标签：Name od 查询 联表 CustomId Id Select Left
用到的几个实体类
使用 CodeFirst 创建表
public class Custom
{
[SugarColumn(IsPrimaryKey = true, IsIdentity = true)]
public int Id { get; set; }
public string Name { get; set; }
}
public class Order
{
[SugarColumn(IsPrimaryKey = true, IsIdentity = true)]
public int Id { get; set; }
public string Name { get; set; }
public decimal Price { get; set; }
[SugarColumn(IsNullable = true)]
public DateTime CreateTime { get; set; }
[SugarColumn(IsNullable = true)]
public int CustomId { get; set; }
}
public class OrderDetail
{
[SqlSugar.SugarColumn(IsPrimaryKey = true, IsIdentity = true)]
public int ItemId { get; set; }
public int OrderId { get; set; }
public decimal? Price { get; set; }
[SqlSugar.SugarColumn(IsNullable = true)]
public DateTime? CreateTime { get; set; }
[SugarColumn(IsIgnore = true)]
public Order Order { get; set; }
}
public class ViewOrder : Order
{
public string CustomName { get; set; }
}
1.Join用法
1.1 语法糖1
优点：好理解，五个表以内的联表比较推荐
1.1.1 表和表的连接
List<ViewOrder> list = db.Queryable<Order>()
.LeftJoin<Custom>((o, cus) => o.CustomId == cus.Id) //若是多个条件 用 &&
.LeftJoin<OrderDetail>((o, cus, oritem) => o.Id == oritem.OrderId)
.Where((o, cus, oritem) => o.Id == 4 && oritem.Price == 50)
.Select((o, cus) => new ViewOrder { Id = o.Id, CustomName =cus.Name })
.ToList();
// SELECT `o`.`Id` AS `Id` , `cus`.`Name` AS `CustomName` FROM `Order` o
// Left JOIN `Custom` cus ON( `o`.`CustomId` = `cus`.`Id` )
// Left JOIN `OrderDetail` oritem ON( `o`.`Id` = `oritem`.`OrderId` )
// WHERE( `o`.`Id` = '4')
若将 .Select((o, cus) => new ViewOrder { Id = o.Id, CustomName =cus.Name }) 修改成.Select((o, cus) => new ViewOrder()) 那就是查询所有字段
1.1.2 表和Queryable的连接 (主表左连了一个由子查询组合的表)
var rightQueryable = db.Queryable<Custom>()
.LeftJoin<OrderDetail>((c, o) => c.Id == o.ItemId)
.Select(c => c);
var list = db.Queryable<Order>()
.LeftJoin(rightQueryable, (o, r) => o.CustomId == r.Id)
.Where(o=>o.Id==4)
.Select(o => o)
.ToList();
//SELECT o.* FROM `Order` o
//Left JOIN(SELECT c.*FROM `Custom` c Left JOIN `OrderDetail` o ON( `c`.`Id` = `o`.`ItemId` ) ) r ON ( `o`.`CustomId` = `r`.`Id` )
//WHERE( `o`.`Id` = '4')
1.1.3 Queryable和表的连接 (以一个子查询为主表关联其他表)
var queryable = db.Queryable<Order>();
var list = db.Queryable(queryable)
.LeftJoin<Custom>((o, c) => o.CustomId == c.Id)
.LeftJoin<OrderDetail>((o, c, od) => o.Id == od.OrderId).Select(o => o)
.Where(o => o.Id == 4)
.ToList();
//SELECT o.* FROM
//(SELECT * FROM (SELECT `Id`,`Name`,`Price`,`CreateTime`,`CustomId` FROM `Order` ) t ) o
//Left JOIN `Custom` c ON ( `o`.`CustomId` = `c`.`Id` )
//Left JOIN `OrderDetail` od ON ( `o`.`Id` = `od`.`OrderId` )
//WHERE ( `o`.`Id` = '4' )
1.2 语法糖2
优点：五个表以上用这种方式比较快捷缺点：不能套子查询( leftjoin(queryable) )
var list = db.Queryable<Order, Custom, OrderDetail>((o, c, od) => new JoinQueryInfos(
JoinType.Left, o.CustomId == c.Id,
JoinType.Left, o.Id == od.OrderId
))
.Select((o, c, od) => new { Id = o.Id, Name = o.Name, Cname = c.Name, Price = od.Price, CreateTime = od.CreateTime})
