FreeSql （二十九）Lambda 表达式

类别：学习文档
日期：2021-07-15 浏览：2243 评论：0

FreeSql是功能强大的 .NET ORM，支持 .NetFramework 4.0+、.NetCore 2.1+、Xamarin 等支持 NetStandard 所有运行平台。

In查询

var t1 = fsql.Select<T>()
  .Where(a => new[] { 1, 2, 3 }.Contains(a.Id))
  .ToList();//SELECT .. FROM ..//WHERE (a.`Id` in (1,2,3))

已优化，防止 where in 元素多过的 SQL 错误，如：

[Err] ORA-01795: maximum number of expressions in a list a 1000

原来：where id in (1..1333)

现在：where id in (1..500) or id in (501..1000) or id in (1001..1333)

In多列查询

//元组集合vae lst = new List<(Guid, DateTime)>();
lst.Add((Guid.NewGuid(), DateTime.Now));
lst.Add((Guid.NewGuid(), DateTime.Now));var t2 = fsql.Select<T>()
  .Where(a => lst.Contains(a.Id, a.ct1))
  .ToList();//SELECT .. FROM ..//WHERE (a."Id" = '685ee1f6-bdf6-4719-a291-c709b8a1378f' AND a."ct1" = '2019-12-07 23:55:27' OR //a."Id" = '5ecd838a-06a0-4c81-be43-1e77633b7404' AND a."ct1" = '2019-12-07 23:55:27')

实现代码：https://github.com/2881099/FreeSql/issues/243

In子表

var list2 = fsql.Select<T>()
  .Where(a => fsql.Select<T>()
      .ToList(b => b.Id)
      .Contains(a.Id))
  .ToList();
  // SELECT a.`Id`, a.`Clicks`, a.`TypeGuid`, a.`Title`, a.`CreateTime` 
  // FROM `tb_topic` a 
  // WHERE (((cast(a.`Id` as char)) in (SELECT b.`Title` 
  // 	FROM `tb_topic` b)))

Exists子表

var list2 = fsql.Select<T>()
  .Where(a => fsql.Select<T>()
    .Any(b => b.Id == a.Id))
  .ToList();
  // SELECT a.`Id`, a.`TypeGuid`, a.`Title`, a.`CreateTime` 
  // FROM `xxx` a 
  // WHERE (exists(SELECT 1 // FROM `xxx` b 
  // WHERE (b.`Id` = a.`Id`)))

查找今天创建的数据

var t3 = fsql.Select<T>()
  .Where(a => a.CreateTime.Date == DateTime.Today)
  .ToList();//这行代码说明 FreeSql 表达式解析强大，不是所有 ORM 都支持var t4 = fsql.Select<T>()
  .Where(a => a.CreateTime.Between(DateTime.Today, DateTime.Today.AddDays(1)))
  .ToList();//正常用法应该是这样

SqlServer nvarchar/varchar 已兼容表达式解析，分别解析为：N'' 和 ''，优化索引执行计划；

日期格式化

var t4 = fsql.Select<T>()
  .First(a => a.CreateTime.ToString("HH:mm:ss");
  // SELECT date_format(a.`CreateTime`, '%H:%i:%s') as1 
  // FROM `xxx` a // limit 0,1

v1.5.0 支持了常用 c# 日期格式化，yyyy MM dd HH mm ss yy M d H hh h m s tt t

tt t 为 AM PM

开窗函数

fsql.Select<T1, T2>()
.InnerJoin((a, b) => b.Id == a.Id)
.ToList((a, b) => new{
    Id = a.Id,
    EdiId = b.Id,
    over1 = SqlExt.Rank().Over().OrderBy(a.Id).OrderByDescending(b.EdiId).ToValue()
});

v1.6.0 利用自定义解析功能，增加 SqlExt.Rank().Over().PartitionBy(...) 常用的开窗函数，欢迎 PR 补充

自定义解析

[ExpressionCall]
public static class DbFunc{
  //必要定义 static + ThreadLocal
  static ThreadLocal<ExpressionCallContext> context = new ThreadLocal<ExpressionCallContext>();  
  public static DateTime FormatDateTime(this DateTime that, string arg1)
  {
      var up = context.Value;    
      if (up.DataType == FreeSql.DataType.Sqlite) //重写内容
      up.Result = $"date_format({up.ParsedContent["that"]}, {up.ParsedContent["arg1"]})";    
      return that;
  }
}var sql1 = fsql.Select<SysModule>()
  .ToSql(a => a.CreateTime.FormatDateTime("yyyy-MM-dd"));
  //SELECT date_format(a."CreateTime", 'yyyy-MM-dd') as1 
  //FROM "SysModule" a

