appdelegate.m

sqlite book source code for references

/*
     File: AppDelegate.m
 Abstract: 
This class is the application delegate. That means it receives (and should handle) messages 
from the application informing it of launch and termination state. The application delegate 
initiates the user interface setup and acts as a central coordinator for the database backing 
the application.

  Version: 1.9
 
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 */

#import "AppDelegate.h"
#import "MasterViewController.h"
#import "DetailViewController.h"
#import "AddViewController.h"
#import "EditingViewController.h"
#import "Book.h"

// Private interface for AppDelegate - internal only methods.
@interface AppDelegate (Private)
- (void)createEditableCopyOfDatabaseIfNeeded;
- (void)initializeDatabase;
@end

@implementation AppDelegate

// Instruct the compiler to create accessor methods for the property. It will use the internal 
// variable with the same name for storage.
@synthesize books, window, navigationController;

- (void)applicationDidFinishLaunching:(UIApplication *)application {
    // The application ships with a default database in its bundle. If anything in the application
    // bundle is altered, the code sign will fail. We want the database to be editable by users, 
    // so we need to create a copy of it in the application's Documents directory.     
    [self createEditableCopyOfDatabaseIfNeeded];
    // Call internal method to initialize database connection
    [self initializeDatabase];
    // Add the navigation controller's view to the window
    [window addSubview:navigationController.view];
    [window makeKeyAndVisible];
}

- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application {
    // "dehydrate" all data objects - flushes changes back to the database, removes objects from memory
    [books makeObjectsPerformSelector:@selector(dehydrate)];
}

- (void)dealloc {
    [navigationController release];   
    [window release];
    [books release];
    [super dealloc];
}

// Creates a writable copy of the bundled default database in the application Documents directory.
- (void)createEditableCopyOfDatabaseIfNeeded {
    // First, test for existence.
    BOOL success;
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSError *error;
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"bookdb.sql"];
    success = [fileManager fileExistsAtPath:writableDBPath];
    if (success) return;
    // The writable database does not exist, so copy the default to the appropriate location.
    NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"bookdb.sql"];
    success = [fileManager copyItemAtPath:defaultDBPath toPath:writableDBPath error:&error];
    if (!success) {
        NSAssert1(0, @"Failed to create writable database file with message '%@'.", [error localizedDescription]);
    }
}

// Open the database connection and retrieve minimal information for all objects.
- (void)initializeDatabase {
    NSMutableArray *bookArray = [[NSMutableArray alloc] init];
    self.books = bookArray;
    [bookArray release];
    // The database is stored in the application bundle. 
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:@"bookdb.sql"];
    // Open the database. The database was prepared outside the application.
    if (sqlite3_open([path UTF8String], &database) == SQLITE_OK) {
        // Get the primary key for all books.
        const char *sql = "SELECT pk FROM book";
        sqlite3_stmt *statement;
        // Preparing a statement compiles the SQL query into a byte-code program in the SQLite library.
        // The third parameter is either the length of the SQL string or -1 to read up to the first null terminator.        
        if (sqlite3_prepare_v2(database, sql, -1, &statement, NULL) == SQLITE_OK) {
            // We "step" through the results - once for each row.
            while (sqlite3_step(statement) == SQLITE_ROW) {
                // The second parameter indicates the column index into the result set.
                int primaryKey = sqlite3_column_int(statement, 0);
                // We avoid the alloc-init-autorelease pattern here because we are in a tight loop and
                // autorelease is slightly more expensive than release. This design choice has nothing to do with
                // actual memory management - at the end of this block of code, all the book objects allocated
                // here will be in memory regardless of whether we use autorelease or release, because they are
                // retained by the books array.
                Book *book = [[Book alloc] initWithPrimaryKey:primaryKey database:database];
                [books addObject:book];
                [book release];
            }
        }
        // "Finalize" the statement - releases the resources associated with the statement.
        sqlite3_finalize(statement);
    } else {
        // Even though the open failed, call close to properly clean up resources.
        sqlite3_close(database);
        NSAssert1(0, @"Failed to open database with message '%s'.", sqlite3_errmsg(database));
        // Additional error handling, as appropriate...
    }
}

// Save all changes to the database, then close it.
- (void)applicationWillTerminate:(UIApplication *)application {
    // Save changes.
    [books makeObjectsPerformSelector:@selector(dehydrate)];
    [Book finalizeStatements];
    // Close the database.
    if (sqlite3_close(database) != SQLITE_OK) {
        NSAssert1(0, @"Error: failed to close database with message '%s'.", sqlite3_errmsg(database));
    }
}

// Remove a specific book from the array of books and also from the database.
- (void)removeBook:(Book *)book {
    // Delete from the database first. The book knows how to do this (see Book.m)
    [book deleteFromDatabase];
    [books removeObject:book];
}

// Insert a new book into the database and add it to the array of books.
- (void)addBook:(Book *)book {
    // Create a new record in the database and get its automatically generated primary key.
    [book insertIntoDatabase:database];
    [books addObject:book];
}

@end