simple.cpp

全新的纯内存式实时数据库

/*******************************************************************
 *                                                                 *
 *  simple.cpp                                                      *
 *                                                                 *
 *  This file is a part of the eXtremeDB source code               *
 *  Copyright (c) 2001-2007 McObject LLC                           * 
 *  All Rights Reserved                                            *
 *                                                                 *
 *******************************************************************/
#include "mcosql.h"

using namespace McoSql;

size_t const PAGE_SIZE = 1024/*128*/; // define eXtremeDB page size
size_t const DATABASE_SIZE = 4*1024*1024; // define size of eXtrmeDB database
void*  const MAP_ADDRESS = (void*)0x20000000; // definemapping address for eXtremeDB database

// Define structure correponding to database record 
// (will be done automatically by mcocomp in future
struct Person { 
    char const* name;
    int         age;
    float       weight;
};

// Forward declaration of function describing database schema
GET_DICTIONARY(simpledb);

McoSqlEngine engine; // McoSQL engine 

// This function will add new record in database
void addPerson(Person* p) 
{
    // Add new record to the table. 
    // Record will be initialized with data passed throgh Person struct.
    engine.executeStatement("insert into Person %r", p);
}
 
// This function select all records from the table
void listPersons()  
{
    // Execute query and store returned data sourse in QueryResult object 
    // which destructor will automatically release this data source after return from 
    // the function
    QueryResult result(engine.executeQuery("select * from Person order by age"));

    // Get cursor
    Cursor* cursor = result->records();
    
    // Loop for all records
    while (cursor->hasNext()) { 
        Person p;

        // Get next record
        Record* rec = cursor->next();

        // Extract record to the correspondent struct
        result->extract(rec, &p, sizeof(p));
    
        printf("%s %d %f\n", p.name, p.age, p.weight);
    }
}

// Serach person by name pattern 
void searchPersonByName(char const* name) 
{
    // Excecute query with given parameter "name"
    QueryResult result(engine.executeQuery("select * from Person where name like %s", name));

    // Get cursor
    Cursor* cursor = result->records();
    
    // Loop for all records
    while (cursor->hasNext()) { 
        Person p;

        // Get next record
        Record* rec = cursor->next();

        // Extract record to the correspondent struct
        result->extract(rec, &p, sizeof(p));
    
        printf("%s %d %f\n", p.name, p.age, p.weight);
    }
}

// Calculate average age of persons using aggregate functions 
void calculateAverageAge()
{
    // Execute query calculating average age of all persons
    QueryResult result(engine.executeQuery("select avg(age) from Person"));

    // Get cursor
    Cursor* cursor = result->records();

    // Result data source consists of one record with single column.
    // Indices of columns starts from 0
    Value* avgAge = cursor->next()->get(0);

    printf("Average age: %d\n", (int)avgAge->intValue());
}

// Update record
void updatePersonData(char const* name, int age, float weight)
{
    // Update person with specified name (passed as query parameter).
    // Result of this statement execution is number of updated records.
    int ret = engine.executeStatement("update Person set age=%i, weight=%f where name=%s", 
                                      age, weight, name);

    if (ret == 0) { 
        printf("Person %s not found\n", name);
    }
}
   

// Delete record from the table
void deletePerson(char const* name)
{
    // Delete person with specified name (passed as query parameter).
    // Result of this statement execution is number of removed records.
    int ret = engine.executeStatement("delete from Person where name=%s", name);

    if (ret == 0) { 
        printf("Person %s not found\n", name);
    }
}


int main()
{
    Person p;

    // Open eXtremeDB database and SQL engine
    engine.open("simpledb", // database name
                simpledb_get_dictionary(), // database dictionary
                DATABASE_SIZE, // database size
                PAGE_SIZE,  // page size
                MAP_ADDRESS); // mapping address for shared memory mode

    p.name = "John Smith";
    p.age = 35;
    p.weight = 72.1f;    
    addPerson(&p);

    p.name = "Peter Brown";
    p.age = 40;
    p.weight = 62.1f;    
    addPerson(&p);

    listPersons();
    
    searchPersonByName("John%");
    searchPersonByName("%Brown%");
    
    calculateAverageAge();

    updatePersonData("John Smith", 36, 75.2f);
    updatePersonData("Peter Brown", 41, 65.0f);

    listPersons();

    deletePerson("John Smith");
    deletePerson("Peter Brown");

    // Close daatbase and SQL engine
    engine.close();
    return 0;
}