LinqToSql
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原本不支持 IQueryable 主要出于使用习惯的考虑，编写代码的智能总会提示出现一堆你不想使用的方法（对不起，我有强迫症），IQueryable 自身提供了一堆没法实现的方法，还有外部入侵的扩展方法，严重影响编码体验。如下图：
v1.4.0+ 版本请使用以下命令安装（老版本不需要安装）：
dotnet add package FreeSql.Extensions.Linq
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请尽量不要在 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，请务必在 .ToList() 之前调用它；
FreeSql 提供强大的数据查询对象 ISelect。
FreeSql.Extensions.Linq v1.4.0+ 实现了 IQueryable 查询对象常用功能，以便在各框架中交互使用。
//将 ISelect 转为 IQueryable IQueryable<Student> queryable = fsql.Select<Student>().AsQueryable(); //Linq 方法查询 var t1 = queryable.Where(a => a.id == 1).FirstOrDefault(); //将 IQueryable 还原为 ISelect ISelect<Studeng> select = queryable.RestoreToSelect();注意：IQueryable 的实现目前不支持 GroupBy，可以考虑使用 RestoreSelect 方法转回 ISelect 进行查询
var t1 = ( from a in fsql.Select<Student>() where a.id == item.id select a ).ToList();var t1 = ( from a in fsql.Select<Student>() where a.id == item.id select new { a.id } ).ToList();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 ? "大于" : "小于或等于" } } ).ToList();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();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();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();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();