FMDB实战

FMDB对 sqlite3 的api进行了简单封装，支持MRC和ARC，不需要设置flag。

1. 首先，从
github 上 clone源代码，或者用 cocoapods（推荐），并导入到项目中

2. 添加 libsqlite3.dylib 到链接库中

这样就可以使用FMDB来管理数据库了。

1. 创建db

新建一个 DBManager，用来统一管理db的操作。

#import <Foundation/Foundation.h>

@interface DBManager : NSObject

+ (DBManager*)sharedInstance;
+ (void)destory;

@end

DBManager是一个单例。在获取实例时创建db，并在第一次使用时建表。

<pre name="code" class="objc">static DBManager *sharedDBManager = nil;
static dispatch_once_t token;

@implementation DBManager

- (void)dealloc {
DDLogDebug(@"======= DBManager DEALLOC ========");
[_db close];
}

+(DBManager*)sharedInstance {
dispatch_once(&token, ^{
sharedDBManager = [[DBManager alloc]init];
});

return sharedDBManager;
}

+ (void)destory {
if (sharedDBManager) {
sharedDBManager = nil;
token = 0;
}
}

- (id)init {
if (self = [super init]) {
[self initDataBase];
}

return self;
}

- (void)initDataBase {
NSString *dbPath = [self defaultDbPath]; // ugirls.db
BOOL created = NO;
if (![FCFileManager existsItemAtPath:dbPath]) {
created = [FCFileManager createDirectoriesForFileAtPath:[self defaultDbDir]];
}
//_db = [[FMDatabase alloc] initWithPath:dbPath];
_db = [FMDatabase databaseWithPath:dbPath];
if (![_db open]) {
DDLogError(@"open db fail : %@", dbPath);
} else {
if (created) {
//第一次要创建table
[_db beginTransaction];

// read message ids
NSString *dropReadSql = [NSString stringWithFormat:@"DROP TABLE IF EXISTS '%@';", readPublicIds];
// create readPublicIds
NSString *readIdsSql = [NSString stringWithFormat:@"CREATE TABLE '%@' ('msg_id' integer NOT NULL PRIMARY KEY AUTOINCREMENT);", readPublicIds];
// delete message ids
NSString *dropDeleteSql = [NSString stringWithFormat:@"DROP TABLE IF EXISTS '%@';", deletePublicIds];
NSString *deleteIdsSql  = [NSString stringWithFormat:@"CREATE TABLE '%@' ('msg_id' integer NOT NULL PRIMARY KEY AUTOINCREMENT);", deletePublicIds];
// public message models
NSString *dropPubMsgSql = [NSString stringWithFormat:@"DROP TABLE IF EXISTS '%@';", publicMessages];
// 以blob形式保存消息: UGMessageModel
NSString *pubMessageSql = [NSString stringWithFormat:@"CREATE TABLE '%@' ('msg_id' integer NOT NULL PRIMARY KEY AUTOINCREMENT, 'msg_model' blob NOT NULL);", publicMessages];
// private messages models
NSString *dropPriMsgSql = [NSString stringWithFormat:@"DROP TABLE IF EXISTS '%@';", privateMessages];
// 以blob形式保存消息: UGMessageModel
NSString *priMessageSql = [NSString stringWithFormat:@"CREATE TABLE '%@' ('msg_id' integer NOT NULL PRIMARY KEY AUTOINCREMENT, 'user_id' integer NOT NULL, 'msg_model' TEXT NOT NULL);", privateMessages];

[_db executeUpdate:dropReadSql];
[_db executeUpdate:readIdsSql];
[_db executeUpdate:dropDeleteSql];
[_db executeUpdate:deleteIdsSql];
[_db executeUpdate:dropPubMsgSql];
[_db executeUpdate:pubMessageSql];
[_db executeUpdate:dropPriMsgSql];
[_db executeUpdate:priMessageSql];

if (![_db commit]) {
DDLogError(@"create table error %@", [_db lastError]);
[_db close];
[FCFileManager removeItemAtPath:[self defaultDbDir]];
}
}
}
}

在扩展中申明db：

@interface UGDBManager () {
FMDatabase      *_db;
}

数据库的路径：

///每个用户一个DB目录
- (NSString *)defaultDbDir  {
NSString *userId = [NSString stringWithFormat:@"%lld", [LoginManager sharedInstance].userid];
NSString *dbDir = [FCFileManager pathForDocumentsDirectoryWithPath:userId];
return dbDir;
}

- (NSString *)defaultDbPath {
return [[self defaultDbDir] stringByAppendingPathComponent:localDbName];
}

