Uses of Database class and it's methods in Objective C iOS

Question

I am trying to use Database SQLite in iOS. i have several questions in the following code.

#import "DBManager.h"

static DBManager *sharedInstance = nil;
static sqlite3 *database = nil;
static sqlite3_stmt *statement = nil;


@implementation DBManager

+(DBManager*)getSharedInstance{
    if (!sharedInstance) {
        sharedInstance = [[     super allocWithZone:NULL]init];
        [sharedInstance createDB];
    }
    return sharedInstance;
}

-(BOOL)createDB{
    NSString *docsDir;
    NSArray *dirPaths;
    // Get the documents directory
    dirPaths = NSSearchPathForDirectoriesInDomains
    (NSDocumentDirectory, NSUserDomainMask, YES);
    docsDir = dirPaths[0];
    // Build the path to the database file
    databasePath = [[NSString alloc] initWithString:
                    [docsDir stringByAppendingPathComponent: @"calc.db"]];
    BOOL isSuccess = YES;
    NSFileManager *filemgr = [NSFileManager defaultManager];
    if ([filemgr fileExistsAtPath: databasePath ] == NO)
    {
        const char *dbpath = [databasePath UTF8String];
        if (sqlite3_open(dbpath, &database) == SQLITE_OK)
        {
            char *errMsg;
            const char *sql_stmt =
            "create table if not exists resultDetail (results integer)";
            if (sqlite3_exec(database, sql_stmt, NULL, NULL, &errMsg)
                != SQLITE_OK)
            {
                isSuccess = NO;
                NSLog(@"Failed to create table");
            }
            sqlite3_close(database);
            return  isSuccess;
        }
        else {
            isSuccess = NO;
            NSLog(@"Failed to open/create database");
        }
    }
    return isSuccess;
}


- (BOOL) saveData:(int)resultValue ;
{
    const char *dbpath = [databasePath UTF8String];
    if (sqlite3_open(dbpath, &database) == SQLITE_OK)
    {
        NSString *insertSQL = [NSString stringWithFormat:@"insert into resultDetail (results) values (\"%d\")",resultValue];
        const char *insert_stmt = [insertSQL UTF8String];
        sqlite3_prepare_v2(database, insert_stmt,-1, &statement, NULL);
            if (sqlite3_step(statement) == SQLITE_DONE)
            {
                sqlite3_reset(statement);
                return YES;
            }
            else
            {
                return NO;
            }
         //   sqlite3_reset(statement);
    }
    sqlite3_reset(statement);
    return NO;
}


- (int) findResult:(int)resultValue
{
    int n=0;
    const char *dbpath = [databasePath UTF8String];
    if (sqlite3_open(dbpath, &database) == SQLITE_OK)
    {
        NSString *querySQL = [NSString stringWithFormat:@"select results from resultDetail where results=\"%d\"",resultValue];

   //     NSString *querySQL = [NSString stringWithFormat:@"select * from resultDetail"];
        const char *query_stmt = [querySQL UTF8String];
    //    NSMutableArray *resultArray = [[NSMutableArray alloc]init];
        if (sqlite3_prepare_v2(database,
                               query_stmt, -1, &statement, NULL) == SQLITE_OK)
        {
         /*  if (sqlite3_step(statement) == SQLITE_ROW)
            {
                int n = sqlite3_column_int(statement, 0);
                NSLog(@"%d let's see",n);
                sqlite3_reset(statement);
                return n;
            }
            else{
                NSLog(@"Not found");
                return 0;
            }    */
           while(sqlite3_step(statement) == SQLITE_ROW){
                n = sqlite3_column_int(statement, 0);
                NSLog(@"%d is the value",n);

            }
            return n;
         //   sqlite3_reset(statement);
        }
        sqlite3_reset(statement);
    }
    sqlite3_reset(statement);
    return 0;
}

-(BOOL)isEmpty{
    const char *dbpath = [databasePath UTF8String];
    if (sqlite3_open(dbpath, &database) == SQLITE_OK)
    {
        NSString *querySQL = [NSString stringWithFormat:@"select * from resultDetail"];

        //     NSString *querySQL = [NSString stringWithFormat:@"select * from resultDetail"];
        const char *query_stmt = [querySQL UTF8String];
        //    NSMutableArray *resultArray = [[NSMutableArray alloc]init];
        if (sqlite3_prepare_v2(database,
                               query_stmt, -1, &statement, NULL) == SQLITE_OK)
        {

            if(sqlite3_step(statement) == SQLITE_ROW){
               sqlite3_reset(statement);
                NSLog(@"Not Empty");
                return NO;
            }
        }
        sqlite3_reset(statement);
    }
    sqlite3_reset(statement);
    return YES;
}

-(BOOL)isDuplicate:(int)resultValue{
    BOOL n=NO;
    const char *dbpath = [databasePath UTF8String];
    if (sqlite3_open(dbpath, &database) == SQLITE_OK)
    {
        NSString *querySQL = [NSString stringWithFormat:@"select results from resultDetail where results=\"%d\"",resultValue];

