原本不支持 IQueryable 主要出於使用習慣的考慮，編寫代碼的智能總會提示出現一堆你不想使用的方法（對不起，我有強迫症），IQueryable 自身提供了一堆沒法實現的方法，還有外部入侵的擴展方法，嚴重影響編碼體驗。如下圖：
v1.4.0+ 版本請使用以下命令安裝（老版本不需要安裝）：
dotnet add package FreeSql.Extensions.Linq
特別說明
-
請盡量不要在 ISelect 模式下的使用 Linq 方法：GroupJoin、Select、SelectMany、Join、DefaultIfEmpty；
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如果一定要在 ISelect 中使用 .Select() 方法，請務必在 .ToList() 之前調用它；
IQueryable
FreeSql 提供強大的數據查詢對象 ISelect。
FreeSql.Extensions.Linq v1.4.0+ 實現了 IQueryable 查詢對象常用功能，以便在各框架中交互使用。
//將 ISelect 轉為 IQueryable
IQueryable<Student> queryable = fsql.Select<Student>().AsQueryable();
//Linq 方法查詢
var t1 = queryable.Where(a => a.id == 1).FirstOrDefault();
//將 IQueryable 還原為 ISelect
ISelect<Studeng> select = queryable.RestoreToSelect();
注意：IQueryable 的實現目前不支持 GroupBy，可以考慮使用 RestoreSelect 方法轉回 ISelect 進行查詢
Where
var t1 = (
from a in fsql.Select<Student>()
where a.id == item.id
select a
).ToList();
Select(指定字段)
var t1 = (
from a in fsql.Select<Student>()
where a.id == item.id
select new { a.id }
).ToList();
CaseWhen
var t1 = (
from a in fsql.Select<Student>()
where a.id == item.id
select new {
a.id,
a.name,
testsub = new {
time = a.age > 10 ? "大於" : "小於或等於"
}
}
).ToList();
Join
var t1 = (
from a in fsql.Select<Student>()
join b in fsql.Select<School>() on a.id equals b.StudentId
select a
).ToList();
var t2 = (
from a in fsql.Select<Student>()
join b in fsql.Select<School>() on a.id equals b.StudentId
select new { a.id, bid = b.id }
).ToList();
var t3 = (
from a in fsql.Select<Student>()
join b in fsql.Select<School>() on a.id equals b.StudentId
where a.id == item.id
select new { a.id, bid = b.id }
).ToList();
LeftJoin
var t1 = (
from a in fsql.Select<Student>()
join b in fsql.Select<School>() on a.id equals b.StudentId into temp
from tc in temp.DefaultIfEmpty()
select a
).ToList();
var t2 = (
from a in fsql.Select<Student>()
join b in fsql.Select<School>() on a.id equals b.StudentId into temp
from tc in temp.DefaultIfEmpty()
select new { a.id, bid = tc.id }
).ToList();
var t3 = (
from a in fsql.Select<Student>()
join b in fsql.Select<School>() on a.id equals b.StudentId into temp
from tc in temp.DefaultIfEmpty()
where a.id == item.id
select new { a.id, bid = tc.id }
).ToList();
From(多表查詢)
var t1 = (
from a in fsql.Select<Student>()
from b in fsql.Select<School>()
where a.id == b.StudentId
select a
).ToList();
var t2 = (
from a in fsql.Select<Student>()
from b in fsql.Select<School>()
where a.id == b.StudentId
select new { a.id, bid = b.id }
).ToList();
var t3 = (
from a in fsql.Select<Student>()
from b in fsql.Select<School>()
where a.id == b.StudentId
where a.id == item.id
select new { a.id, bid = b.id }
).ToList();
GroupBy(分組)
var t1 = (
from a in fsql.Select<Student>()
where a.id == item.id
group a by new {a.id, a.name } into g
select new {
g.Key.id, g.Key.name,
cou = g.Count(),
avg = g.Avg(g.Value.age),
sum = g.Sum(g.Value.age),
max = g.Max(g.Value.age),
min = g.Min(g.Value.age)
}
).ToList();
系列文章導航
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（二十四）Linq To Sql 語法使用介紹