FreeSql (二十八)Lambda 表达式

时间:2019-09-17
本文章向大家介绍FreeSql (二十八)Lambda 表达式,主要包括FreeSql (二十八)Lambda 表达式使用实例、应用技巧、基本知识点总结和需要注意事项,具有一定的参考价值,需要的朋友可以参考一下。

FreeSql 支持功能丰富的表达式函数解析,方便程序员在不了解数据库函数的情况下编写代码。这是 FreeSql 非常特色的功能之一,深入细化函数解析尽量做到满意,所支持的类型基本都可以使用对应的表达式函数,例如 日期、字符串、IN查询、数组(PostgreSQL的数组)、字典(PostgreSQL HStore)等等。

IFreeSql fsql = new FreeSql.FreeSqlBuilder()
    .UseConnectionString(FreeSql.DataType.MySql, "Data Source=127.0.0.1;Port=3306;User ID=root;Password=root;Initial Catalog=cccddd;Charset=utf8;SslMode=none;Max pool size=10")
    .Build();

[Table(Name = "tb_topic")]
class Topic {
    [Column(IsIdentity = true, IsPrimary = true)]
    public int Id { get; set; }
    public int Clicks { get; set; }
    public int TestTypeInfoGuid { get; set; }
    public string Title { get; set; }
    public DateTime CreateTime { get; set; }
}

ISelect<Topic> select => fsql.Select<Topic>();

In查询

var t1 = select.Where(a => new[] { 1, 2, 3 }.Contains(a.testFieldInt)).ToSql();
//SELECT a.`Id`, a.`Clicks`, a.`TestTypeInfoGuid`, a.`Title`, a.`CreateTime` 
//FROM `tb_topic` a 
//WHERE (a.`Id` in (1,2,3))

查找今天创建的数据

var t2 = select.Where(a => a.CreateTime.Date == DateTime.Now.Date).ToSql();

SqlServer 下随机获取记录

var t3 = select.OrderBy(a => Guid.NewGuid()).Limit(1).ToSql();
//SELECT top 1 ...
//FROM [tb_topic] a 
//ORDER BY newid()

AOP拦截实现自定义解析

IFreeSql 对象有 Aop 成员,那里提供一堆 AOP 拦截的方法。其实有一个事件名称:ParseExpression。

/// <summary>
/// 可自定义解析表达式
/// </summary>
EventHandler<AopParseExpressionEventArgs> ParseExpression { get; set; }

public class AopParseExpressionEventArgs : EventArgs {
    public AopParseExpressionEventArgs(Expression expression, Func<Expression, string> freeParse) {
        this.Expression = expression;
        this.FreeParse = freeParse;
    }

    /// <summary>
    /// 内置解析功能,可辅助您进行解析
    /// </summary>
    public Func<Expression, string> FreeParse { get; }

    /// <summary>
    /// 需要您解析的表达式
    /// </summary>
    public Expression Expression { get; }
    /// <summary>
    /// 解析后的内容
    /// </summary>
    public string Result { get; set; }
}

FreeParse 是提供给外部的解析工具,它拥有 FreeSql 所有表达式功能,当您自定义解析的过程中遇到特别难处理的,可通过它快速解析出表达式的子部分内容。

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
a * b a * b a * b a * b a * b
a / b a / b a / b a / b a / b
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)

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

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)

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)
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()

原文地址:https://www.cnblogs.com/FreeSql/p/11531423.html