极客教程

删除是一个非常危险的操作，FreeSql对删除支持并不强大，默认仅支持单表、且有条件的删除方法。

若Where条件为空的时候执行，仅返回0或默认值，不执行真正的SQL删除操作。

static IFreeSql fsql = new FreeSql.FreeSqlBuilder()
    .UseConnectionString(FreeSql.DataType.MySql, connectionString)
    .UseAutoSyncStructure(true) //自动同步实体结构到数据库
    .Build(); //请务必定义成 Singleton 单例模式class Topic {
    [Column(IsIdentity = true, IsPrimary = true)]    public int Id { get; set; }    public int Clicks { get; set; }    public string Title { get; set; }    public DateTime CreateTime { get; set; }
}

动态条件

fsql.Delete<Topic>(object dywhere)

dywhere 支持

• 主键值
• new[] { 主键值1, 主键值2 }
• Topic对象
• new[] { Topic对象1, Topic对象2 }
• new { id = 1 }

var t1 = fsql.Delete<Topic>(new[] { 1, 2 }).ToSql();//DELETE FROM `Topic` WHERE (`Id` = 1 OR `Id` = 2)var t2 = fsql.Delete<Topic>(new Topic { Id = 1, Title = "test" }).ToSql();//DELETE FROM `Topic` WHERE (`Id` = 1)var t3 = fsql.Delete<Topic>(new[] { new Topic { Id = 1, Title = "test" }, new Topic { Id = 2, Title = "test" } }).ToSql();//DELETE FROM `Topic` WHERE (`Id` = 1 OR `Id` = 2)var t4 = fsql.Delete<Topic>(new { id = 1 }).ToSql();//DELETE FROM `Topic` WHERE (`Id` = 1)

删除条件

出于安全考虑，没有条件不执行删除动作，避免误删除全表数据。删除全表数据：fsql.Delete<T>().Where("1=1").ExecuteAffrows()

var t5 = fsql.Delete<Topic>().Where(a => a.Id == 1).ToSql();//DELETE FROM `Topic` WHERE (`Id` = 1)var t6 = fsql.Delete<Topic>().Where("id = @id", new { id = 1 }).ToSql();//DELETE FROM `Topic` WHERE (id = @id)var item = new Topic { Id = 1, Title = "newtitle" };var t7 = fsql.Delete<Topic>().Where(item).ToSql();//DELETE FROM `Topic` WHERE (`Id` = 1)var items = new List<Topic>();for (var a = 0; a < 10; a++) items.Add(new Topic { Id = a + 1, Title = $"newtitle{a}", Clicks = a * 100 });var t8 = fsql.Delete<Topic>().Where(items).ToSql();//DELETE FROM `Topic` WHERE (`Id` IN (1,2,3,4,5,6,7,8,9,10))

ISelect.ToDelete 高级删除

IDelete 默认不支持导航对象，多表关联等。ISelect.ToDelete 可将查询转为 IDelete，以便使用导航对象删除数据，如下：

fsql.Select<T1>().Where(a => a.Options.xxx == 1).ToDelete().ExecuteAffrows();

注意：此方法不是将数据查询到内存循环删除，上面的代码产生如下 SQL 执行：

DELETE FROM `T1` WHERE id in (select a.id from T1 a left join Options b on b.t1id = a.id where b.xxx = 1)

复杂删除使用此方法的好处：

• 删除前可预览测试数据，防止错误删除操作；
• 支持复杂的删除操作，例如：ISelect 上使用 Limit(10) 删除附合条件的前 10 条记录；

API