linq2db.EntityFrameworkCore 是一个ef core的插件，对linq语法的扩展

对复杂的sql都有很好的支持，他是基于linq2db （provided by LINQ To DB）

如果你使用了linq2db的语法扩展那么你必须使用下面的方法进行查询

 // ToLinqToDB是必须的

 var temp = qry.ToLinqToDB().ToList();

---

下面是 linq2db 的冰山一角

JOIN

1. InnerJoin

 var qry = from t1 in db.T

           from t2 in db.T2.InnerJoin(m => m.T1Id == t1.Id)

2.LeftJoin

 var qry = from t1 in db.T

           from t2 in db.T2.LeftJoin(m => m.T1Id == t1.Id)

3.RightJoin

 var qry = from t1 in db.T

           from t2 in db.T2.RightJoin(m => m.T1Id == t1.Id)

---

SUM

// 相比于原来linq，简洁了很多。

var qry = from t1 in db.T

          from t2 in db.T2.LeftJoin(m => m.T1Id == t1.Id)

          select Sql.Ext.Sum(t1.Type == "A" ? t1.Number * (t1.SalePrice-t2.OriginalPrice) : 0).ToValue();

CountExt

//我要查t2中不重复的 t1的Id有多少个

var qry = from t1 in db.T

          from t2 in db.T2.LeftJoin(m => m.T1Id == t1.Id)

          where t1.some==''

          group new {t1,t2} by t2.some into g

          select new

          {

              //相当于sql Count(distinct t2.T1Id)

              Number = g.CountExt(m => m.t2.T1Id, Sql.AggregateModifier.Distinct)

          }

对于一些sql函数的支持

DatePart

var qry = from t1 in db.T

                    where t1.SaleDate > beginTime

                    group t1 by Sql.DatePart(Sql.DateParts.Month, t1 .SaleDate) into g

                    select new

                    {

                        Month = g.Key,

                        FlowAmount = g.Sum(m => m.SaleWay == "A" ? Sql.Abs(m.Number * m.SalePrice) : 0) -

                                     g.Sum(m => m.SaleWay == "B" ? Sql.Abs(m.Number * m.SalePrice) : 0)

                    };

当然还有更多的扩展方法，分别位于

包含于 Sql ， Sql.Ext，AnalyticFunctions 中

linq2db文档 : https://linq2db.github.io/index.html

当然还有批量更新的操作

如果是需要使用，那么最好再程序开始时运行以下代码

//因为他是幂等的 ，所以可以多次运行

LinqToDBForEFTools.Initialize();

以下代码都是从github上抄下来的。

// fast insert big recordsets

ctx.BulkCopy(new BulkCopyOptions {...}, items);

// query for retrieving products that do not have duplicates by Name

var query =

	from p in ctx.Products

	from op in ctx.Products.LeftJoin(op => op.ProductID != p.ProductID && op.Name == p.Name)

	where Sql.ToNullable(op.ProductID) == null

	select p;

// insert these records into the same or another table

query.Insert(ctx.Products.ToLinqToDBTable(), s => new Product { Name = s.Name ... });

// update these records by changing name based on previous value

query.Update(prev => new Product { Name = "U_" + prev.Name ... });

// delete records that matched by query

query.Delete();