include/sqlpp23/core/detail/fixed_string.h‎

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#pragma once
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/*
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* Copyright (c) 2026, Roland Bock
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <cstddef>
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#include <format>
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#include <stdexcept>
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#include <string_view>
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namespace sqlpp::detail {
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template <::std::size_t Size>
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struct fixed_string {
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static constexpr ::std::size_t size = Size;
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consteval fixed_string(const char (&str)[Size]) noexcept {
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for (::std::size_t i = 0; i < Size; ++i) {
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value[i] = str[i];
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}
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}
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constexpr operator ::std::string_view() const {
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return ::std::string_view(value, Size);
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}
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constexpr operator const char*() const { return value; }
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consteval auto operator[](::std::size_t index) -> char {
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if (index >= Size) {
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throw ::std::out_of_range("index is out of range of fixed_string");
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}
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return value[index];
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}
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char value[Size]{};
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};
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} // namespace sqlpp::detail

‎include/sqlpp23/core/name/create_reflection_name_tag.h‎

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#pragma once
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/*
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* Copyright (c) 2026, Roland Bock
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef SQLPP_INCLUDE_REFLECTION
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#if defined(__cpp_impl_reflection) && __cpp_impl_reflection >= 202506L
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#define SQLPP_INCLUDE_REFLECTION 1
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#else
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#define SQLPP_INCLUDE_REFLECTION 0
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#endif
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#endif
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#if SQLPP_INCLUDE_REFLECTION == 1
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#include <meta>
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#include <optional>
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#include <sqlpp23/core/detail/fixed_string.h>
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namespace sqlpp::meta {
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template <::sqlpp::detail::fixed_string Alias>
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struct reflection_alias {
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struct _sqlpp_name_tag {
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[[maybe_unused]] static constexpr bool require_quotes = false;
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[[maybe_unused]] static constexpr auto name = Alias;
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template <typename T>
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struct _member_impl_outer_t {
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struct _member_impl_inner_t;
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consteval {
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::std::meta::define_aggregate(
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^^_member_impl_inner_t,
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{
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::std::meta::data_member_spec(
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^^T, {
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.name = _sqlpp_name_tag::name,
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.alignment = std::nullopt,
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.bit_width = std::nullopt,
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.no_unique_address = false})});
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}
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};
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// separate struct with base class necessary because it's not possible to
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// add a member function with `define_aggregate`
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template <typename T>
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struct _member_t : _member_impl_outer_t<T>::_member_impl_inner_t {
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auto& operator()(this auto&& self) {
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// used to access members of base
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constexpr auto ctx1 = ::std::meta::access_context::current();
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constexpr auto ctx2 = ctx1.via(^^_member_t);
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// get first (and single) member of this struct which has `Alias` as its
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// name
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return self
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.[: ::std::meta::nonstatic_data_members_of(
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^^typename _member_impl_outer_t<T>::_member_impl_inner_t,
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ctx2)[0]:];
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}
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};
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};
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};
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template <::sqlpp::detail::fixed_string Alias>
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consteval auto make_alias() -> ::sqlpp::meta::reflection_alias<Alias> {
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return {};
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}
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} // namespace sqlpp::meta
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#endif

‎include/sqlpp23/core/operator/enable_as.h‎

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#include <sqlpp23/core/operator/as_expression.h>
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#include <sqlpp23/core/type_traits.h>
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#include <sqlpp23/core/name/create_reflection_name_tag.h>
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namespace sqlpp {
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// To be used as CRTP base for expressions that should offer the as() member
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// function.
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-> decltype(::sqlpp::as(std::forward<Expr>(self), alias)) {
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return ::sqlpp::as(std::forward<Expr>(self), alias);
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}
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#if SQLPP_INCLUDE_REFLECTION == 1
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template <::sqlpp::detail::fixed_string Alias, typename Expr>
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constexpr auto as(this Expr&& self)
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-> decltype(::sqlpp::as(::std::forward<Expr>(self),
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::sqlpp::meta::make_alias<Alias>())) {
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return ::sqlpp::as(::std::forward<Expr>(self),
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::sqlpp::meta::make_alias<Alias>());
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}
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#endif
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};
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template <typename T>

‎tests/core/CMakeLists.txt‎

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add_subdirectory(serialize)
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add_subdirectory(types)
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add_subdirectory(usage)
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add_subdirectory(meta)

‎tests/core/meta/CMakeLists.txt‎

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# Copyright (c) 2026, Roland Bock
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# All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without modification,
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# are permitted provided that the following conditions are met:
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#
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# Redistributions of source code must retain the above copyright notice, this
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# list of conditions and the following disclaimer.
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#
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# Redistributions in binary form must reproduce the above copyright notice, this
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# list of conditions and the following disclaimer in the documentation and/or
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# other materials provided with the distribution.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
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# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
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# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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function(create_test name)
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set(target sqlpp23_core_meta_${name})
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add_executable(${target} ${name}.cpp)
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target_link_libraries(${target} PRIVATE sqlpp23::core sqlpp23_testing sqlpp23_core_testing sqlpp23_core_testing)
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add_test(NAME ${target} COMMAND ${target})
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endfunction()
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create_test(alias)

‎tests/core/meta/alias.cpp‎

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/*
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* Copyright (c) 2026 Roland Bock
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <sqlpp23/tests/core/all.h>
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int main(int, char*[]) {
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#if SQLPP_INCLUDE_REFLECTION == 1
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const auto foo = test::TabFoo{};
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const auto bar = test::TabBar{};
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SQLPP_COMPARE(avg(bar.id + 7).as<"my_average">(),
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"AVG(tab_bar.id + 7) AS my_average");
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const auto table_a = foo.as<"table_a">();
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const auto table_b = bar.as<"table_b">();
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SQLPP_COMPARE(sqlpp::select(table_a.id.as<"id_a">(), table_a.intN,
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table_b.id.as<"id_b">(), table_b.textN)
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.from(table_a.join(table_b).on(table_a.id == table_b.id)),
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"SELECT table_a.id AS id_a, table_a.int_n, table_b.id AS id_b, "
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"table_b.text_n "
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"FROM tab_foo AS table_a "
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"INNER JOIN tab_bar AS table_b "
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"ON table_a.id = table_b.id");
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sqlpp::mock_db::connection db = sqlpp::mock_db::make_test_connection();
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for (const auto& row :
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db(sqlpp::select(table_a.id.as<"id_a">()).from(table_a))) {
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std::cout << row.id_a << std::endl;
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}
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#endif
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return 0;
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}

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