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d0d5e94bf1
eval wraps whatever you give to it into a select call, sends it to the database and returns the value as a result field.
63 lines
2.6 KiB
C++
63 lines
2.6 KiB
C++
/*
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* Copyright (c) 2013-2014, 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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*/
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#ifndef SQLPP_EVAL_H
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#define SQLPP_EVAL_H
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#include <sqlpp11/type_traits.h>
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#include <sqlpp11/field_spec.h>
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#include <sqlpp11/alias_provider.h>
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#include <sqlpp11/verbatim.h>
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namespace sqlpp
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{
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template<typename Db, typename Expr>
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struct eval_t
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{
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static_assert(is_database<Db>::value, "Db parameter of eval has to be a database connection");
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static_assert(is_expression_t<Expr>::value, "Expression parameter of eval has to be an sqlpp expression or a string");
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static_assert(required_tables_of<Expr>::size::value == 0, "Expression cannot be used in eval because it requires tables");
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using _name_type = alias::a_t::_name_t;
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using _value_type = value_type_of<Expr>;
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using _field_spec = field_spec_t<_name_type, _value_type, true, false>;
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using type = result_field_t<_value_type, Db, _field_spec>;
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};
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template<typename Db, typename Expr, typename std::enable_if<not std::is_convertible<Expr, std::string>::value, int>::type = 0>
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auto eval(Db& db, Expr expr) -> typename eval_t<Db, Expr>::type
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{
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return db(select(expr.as(alias::a))).front().a;
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}
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template<typename ValueType, typename Db>
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auto eval(Db& db, std::string sql_code) -> decltype(eval(db, verbatim<ValueType>(sql_code)))
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{
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return eval(db, verbatim<ValueType>(sql_code));
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}
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}
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#endif
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