IOS——从头介绍数据库sqlite3的创建，使用及可能出现的问题

首先导入数据库sqlite3.h，这个就不多说了(以项目Book为例)

1. 创建新的数据库，表格以及查询，插入，删除，更新操作。

1.1 创建一个.plist文件存储数据库数据

当然，这个文件也可以存储别的固定参数

方法：NewFile -> Resource选项 -> Property List（例如命名为BookDocumentSetting.plist）

添加两个键值对：

Key	Value
DataBaseName	BookDatabase
DataBaseDir	Database

1.2 创建DBManager，统一创建，管理和获取数据库路径

不多说，贴代码：

.h文件

#import <Foundation/Foundation.h>
#import <sqlite3.h>

#define BOOK_DOCUMENT_SETTING @"BookDocumentSetting"
#define DB_DIRECTORY_KEY @"DataBaseDir"
#define DB_NAME_KEY @"DataBaseName"
#define BOOK_DB_RECORD_NOTFOUND -1

@interface DBManager : NSObject
+(NSString *) getDBPath;
@end

该Manager只能提供getDBPath方法

.m文件：

#import "DBManager.h"

static sqlite3 *database=nil;
@implementation DBManager

+ (void)initialize
{
if (self == [DBManager class]) {
[DBManager initDB];
[DBManager initTables];
}
}

+ (void) initDB {
NSError *initDB_Error;
//get db setting
NSString *dbSettingPlist=[[NSBundle mainBundle] pathForResource:BOOK_DOCUMENT_SETTING ofType:@"plist"];
NSMutableDictionary *dbSettingDictionary=[[NSMutableDictionary alloc]initWithContentsOfFile:dbSettingPlist];
NSString *dbDir=[dbSettingDictionary objectForKey:DB_DIRECTORY_KEY];
NSString *dbName=[dbSettingDictionary objectForKey:DB_NAME_KEY];

//create db dir if not exists
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDir2 = [paths objectAtIndex:0];
NSString *dataPath = [documentsDir2 stringByAppendingPathComponent:dbDir];

if (![[NSFileManager defaultManager] fileExistsAtPath:dataPath]){
if ([[NSFileManager defaultManager] createDirectoryAtPath:dataPath withIntermediateDirectories:NO attributes:nil error:&initDB_Error]) {
NSLog(@"initDB Database Dir created success");
}else{
NSLog(@"initDB Database Dir created failed");
}
}else{
NSLog(@"initDB Database Dir did existed");
}

//create DB if not exists
//Using NSFileManager we can perform many file system operations.
NSFileManager *fileManager = [NSFileManager defaultManager];
NSString *dbPath = [DBManager getDBPath];
if ([fileManager fileExistsAtPath:dbPath]) {
NSLog(@"DB file exists");
}else{
if (sqlite3_open([[DBManager getDBPath] UTF8String], &database) == SQLITE_OK) {
NSLog(@"initDB Database Created Success");
sqlite3_close(database);
}
else {
NSLog(@"initDB Databse Created Failed");
}
}
}

+(void)initTables{
NSLog(@"start to initTables");
if (sqlite3_open([[self getDBPath] UTF8String], &database) == SQLITE_OK) {
[self createTable_AllBook];
<pre name="code" class="objc">        // 这里可以插入多条创建Table的代码
}else{
NSLog(@"initTables Failed");
}
sqlite3_close(database);
}

+(BOOL)createTable_AllBook{
char *errorMsg=NULL;
const char *sql_stmt2 = "CREATE TABLE IF NOT EXISTS ALLBOOK  (BOOKID INTEGER PRIMARY KEY AUTOINCREMENT, BOOKTYPE INTEGER, BOOKAMOUNT TEXT, TIME TEXT)";
if (sqlite3_exec(database, sql_stmt2, NULL, NULL, &errorMsg) == SQLITE_OK) {
NSLog(@"Create table AllBook success");
return YES;
}else{
NSLog(@"Create table AllBook failed");
return NO;
}
}

+(NSString *) getDBPath{
NSError *error;
NSString *dbSettingPlist=[[NSBundle mainBundle] pathForResource:BOOK_DOCUMENT_SETTING ofType:@"plist"];
NSMutableDictionary *dbSettingDictionary=[[NSMutableDictionary alloc]initWithContentsOfFile:dbSettingPlist];
NSString *dbDir=[dbSettingDictionary objectForKey:DB_DIRECTORY_KEY];
NSString *dbName=[dbSettingDictionary objectForKey:DB_NAME_KEY];