[ExpressionCall] 特性可在静态扩展类上标记，也可以在单个静态方法上标记；

ExpressionCallContext 属性	类型	描述
DataType	FreeSql.DataType	用于实现不同数据库的适配判断条件
ParsedContent	Dictionary<string, string>	函数的各参数解析结果
DbParameter	DbParameter	that 被参数化的对象（有可能为 null)
UserParameters	List<DbParameter>	可附加参数化对象
Result	string	返回表达式函数表示的 SQL 字符串

当扩展方法返回值为 string 时，其返回值也可以当作 context.Value.Result 功能

当不想解析指定参数时，使用特性 [RawValue] 标记

表达式函数全览

表达式	MySql	SqlServer	PostgreSQL	Oracle	功能说明
a ? b : c	case when a then b else c end	case when a then b else c end	case when a then b else c end	case when a then b else c end	a成立时取b值，否则取c值
a ?? b	ifnull(a, b)	isnull(a, b)	coalesce(a, b)	nvl(a, b)	当a为null时，取b值
数字 + 数字	a + b	a + b	a + b	a + b	数字相加
数字 + 字符串	concat(a, b)	cast(a as varchar) + cast(b as varchar)	case(a as varchar)\|\| b	a\|\| b	字符串相加，a或b任意一个为字符串时
a - b	a - b	a - b	a - b	a - b	减
a * b	a * b	a * b	a * b	a * b	乘
a / b	a / b	a / b	a / b	a / b	除
a / b	a div b	a / b	a / b	trunc(a / b)	整除(a,b都为整数)
a % b	a % b	a % b	a % b	mod(a,b)	模

等等...

数组

表达式	MySql	SqlServer	PostgreSQL	Oracle	功能说明
a.Length	-	-	case when a is null then 0 else array_length(a,1) end	-	数组长度
常量数组.Length	-	-	array_length(array[常量数组元素逗号分割],1)	-	数组长度
a.Any()	-	-	case when a is null then 0 else array_length(a,1) end > 0	-	数组是否为空
常量数组.Contains(b)	b in (常量数组元素逗号分割)	b in (常量数组元素逗号分割)	b in (常量数组元素逗号分割)	b in (常量数组元素逗号分割)	IN查询
a.Contains(b)	-	-	a @> array[b]	-	a数组是否包含b元素
a.Concat(b)	-	-	a \|\| b	-	数组相连
a.Count()	-	-	同 Length	-	数组长度

一个细节证明 FreeSql 匠心制作

通用的 in 查询 select.Where(a => new []{ 1,2,3 }.Contains(a.xxx))

假设 xxxs 是 pgsql 的数组字段类型，其实会与上面的 in 查询起冲突，FreeSql 解决了这个矛盾 select.Where(a => a.xxxs.Contains(1))

字典 Dictionary<string, string>

表达式	MySql	SqlServer	PostgreSQL	Oracle	功能说明
a.Count	-	-	case when a is null then 0 else array_length(akeys(a),1) end	-	字典长度
a.Keys	-	-	akeys(a)	-	返回字典所有key数组
a.Values	-	-	avals(a)	-	返回字典所有value数组
a.Contains(b)	-	-	a @> b	-	字典是否包含b
a.ContainsKey(b)	-	-	a? b	-	字典是否包含key
a.Concat(b)	-	-	a \|\| b	-	字典相连
a.Count()	-	-	同 Count	-	字典长度

JSON JToken/JObject/JArray

表达式	MySql	SqlServer	PostgreSQL	Oracle	功能说明
a.Count	-	-	jsonb_array_length(coalesce(a, '[]))	-	json数组类型的长度
a.Any()	-	-	jsonb_array_length(coalesce(a, '[])) > 0	-	json数组类型，是否为空
a.Contains(b)	-	-	coalesce(a, '{}') @> b::jsonb	-	json中是否包含b
a.ContainsKey(b)	-	-	coalesce(a, '{}') ? b	-	json中是否包含键b
a.Concat(b)	-	-	coalesce(a, '{}')		b::jsonb
Parse(a)	-	-	a::jsonb	-	转化字符串为json类型
a.Field["x"]	-	-	a.Field->x	-	json成员访问

