使用Boost.Spirit解析C ++中的SQL查询 [英] Parsing SQL Queries in C++ using Boost.Spirit
问题描述
我创建了一个数据库引擎，在其中我可以创建和修改表，并将它们添加到数据库。为了解析SQL查询，我已经使用EBNF形式实现了Boost.Spirit库。我正确的解析器设置，它成功地解析每个规则。
I have created a database engine in which I can create and modify tables, and add them to a database. For parsing the SQL queries, I have implemented the Boost.Spirit library using EBNF form. I have the parser setup properly and it successfully parses every rule.
我的问题是我现在不知道如何整合这两个。 Boost.Spirit解析器只验证输入是正确的，但我需要它实际上做的东西。我查看了语义动作，但他们似乎不处理我正在寻找。
My problem is I now have no idea how to integrate the two. The Boost.Spirit parser only validates that input is correct, however I need it to actually do something. I looked up semantic actions but they don't seem to handle what I'm looking for.
例如，如果我有一个查询，例如：
new_table< - SELECT（id< 5） old_table;
For example, if I have a query such as:
new_table <- SELECT (id < 5) old_table;
我想让它使用规则验证输入，然后调用函数
Table Database :: Select（Table t，Condition c）{...}
并将令牌作为参数传递。
I want it to validate the input using the rules, then call the function
Table Database::Select(Table t , Condition c){ ... }
and pass the tokens as arguments.
如何整合解析器？
推荐答案
注意：我选择在此演示示例语法，不会显示你的。使用这里推荐的方法，解析后不应该难以编写函数来执行你的查询。
Note: I opted to invent a sample grammar here for demonstration purposes, since your question doesn't show yours. Using the approach recommended here, it should not be hard to code a function to execute your queries after parsing.
解析树。
我会建议属性传播优先于语义动作。参见例如
I would recommend attribute propagation in preference to semantic actions. See e.g.
- Boost Spirit: "Semantic actions are evil"?
属性传播规则在Spirit 。
Attribute propagation rules are very flexible in Spirit. The default exposed attributes types are well documented right with each Parser's documentation
- http://www.boost.org/doc/libs/1_48_0/libs/spirit/doc/html/spirit/qi/reference.html
- qi :: char _ 会导致 boost :: optional< char> 和 qi： ：double_ | qi :: int _ 会导致 boost :: variant
E.g. -qi::char_ would result in boost::optional<char> and qi::double_ | qi::int_ would result in boost::variant<double, int>.
您可能希望在您自己的发明的AST数据类型中累积解析的元素，例如：
You will probably want to accumulate the parsed elements in a AST datatype of your own invention, e.g.:
struct SelectStatement
{
std::vector<std::string> columns, fromtables;
std::string whereclause; // TODO model as a vector<WhereCondition> :)
friend std::ostream& operator<<(std::ostream& os, SelectStatement const& ss)
{
return os << "SELECT [" << ss.columns.size() << " columns] from [" << ss.fromtables.size() << " tables]\nWHERE " + ss.whereclause;
}
};
您可以通过将结构适配为融合序列来将其适用于Spirits属性传播机制：
You could adapt this to Spirits attribute propagation machinery by adapting the struct as a Fusion sequence:
BOOST_FUSION_ADAPT_STRUCT(SelectStatement,
(std::vector<std::string>, columns)
(std::vector<std::string>, fromtables)
(std::string, whereclause)
)
现在您可以将以下规则解析为该类型：
Now you could parse the following rule into that type:
sqlident = lexeme [ alpha >> *alnum ]; // table or column name
columns = no_case [ "select" ] >> (sqlident % ',');
tables = no_case [ "from" ] >> (sqlident % ',');
start = columns >> tables
>> no_case [ "where" ]
>> lexeme [ +(char_ - ';') ]
>> ';';
您可以看到此 代码正在运行这里： http://liveworkspace.org/code/0b525234dbce22cbd8becd69f84065c1
完整演示代码：
// #define BOOST_SPIRIT_DEBUG
#include <boost/fusion/adapted.hpp>
#include <boost/spirit/include/qi.hpp>
namespace qi = boost::spirit::qi;
struct SelectStatement
{
std::vector<std::string> columns, fromtables;
std::string whereclause; // TODO model as a vector<WhereCondition> :)
friend std::ostream& operator<<(std::ostream& os, SelectStatement const& ss)
{
return os << "SELECT [" << ss.columns.size() << " columns] from [" << ss.fromtables.size() << " tables]\nWHERE " + ss.whereclause;
}
};
BOOST_FUSION_ADAPT_STRUCT(SelectStatement,
(std::vector<std::string>, columns)
(std::vector<std::string>, fromtables)
(std::string, whereclause)
)
template <typename It, typename Skipper = qi::space_type>
struct parser : qi::grammar<It, SelectStatement(), Skipper>
{
parser() : parser::base_type(start)
{
using namespace qi;
sqlident = lexeme [ alpha >> *alnum ]; // table or column name
columns = no_case [ "select" ] >> (sqlident % ',');
tables = no_case [ "from" ] >> (sqlident % ',');
start = columns >> tables
>> no_case [ "where" ]
>> lexeme [ +(char_ - ';') ]
>> ';';
BOOST_SPIRIT_DEBUG_NODE(start);
BOOST_SPIRIT_DEBUG_NODE(sqlident);
BOOST_SPIRIT_DEBUG_NODE(columns);
BOOST_SPIRIT_DEBUG_NODE(tables);
}
private:
qi::rule<It, std::string() , Skipper> sqlident;
qi::rule<It, std::vector<std::string>(), Skipper> columns , tables;
qi::rule<It, SelectStatement() , Skipper> start;
};
template <typename C, typename Skipper>
bool doParse(const C& input, const Skipper& skipper)
{
auto f(std::begin(input)), l(std::end(input));
parser<decltype(f), Skipper> p;
SelectStatement query;
try
{
bool ok = qi::phrase_parse(f,l,p,skipper,query);
if (ok)
{
std::cout << "parse success\n";
std::cout << "query: " << query << "\n";
}
else std::cerr << "parse failed: '" << std::string(f,l) << "'\n";
if (f!=l) std::cerr << "trailing unparsed: '" << std::string(f,l) << "'\n";
return ok;
} catch(const qi::expectation_failure<decltype(f)>& e)
{
std::string frag(e.first, e.last);
std::cerr << e.what() << "'" << frag << "'\n";
}
return false;
}
int main()
{
const std::string input = "select id, name, price from books, authors where books.author_id = authors.id;";
bool ok = doParse(input, qi::space);
return ok? 0 : 255;
}
将打印输出：
parse success
query: SELECT [3 columns] from [2 tables]
WHERE books.author_id = authors.id
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