//create db dir if not exists
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDir2 = [paths objectAtIndex:0];
NSString *dataPath = [documentsDir2 stringByAppendingPathComponent:dbDir];
if (![[NSFileManager defaultManager] fileExistsAtPath:dataPath]){

if ([[NSFileManager defaultManager] createDirectoryAtPath:dataPath withIntermediateDirectories:NO attributes:nil error:&error]) {
NSLog(@"getDBPath Database create successed");
}else{
NSLog(@"getDBPath Databse DIR create failed");
}
}else{
NSLog(@"getDBPath Database is existed.");
}
return [[NSMutableString stringWithString:dataPath] stringByAppendingPathComponent:[dbName stringByAppendingString:@".sqlite"]];
}

解释说明：

（1）. initialize方法是每个类初次创建的时候系统都会调用的方法，无论你是否alloc，例如直接使用类方法[DBManager getDBPath]， 系统都会调用initialize方法。

所以我把初始化数据库和创建表格的方法写在这里。

（2）. 例子中创建的表格名字是AllBook，里面包含的参数有：BOOKID（自增长int类型，primary key），BOOKTYPE（int类型，记录书的类型），BOOKAMOUNT（书的价格，本来SQL3中有浮点数REAL，但是浮点存储不符合我的需求，所以使用String类型存储），TIME（记录时间）

（3）. 需要更多的表格可以仿照方法createTable来写，添加到initTable即可。

（4）. getDBPath是唯一给外界调用的方法，目的是确保数据库的路径正确，才可以打开数据库进行操作。

1.3 每个表格的增删改查操作(持续添加中)

实现对每个表格的数据操作，以AllBOOK为例，创建AllBOOKDAO

.h文件

#import <Foundation/Foundation.h>
#import <sqlite3.h>
#import "DBManager.h"

@interface AllBookDAO : NSObject{
int bookID;
int bookType;
NSString *bookAmount;
NSString *time;
}

@property (nonatomic, readwrite) int bookID;
@property (nonatomic, readwrite) int bookType;
@property (nonatomic, readwrite,retain) NSString *bookAmount;
@property (nonatomic, readwrite,retain) NSString *time;

+ (NSMutableArray *) getAllBookList;
@end

.m文件

#import "AllBookDAO.h"

@implementation AllBookDAO
@synthesize bookID,bookType,bookAmount,time;
static sqlite3 *database = nil;

 //查询

+ (NSMutableArray *) getAllBookList{
NSMutableArray *resultArray = [[NSMutableArray alloc] init ];
if (sqlite3_open([[DBManager getDBPath] UTF8String], &database) == SQLITE_OK) {
const char *sql = "select BOOKID,BOOKTYPE,BOOKAMOUNT,TIME from ALLBOOK";
sqlite3_stmt *selectstmt;
if(sqlite3_prepare_v2(database, sql, -1, &selectstmt, NULL) == SQLITE_OK) {

while(sqlite3_step(selectstmt) == SQLITE_ROW) {
AllBookDAO *allBook = [[AllBookDAO alloc] init];
allBook.bookID = sqlite3_column_int(selectstmt, 0);
allBook.bookType=sqlite3_column_int(selectstmt, 1);
allBook.bookAmount=[NSString stringWithUTF8String:(char *)sqlite3_column_text(selectstmt, 2)];
allBook.time = [NSString stringWithUTF8String:(char *)sqlite3_column_text(selectstmt, 3)];
[resultArray addObject:allBook];
}
}
sqlite3_reset(selectstmt);
if(selectstmt) sqlite3_finalize(selectstmt);
}
else{
NSLog(@"Open Database Failed.");

}
sqlite3_close(database);
return resultArray;
}

@end

2. 如何使用现有数据库

例如数据库的名字叫做Test.db

NSString *dbFilePath = [[NSBundlemainBundle]pathForResource:@"数据库名字，如Test"ofType:@"db"];

NSLog(@"DB file path: %@",dbFilePath);

//    FMDatabaseQueue *queue = [FMDatabaseQueue databaseQueueWithPath:dbFilePath];

sqlite3 *database;

if (sqlite3_open([dbFilePathUTF8String], &database) ==SQLITE_OK)

{

NSLog(@"DB open success");

}

else {

sqlite3_close(database);

NSLog(@"DB open failed");

}

3. 使用数据库可能出现的问题

3.1 提示database is locked解决方法

我在这里并没有使用多线程，我的问题是select语句没有进行reset操作

sqlite3_reset(selectStmt);

if(selectStmt)sqlite3_finalize(selectStmt);

添上这两行就好