字符串

表达式	MySql	SqlServer	PostgreSQL	Oracle	Sqlite
string.Empty	''	''	''	''
string.IsNullOrEmpty(a)	(a is null or a = '')	(a is null or a = '')	(a is null or a = '')	(a is null or a = '')	(a is null or a = '')
string.Concat(a,b,c...)	concat(a, b, c)	a + b + c	a \|\| b \|\| c	a \|\| b \|\| c	a \|\| b \|\| c
a.CompareTo(b)	strcmp(a, b)	-	case when a = b then 0 when a > b then 1 else -1 end	case when a = b then 0 when a > b then 1 else -1 end	case when a = b then 0 when a > b then 1 else -1 end
a.Contains('b')	a like '%b%'	a like '%b%'	a ilike'%b%'	a like '%b%'	a like '%b%'
a.EndsWith('b')	a like '%b'	a like '%b'	a ilike'%b'	a like '%b'	a like '%b'
a.IndexOf(b)	locate(a, b) - 1	locate(a, b) - 1	strpos(a, b) - 1	instr(a, b, 1, 1) - 1	instr(a, b) - 1
a.Length	char_length(a)	len(a)	char_length(a)	length(a)	length(a)
a.PadLeft(b, c)	lpad(a, b, c)	-	lpad(a, b, c)	lpad(a, b, c)	lpad(a, b, c)
a.PadRight(b, c)	rpad(a, b, c)	-	rpad(a, b, c)	rpad(a, b, c)	rpad(a, b, c)
a.Replace(b, c)	replace(a, b, c)	replace(a, b, c)	replace(a, b, c)	replace(a, b, c)	replace(a, b, c)
a.StartsWith('b')	a like 'b%'	a like 'b%'	a ilike'b%'	a like 'b%'	a like 'b%'
a.Substring(b, c)	substr(a, b, c + 1)	substring(a, b, c + 1)	substr(a, b, c + 1)	substr(a, b, c + 1)	substr(a, b, c + 1)
a.ToLower	lower(a)	lower(a)	lower(a)	lower(a)	lower(a)
a.ToUpper	upper(a)	upper(a)	upper(a)	upper(a)	upper(a)
a.Trim	trim(a)	trim(a)	trim(a)	trim(a)	trim(a)
a.TrimEnd	rtrim(a)	rtrim(a)	rtrim(a)	rtrim(a)	rtrim(a)
a.TrimStart	ltrim(a)	ltrim(a)	ltrim(a)	ltrim(a)	ltrim(a)
a.FirstOrDefault	substr(a,1,1)	substring(a,1,1)	substr(a,1,1)	substr(a,1,1)	substr(a,1,1)

