我正在编写一个LINQ to SQL语句,我正在使用C#中带有ON
子句的普通内连接的标准语法。
如何在LINQ to SQL中表示以下内容:
select DealerContact.*
from Dealer
inner join DealerContact on Dealer.DealerID = DealerContact.DealerID
它类似于:
from t1 in db.Table1
join t2 in db.Table2 on t1.field equals t2.field
select new { t1.field2, t2.field3}
为表格提供合理的名称和字段会更好。 :)
更新
我认为对于您的查询,这可能更合适:
var dealercontacts = from contact in DealerContact
join dealer in Dealer on contact.DealerId equals dealer.ID
select contact;
既然您正在寻找联系人,而不是经销商。
试试这个 :
var data =(from t1 in dataContext.Table1 join
t2 in dataContext.Table2 on
t1.field equals t2.field
orderby t1.Id select t1).ToList();
var q=(from pd in dataContext.tblProducts join od in dataContext.tblOrders on pd.ProductID equals od.ProductID orderby od.OrderID select new { od.OrderID,
pd.ProductID,
pd.Name,
pd.UnitPrice,
od.Quantity,
od.Price,
}).ToList();
OperationDataContext odDataContext = new OperationDataContext();
var studentInfo = from student in odDataContext.STUDENTs
join course in odDataContext.COURSEs
on student.course_id equals course.course_id
select new { student.student_name, student.student_city, course.course_name, course.course_desc };
学生和课程表具有主键和外键关系
试试这个,
var dealer = from d in Dealer
join dc in DealerContact on d.DealerID equals dc.DealerID
select d;
var Data= (from dealer in Dealer join dealercontact in DealerContact on dealer.ID equals dealercontact.DealerID
select new{
dealer.Id,
dealercontact.ContactName
}).ToList();
var data=(from t in db.your tableName(t1)
join s in db.yourothertablename(t2) on t1.fieldname equals t2.feldname
(where condtion)).tolist();
var list = (from u in db.Users join c in db.Customers on u.CustomerId equals c.CustomerId where u.Username == username
select new {u.UserId, u.CustomerId, u.ClientId, u.RoleId, u.Username, u.Email, u.Password, u.Salt, u.Hint1, u.Hint2, u.Hint3, u.Locked, u.Active,c.ProfilePic}).First();
编写所需的表名,并初始化select以获取字段的结果。
来自DealerContrac的d1加入daler在dealerContrac上的d1.dealearid等于d2.dealerid选择新的{dealercontract。*}
在linq C#中内连接两个表
var result = from q1 in table1
join q2 in table2
on q1.Customer_Id equals q2.Customer_Id
select new { q1.Name, q1.Mobile, q2.Purchase, q2.Dates }
一个最好的例子
表名:TBL_Emp
和TBL_Dep
var result = from emp in TBL_Emp join dep in TBL_Dep on emp.id=dep.id
select new
{
emp.Name;
emp.Address
dep.Department_Name
}
foreach(char item in result)
{ // to do}
因为我更喜欢表达式链接语法,所以这是你如何做到这一点:
var dealerContracts = DealerContact.Join(Dealer,
contact => contact.DealerId,
dealer => dealer.DealerId,
(contact, dealer) => contact);
要扩展Clever Human的表达链语法answer:
如果你想在两个表连接在一起的字段上做某些事情(比如过滤或选择) - 而不只是这两个表中的一个 - 你可以在Join方法的最后一个参数的lambda表达式中创建一个新对象合并这两个表格,例如:
var dealerInfo = DealerContact.Join(Dealer,
dc => dc.DealerId,
d => d.DealerId,
(dc, d) => new { DealerContact = dc, Dealer = d })
.Where(dc_d => dc_d.Dealer.FirstName == "Glenn"
&& dc_d.DealerContact.City == "Chicago")
.Select(dc_d => new {
dc_d.Dealer.DealerID,
dc_d.Dealer.FirstName,
dc_d.Dealer.LastName,
dc_d.DealerContact.City,
dc_d.DealerContact.State });
有趣的部分是该示例的第4行中的lambda表达式:
(dc, d) => new { DealerContact = dc, Dealer = d }
...我们构造一个新的匿名类型对象,它具有DealerContact和Dealer记录的属性以及它们的所有字段。
然后,我们可以在过滤和选择结果时使用这些记录中的字段,如示例的其余部分所示,该示例使用dc_d
作为我们构建的匿名对象的名称,该对象同时具有DealerContact和Dealer记录作为其属性。
var results = from c in db.Companies
join cn in db.Countries on c.CountryID equals cn.ID
join ct in db.Cities on c.CityID equals ct.ID
join sect in db.Sectors on c.SectorID equals sect.ID
where (c.CountryID == cn.ID) && (c.CityID == ct.ID) && (c.SectorID == company.SectorID) && (company.SectorID == sect.ID)
select new { country = cn.Name, city = ct.Name, c.ID, c.Name, c.Address1, c.Address2, c.Address3, c.CountryID, c.CityID, c.Region, c.PostCode, c.Telephone, c.Website, c.SectorID, Status = (ContactStatus)c.StatusID, sector = sect.Name };
return results.ToList();
使用Linq Join运算符:
var q = from d in Dealer
join dc in DealerConact on d.DealerID equals dc.DealerID
select dc;
您创建了一个外键,LINQ-to-SQL为您创建了导航属性。每个Dealer
将有一个DealerContacts
的集合,您可以选择,过滤和操纵。
from contact in dealer.DealerContacts select contact
要么
context.Dealers.Select(d => d.DealerContacts)
如果您没有使用导航属性,那么您将错过LINQ-to-SQL的主要优势之一 - 映射对象图的部分。
基本上LINQ join运算符对SQL没有任何好处。即以下查询
var r = from dealer in db.Dealers
from contact in db.DealerContact
where dealer.DealerID == contact.DealerID
select dealerContact;
将导致SQL中的INNER JOIN
join对IEnumerable <>非常有用,因为它更有效:
from contact in db.DealerContact
每个经销商都会重新执行该条款但对于IQueryable <>则不是这样。加入也不太灵活。
实际上,通常最好不要加入linq。当有导航属性时,编写linq语句的一种非常简洁的方法是:
from dealer in db.Dealers
from contact in dealer.DealerContacts
select new { whatever you need from dealer or contact }
它转换为where子句:
SELECT <columns>
FROM Dealer, DealerContact
WHERE Dealer.DealerID = DealerContact.DealerID
使用LINQ joins执行内部连接。
var employeeInfo = from emp in db.Employees
join dept in db.Departments
on emp.Eid equals dept.Eid
select new
{
emp.Ename,
dept.Dname,
emp.Elocation
};