Question

我想使用id作为主键，并且必须将2个表与此主键链接。结果必须像这样

首先检查主键是否存在于第二个表中
根据密钥

代码：

 DataTable dt1 = new DataTable("Table1");
    dt1.Columns.Add("Id",typeof(int)); 
    dt1.Columns.Add("Name");
    dt1.Columns.Add("Occupation");

    DataTable dt2 = new DataTable("Table2");
    dt2.Columns.Add("Id",typeof(int));
    dt2.Columns.Add("Name");
    dt2.Columns.Add("Occupation");

    DataTable Final = dt1.AsEnumerable()
                         .Except(dt2.AsEnumerable(), DataRowComparer.Default)
                         .CopyToDataTable();

[I need the result to be like this][1]

  [1]: http://i.stack.imgur.com/brqCF.jpg


new Code : 







DataTable dtFinal = new DataTable();

        DataTable dtNew = new DataTable();
        dtNew.Columns.Add("Id");
        dtNew.Columns.Add("Name");
        dtNew.Rows.Add("1", "Yash Fale");
        dtNew.Rows.Add("3", "Rahul");


        DataTable dtOld = new DataTable();
        dtOld.Columns.Add("Id");
        dtOld.Columns.Add("Name");
        dtOld.Rows.Add("1", "Yash");
        dtOld.Rows.Add("2", "pops");


        var addOrUpdateRecords =
                                (from drNew in dtNew.AsEnumerable()
                                 join drOld in dtOld.AsEnumerable() on drNew.Field<string>("Id") equals drOld.Field<string>("Id") into match
                                 from drOld in match.DefaultIfEmpty()
                                 where drOld == null /* new */ || !DataRowComparer.Default.Equals(drNew, drOld) /* changed */
                                 select drNew).ToList();
            if (addOrUpdateRecords.Any())
                dtFinal = addOrUpdateRecords.CopyToDataTable();

        // i want to add new column like as Status for below condition 
        // for added Records = status : newRecord
        // for updated Records = status : UpdatedRecord


        //OutPut : ie. dtFinal
        // ID Name Status
        //  1  Yash Fale UpdatedRecord
        //  3  Rahul     newRecord

Answer 1

用于按某些标准关联两个序列的LINQ运算符称为join。

将dt1重命名为dtOld，将dt2重命名为dtNew。

添加的记录可以通过使用group join在dtNew字段上加入dtOld到Id并过滤dtNew中没有匹配的记录来确定记录在dtOld：

var addRecords =
    (from drNew in dtNew.AsEnumerable()
     join drOld in dtOld.AsEnumerable() on drNew.Field<int>("Id") equals drOld.Field<int>("Id") into match
     where !match.Any()
     select drNew).ToList();

请注意，上面会产生List<DataRecord>。当传递的序列为空时，CopyToDataTable调用失败，因此如果您确实需要数据表，请使用以下内容：

var dtAdd = addRecords.Any() ? addRecords.CopyToDataTable() : null;

确定已删除的记录完全相同，只交换了dtOld和dtNew：

var deleteRecords =
    (from drOld in dtOld.AsEnumerable()
     join drNew in dtNew.AsEnumerable() on drOld.Field<int>("Id") equals drNew.Field<int>("Id") into match
     where !match.Any()
     select drOld).ToList();

最后，可以使用inner join检索修改后的记录，并过滤不同的匹配记录（方便的DataRowComparer.Default可用于比较数据行值）：

var updateRecords =
    (from drNew in dtNew.AsEnumerable()
     join drOld in dtOld.AsEnumerable() on drNew.Field<int>("Id") equals drOld.Field<int>("Id")
     where !DataRowComparer.Default.Equals(drNew, drOld)
     select drNew).ToList();

更新：为了完整起见，以下是使用left outer join一次查询新查询和已修改记录的方法，这次使用{{3}}：

var addOrUpdateRecords =
    (from drNew in dtNew.AsEnumerable()
     join drOld in dtOld.AsEnumerable() on drNew.Field<int>("Id") equals drOld.Field<int>("Id") into match
     from drOld in match.DefaultIfEmpty()
     where drOld == null /* new */ || !DataRowComparer.Default.Equals(drNew, drOld) /* changed */
     select drNew).ToList();

比较使用Linq在c＃中与主键链接的2个dataTable

1 个答案: