FreeSql （二十九）Lambda 表达式
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')
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；
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) |
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
（二十九）Lambda 表达式
FreeSql （二十九）Lambda 表达式的更多相关文章
- javaweb学习总结(二十九)——EL表达式
一.EL表达式简介 EL 全名为Expression Language.EL主要作用: 1.获取数据 EL表达式主要用于替换JSP页面中的脚本表达式,以从各种类型的web域 中检索java对象.获取数 ...
- [转]javaweb学习总结(二十九)——EL表达式
原文地址:https://www.cnblogs.com/xdp-gacl/p/3938361.html 一.EL表达式简介 EL 全名为Expression Language.EL主要作用: 1.获 ...
- javaweb(二十九)——EL表达式
一.EL表达式简介 EL 全名为Expression Language.EL主要作用: 1.获取数据 EL表达式主要用于替换JSP页面中的脚本表达式,以从各种类型的web域 中检索java对象.获取数 ...
- FreeSql （十九）多表查询
多表查询,常用的有联表 LeftJoin/InnerJoin/RightJoin ,这三个方法在上篇文章已经介绍过. 除了联表,还有子查询 Where Exists,和 Select 子表: IFre ...
- mysql进阶(二十九)常用函数
mysql进阶(二十九)常用函数 一.数学函数 ABS(x) 返回x的绝对值 BIN(x) 返回x的二进制(OCT返回八进制,HEX返回十六进制) CEILING(x) 返回大于x的最小整数值 EXP ...
- Bootstrap <基础二十九>面板（Panels）
Bootstrap 面板(Panels).面板组件用于把 DOM 组件插入到一个盒子中.创建一个基本的面板,只需要向 <div> 元素添加 class .panel 和 class .pa ...
- Web 开发人员和设计师必读文章推荐【系列二十九】
<Web 前端开发精华文章推荐>2014年第8期(总第29期)和大家见面了.梦想天空博客关注 前端开发 技术,分享各类能够提升网站用户体验的优秀 jQuery 插件,展示前沿的 HTML5 ...
- WCF技术剖析之二十九：换种不同的方式调用WCF服务[提供源代码下载]
原文:WCF技术剖析之二十九:换种不同的方式调用WCF服务[提供源代码下载] 我们有两种典型的WCF调用方式:通过SvcUtil.exe(或者添加Web引用)导入发布的服务元数据生成服务代理相关的代码 ...
- VMwarevSphere 服务器虚拟化之二十九 桌面虚拟化之安装View副本服务器
VMwarevSphere 服务器虚拟化之二十九 桌面虚拟化之安装View副本服务器 VMware View中高可用性可是一个必须要考虑的问题.在整个虚拟桌面环境中View Connection S ...
随机推荐
- git语句（后续补充）
如果你是windows用户,需要下载一个git应用程序,一路点就行,没有什么需要注意的地方 安装完成后在任一文件夹内右键都有显示,单击git bash here即可 简易的命令行入门教程: Git 全 ...
- 大陆争霸[SDOI2010]带限制最短路
只要你有无限个自爆机器人,你就能为所欲为 斯普林·布拉泽 [题目描述] 略 一句话题意: 杰森国有 \(N\) 个城市,由 \(M\) 条单向道 路连接.杰森国的首都是城市 \(N\).你只需摧毁杰森 ...
- 通过Blazor使用C#开发SPA单页面应用程序(3)
今天我们来看看Blazor开发的一些基本知识. 一.Blazor组件结构 Blazor中组件的基本结构可以分为3个部分,如下所示: //Counter.razor //Directives secti ...
- ASP.NET Core MVC 之依赖注入 Controller
ASP.NET Core MVC 控制器应通过构造函数明确地请求它们地依赖关系,在某些情况下,单个控制器地操作可能需要一个服务,在控制器级别上的请求可能没有意义.在这种情况下,也可以将服务作为 Ac ...
- java多线程与并发（基础篇）
一.进程与线程 进程:是代码在数据集合上的一次运行活动,是系统进行资源分配和调度的基本单位. 线程:是进程的一个执行路径,一个进程中至少有一个线程,进程中的多个线程共享进程的 资源. 虽然系统是把资源 ...
- Go_笔试题记录-指针与值类型实现接口的区别
1.如果Add函数的调用代码为: func main() { var a Integer = 1 var b Integer = 2 var i interface{} = &a sum := ...
- Elasticsearch核心技术(1)--- Docker容器中运行ES、Kibana、Cerebro
Docker容器中运行ES,Kibana,Cerebro和Logstash安装与数据导入ES 想加强ES有关的知识,看了阮一鸣老师讲的<Elasticsearch核心技术与实战>收获很大, ...
- 技术改变生活| 免费看VIP视频，屏蔽广告，解锁新姿势！
说到这个,我就忍不住的要介绍一下今天的主角 Tampermonkey 了.Tampermonkey 是一款免费的浏览器扩展和最为流行的用户脚本管理器,它适用于Chrome, Microsoft Edg ...
- Delphi - Indy TIdFTP控件实现文件的上传和下载
FTP信息保存和获取 我们在做FTP相关开发时,为方便后续FTP切换,一般先把FTP账户信息保存到数据库表中,在使用时再通过Query获取出来. 一般通过如下方式获取到FTP相关信息,代码如下: // ...
- openSession 与 getCurrentSession的区别
1.openSession 每一次获得的是一个全新的session对象,而getCurrentSession获得的是与当前线程绑定的session对象 package cn.kiwifly.view; ...