使用字符串函数可能会出现性能瓶颈，虽然不推荐使用，但是作为功能库这也是不可缺少的功能之一。

日期

表达式	MySql	SqlServer	PostgreSQL	Oracle
DateTime.Now	now()	getdate()	current_timestamp	systimestamp
DateTime.UtcNow	utc_timestamp()	getutcdate()	(current_timestamp at time zone 'UTC')	sys_extract_utc(systimestamp)
DateTime.Today	curdate	convert(char(10),getdate(),120)	current_date	trunc(systimestamp)
DateTime.MaxValue	cast('9999/12/31 23:59:59' as datetime)	'9999/12/31 23:59:59'	'9999/12/31 23:59:59'::timestamp	to_timestamp('9999-12-31 23:59:59','YYYY-MM-DD HH24:MI:SS.FF6')
DateTime.MinValue	cast('0001/1/1 0:00:00' as datetime)	'1753/1/1 0:00:00'	'0001/1/1 0:00:00'::timestamp	to_timestamp('0001-01-01 00:00:00','YYYY-MM-DD HH24:MI:SS.FF6')
DateTime.Compare(a, b)	a - b	a - b	extract(epoch from a::timestamp-b::timestamp)	extract(day from (a-b))
DateTime.DaysInMonth(a, b)	dayofmonth(last_day(concat(a, '-', b, '-1')))	datepart(day, dateadd(day, -1, dateadd(month, 1, cast(a as varchar) + '-' + cast(b as varchar) + '-1')))	extract(day from (a
DateTime.Equals(a, b)	a = b	a = b	a = b	a = b
DateTime.IsLeapYear(a)	a%4=0 and a%100<>0 or a%400=0	a%4=0 and a%100<>0 or a%400=0	a%4=0 and a%100<>0 or a%400=0	mod(a,4)=0 AND mod(a,100)<>0 OR mod(a,400)=0
DateTime.Parse(a)	cast(a as datetime)	cast(a as datetime)	a::timestamp	to_timestamp(a,'YYYY-MM-DD HH24:MI:SS.FF6')
a.Add(b)	date_add(a, interval b microsecond)	dateadd(millisecond, b / 1000, a)	a::timestamp+(b
a.AddDays(b)	date_add(a, interval b day)	dateadd(day, b, a)	a::timestamp+(b
a.AddHours(b)	date_add(a, interval b hour)	dateadd(hour, b, a)	a::timestamp+(b
a.AddMilliseconds(b)	date_add(a, interval b*1000 microsecond)	dateadd(millisecond, b, a)	a::timestamp+(b
a.AddMinutes(b)	date_add(a, interval b minute)	dateadd(minute, b, a)	a::timestamp+(b
a.AddMonths(b)	date_add(a, interval b month)	dateadd(month, b, a)	a::timestamp+(b
a.AddSeconds(b)	date_add(a, interval b second)	dateadd(second, b, a)	a::timestamp+(b
a.AddTicks(b)	date_add(a, interval b/10 microsecond)	dateadd(millisecond, b / 10000, a)	a::timestamp+(b
a.AddYears(b)	date_add(a, interval b year)	dateadd(year, b, a)	a::timestamp+(b
a.Date	cast(date_format(a, '%Y-%m-%d') as datetime)	convert(char(10),a,120)	a::date	trunc(a)
a.Day	dayofmonth(a)	datepart(day, a)	extract(day from a::timestamp)	cast(to_char(a,'DD') as number)
a.DayOfWeek	dayofweek(a)	datepart(weekday, a) - 1	extract(dow from a::timestamp)	case when to_char(a)='7' then 0 else cast(to_char(a) as number) end
a.DayOfYear	dayofyear(a)	datepart(dayofyear, a)	extract(doy from a::timestamp)	cast(to_char(a,'DDD') as number)
a.Hour	hour(a)	datepart(hour, a)	extract(hour from a::timestamp)	cast(to_char(a,'HH24') as number)
a.Millisecond	floor(microsecond(a) / 1000)	datepart(millisecond, a)	extract(milliseconds from a::timestamp)-extract(second from a::timestamp)*1000	cast(to_char(a,'FF3') as number)
a.Minute	minute(a)	datepart(minute, a)	extract(minute from a::timestamp)	cast(to_char(a,'MI') as number)
a.Month	month(a)	datepart(month, a)	extract(month from a::timestamp)	cast(to_char(a,'FF3') as number)
a.Second	second(a)	datepart(second, a)	extract(second from a::timestamp)	cast(to_char(a,'SS') as number)
a.Subtract(b)	timestampdiff(microsecond, b, a)	datediff(millisecond, b, a) * 1000	(extract(epoch from a::timestamp-b::timestamp)*1000000)	a - b
a.Ticks	timestampdiff(microsecond, '0001-1-1', a) * 10	datediff(millisecond, '1970-1-1', a) * 10000 + 621355968000000000	extract(epoch from a::timestamp)*10000000+621355968000000000	cast(to_char(a,'FF7') as number)
a.TimeOfDay	timestampdiff(microsecond, date_format(a, '%Y-%m-%d'), a)	'1970-1-1 ' + convert(varchar, a, 14)	extract(epoch from a::time)*1000000	a - trunc(a)
a.Year	year(a)	datepart(year, a)	extract(year from a::timestamp)	年
a.Equals(b)	a = b	a = b	a = b	a = b
a.CompareTo(b)	a - b	a - b	a - b	a - b
a.ToString()	date_format(a, '%Y-%m-%d %H:%i:%s.%f')	convert(varchar, a, 121)	to_char(a, 'YYYY-MM-DD HH24:MI:SS.US')	to_char(a,'YYYY-MM-DD HH24:MI:SS.FF6')

