LINQ-完全外部联接

我不知道这是否涵盖所有情况，从逻辑上讲似乎是正确的。这个想法是采用左外部联接和右外部联接，然后取结果的并集。

var firstNames = new[]{    new { ID = 1, Name = "John" },    new { ID = 2, Name = "Sue" },};var lastNames = new[]{    new { ID = 1, Name = "Doe" },    new { ID = 3, Name = "Smith" },};var leftOuterJoin =    from first in firstNames    join last in lastNames on first.ID equals last.ID into temp    from last in temp.DefaultIfEmpty()    select new    {        first.ID,        FirstName = first.Name,        LastName = last?.Name,    };var rightOuterJoin =    from last in lastNames    join first in firstNames on last.ID equals first.ID into temp    from first in temp.DefaultIfEmpty()    select new    {        last.ID,        FirstName = first?.Name,        LastName = last.Name,    };var fullOuterJoin = leftOuterJoin.Union(rightOuterJoin);

由于它是在LINQ to Objects中编写的，因此按其编写的方式工作。如果是LINQ to
SQL或其他，则查询处理器可能不支持安全导航或其他操作。您必须使用条件运算符有条件地获取值。

即

var leftOuterJoin =    from first in firstNames    join last in lastNames on first.ID equals last.ID into temp    from last in temp.DefaultIfEmpty()    select new    {        first.ID,        FirstName = first.Name,        LastName = last != null ? last.Name : default,    };