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/***只查一列***/
//First: select top 1 id
SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Select(s => s.Id)     
//max例1: 
SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Max(s => s.Id)
//max例2: 
SqlFunc.Subqueryable<School>()..Where(s=>s.Id==st.Id).Select(s=>SqlFunc.AggregateMax(s.Id))      
//min:
SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Min(s => s.Id)
//avg:
SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Avg(s => s.Id)
//count:
SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Count()
//sum:
SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Sum(s => s.num)
//去重后汇总数量
SqlFunc.Subqueryable<School>().Where(s => z.Id == st.Id).Select(s=>SqlFunc.AggregateDistinctCount(s.Name))
//逗号分割列 
SqlFunc.Subqueryable<Order>().Where(z=>z.Id==it.Id).SelectStringJoin(z => z.Name, ",")
//完整用例：看标题8/***返回List或者实体***/
新功能：5.1.3.36
//SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList()
//SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList(it=>new Class(){ Name=it.Name})
//更多看标题4/***返回单个实体***/
//SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).First() 
//更多看标题9/***IN、Not in、Exists、Not Exists***/
//看标题2

var getAll = db.Queryable<Student, School>((st, sc) => new JoinQueryInfos(JoinType.Left,st.Id==sc.Id) )
.Where(st => st.Id == SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Select(s => s.Id))
.ToList();/*生成的MYSQL语句，如果是SqlServer就是TOP 1
SELECT `st`.`ID`,`st`.`SchoolId`,`st`.`Name`,`st`.`CreateTime` FROM `STudent` st Left JOIN `School` sc ON ( `st`.`ID` = `sc`.`Id` )  WHERE ( `st`.`ID` =(SELECT `Id` FROM `School` WHERE ( `Id` = `st`.`ID` ) limit 0,1))
*/

//等同于IN
var getAll7 = db.Queryable<Student>()
.Where(it => SqlFunc.Subqueryable<School>().Where(s =>s.Id==it.Id).Any()).ToList();/*生成的SQL(等于同于it.id in(select id from school)只是写法不一样
SELECT `ID`,`SchoolId`,`Name`,`CreateTime` FROM `STudent` it 
WHERE (EXISTS ( SELECT * FROM `School` WHERE ( `Id` = `it`.`ID` ) )) 
*///等同于NOT IN
var getAll8 = db.Queryable<Student>().Where(it => 
SqlFunc.Subqueryable<School>().Where(s => s.Id == it.Id).NotAny()).ToList();/*生成的SQL
SELECT `ID`,`SchoolId`,`Name`,`CreateTime` FROM `STudent` it  
WHERE (NOT EXISTS ( SELECT * FROM `School` WHERE ( `Id` = `it`.`ID` ) ))
*///搜索关键词：exits

db.Queryable<Order>()
.Where(it=>it.Id==SqlFunc.Subqueryable<Custom>().GroupBy(z=>z.OrderId).Select(z=>z.OrderId)).ToList()//Sql
//SELECT [Id],[Name] FROM [Order]  
// WHERE  [Id] in ((SELECT [OrderId] FROM [Custom] GROUP BY [OrderId]))

db.Queryable<Order>().In(it=>it.Id,db.Queryable<Order>().Skip(1).Take(100).Select(it=>it.Id)).ToList();

 string sql=" (select top 1 id from [Order] ) ";var list = db.Queryable<Order>().Select(it => new{name=it.Name,customName= SqlFunc.MappingColumn<string>(sql)//老版本MappingColumn(default(string),sql) }).ToList();//如果存在SQL拼接将SQL提取到外面在传进来，有些VS拼接会有问题

SELECT  [Name] AS [name] , (select top 1 id from [Order] ) AS [customName] FROM [Order]

//请升级到 5.1.3.36+ db.Queryable<Order>().Select(it => new{CustomId = it.CustomId,OrderId = it.Id,OrderName = it.Name,CustomList = SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList()}).ToList();//也可以DTOSqlFunc.Subqueryable<Custom>().Where(c=> c.Id == it.CustomId).ToList(c=> new Class(){ Name=c.Name}) //转成DTO//注意：where  ToList里面 c 的别名要一致//只查List<string>这种集合 
SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList(c=>c.Name)//最新版本//自动DTO 5.1.4.70
SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList<DTO>()
SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList(it=>new DTO(){},true);//和Queryable类似

var treeRoot=db.Queryable<Tree>().ToList();//可以联表查询，只要返回List中有关联字段就可以//填充子对象 
//原理： 数据库一次读取 In (list[0].id,list[1].id,list[2].id...) 内存分配到对应Child
//所以无论集合多少条记录  ThenMapper 只会操作一次库  
db.ThenMapper(treeRoot, item =>{   //用例1：简单填充  //参数解释：子表的ParentId和主表的Id 进行关联查询（有Select写到SetContext前面）//可以额外加Where写SetContext前面，但是不能带有item对象,item要写SetContext里面item.Child = db.Queryable<Tree>().SetContext(x => x.ParentId, () => item.Id, item).ToList();//用例2：可以多属性//item.Child=xxxx//item.Parent=xxxx//用例3：类型转换类转成DTO （注意：Select中的关联字段要赋值）//item.Child = db.Queryable<Tree>()//         .Select(it=>new ViewTree(){ParentId=x.ParentId,Id=i.Id,Name=it.Name }) //         .SetContext(x => x.ParentId, () => item.Id, item).ToList();//用例4：联表填充//item.Child=db.Queryable<Tree>()//.LeftJoin<Tree>((i,y)=>i.ParentId==y.Id)//.Select((i,y)=>new viewmodel(){ Parentid=i.Parentid..........})//.SetContext(x => x.ParentId, () => item.Id, item).ToList();});//异步
var treeRoot=await db.Queryable<Tree>().ToListAsync(); 
await db.ThenMapperAsync(treeRoot, async item =>
{   //给集合赋值  参数解释  子表的ParentId和主表的Id 进行关联查询item.Child =await db.Queryable<Tree>().SetContextAsync(x=>x.ParentId,()=>item.Id, item);
});//无限层级
var treeRoot=db.Queryable<Tree>().Where(it => it.Id == 1).ToList();
//第一层
db.ThenMapper(treeRoot, item =>
{item.Child = db.Queryable<Tree>().SetContext(x => x.ParentId, () => item.Id, item).ToList();
});
//第二层
db.ThenMapper(treeRoot.SelectMany(it=>it.Child), it =>
{it.Child = db.Queryable<Tree>().SetContext(x => x.ParentId, () => it.Id, it).ToList();
});//跨库 
var mydb=db.GetConnection(1);
mydb.ThenMapper(root,item=>{...});

var list = db.Queryable<Order>().Where(it =>SqlFunc.Subqueryable<A>() .LeftJoin<B>((i,y)=>i.ItemId==y.ItemId).InnerJoin<C>((i,y,z) => i.ItemId == z.ItemId).Where((i,y,z)=>i.ItemId==it.Aid).Any()).ToList();
//新版本支持了Subquery.join使用 Where<T1,T2>((x,y)=> x.id==y.id)