时间

表达式	MySql(微秒)	SqlServer(秒)	PostgreSQL(微秒)	Oracle(Interval day(9) to second(7))
TimeSpan.Zero	0	0	-	0微秒
TimeSpan.MaxValue	922337203685477580	922337203685477580	-	numtodsinterval(233720368.5477580,'second')
TimeSpan.MinValue	-922337203685477580	-922337203685477580	-	numtodsinterval(-233720368.5477580,'second')
TimeSpan.Compare(a, b)	a - b	a - b	-	extract(day from (a-b))
TimeSpan.Equals(a, b)	a = b	a = b	-	a = b
TimeSpan.FromDays(a)	a * 1000000 * 60 * 60 * 24	a * 1000000 * 60 * 60 * 24	-	numtodsinterval(a*86400,'second')
TimeSpan.FromHours(a)	a * 1000000 * 60 * 60	a * 1000000 * 60 * 60	-	numtodsinterval(a*3600,'second')
TimeSpan.FromMilliseconds(a)	a * 1000	a * 1000	-	numtodsinterval(a/1000,'second')
TimeSpan.FromMinutes(a)	a * 1000000 * 60	a * 1000000 * 60	-	numtodsinterval(a*60,'second')
TimeSpan.FromSeconds(a)	a * 1000000	a * 1000000	-	numtodsinterval(a,'second')
TimeSpan.FromTicks(a)	a / 10	a / 10	-	numtodsinterval(a/10000000,'second')
a.Add(b)	a + b	a + b	-	a + b
a.Subtract(b)	a - b	a - b	-	a - b
a.CompareTo(b)	a - b	a - b	-	extract(day from (a-b))
a.Days	a div (1000000 * 60 * 60 * 24)	a div (1000000 * 60 * 60 * 24)	-	extract(day from a)
a.Hours	a div (1000000 * 60 * 60) mod 24	a div (1000000 * 60 * 60) mod 24	-	extract(hour from a)
a.Milliseconds	a div 1000 mod 1000	a div 1000 mod 1000	-	cast(substr(extract(second from a)-floor(extract(second from a)),2,3) as number)
a.Seconds	a div 1000000 mod 60	a div 1000000 mod 60	-	extract(second from a)
a.Ticks	a * 10	a * 10	-	(extract(day from a)86400+extract(hour from a)3600+extract(minute from a)60+extract(second from a))10000000
a.TotalDays	a / (1000000 * 60 * 60 * 24)	a / (1000000 * 60 * 60 * 24)	-	extract(day from a)
a.TotalHours	a / (1000000 * 60 * 60)	a / (1000000 * 60 * 60)	-	(extract(day from a)*24+extract(hour from a))
a.TotalMilliseconds	a / 1000	a / 1000	-	(extract(day from a)86400+extract(hour from a)3600+extract(minute from a)60+extract(second from a))1000
a.TotalMinutes	a / (1000000 * 60)	a / (1000000 * 60)	-
a.TotalSeconds	a / 1000000	a / 1000000	-	(extract(day from a)86400+extract(hour from a)3600+extract(minute from a)*60+extract(second from a))
a.Equals(b)	a = b	a = b	-	a = b
a.ToString()	cast(a as varchar)	cast(a as varchar)	-	to_char(a)

