examples/key_value.cpp - master - UCS/sqlite_orm

examples/key_value.cpp
86 строк3 KB
fnc12
changed PointerAlignment from Right to Left
21 ноя 2020, 20:38
21 ноя 2020, 20:381eaff43

/******
 This is an implementation of key-value storage just like
 NSUserDefaults on iOS or SharedPreferences on Android.
 Here is the deal: we need to have `setValueForKey` and `getValueByKey` interface. All data must ba saved in sqlite
 database.
 To perform this we create schema with table `key_value` and two columns: key:string and value:string.
 Key column has PRIMARY KEY constraint cause keys must be unique. `setValue` function takes two string arguments: key
 and value. It creates a KeyValue object (KeyValue is a class mapped to the storage) with arguments and calls REPLACE.
 REPLACE (shorter version of INSERT OR REPLACE) removes row with a given primary key if it exists and inserts a given
 value in the table. After this there is a row in the `key_value` table with key and value passed into `setValue`
 function. `getValue` performs `get_pointer` by id and returns its value or returns empty string if nothing obtained
 from db.
 ******/

#include <sqlite_orm/sqlite_orm.h>

#include <iostream>

using std::cerr;
using std::cout;
using std::endl;

/**
 *  This is just a mapped type. User doesn't have to interact with it directly.
 */
struct KeyValue {
    std::string key;
    std::string value;
};

auto& getStorage() {
    using namespace sqlite_orm;
    static auto storage = make_storage("key_value_example.sqlite",
                                       make_table("key_value",
                                                  make_column("key", &KeyValue::key, primary_key()),
                                                  make_column("value", &KeyValue::value)));
    return storage;
}

void setValue(const std::string& key, const std::string& value) {
    using namespace sqlite_orm;
    KeyValue kv{key, value};
    getStorage().replace(kv);
}

std::string getValue(const std::string& key) {
    using namespace sqlite_orm;
    if(auto kv = getStorage().get_pointer<KeyValue>(key)) {
        return kv->value;
    } else {
        return {};
    }
}

int storedKeysCount() {
    return getStorage().count<KeyValue>();
}

int main(int, char** argv) {

    cout << argv[0]
         << endl;  //  to know executable path in case if you need to access sqlite directly from sqlite client

    getStorage().sync_schema();  //  to create table if it doesn't exist

    struct {
        std::string userId = "userId";
        std::string userName = "userName";
        std::string userGender = "userGender";  //  this key will be missing
    } keys;  //  to keep keys in one place

    setValue(keys.userId, "6");
    setValue(keys.userName, "Peter");

    auto userId = getValue(keys.userId);
    cout << "userId = " << userId << endl;  //  userId = 6

    auto userName = getValue(keys.userName);
    cout << "userName = " << userName << endl;  //  userName = Peter

    auto userGender = getValue(keys.userGender);
    cout << "userGender = " << userGender << endl;  //  userGender =

    auto kvsCount = storedKeysCount();
    cout << "kvsCount = " << kvsCount << endl;  //  kvsCount = 2
}