3.7.6 SQLite 集成 TODO

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2023-12-01

SQLite

SQLite is a self-contained SQL database engine. This means there is no server involved. SQLite runs while your game is running and you write code to connect to the database and manipulate its contents. This is by no means a comprehensive guide, in fact, we cover 1% of what SQLite can do for you. Please read their website for a lot more detail as to what functionality SQLIte offers developers.

Getting Started.

In-order to use SQLite you must download it and add it to your project. Please see the SQLite Downloads page for more details. For our purposes you will just need sqlite.h and sqlite.c in your project. Add these files to your environment and make sure they are part of your build process.

How Does SQL Work In A Game?

Now that you have SQLite you must understand how using a database in your app works. There isn't any automatic benefit, unless you code it. There are no wizards and no functionality for free. This is hand coded, by you, to meet your specific needs. Generally speaking, you will need to evaluate the following:

Does your database already exist?
- Yes? Connect to it.
- No? Create it, probably using create table queries. Then connect to it.
Are you connected to the database?
- Yes? Issue queries against it to achieve your goals.
- No? Connect to it, then issue queries against it to achieve your goals.
Do you need to update your database based upon player achievements?
- Yes? Run insert/update queries to change the database.
- No? Probably select queries are enough to use the database to drive your game play.
Is the player done with your game?
- Yes? Make sure to close the database when your game exists. Failure to do so may corrupt your database and make it unusable.

Basic Database Creation And Manipulation

Let's cover how to create a simple database, connect to it and then manipulate it.

Creating A Simple Database

In order to use your database, it must exist. SQLite is file based. Simply creating a new file to house your database is sufficient. Notice that we use a .db file extension to help notate that this is indeed our database. It is also important to understand where the database lives on the players device. When you create the database it must be put in a location that the device allows the player to write data to. Cocos2d-x helps make this easy with a file system API called getWriteablePath(). Here is an example:

sqlite3* pdb;

pdb = NULL;

std::string dbPath = cocos2d::FileUtils::getInstance()->getWritablePath() + "mydatabase.db";

int result = sqlite3_open(dbPath.c_str(), &pdb);

if(result == SQLITE_OK)
  std::cout << "open database successful!" << std::endl;
else
  std::cout << "open database failed!" << std::endl;

With the database open, you can now use it.

Creating A Table

Databases use tables to store data. You need at least one table in your database. The caveat is that you must know what data your table will contain in-order to create it. You can always use the SQL alter table command if at a later tine you need to modify your tables structure. This is outside the scope of this document, however. Creating a simple table:

int result = 0;
std::string sql;

sql = "create table " +
std::string("Master") +
std::string(" (id TEXT PRIMARY KEY, value INT);");

result = sqlite3_exec(pdb, sql.c_str(), NULL, NULL, NULL);

if(result == SQLITE_OK)
{
  // table created successfully
}
else
{
  // table was NOT created successfully
}

Querying Data

When you want information from your database you must execute a select query to get it. A select query is a read-only query. You don't have to worry about accidentally modifying your game data when running these types of queries. An example select query;

std::string key = "Brown";

std::string sql = "SELECT NAME " +
std::string(" FROM ") +
std::string("Master") +
std::string(" WHERE id='") +
std::string(key.c_str()) +
std::string("' LIMIT 1;");

sqlite3_stmt* statement;

if (sqlite3_prepare_v2(&pdb, sql.c_str(), -1, &statement, 0) == SQLITE_OK)
{
  int result = 0;

  while(true)
  {
      result = sqlite3_step(statement);

      if(result == SQLITE_ROW)
      {
          // do something with the row.
      }
      else
      {
          break;
      }
  }
}

Inserting Data

You may need to insert data into your database to use again at a later time. Use an insert query to do this. Example: