C# 使用实体框架连接多个表
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Joining multiple tables using Entity Framework
提问by
i am trying to join 3 tables using EF but it throws an error saying
我正在尝试使用 EF 连接 3 个表，但它抛出一个错误说
consider swaping conditions on either side of equals
can some one pls help
有人可以帮忙吗
var billdata = from billtotal in context.billTotals
join billcard in context.billClubcards
on billtotal.OrderID equals billcard.OrderID
join billtender in context.billTenders
on billtender.OrderID equals billtotal.OrderID
select billtotal;
采纳答案by Iain Galloway
The compiler error is quite correct:-
编译器错误是非常正确的：-
The name 'billtender' is not in scope on the left side of 'equals'. Consider swapping the expressions on either side of 'equals'.
The name 'billtender' is not in scope on the left side of 'equals'. Consider swapping the expressions on either side of 'equals'.
The table you're joining from needs to be on the left, the one you're joining onto needs to be on the right. Hence:-
你加入的那张桌子需要在左边，你加入的桌子需要在右边。因此：-
var billData =
from billtotal in context.billTotals
join billcard in context.billClubcards
on billtotal.OrderId equals billcard.OrderId
join billtender in context.billTenders
on billtotal.OrderId equals billtender.OrderId
select billtotal;
If you're wondering why, it's because the query syntax is just syntactic sugar for the underlying extension method:-
如果你想知道为什么，那是因为查询语法只是底层扩展方法的语法糖：-
context.billTotals
.Join(
context.billClubcards,
billtotal => billtotal.OrderId,
billclubcard => billclubcard.OrderId,
(billtotal, billclubcard) => billtotal)
.Join(
context.billTenders,
billtotal => billtotal.OrderId,
billtender => billtender.OrderId,
(billtotal, billtender) => billtotal);
Your original implementation would expand to:-
您的原始实施将扩展为：-
context.billTotals
.Join(
context.billClubcards,
billtotal => billtotal.OrderId,
billclubcard => billclubcard.OrderId,
(billtotal, billclubcard) => billtotal)
.Join(
context.billTenders,
billtotal => billtender.OrderId, // billtender isn't in scope!
billtender => billtotal.OrderId, // billtotal isn't in scope!
(billtotal, billtender) => billtotal);
回答by Aducci
The property of the table you are joining needs to be on the right side of equals
你加入的表的属性需要在equals的右边
switch
转变
from: on billtender.OrderID equals billtotal.OrderID
从： on billtender.OrderID equals billtotal.OrderID
to: on billtotal.OrderID equals billtender.OrderID
到： on billtotal.OrderID equals billtender.OrderID
