Question

So after what felt like a lot of head banging, I have this query:

var widgets = db.Updates
      .Where(c => c.Sold.Equals(false))
      .GroupBy(c => c.widgetType)       
  .Select(x => x.OrderByDescending(y => y.TimeStamp).First()).ToList();
   widgetGrid.DataSource = widgets;
   widgetGrid.DataBind();

Now that I have all the sold widgets I need to add a join, let's say for instance that I want to join the the "Owner" table on ID in Owner equals ID in Widgets and then select Owner.Name and Widget.Style

For the life of me, I seem to be getting nowhere fast... anyone?

As always... I'm deeply grateful for anyone's time in helping me clear out my cobwebs.

Answer 1

You could do this:

var widgets = db.Updates
      .Where(c => !c.Sold)
      .GroupBy(c => c.widgetType)       
      .Select(x => x.OrderByDescending(y => y.TimeStamp).FirstOrDefault());

var result= (from w in widgets
             join o in db.Owners on w.OwnerId equals o.Id
             select new {o.Name, w.Style}).ToList();

Answer 2

you may also try:

var widgets = db.Updates
      .Where(c => c.Sold.Equals(false))
      .GroupBy(c => c.widgetType)       
      .Select(x => x.OrderByDescending(y => y.TimeStamp).First())
      .Join( db.Owners,
             u => u.ID,
             o => o.ID,
             (u, o) => new { o.Name, u.Style }).ToList();

Answer 3

如果我理解正确，你有两个序列：

一系列小部件，其中每个小部件都有一个属性ID。
您有一系列所有者，每个所有者都有一个属性ID

并且您想要具有匹配Id的序列和所有者的组合。

顺便说一句，您的小部件可能会有ownerId，或者您的所有者会有一个widgetId，但这不会影响解决方案。

联接如下：

var joinedTable = widgets.join(owners,  // join table widgets with table owners
    w => w.Id                 // from widgets take the Id
    o => o.Id                 // from owners also take the Id
    (widget, owner) => new    // where those Ids match, take the owner and the widget
    {                         // and take the properties you want
        Id = widget.Id,
        MyXProperty = owner.X,
        MyYProperty = widget.Y,

        Widget = widget,      // or take the complete widget and owner
        Owner = owner,
    });

顺便说一句，你写了＃34;现在我已经拥有了所有出售的小部件＆＃34;。从您的代码中我了解到每个更新都有一个布尔属性已售出，并且您希望所有更新在哪里！已售出。我假设你最终得到的产品没有出售？

谓词在where子句中的优点是什么？为什么不呢：

var widgets = db.Updates.Where(c => !c.Sold)
    .GroupBy // etc.

Add a Join to this LINQ Query?

3 个答案: