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 | 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 |
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) | 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() |
系列文章导航
（一）入门
（二）自动迁移实体
（三）实体特性
（四）实体特性 Fluent Api
（五）插入数据
（六）批量插入数据
（七）插入数据时忽略列
（八）插入数据时指定列
（九）删除数据
（十）更新数据
（十一）更新数据 Where
（十二）更新数据时指定列
（十三）更新数据时忽略列
（十四）批量更新数据
（十五）查询数据
（十六）分页查询
（十七）联表查询
（十八）导航属性
（十九）多表查询
（二十）多表查询 WhereCascade
（二十一）查询返回数据
（二十二）Dto 映射查询
（二十三）分组、聚合
（二十四）Linq To Sql 语法使用介绍
（二十五）延时加载
（二十六）贪婪加载 Include、IncludeMany、Dto、ToList
（二十七）将已写好的 SQL 语句，与实体类映射进行二次查询
（二十八）事务
（二十九）Lambda 表达式
（三十）读写分离
（三十一）分区分表
（三十二）Aop
（三十三）CodeFirst 类型映射
（三十四）CodeFirst 迁移说明
（三十五）CodeFirst 自定义特性
