12. FMDatabaseQueue的简单使用

1. 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

2. 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