LINQ而不是IN子句

时间:2012-06-27 06:49:01

标签: c# linq datatable

我有2个数据表,一个是查找列表,另一个是数据。我在表中有许多列列保存数据,其中一列是查找数据表的外键列。

我想为所有查找行生成另一个列表,这些列表不会出现在包含基于外键列上的Id的数据的表中。

我想使用linq查询,或者对2个数据表起作用的东西

好像我正在做一个SQL NOT IN。

干杯

这是一些数据。我希望新列表中包含第4类和第5类。

           DataTable dtData = new DataTable( "Data" );
        dtData.Columns.Add( "Id", Type.GetType( "System.Int32" ) );
        dtData.Columns.Add( "CategoryId", Type.GetType( "System.Int32" ) );
        dtData.Columns.Add( "Qty", Type.GetType( "System.Int32" ) );
        dtData.Columns.Add( "Cost", Type.GetType( "System.Decimal" ) );
        dtData.Columns.Add( "TotalCost", Type.GetType( "System.Decimal" ) );
        dtData.Columns.Add( "TypeId", Type.GetType( "System.Int32" ) );

        dtData.Rows.Clear();

        DataRow row = dtData.NewRow();
        row["Id"] = 1;
        row["CategoryId"] = 1;
        row["Qty"] = 3;
        row["Cost"] = 237.00;
        row["TotalCost"] = 711.00;
        row["TypeId"] = DBNull.Value;
        dtData.Rows.Add( row );

        row = dtData.NewRow();
        row["Id"] = 2;
        row["CategoryId"] = 1;
        row["Qty"] = 5;
        row["Cost"] = 45.00;
        row["TotalCost"] = 225.00;
        row["TypeId"] = DBNull.Value;
        dtData.Rows.Add( row );

        row = dtData.NewRow();
        row["Id"] = 3;
        row["CategoryId"] = 3;
        row["Qty"] = 30;
        row["Cost"] = 1.00;
        row["TotalCost"] = 30.00;
        row["TypeId"] = 1;
        dtData.Rows.Add( row );

        row = dtData.NewRow();
        row["Id"] = 4;
        row["CategoryId"] = 2;
        row["Qty"] = 1;
        row["Cost"] = 15.00;
        row["TotalCost"] = 15.00;
        row["TypeId"] = 2;
        dtData.Rows.Add( row );

        row = dtData.NewRow();
        row["Id"] = 5;
        row["CategoryId"] = 1;
        row["Qty"] = 4;
        row["Cost"] = 3.00;
        row["TotalCost"] = 12.00;
        row["TypeId"] = 2;
        dtData.Rows.Add( row );

        DataTable dtlookup = new DataTable( "LookUp" );
        dtlookup.Columns.Add( "CategoryId", Type.GetType( "System.Int32" ) );
        dtlookup.Columns.Add( "Description", Type.GetType( "System.String" ) );

        dtlookup.Rows.Clear();

        DataRow lup = dtlookup.NewRow();
        lup["CategoryId"] = 1;
        lup["Description"] = "Category 1";
        dtlookup.Rows.Add( lup );

        lup = dtlookup.NewRow();
        lup["CategoryId"] = 2;
        lup["Description"] = "Category 2";
        dtlookup.Rows.Add( lup );

        lup = dtlookup.NewRow();
        lup["CategoryId"] = 3;
        lup["Description"] = "Category 3";
        dtlookup.Rows.Add( lup );

        lup = dtlookup.NewRow();
        lup["CategoryId"] = 4;
        lup["Description"] = "Category 4";
        dtlookup.Rows.Add( lup );

        lup = dtlookup.NewRow();
        lup["CategoryId"] = 5;
        lup["Description"] = "Category 5";
        dtlookup.Rows.Add( lup );


 var qqq = ( from r in dtlookup.AsEnumerable()
                    where !dtData.AsEnumerable().Any( b => b["CategoryId"] == r["CategoryId"] )
                    select r ).ToList();

2 个答案:

答案 0 :(得分:2)

我怀疑dahlbyk的答案对你很有帮助,所以我会把它贴在这里。

Linq not in select on datatable


除非在国家/地区的序列中使用它,否则会起作用:

使用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);

如果您需要未禁止国家/地区的完整行,则可以尝试左外连接:

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;

答案 1 :(得分:0)

您可以使用DataTable.AsEnumerable()扩展方法返回可枚举的数据集合。从那里,您可以使用LINQ有效地查询您的数据。

var myData = myDataTable.AsEnumerable()

编辑:如果您需要确定数据表中是否包含ID,则必须首先选择ID列表(因为您无法比较整个DataRow对象)。

bool idExists = dtData
                    .AsEnumerable()
                    .Select(item => (int) item["Id"])
                    .Contains(myId);