.ToList();
//SELECT `o`.`Id` AS `Id` , `o`.`Name` AS `Name` , `c`.`Name` AS `Cname` , `od`.`Price` AS `Price` , `od`.`CreateTime` AS `CreateTime` FROM `Order` o
//Left JOIN `Custom` c ON( `o`.`CustomId` = `c`.`Id` )
//Left JOIN `OrderDetail` od ON( `o`.`Id` = `od`.`OrderId` )
1.3 语法糖3
- 'inner join 可以用这种方式'
var list = db.Queryable<Order, Custom, OrderDetail>((o, c, od) => o.CustomId == c.Id && o.Id == od.OrderId)
.Select((o, c, od) => new { Id = o.Id, Name = o.Name, Cname = c.Name, Price = od.Price, CreateTime = od.CreateTime })
.ToList();
//SELECT `o`.`Id` AS `Id` , `o`.`Name` AS `Name` , `c`.`Name` AS `Cname` , `od`.`Price` AS `Price` , `od`.`CreateTime` AS `CreateTime`
//FROM `Order` o ,`Custom` c ,`OrderDetail` od
//WHERE(( `o`.`CustomId` = `c`.`Id` ) AND( `o`.`Id` = `od`.`OrderId` ))
2.Where用法
注意：写在 Select() 之前
.Where(o => o.Id == 4)
.Where((o, cus, oritem) => o.Id == 4 && oritem.Price == 50)
3.OrderBy用法
注意：写在 Select() 之前
.OrderBy(st => st.StudentId)
.OrderBy((st, sc) => sc.SchoolId, OrderByType.Desc)
4.GroupBy用法
注意：写在 Select() 之前
.GroupBy(it => it.Name)
.GroupBy((st, sc) => sc.SchoolId)
5.Select用法
连表必须加上 Select 不然会查询出重复列而报错，一般 Select() 写在 ToList() 之前
基础用法
//新类
.Select((o,i)=>new 类名{Id=o.Id,Name=o.Name,SchoolName=i.Name}).ToList();
//匿名对象
.Select((o,i)=>new {Id=o.Id,Name=o.Name,SchoolName=i.Name}).ToList();
5.1 返回匿名对象
5.1.1 一个一个字段赋值
参考 "1.2 语法糖2" 中 Select的写法
5.1.2 自动主表赋值 表.*
o.Id是表的任意一个属性， SelectAll是查询全部 o.*.SelectAll等同于SqlFunc.GetSelfAndAutoFill是个语法糖
var list = db.Queryable<Order, Custom, OrderDetail>((o, c, od) => new
JoinQueryInfos(
JoinType.Left, o.CustomId == c.Id,
JoinType.Left, o.Id == od.OrderId
))
.Select((o, c, od) => new {
d = o.Id.SelectAll(),
CName = c.Name,
Time = od.CreateTime })
.ToList();
//SELECT o.*, `c`.`Name` AS `CName` , `od`.`CreateTime` AS `Time` FROM `Order` o
//Left JOIN `Custom` c ON ( `o`.`CustomId` = `c`.`Id` )
//Left JOIN `OrderDetail` od ON ( `o`.`Id` = `od`.`OrderId` )
5.2 返回到新类
参考 "1.1.1 表和表的连接" 中 Select的写法
5.3 自动映射机制
Select用的是自动填充这样使用方便，高并发的地方还是写成上面那种方式
var list = db.Queryable<Order, Custom, OrderDetail>((o, c, od) => new
JoinQueryInfos(
JoinType.Left, o.CustomId == c.Id,
JoinType.Left, o.Id == od.OrderId
))
.Select<ViewOrder>()
.ToList();
//SELECT c.`Name` AS `CustomName`,o.`Id` AS `Id`,o.`Name` AS `Name`,o.`Price` AS `Price`,o.`CreateTime` AS `CreateTime`,o.`CustomId` AS `CustomId`
//FROM `Order` o
//Left JOIN `Custom` c ON( `o`.`CustomId` = `c`.`Id` )
//Left JOIN `OrderDetail` od ON( `o`.`Id` = `od`.`OrderId` )
5.4 更多用法
Select用法太多，这篇文章主要讲联表查询- 更多用法看官网
6.Full Join用法
标签：Name,od,查询,联表,CustomId,Id,Select,Left 来源： https://www.cnblogs.com/DotNeter-Hpf/p/16619624.html
本站声明： 1. iCode9 技术分享网（下文简称本站）提供的所有内容，仅供技术学习、探讨和分享； 2. 关于本站的所有留言、评论、转载及引用，纯属内容发起人的个人观点，与本站观点和立场无关； 3. 关于本站的所有言论和文字，纯属内容发起人的个人观点，与本站观点和立场无关； 4. 本站文章均是网友提供，不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属；如您发现该文章侵犯了您的权益，可联系我们第一时间进行删除； 5. 本站为非盈利性的个人网站，所有内容不会用来进行牟利，也不会利用任何形式的广告来间接获益，纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。