我想创建递归类别。在使用join时不加载任何项目。我不想外连接,因为如果某个类别没有项目,请不要显示。如何解决此问题?
public string CategoryTree(int depth)
{
StringBuilder sBuilder;
using (DataContext db = new DataContext())
{
var query = from n in db.Categories join m in db.Products on n.CatId equals m.CategoryId where n.ParentId == depth select new{n, m};
sBuilder = new StringBuilder("<ul>");
foreach (var q in query)
{
sBuilder.Append("<li>");
sBuilder.Append("<a href='/Product/"+q.m.ProdId+">'"+q.n.Title+"</a>"+CategoryTree(q.n.CatId));
sBuilder.Append("</li>");
}
sBuilder.Append("</ul>");
}
return sBuilder.ToString();
}
Categories
+---------+---------------+------------+
| CatId | Title | ParentId |
+---------+---------------+------------+
| 1 | Electronic | NULL |
+---------+---------------+------------+
| 2 | Computer | NULL |
+---------+---------------+------------+
| 3 | Television | 1 |
+---------+---------------+------------+
| 4 | Led | 3 |
+---------+---------------+------------+
| 5 | Printer | 2 |
+---------+---------------+------------+
| 6 | Laser Printer | 5 |
+---------+---------------+------------+
Products
+---------+---------------+------------+
| ProdId | ProductName | CategoryId |
+---------+---------------+------------+
| 1 | Samsung LED | 4 |
+---------+---------------+------------+
| 2 | Sony LED TV | 4 |
+---------+---------------+------------+
答案 0 :(得分:0)
我将您的代码直接翻译成更可行的递归函数。我将它分成两部分以避免实例化多个DataContext
类(可能非常慢)。我还使用Linq to XML来使代码更安全。
public string CategoryTree(int? parentId)
{
using (DataContext db = new DataContext())
{
return CategoryTree(db, parentId).ToString();
}
}
private XElement CategoryTree(DataContext db, int? parentId)
{
return new XElement(
"ul",
from n in db.Categories
join m in db.Products on n.CatId equals m.CategoryId
where n.ParentId == parentId
select new XElement(
"li",
new XElement(
"a",
new XAttribute(
"href",
"/Product/" + m.ProdId),
n.Title),
CategoryTree(db, n.CatId)));
}
现在,当然,这不起作用,因为parentId
等于null
没有返回任何元素,因为您的数据在该级别没有任何产品,因此连接不返回任何内容。在获得产品之前,您必须构建类别树。
所以这就是你真正需要做的事情:
private XElement CategoryTree(DataContext db, int? parentId)
{
return new XElement(
"ul",
from n in db.Categories
where n.ParentId == parentId
select new XElement(
"li",
new XElement(
"span",
n.Title),
from m in db.Products
where m.CategoryId == n.CatId
select new XElement(
"div",
new XElement(
"a",
new XAttribute(
"href",
"/Product/" + m.ProdId),
m.ProductName)),
CategoryTree(db, n.CatId)));
}
现在构建以下树:
<ul>
<li>
<span>Electronic</span>
<ul>
<li>
<span>Television</span>
<ul>
<li>
<span>Led</span>
<div>
<a href="/Product/1">Samsung LED</a>
</div>
<div>
<a href="/Product/2">Sony LED TV</a>
</div>
<ul />
</li>
</ul>
</li>
</ul>
</li>
<li>
<span>Computer</span>
<ul>
<li>
<span>Printer</span>
<ul>
<li>
<span>Laser Printer</span>
<ul />
</li>
</ul>
</li>
</ul>
</li>
</ul>
但您不希望任何不包含产品的类别。但我们不知道在构建树时哪个不是,所以我们必须在之后进行修剪。
以下是我修剪的方法:
public string CategoryTree(int? parentId)
{
using (DataContext db = new DataContext())
{
var tree = CategoryTree(db, parentId);
Action<string> prune = tag =>
{
foreach (var empty in tree
.Descendants(tag)
.Where(ul => !ul.Descendants("a").Any())
.ToArray())
{
empty.Remove();
}
};
prune("ul");
prune("li");
return tree.ToString();
}
}
我首先修剪了无产品ul
标签,但这仍然可以保留无产品li
标签,因此我也必须修剪它们。
这是最终结果:
<ul>
<li>
<span>Electronic</span>
<ul>
<li>
<span>Television</span>
<ul>
<li>
<span>Led</span>
<div>
<a href="/Product/1">Samsung LED</a>
</div>
<div>
<a href="/Product/2">Sony LED TV</a>
</div>
</li>
</ul>
</li>
</ul>
</li>
</ul>
我希望这就是你要找的东西。