C# Linq 不在数据表上的选择中
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Linq not in select on datatable
提问by nLL
Hi i've got 2 data tables (bannedlist,countrylist), both contains list of country names and cods in columns cc and country. I am trying to do a query where i can select countries from countrylist table that are not in bannedlist table in order to create a 3rd table.
嗨，我有 2 个数据表（bannedlist、countrylist），它们都包含在 cc 和 country 列中的国家名称和鳕鱼列表。我试图做一个查询，我可以从countrylist 表中选择不在bannedlist 表中的国家，以创建第三个表。
Any ideas?
有任何想法吗？
I haven't got too far with this.
我还没有走得太远。
var ccList = ds.Tables[2].AsEnumerable();
var bannedCCList = ds.Tables[1].AsEnumerable();
var query = from r in ccList....
..
..
after trying
尝试后
var bannedCCList = ds.Tables[1].AsEnumerable();
var query = from r in ccList where !bannedCCList.Any(b => b["cc"] == r["cc"])select r;
i still get same country list. banned ones haven't been removed. here is more detail in order to explain more. not sure what i am doing wrong
我仍然得到相同的国家/地区列表。被禁止的没有被删除。为了解释更多，这里有更多细节。不知道我做错了什么
protected void BindCountryBan(string subd)
{
DataSet ds = new DataSet();
ds = new DB().CountryBan_GetSiteSettings();
BannedCountryListBox.DataSource = ds.Tables[1];
BannedCountryListBox.DataValueField = "cc";
BannedCountryListBox.DataTextField = "country";
BannedCountryListBox.DataBind();
//bind country list
var ccList = ds.Tables[2].AsEnumerable();
var bannedCCList = ds.Tables[1].AsEnumerable();
var query = from r in ccList where !bannedCCList.Any(b => b["cc"] == r["cc"])select r;
//var query = ccList.Except(bannedCCList);
//CountryListBox.DataSource = ds.Tables[2];
DataTable boundTable = query.CopyToDataTable<DataRow>();
CountryListBox.DataSource = boundTable;
CountryListBox.DataValueField = "cc";
CountryListBox.DataTextField = "country";
CountryListBox.DataBind();
}
采纳答案by dahlbyk
Except would work if you use it on sequences of the countries:
如果您在国家/地区的序列上使用它，则除外：
using System.Linq;
...
var ccList = from c in ds.Tables[2].AsEnumerable()
select c.Field<string>("Country");
var bannedCCList = from c in ds.Tables[1].AsEnumerable()
select c.Field<string>("Country");
var exceptBanned = ccList.Except(bannedCCList);
If you need the full rows where the countries aren't banned, you could try a left outer join:
如果您需要未禁止国家/地区的完整行，您可以尝试使用左外连接：
var ccList = ds.Tables[2].AsEnumerable();
var bannedCCList = ds.Tables[1].AsEnumerable();
var exceptBanned = from c in ccList
join b in bannedCCList
on c.Field<string>("Country") equals b.Field<string>("Country") into j
from x in j.DefaultIfEmpty()
where x == null
select c;
回答by Meta-Knight
Try this:
尝试这个：
var query = ccList.Except(bannedCCList);
回答by Sébastien Ros - MSFT
You can use the Except() LINQ extension method like this:
您可以像这样使用 except() LINQ 扩展方法：
var result = full.Except(banned);
However this will work fine with the default comparer of the contained type. Thus if you want to use a specific column like in your example, you might need another approach like:
但是，这对于包含类型的默认比较器可以正常工作。因此，如果您想使用示例中的特定列，则可能需要另一种方法，例如：
from r in ccList
where !bannedCCList.Any(b => b["cc"] == r["cc"])
select r;
Using Except() implies the references are the same in both collections, which I think is not the case with Tables, or correct me if I'm wrong.
使用 Except() 意味着两个集合中的引用是相同的，我认为 Tables 不是这种情况，或者如果我错了，请纠正我。
