4

我有以下 linq 查询，可在两个表之间创建左连接：

            var joinResultRows = from leftTable in dataSet.Tables[leftTableName].AsEnumerable()
                             join
                                  rightTable in dataSet.Tables[rightTableName].AsEnumerable()
                                    on leftTable.Field<string>(leftComparedColumnName) equals rightTable.Field<string>(rightComparedColumnName)
                                        into leftJoinedResult
                             select new { leftTable, leftJoinedResult };

我想得到回答这个问题的行：左列中的字符串值包含右列中的字符串值。

我试过这个：

            var joinResultRows = from leftTable in dataSet.Tables[leftTableName].AsEnumerable()
                             join
                                  rightTable in dataSet.Tables[rightTableName].AsEnumerable()
                                    on leftTable.Field<string>(leftComparedColumnName).Contains(rightTable.Field<string>(rightComparedColumnName)) equals true
                                        into leftJoinedResult
                             select new { leftTable, leftJoinedResult };

但它不起作用，因为在连接的左侧无法识别 rightTable。

如何创建导致 String.Contains 的连接，我是在“where”子句还是“On”子句中执行包含？

4

2 回答 2

5

您是否尝试过 SelectMany？

var result =
 from left in dataSet.Tables[leftTableName].AsEnumerable()
 from right in dataSet.Tables[rightTableName].AsEnumerable()
 where left.Field<string>(leftComparedColumnName).Contains(right.Field<string>(rightComparedColumnName))
 select new { left, right };

编辑：

以下应该有预期的效果：

class ContainsEqualityComparer: IEqualityComparer<string>
{
    public bool Equals(string right, string left) { return left.Contains(right); }
    public int GetHashCode(string obj) { return 0; }
}

var result =
    dataSet.Tables[leftTableName].AsEnumerable().GroupJoin(
        dataSet.Tables[rightTableName].AsEnumerable(),
        left => left,
        right => right,
        (left, leftJoinedResult) => new { left = left, leftJoinedResult = leftJoinedResult },
        new ContainsEqualityComparer());

关键比较是通过自定义 IEqualityComparer 运行的。只有左右的GetHashCode()相同，且Equals返回true时才会连接两行。

希望能帮助到你。

于 2009-09-01T14:18:46.447 回答
3

我通过创建 SelectMany (join) 解决了这个问题，左表包含所有记录，如果没有匹配项，右表包含 null：

var joinResultRows = from leftDataRow in dataSet.Tables[leftTableName].AsEnumerable()
                             from rightDataRow in dataSet.Tables[rightTableName].AsEnumerable()
                             .Where(rightRow => 
                                 {
                                     // Dont include "" string in the Contains, because "" is always contained
                                     // in any string.                                         
                                     if ( String.IsNullOrEmpty(rightRow.Field<string>(rightComparedColumnName)))
                                         return false;

                                     return leftDataRow.Field<string>(leftComparedColumnName).Contains(rightRow.Field<string>(rightComparedColumnName));

                                 }).DefaultIfEmpty() // Makes the right table nulls row or the match row
                              select new { leftDataRow, rightDataRow };

谢谢你的提示：）

于 2009-09-09T10:08:19.300 回答