为什么要使用FMDatabaseQueue

• FMDatabase这个类, 他不是线程安全的, 如果在多个线程中同时使用一个FMDataBase对象来存取数据的话, 有可能会发生数据错乱
• 因此为了保证线程安全, 要使用FMDatabaseQueue这个类来操作数据
• FMDatabaseQueue这个类, 还提供了在一个SQL字符串中, 同时编写多个代码的方法, 因此使用起来十分的效率

简单的代码实现

 #import "DataBaseTool.h"
 #import "FMDatabase.h"
 #import "FMDatabaseQueue.h"
 
 static DataBaseTool *_instance;
 
 @interface DataBaseTool ()
 @property (nonatomic, strong) FMDatabaseQueue *queue;
 @end
 
 @implementation DataBaseTool
 
 + (instancetype)shareInstance {
     static dispatch_once_t onceToken;
     dispatch_once(&onceToken, ^{
         _instance = [[self alloc] init];
     });
     
     return _instance;
 }
 
 // 懒加载数据库队列
 - (FMDatabaseQueue *)queue {
     if (_queue == nil) {
         _queue = [FMDatabaseQueue databaseQueueWithPath:@"/Users/fanghe/Desktop/数据库/demo.sqlite"];
     }
     
     return _queue;
 }
 
 // 创建表
 - (void)createTableWithSQL:(NSString *)sql {
     
     [self.queue inDatabase:^(FMDatabase *db) {
         BOOL result = [db executeUpdate:sql withArgumentsInArray:nil];
         if (result) {
             NSLog(@"创建表格成功");
         } else {
             NSLog(@"创建表格失败");
         }
     }];
 }
 
 // 删除表格
 - (void)dropTableWithSQL:(NSString *)sql {
     
     [self.queue inDatabase:^(FMDatabase *db) {
         BOOL result = [db executeUpdate:sql withArgumentsInArray:nil];
         if (result) {
             NSLog(@"删除表格成功");
         } else {
             NSLog(@"删除表格失败");
         }
     }];
 }
 
 // 插入数据
 - (void)insertDataWithSQL:(NSString *)sql {
     
     [self.queue inDatabase:^(FMDatabase *db) {
         BOOL result = [db executeUpdate:sql withArgumentsInArray:nil];
         if (result) {
             NSLog(@"插入数据成功");
         } else {
             NSLog(@"插入数据失败");
         }
     }];
 }
 
 // 查询所有数据
 - (void)queryAll {
     
     [self.queue inDatabase:^(FMDatabase *db) {
         NSString *sql = @"select * from T_human";
         
         FMResultSet *resultSet = [db executeQuery:sql withArgumentsInArray:nil];
         
         while (resultSet.next) {
             NSString *name = [resultSet stringForColumn:@"name"];
             int age = [resultSet intForColumn:@"age"];
             double height = [resultSet doubleForColumn:@"height"];
             
             NSLog(@"%@, %i, %lf", name, age, height);
         }
     }];
 }
 
 // 执行多条语句
 - (void)excuteStaments {
     
     NSString *sql = @"insert into T_human(name, age, height) values('wangwu', 15, 170);insert into T_human(name, age, height) values('zhaoliu', 13, 160);";
     
     [self.queue inDatabase:^(FMDatabase *db) {
         BOOL result = [db executeStatements:sql];
         if (result) {
             NSLog(@"执行多条语句成功");
         } else {
             NSLog(@"执行多条语句失败");
         }
     }];
 }
 
 // 开启事务执行语句
 - (void)transaction {
     
     [self.queue inTransaction:^(FMDatabase *db, BOOL *rollback) {
         NSString *sql = @"insert into T_human(name, age, height) values('wangwu', 15, 170);insert into T_human(name, age, height) values('zhaoliu', 13, 160);";
         NSString *sql2 = @"insert into T_human(name, age, height) values('zhaoliu', 13, 160);insert into T_human(name, age, height) values('wangwu', 15, 170);";
         
         BOOL result1 = [db executeUpdate:sql withArgumentsInArray:nil];
         BOOL result2 = [db executeUpdate:sql2 withArgumentsInArray:nil];
         
         if (result1 && result2) {
             NSLog(@"执行成功");
         } else {
             [db rollback];
         }
     }];
 }
 
 @end