Question

我需要将最近的动作（如果有的话）与每个节点相关联。下面的SQL查询对我这样做：

select n.*, o.* from Nodes n
left outer join (
  select min(s.ActionAt) as ActionAt, min(s.Ahead) as Ahead, s.NodeId
  from SuggestedActions s
  group by s.NodeId
) o1 
  on o1.NodeId=n.Id
left outer join SuggestedActions o 
  on o.NodeId=o1.NodeId and o.ActionAt=o1.ActionAt and o.Ahead=o1.Ahead

但我无法使用LINQ制定相同的查询。我已经离开了选择最近操作的联接，我不知道如何继续加入更多数据：

from node in db.Nodes
join no in db.SuggestedActions on node.Id equals no.NodeId into no1
from o1 in no1.DefaultIfEmpty()
group o1 by node.Id into go1
select new {
  NodeId = go1.Key,
  ActionAt = go1.Min(c => c.ActionAt),
  Ahead = go1.Min(c => c.Ahead)
} ...

Answer 1

试试这个，它没有经过测试，但可能会给你一个方向：

var nodeActions = from node in db.Nodes
    join action in db.SuggestedActions on node.Id equals action.NodeId into actions
    from action in actions.DefaultIfEmpty()
    select new { node, action };

var minNodes = from nodeAction in nodeActions
    group nodeAction by nodeAction.node.Id
    into groupedActions
    select new
    {
        NodeId = groupedActions.Key,
        ActionAt = groupedActions.Min(c => c.action.ActionAt),
        Ahead = groupedActions.Min(c => c.action.Ahead)
    };

var result = from minNode in minNodes
    join nodeAction in nodeActions on new { Id = minNode.NodeId, minNode.ActionAt, minNode.Ahead }
        equals new { nodeAction.node.Id, nodeAction.action.ActionAt, nodeAction.action.Ahead } into nodeActionJ
    from action in nodeActionJ
    select action;

级联左连接LINQ

1 个答案: