FreeSql （九）删除数据

删除是一个非常危险的操作，FreeSql对删除支持并不强大，仅支持了单表有条件的删除方法。

不想过多的介绍拉长删除数据的系列文章，删除数据的介绍仅此一篇。

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

为了增强系统的安全性，强烈建议在实体中增加 is_deledted 字段做软删除标识。

var connstr = "Data Source=127.0.0.1;Port=3306;User ID=root;Password=root;" + 
    "Initial Catalog=cccddd;Charset=utf8;SslMode=none;Max pool size=10";

IFreeSql fsql = new FreeSql.FreeSqlBuilder()
    .UseConnectionString(FreeSql.DataType.MySql, connstr)
    .UseAutoSyncStructure(true) //自动同步实体结构到数据库
    .Build();

[Table(Name = "tb_topic")]
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

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 }

fsql.Delete<Topic>(new[] { 1, 2 }).ExecuteAffrows();
//DELETE FROM `tb_topic` WHERE (`Id` = 1 OR `Id` = 2)

fsql.Delete<Topic>(new Topic { Id = 1, Title = "test" }).ExecuteAffrows();
//DELETE FROM `tb_topic` WHERE (`Id` = 1)

fsql.Delete<Topic>(new[] { new Topic { Id = 1, Title = "test" }, new Topic { Id = 2, Title = "test" } }).ExecuteAffrows();
//DELETE FROM `tb_topic` WHERE (`Id` = 1 OR `Id` = 2)

fsql.Delete<Topic>(new { id = 1 }).ExecuteAffrows();
//DELETE FROM `tb_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()

fsql.Delete<Topic>().Where(a => a.Id == 1).ExecuteAffrows();
//DELETE FROM `tb_topic` WHERE (`Id` = 1)

fsql.Delete<Topic>().Where("id = ?id", new { id = 1 }).ExecuteAffrows();
//DELETE FROM `tb_topic` WHERE (id = ?id)

var item = new Topic { Id = 1, Title = "newtitle" };
fsql.Delete<Topic>().Where(item).ExecuteAffrows();
//DELETE FROM `tb_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 });
fsql.Delete<Topic>().Where(items).ExecuteAffrows();
//DELETE FROM `tb_topic` WHERE (`Id` IN (1,2,3,4,5,6,7,8,9,10))

API

方法	返回值	参数	描述
Where	<this>	Lambda	表达式条件，仅支持实体基础成员（不包含导航对象）
Where	<this>	string, parms	原生sql语法条件，Where("id = ?id", new { id = 1 })
Where	<this>	T1 | IEnumerable	传入实体或集合，将其主键作为条件
WhereExists	<this>	ISelect	子查询是否存在
WithTransaction	<this>	DbTransaction	设置事务对象
ToSql	string		返回即将执行的SQL语句
ExecuteAffrows	long		执行SQL语句，返回影响的行数
ExecuteDeleted	List<T1>		执行SQL语句，返回被删除的记录