2. CRUD操作

添加一条记录：

- (BOOL)insertOneMessage:(MessageModel *)msg{
BOOL result = NO;
NSString *sql = [NSString stringWithFormat:@"SELECT msg_id FROM %@ WHERE msg_id = '%@';",
privateMessages, [NSNumber numberWithInteger:msg.iId]];
FMResultSet *rs = [_db executeQuery:sql];
// if data does not exist, then insert a item
if (![rs next]) {
NSData *data  = [NSKeyedArchiver archivedDataWithRootObject:msg];
NSString *base64 = [data base64EncodedStringWithOptions:NSDataBase64EncodingEndLineWithLineFeed];
sql = [NSString stringWithFormat:@"INSERT INTO %@ (msg_id, user_id, msg_model) VALUES(%@, %@, '%@');",
privateMessages,
[NSNumber numberWithInteger: msg.iId],
[NSNumber numberWithInteger: msg.iSenderId],
base64];
result = [_db executeUpdate:sql];
}

if (!result) {
DDLogError(@"insertMsgs error: %@", [_db lastError]);
}

return result;
}

注意：这里如果直接用 Blob 存储自定义的对象在unarchive时会直接崩溃：

reason: -[__NSCFData objectForKey:]: unrecognized selector sent to instance 0x7f9e1c03d940

所以，这里我先把data转成NSString然后再存到db中，这样就行了。而且，自定义对象要实现 NSCoding 协议里的两个方法：

@interface MessageModel : NSObject <NSCoding>

/**************shared message fields******************/
@property (nonatomic, assign) NSInteger iId;
@property (nonatomic, copy) NSString* sHeader;
@property (nonatomic, copy) NSString* sUri;

@end

@implementation MessageModel

- (id)initWithCoder:(NSCoder *)coder{
if (self = [super initWithCoder:coder]) {
self.sUri = [coder decodeObjectForKey:@"sUri"];
self.sHeader = [coder decodeObjectForKey:@"sHeader"];
self.iId = [coder decodeIntegerForKey:@"iId"];
}
return self;
}

- (void)encodeWithCoder:(NSCoder *)coder{
[coder encodeObject:self.sHeader forKey:@"sHeader"];
[coder encodeObject:self.sUri forKey:@"sUri"];
[coder encodeInteger:self.iId forKey:@"iId"];

}

@end

删除一条记录：

- (BOOL)deleteOneMessage:(MessageModel *)msg{
BOOL result = NO;
NSString *sql = [NSString stringWithFormat:@"SELECT msg_id FROM %@ WHERE msg_id = '%@';",
privateMessages, [NSNumber numberWithInteger:msg.iId]];
FMResultSet *rs = [_db executeQuery:sql];
// if data does not exist, then insert a item
if ([rs next]) {
sql = [NSString stringWithFormat:@"DELETE FROM %@ WHERE msg_id = '%@';",
privateMessages,
[NSNumber numberWithInteger: msg.iId]];
result = [_db executeUpdate:sql];
}

if (!result) {
DDLogError(@"deleteprivateMsgs error: %@", [_db lastError]);
}

return result;
}

当删除多条记录时，可以用事务：

- (BOOL)deleteMessages:(NSArray *)msgs{
[_db beginTransaction];
for (MessageModel *msg in msgs) {
[self deletePrivateMessage:msg];
}
return [_db commit];
}

查询记录：

- (NSMutableArray *)fetchMessageByUserId:(NSInteger)userId{
NSString *sql = [NSString stringWithFormat:@"SELECT * FROM %@;", privateMessages];
FMResultSet *rs = [_db executeQuery:sql];
NSMutableArray *messages = [NSMutableArray array];
while([rs next]) {
//NSData *data = [rs dataForColumn:@"msg_model"];
NSString *text = [rs stringForColumn:@"msg_model"];
NSData *data = [[NSData alloc]initWithBase64EncodedString:text options:NSDataBase64DecodingIgnoreUnknownCharacters];
MessageModel *msg = [NSKeyedUnarchiver unarchiveObjectWithData:data];
//NSString *ss = NSStringFromClass([msg class]);
[messages addObject: msg];
}
//NSLog(@"database:messages===>%@", messages);
return messages;
}

一般，executeQuery 和 executeUpdate 这两个方法就能应对所有的操作了，只是改改sql语句而已。

总得来说，是比apple提供的原始api友好，但是还是没有CoreData封装的彻底，不过比CoreData效率高。这个主要是sql语句比较繁琐，还能继续封装成完全的面向对象，
不用写sql语句，也有相关的开源库。