C# 我如何介绍一个;或;运算符转换为linq查询联接
将“or”运算符引入linq查询联接的语法是什么。它似乎不喜欢“| |”或“?我需要将一个外键与users表中两个可能的键连接起来C# 我如何介绍一个;或;运算符转换为linq查询联接,c#,sql,entity-framework,linq,linq-to-sql,C#,Sql,Entity Framework,Linq,Linq To Sql,将“or”运算符引入linq查询联接的语法是什么。它似乎不喜欢“| |”或“?我需要将一个外键与users表中两个可能的键连接起来 var thirdQuery = (from u in tbl_users join ua in tbl_userDocuments on (u.TransportUserID equals ua.fkDocumentID || u.WorkUserID equals ua.fkDocumentID) int
var thirdQuery = (from u in tbl_users
join ua in tbl_userDocuments on (u.TransportUserID equals ua.fkDocumentID
|| u.WorkUserID equals ua.fkDocumentID) into uaGroup
from uaTrans in uaGroup.DefaultIfEmpty()
join ul in tbl_user_logins on uaTrans.fkUserID equals ul.user_login_id_pk into ulGroup
如果没有或部分,则可以工作,但缺少额外的键
var thirdQuery = (from u in tbl_users
join ua in tbl_userDocuments on (u.TransportUserID equals ua.fkDocumentID) into uaGroup
from uaTrans in uaGroup.DefaultIfEmpty()
join ul in tbl_user_logins on uaTrans.fkUserID equals ul.user_login_id_pk into ulGroup
因此,您的数据库至少有两个表:
Users
和UserDocuments
。每个UserDocument
都有一个属性fkDocumentId
虽然您并没有这样说,但在我看来,这是表用户中元素的外键。显然,这个外键有时指的是User.TransportUserId
,有时指的是User.WorkUserId
你确定要这个吗?如果fkDocumentId
的值为10,它是指TransportId等于10的用户,还是指WorkUserId等于10的用户,或者两者都指
无论如何,如果您进行调查,您会发现您提供了两个密钥选择器:一个用于从用户中选择密钥,另一个用于从用户文档中选择密钥。当这两个键相等时,ResultSelector参数用于构造联接元素
问题在于“平等”一词。您必须确保您选择了密钥,并提供了一个IEqualityComparer,以便将密钥视为相等
另一个更简单的方法是创建一个新的连接扩展方法
IEnumerable<TResult> Join<TOuter, TInner, TKey, TResult> Join(
this IEnumerable<TSource> outer,
IEnumerable<TInner> inner,
Func<TOuter, TKey> outerKeySelector1,
Func<TOuter, TKey> outerKeySelector2,
Func<TInner, TKey> innerKeySelector,
Func<TOuter, TInner, TResult> resultSelector)
{
// make two lookup tables from Outer: one for key1 and one for key2:
var lookup1 = outer.ToLookup( outerElement => outerKeySelector1(outerElement));
var lookup2 = outer.ToLookup( outerElement => outerKeySelector2(outerElement));
// so if you have a TKey from the innerKeySelector, you can find if it matches key1 or key2
foreach (TInner innerElement in inner)
{
TKey innerKey = innerKeySelector(innerElement)
var matchingElementsKey1 = lookup1[innerKey];
var matchineElementsKey2 = lookup2[innerKey];
var allmatchingElements = matchingElementsKey1.Concat(matchingElementsKey2);
foreach(var matchingElement in allMatchingElements)
{
TResult result = resultSelector(matchingElement, innerElement);
yield return result;
}
}
}
请参见my-基本上,您必须执行交叉联接,并将OR条件放入中的位置。您确定要这样做吗?-别无选择,这是我们团队采用的非常大的遗留应用程序。fkDocumentId是指TransportId还是WorkUserId?它可以是或空。谢谢你花时间帮忙。
var result = tblUsers.Join(tblUserDocuments,
user => user.TransportUserId, // select outerKey1
user => user.WorkUserId, // select outerKey2
document => document.fkDocumentId, // select innerKey
// when inner key matches either outerKey1, or outerKey2, create one new object:
(user, document) => new
{
// Select the user documents that you want:
UserId = user.Id,
Name = user.Name,
...
// Select the document properties that you want:
DocumentId = document.Id,
Author = document.Author,
PublishedDate = document.Date,
...
})