数学函数

表达式	MySql	SqlServer	PostgreSQL	Oracle
Math.Abs(a)	abs(a)	abs(a)	abs(a)
Math.Acos(a)	acos(a)	acos(a)	acos(a)	acos(a)
Math.Asin(a)	asin(a)	asin(a)	asin(a)	asin(a)
Math.Atan(a)	atan(a)	atan(a)	atan(a)	atan(a)
Math.Atan2(a, b)	atan2(a, b)	atan2(a, b)	atan2(a, b)	-
Math.Ceiling(a)	ceiling(a)	ceiling(a)	ceiling(a)	ceil(a)
Math.Cos(a)	cos(a)	cos(a)	cos(a)	cos(a)
Math.Exp(a)	exp(a)	exp(a)	exp(a)	exp(a)
Math.Floor(a)	floor(a)	floor(a)	floor(a)	floor(a)
Math.Log(a)	log(a)	log(a)	log(a)	log(e,a)
Math.Log10(a)	log10(a)	log10(a)	log10(a)	log(10,a)
Math.PI(a)	3.1415926535897931	3.1415926535897931	3.1415926535897931	3.1415926535897931
Math.Pow(a, b)	pow(a, b)	power(a, b)	pow(a, b)	power(a, b)
Math.Round(a, b)	round(a, b)	round(a, b)	round(a, b)	round(a, b)
Math.Sign(a)	sign(a)	sign(a)	sign(a)	sign(a)
Math.Sin(a)	sin(a)	sin(a)	sin(a)	sin(a)
Math.Sqrt(a)	sqrt(a)	sqrt(a)	sqrt(a)	sqrt(a)
Math.Tan(a)	tan(a)	tan(a)	tan(a)	tan(a)
Math.Truncate(a)	truncate(a, 0)	floor(a)	trunc(a, 0)	trunc(a, 0)

类型转换

表达式	MySql	SqlServer	PostgreSQL	Oracle	Sqlite
Convert.ToBoolean(a) \| bool.Parse(a)	a not in ('0','false')	a not in ('0','false')	a::varchar not in ('0','false','f','no')	-	a not in ('0','false')
Convert.ToByte(a) \| byte.Parse(a)	cast(a as unsigned)	cast(a as tinyint)	a::int2	cast(a as number)	cast(a as int2)
Convert.ToChar(a)	substr(cast(a as char),1,1)	substring(cast(a as nvarchar),1,1)	substr(a::char,1,1)	substr(to_char(a),1,1)	substr(cast(a as character),1,1)
Convert.ToDateTime(a) \| DateTime.Parse(a)	cast(a as datetime)	cast(a as datetime)	a::timestamp	to_timestamp(a,'YYYY-MM-DD HH24:MI:SS.FF6')	datetime(a)
Convert.ToDecimal(a) \| decimal.Parse(a)	cast(a as decimal(36,18))	cast(a as decimal(36,19))	a::numeric	cast(a as number)	cast(a as decimal(36,18))
Convert.ToDouble(a) \| double.Parse(a)	cast(a as decimal(32,16))	cast(a as decimal(32,16))	a::float8	cast(a as number)	cast(a as double)
Convert.ToInt16(a) \| short.Parse(a)	cast(a as signed)	cast(a as smallint)	a::int2	cast(a as number)	cast(a as smallint)
Convert.ToInt32(a) \| int.Parse(a)	cast(a as signed)	cast(a as int)	a::int4	cast(a as number)	cast(a as smallint)
Convert.ToInt64(a) \| long.Parse(a)	cast(a as signed)	cast(a as bigint)	a::int8	cast(a as number)	cast(a as smallint)
Convert.ToSByte(a) \| sbyte.Parse(a)	cast(a as signed)	cast(a as tinyint)	a::int2	cast(a as number)	cast(a as smallint)
Convert.ToString(a)	cast(a as decimal(14,7))	cast(a as decimal(14,7))	a::float4	to_char(a)	cast(a as character)
Convert.ToSingle(a) \| float.Parse(a)	cast(a as char)	cast(a as nvarchar)	a::varchar	cast(a as number)	cast(a as smallint)
Convert.ToUInt16(a) \| ushort.Parse(a)	cast(a as unsigned)	cast(a as smallint)	a::int2	cast(a as number)	cast(a as unsigned)
Convert.ToUInt32(a) \| uint.Parse(a)	cast(a as unsigned)	cast(a as int)	a::int4	cast(a as number)	cast(a as decimal(10,0))
Convert.ToUInt64(a) \| ulong.Parse(a)	cast(a as unsigned)	cast(a as bigint)	a::int8	cast(a as number)	cast(a as decimal(21,0))
Guid.Parse(a)	substr(cast(a as char),1,36)	cast(a as uniqueidentifier)	a::uuid	substr(to_char(a),1,36)	substr(cast(a as character),1,36)
Guid.NewGuid()	-	newid()	-	-	-
new Random().NextDouble()	rand()	rand()	random()	dbms_random.value	random()