Sql 使用方法语法的LINQ中的JOIN和LEFT JOIN等价

我正在将一个SQL查询转换为LINQ，它创建一个具有1对1映射的左连接，并且必须使用方法语法。我一直在努力做到这一点。我可以用Lambda语法来做。下面是我尝试运行的示例查询。它们不是实际的代码。有人能指出我做错了什么吗

SQL:

林克：

---

加入。。。进入

成为一个

GroupJoin

，来自的第二个

成为一个
SelectMany
：

var linq_query = Item
    .GroupJoin(
        item_status.Where(x => x.selected_item_status.FLAGGED), // EDIT: Where clause moved here.
        selected_item => selected_item.ID,
        selected_item_status => selected_item_status.itemID,
        (selected_item, joined) => new
        {
            selected_item,
            statuses = joined.DefaultWithEmpty(),
        })
    .SelectMany(x => x.statuses.Select(selected_item_status => new
    {
        x.selected_item,
        selected_item_status,
    }))
    // EDIT: Removed where clause.
    .ToList();

它看起来像是
，其中
使左侧外部联接变得不必要，因为空状态将被过滤掉

编辑：否，在查看SQL时，您的LINQ查询似乎有点不正确。应该是：

var linq_query = (
    from selected_item in item
    join selected_item_status
        in (
            from status in item_status
            where status.FLAGGED
            select status)
        on selected_item.ID equals item_status.itemID into joined
    from item_status in joined.DefaultIfEmpty()
    select new {selected_item, selected_item_status}).ToList();

如果代码不是真正的代码，我们如何告诉您代码有什么问题？我们还可以查看类
项目
，
项目状态
，以及您将匿名类型列表放入的类吗？谢谢！我从来没有想到在连接表上有where子句。谢谢你-我只是得到了这个答案，这正是我想要的。在我看来，将where子句放在那个位置更类似于SQl而不是非方法语法linq。
var linq_query = Item
    .GroupJoin(
        item_status.Where(x => x.selected_item_status.FLAGGED), // EDIT: Where clause moved here.
        selected_item => selected_item.ID,
        selected_item_status => selected_item_status.itemID,
        (selected_item, joined) => new
        {
            selected_item,
            statuses = joined.DefaultWithEmpty(),
        })
    .SelectMany(x => x.statuses.Select(selected_item_status => new
    {
        x.selected_item,
        selected_item_status,
    }))
    // EDIT: Removed where clause.
    .ToList();

var linq_query = (
    from selected_item in item
    join selected_item_status
        in (
            from status in item_status
            where status.FLAGGED
            select status)
        on selected_item.ID equals item_status.itemID into joined
    from item_status in joined.DefaultIfEmpty()
    select new {selected_item, selected_item_status}).ToList();