[英]LINQ: Left Outer Join with multiple conditions
I have two IEnumerables called BaseReportDefinitions and InputReportDefinitions. 我有两个IEnumerables,分别称为BaseReportDefinitions和InputReportDefinitions。 I need to do a left outer join where i want all the InputReportDefinitions and whichever BaseReportDefinitions that match.
我需要做一个左外部连接,在这里我想要所有的InputReportDefinitions和匹配的BaseReportDefinitions。 Both IEnumberables contain ReportDefinition objects that contain ParentName and ReportName properties that need to be used as the join key.
这两个IEnumberables都包含ReportDefinition对象,这些对象包含需要用作联接键的ParentName和ReportName属性。 I want to return the ReportDefinition object for each (in the case of BaseReportDefinition entry it may be null) in an anonymous object.
我想为匿名对象中的每个对象返回ReportDefinition对象(在BaseReportDefinition条目的情况下,它可能为null)。
I have seen many examples of linq outer joins and outer joins with a static second condition that often gets put into a where condition but nothing that really uses two conditions fully for the join. 我已经看到了很多linq外部联接和带有静态第二个条件的外部联接的示例,这些条件通常被置于where条件中,但是没有一个真正为联接完全使用两个条件的情况。
var items = inputReportDefinitions.GroupJoin(
baseReportDefinitions,
firstSelector => new {
firstSelector.ParentName, firstSelector.ReportName
},
secondSelector => new {
secondSelector.ParentName, secondSelector.ReportName
},
(inputReport, baseCollection) => new {inputReport, baseCollection})
.SelectMany(grp => grp.baseCollection.DefaultIfEmpty(),
(col, baseReport) => new
{
Base = baseReport,
Input = col.inputReport
});
I believe this ends up being a left outer join. 我相信这最终将成为左外部联接。 I don't know how to convert this monstrosity to a query statement.
我不知道如何将这种怪异转换为查询语句。 I think if you add
AsQueryable()
to the end it could be used in Linq-to-SQL, but honestly, I have little experience with that. 我认为,如果将
AsQueryable()
添加到最后,则可以在Linq-to-SQL中使用它,但是老实说,我对此几乎没有经验。
EDIT: I figured it out. 编辑:我想通了。 Much easier to read:
更容易阅读:
var otherItems = from i in inputReportDefinitions
join b in baseReportDefinitions
on new {i.ParentName, i.ReportName}
equals new {b.ParentName, b.ReportName} into other
from baseReport in other.DefaultIfEmpty()
select new
{
Input = i,
Base = baseReport
};
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