iphone - iOS Sqlite3 删除查询不删除行

Question

我正在使用这段代码为我的 ipad 应用程序从数据库中删除一行，

-(BOOL) removeSegmentWithSegmentId:(NSInteger)sId
{
    AppDelegate *appDelegate = (AppDelegate *) [[UIApplication sharedApplication] delegate];

    sqlite3_stmt *statement;

    NSString *removeKeyword =[NSString stringWithFormat:@"DELETE FROM segment WHERE segment.segment_id = %d",sId];
    const char *query = [removeKeyword UTF8String];
    NSLog(@"%@",removeKeyword);

    //if(sqlite3_prepare_v2(appDelegate->globalConnection,[removeKeyword UTF8String] , -1, &statement, NULL) == SQLITE_OK)
    if(sqlite3_prepare_v2(appDelegate->globalConnection,query , -1, &statement, NULL) == SQLITE_OK)
    {
        if(sqlite3_step(statement) == SQLITE_DONE) {
            sqlite3_finalize(statement);
            return YES;
        }
    }
    return NO;
}

但是它不起作用，谁能指导我吗？

Answer 1

您的方法是否返回 YES？

一些事情:

• 总是记录 sqlite3_errmsg 任何失败
• 现在，你只是在做 sqlite3_finalize 是 sqlite3_step 返回 SQLITE_DONE，而你真的应该在你成功的时候做 sqlite3_prepare_v2

因此，我建议至少:

-(BOOL) removeSegmentWithSegmentId:(NSInteger)sId
{
    BOOL success = NO;

    AppDelegate *appDelegate = (AppDelegate *) [[UIApplication sharedApplication] delegate];

    sqlite3_stmt *statement;

    NSString *removeKeyword = [NSString stringWithFormat:@"DELETE FROM segment WHERE segment.segment_id = %d",sId];

    if (sqlite3_prepare_v2(appDelegate->globalConnection, [removeKeyword UTF8String], -1, &statement, NULL) == SQLITE_OK)
    {
        if(sqlite3_step(statement) == SQLITE_DONE) 
        {
            success = YES;
        }
        else
        {
            NSLog(@"%s: step not ok: %s", __FUNCTION__, sqlite3_errmsg(appDelegate->globalConnection));
        }
        sqlite3_finalize(statement);
    }
    else
    {
        NSLog(@"%s: prepare failure: %s", __FUNCTION__, sqlite3_errmsg(appDelegate->globalConnection));
    }

    return success;
}

假设此方法始终返回 YES，如果您没有看到删除的记录，那一定是它没有找到要删除的记录。 (这不被认为是 SQLite 失败。SQL 已成功执行，但无法满足 WHERE 子句。)您可以通过定义以下方法来验证这一点:

- (NSInteger)countSegmentWithSegmentId:(NSInteger)sId
{
    NSInteger count = 0;

    AppDelegate *appDelegate = (AppDelegate *) [[UIApplication sharedApplication] delegate];

    sqlite3_stmt *statement;

    NSString *sql = [NSString stringWithFormat:@"SELECT segment_id FROM segment WHERE segment.segment_id = %d", sId];

    if (sqlite3_prepare_v2(appDelegate->globalConnection, [sql UTF8String], -1, &statement, NULL) == SQLITE_OK)
    {
        while ((rc = sqlite3_step(statement)) == SQLITE_ROW)
            count++;

        sqlite3_finalize(statement);
    }
    else
    {
        NSLog(@"%s: prepare failure: %s", __FUNCTION__, sqlite3_errmsg(appDelegate->globalConnection));
        return -1;
    }

    return count;
}

然后将诊断信息放入removeSegmentWithSegmentId:

- (BOOL)removeSegmentWithSegmentId:(NSInteger)sId
{
    BOOL success = NO;
    NSInteger count = [self countSegmentWithSegmentId:sId];

    NSLog(@"%s there are %d records with segment_id of %d", __FUNCTION__, count, sId);

    AppDelegate *appDelegate = (AppDelegate *) [[UIApplication sharedApplication] delegate];

    sqlite3_stmt *statement;

    NSString *removeKeyword = [NSString stringWithFormat:@"DELETE FROM segment WHERE segment.segment_id = %d",sId];

    if (sqlite3_prepare_v2(appDelegate->globalConnection, [removeKeyword UTF8String], -1, &statement, NULL) == SQLITE_OK)
    {
        if(sqlite3_step(statement) == SQLITE_DONE)
        {
            success = YES;
        }
        else
        {
            NSLog(@"%s: step not ok: %s", __FUNCTION__, sqlite3_errmsg(appDelegate->globalConnection));
        }
        sqlite3_finalize(statement);
    }
    else
    {
        NSLog(@"%s: prepare failure: %s", __FUNCTION__, sqlite3_errmsg(appDelegate->globalConnection));
    }

    return success;
}