        //     NSString *querySQL = [NSString stringWithFormat:@"select * from resultDetail"];
        const char *query_stmt = [querySQL UTF8String];
        //    NSMutableArray *resultArray = [[NSMutableArray alloc]init];
        if (sqlite3_prepare_v2(database,
                               query_stmt, -1, &statement, NULL) == SQLITE_OK)
        {
            if(sqlite3_step(statement) == SQLITE_ROW){
                sqlite3_reset(statement);
                n = YES;
            }
            sqlite3_reset(statement);
            return n;
            //   sqlite3_reset(statement);
        }
        sqlite3_reset(statement);
    }
    sqlite3_reset(statement);
    return NO;
}
@end

---

In above code, What is this

static sqlite3 *database = nil;
static sqlite3_stmt *statement = nil;

Is that class or method ?

---

Why are we creating getSharedInstance and what's the use of it?

+(DBManager*)getSharedInstance{
    if (!sharedInstance) {
        sharedInstance = [[     super allocWithZone:NULL]init];
        [sharedInstance createDB];
    }
    return sharedInstance;
}

---

What is NULL arguments in this, what we actually have to do with these?

sqlite3_exec(database, sql_stmt, NULL, NULL, &errMsg)
                != SQLITE_OK

---

I am new to ios so please correct me if i asked anything wrong. Thanks for the time (:

Answer 1

You can save time and efforts if instead of "raw" C-based SQLITE API FMDB wrapper for Obj-C is used.

Look at https://github.com/ccgus/fmdb

Small example of code: I have Core Data entity which should be stored in SQLITE database with custom schema. This method is called on button tap (Mac OS X based, but no difference with IOS)

- (IBAction)saveProcessingButtonTapped:(id)sender
    {
        // Now we can create fresh database file and put there
        // all data from our persistent store
        FMDatabase *db = [FMDatabase databaseWithPath:fileToSave];
        if (!db ) {
            NSLog(@"Cannot create database!");
            return;
        }
        if (![db open]) {
            NSLog(@"Cannot open database at %@",fileToSave);
            return;
        }
        // Create Table for data
        NSString *schema = @"CREATE TABLE LOGDATA ( TIMESTAMP VARCHAR, SESSIONINDEX INTEGER,  EVENT VARCHAR, DESCRIPTION VARCHAR,  VERSION VARCHAR , PLATFORM VARCHAR,  DEVICE VARCHAR,  USERID VARCHAR, PARAMETERS VARCHAR, TIMEINSECS TIMESTAMP)";
        BOOL created = [db executeStatements:schema];
        if (!created) {
            NSLog(@"Cannot create table!");
        }
        // Now we just copy with insert all data from CoreDatastoage to fresh database
        NSFetchRequest *req = [[NSFetchRequest alloc] initWithEntityName:[[SQLITE class] description]];
        NSError *error = nil;
        NSArray *result = [self.managedObjectContext executeFetchRequest:req error:&error];
        if (!result && error) {
            NSAlert *alert = [NSAlert alertWithError:error];
            [alert runModal];
            return;
        }
        for (SQLITE *record in result) {
            NSDictionary *arguments = @{
                                        @"SESSIONINDEX": record.sessionIndex,
                                        @"TIMESTAMP": record.timestamp,
                                        @"DEVICE": record.device,
                                        @"EVENTDESCRIPTION": record.eventDescription,
                                        @"NOTE" : (record.note ? record.note : @""),
                                        @"PARAMETERS" : record.parameters,
                                        @"PLATFORM" : record.platform,
                                        @"USERID" : record.userID,
                                        @"VERSION" : record.version,
                                        @"DATESTRING" : record.dateString,
                                        };
            BOOL success = [db executeUpdate:@"INSERT INTO LOGDATA (SESSIONINDEX, TIMEINSECS, DEVICE, EVENT, DESCRIPTION, PARAMETERS, PLATFORM, USERID, VERSION, TIMESTAMP ) VALUES (:SESSIONINDEX, :TIMESTAMP, :DEVICE, :EVENTDESCRIPTION, :NOTE, :PARAMETERS, :PLATFORM, :USERID, :VERSION, :DATESTRING)" withParameterDictionary:arguments];
            if (!success) {
                NSLog(@"error = %@", [db lastErrorMessage]);
            }
        }

        [db close];
        self.informLabel.stringValue = @"Export completed";
        NSLog(@"\n\n\n CoreDataDatabase is stored - %@", self.sqliteBaseFilename.stringValue);
        NSLog(@"\n Exported database is stored in - %@",fileToSave);

    }

Answer 2

It is too long answer so Please go through this tutorials you can understand the how to SQLite work in iOS

http://www.appcoda.com/sqlite-database-ios-app-tutorial/