commit 143a60e76578ec1b35ac851815479377a362d486 Author: David Sorber Date: Tue Jan 24 10:47:33 2017 -0500 After much contemplation I realized that my previous approach to solving this execute query template function problem was more wrong than right. Several days of staring at and reading about variadic templates later I figured out the correct way to accomplish my goal. diff --git a/software/sqlite_poc/DBManager.cc b/software/sqlite_poc/DBManager.cc index 188c82c..86da533 100644 --- a/software/sqlite_poc/DBManager.cc +++ b/software/sqlite_poc/DBManager.cc @@ -2,9 +2,48 @@ #include "DBManager.h" +// Helper function for int64_t type +void get_value(int64_t& val, int idx, sqlite3_stmt* stmt) +{ + if (sqlite3_column_type(stmt, idx) != SQLITE_INTEGER) + { + assert(false); + } + + val = sqlite3_column_int64(stmt, idx); +} + +// Helper function for double type +void get_value(double& val, int idx, sqlite3_stmt* stmt) +{ + if (sqlite3_column_type(stmt, idx) != SQLITE_FLOAT) + { + assert(false); + } + + val = sqlite3_column_double(stmt, idx); +} + +// Helper function for string type +void get_value(std::string& val, int idx, sqlite3_stmt* stmt) +{ + if (sqlite3_column_type(stmt, idx) == SQLITE_TEXT) + { + val.assign(reinterpret_cast(sqlite3_column_text(stmt, idx))); + } + else if (sqlite3_column_type(stmt, idx) == SQLITE_NULL) + { + val.assign(""); + } + else + { + assert(false); + } +} + DBManager::DBManager(const std::string& db_path) { - + int rc = sqlite3_open(db_path.c_str(), &this->db); if (rc) { diff --git a/software/sqlite_poc/DBManager.h b/software/sqlite_poc/DBManager.h index b9c699a..1649bb9 100644 --- a/software/sqlite_poc/DBManager.h +++ b/software/sqlite_poc/DBManager.h @@ -1,127 +1,96 @@ - #include #include #include #include #include -#include +#include + +// Helper function prototypes +void get_value(int64_t& val, int idx, sqlite3_stmt* stmt); +void get_value(double& val, int idx, sqlite3_stmt* stmt); +void get_value(std::string& val, int idx, sqlite3_stmt* stmt); template struct builder_impl { - template - static void set_value(T& tup, size_t idx, G& val) + template + static void set_values_helper(T& tup, sqlite3_stmt* stmt) { - if (idx == I - 1) - { - std::get(tup) = val; - } - else - { - builder_impl::set_value(tup, idx, val); - } + // Assign the "current" value + get_value(std::get(tup), I - 1, stmt); + + // Recurse to the next value in the tuple + builder_impl::set_values_helper(tup, stmt); } }; - -template <> + +template<> struct builder_impl<0> { - template - static void set_value(T& tup, size_t idx, G& val) - { - assert(false); + template + static void set_values_helper(T& tup, sqlite3_stmt* stmt) + { + // Stop recursing + return; } }; -template -void set_value_at(std::tuple& tup, size_t idx, G const& val) +template +void set_values(std::tuple& tup, sqlite3_stmt* stmt) { - builder_impl::set_value(tup, idx, val); -} - -template -void set_value_at(std::tuple& tup, size_t idx, G& val) -{ - builder_impl::set_value(tup, idx, val); + builder_impl::set_values_helper(tup, stmt); } - class DBManager { public: - + // Constructor DBManager(const std::string& db_path); - + // Destructor ~DBManager(); - - // execute query + + // Execute query template function template std::vector*>* execute_query( const std::string& sql_statement, int& return_code) { sqlite3_stmt* sqlite_statement; - + // Prepare the sqlite statement - return_code = sqlite3_prepare_v2(db, sql_statement.c_str(), -1, + return_code = sqlite3_prepare_v2(db, sql_statement.c_str(), -1, &sqlite_statement, nullptr); if (return_code != SQLITE_OK) { return nullptr; - } - - auto output_vector = new std::vector*>(); - + } + + auto output_vector = new std::vector*>(); + // Iterate until we've collected all the output int step_return = 0; while ((step_return = sqlite3_step(sqlite_statement)) != SQLITE_DONE) { - // Create a new result row to be populated below + // Create a new result row auto result_row = new std::tuple(); - - // Iterate over the columns in the row - int num_cols = sqlite3_data_count(sqlite_statement); - for (int col_idx = 0; col_idx < num_cols; col_idx++) - { - switch(sqlite3_column_type(sqlite_statement, col_idx)) - { - case SQLITE_INTEGER: - set_value_at(*result_row, col_idx, - sqlite3_column_int64(sqlite_statement, - col_idx)); - break; - - case SQLITE_FLOAT: - set_value_at(*result_row, col_idx, - sqlite3_column_double(sqlite_statement, - col_idx)); - break; - - case SQLITE_TEXT: - //~ set_value_at(*result_row, col_idx, - //~ std::string(reinterpret_cast(sqlite3_column_text(sqlite_statement, col_idx)))); - break; - - case SQLITE_BLOB: - break; - - case SQLITE_NULL: - //~ set_value_at(*result_row, col_idx, std::string("")); - break; - } - } - + + // Now populate the result row using some neato variadic + // template function magic NOTE: a small amount of black magic + // is in use here; animal sacrifices not necessary + set_values(*result_row, sqlite_statement); + + // Add the result row to our vector of output rows output_vector->push_back(result_row); } - + return output_vector; } - + private: - + sqlite3 *db; }; diff --git a/software/sqlite_poc/Makefile b/software/sqlite_poc/Makefile index 38d7059..86e9cab 100644 --- a/software/sqlite_poc/Makefile +++ b/software/sqlite_poc/Makefile @@ -7,7 +7,7 @@ all: main main: $(OBJECTS) g++ $(CXXFLAGS) $(OBJECTS) -lsqlite3 -o poc_test -%.o : %.c +%.o : %.c %.h g++ $(CXXFLAGS) -c $< clean: diff --git a/software/sqlite_poc/main.cc b/software/sqlite_poc/main.cc index 15a6edf..45f5326 100644 --- a/software/sqlite_poc/main.cc +++ b/software/sqlite_poc/main.cc @@ -39,14 +39,13 @@ int main(int argc, char** argv) // Make a DBManager instance which will connect to our test DB automagically DBManager db_mgr("database.db"); - // Make a query - std::string query("SELECT Number, Float FROM sample;"); + std::string query("SELECT Number, Words, Float FROM sample;"); // Execute the query making sure the template params match up with the // query params int rc = 0; - auto results = db_mgr.execute_query(query, rc); + auto results = db_mgr.execute_query(query, rc); std::cout << "Return code: " << rc << std::endl; // If we returned successfully, print out the result rows