使用LINQ通过联接从两个表中获取信息

Question

I have a linq statement to populate two labels. The thing is, this information comes from two tables. I Have a join to join the two tables, except i cant get my Terms and Conditions from my Campaign table. Its only picking up the RedemptionLog table columns. Anyone to help with this?

MSCDatabaseDataContext MSCDB = new MSCDatabaseDataContext();
            var q = from row in MSCDB.Tbl_RedemptionLogs 
                    join d in MSCDB.Tbl_Campaigns on row.CampaignId equals d.CampaignId
                    orderby row.VoucherCode descending
                    select row;

            var SeshVoucherDisplay = q.First();

            lblCode.Text = SeshVoucherDisplay.VoucherCode;
            lblTerms.Text = SeshVoucherDisplay

For the SeshVoucherDisplay variable, it only picks up from the RedemptionLogs table, yet i did a join? Any help?

Answer 1

Try something like this :

var SupJoin = from row in MSCDB.Tbl_RedemptionLogs
              join d in MSCDB.Tbl_Campaigns on row.CampaignId equals d.CampaignId
              orderby row.VoucherCode descending
              select new { Id = row.ID, SupplierName = row.SupplierName, 
               CustomerName = d.CompanyName };

The column names are just for example purpose. Put your own there. And thereafter, you can apply First on it and use that particular variable.

Hope this helps.

Answer 2

Well, by writing select row you asked LINQ to give back to you only row .

If you want both elements, you need to ask for both of them, eg by writing select new { row, d } .

In this example

var foo =
    new []
    {
        new { Id = 1, Name = "a" },
        new { Id = 2, Name = "b" },
        new { Id = 3, Name = "c" }
    };

var bar =
    new []
    {
        new { Id = 1, Name = "d" },
        new { Id = 2, Name = "e" },
        new { Id = 3, Name = "f" }
    };

var baz =
    from a in foo
    join b in bar on a.Id equals b.Id
    select new { a, b };

var qux =
    from a in foo
    join b in bar on a.Id equals b.Id
    select new { a, b };

In baz you'll find only a list of foo s, in qux you'll find a list of both foo s and their bar .

Answer 3

Try this:

var query = (from row in MSCDB.Tbl_RedemptionLogs
                                 join d in MSCDB.Tbl_Campaigns on row.CampaignId equals d.CampaignId)
                                 orderby row.VoucherCode descending
                                 select new
                                 {
                                    columnname = row.columnname
                                 });

Answer 4

When writing select row you relate to the row you defined in from row in MSCDB.Tbl_RedemptionLogs .

However if you want the data from both tables you have to write something similar to this:

select new { 
    // the properties of row
    Redemption = row.redemption, 
    // the properties of d
    Campaign = d.CampaignID // alternativly use may also use row.CampaignID, but I wanted to show you may acces all the members from d also 
}