从DataSet 中获取不同的 ID

引言

有时我们需要找出 DataSet 中某行中的不同值，但 ADO.NET 没有提供 Select 或其他函数来执行此操作。因此，我们可以使用本文给出的代码片段来实现类似的功能。

背景

我正在一个项目上工作，发现我们无法从 DataSet 中获取不同的 ID，这在某些情况下是必需的。因此，我编写了一个代码片段，希望能对您有所帮助。

使用代码

代码自明，包含注释。

/// <summary>
/// Gives the uniqueId list from the rows
/// of the table which satisfy the given condition.
/// </summary>
/// <param name="dtSource">The source table from
/// which rows will be selected.</param>
/// <param name="IDColumnName">The ID column name
/// which will be created as list.</param>
/// <param name="Condition">The condition
/// based upon which rows will be selected.
/// If one wants to check all rows pass Condition as ""</param>
/// <returns>List of unique ids as string list
/// which satisfy the given condition</returns>
public List<string> GetDistinctIDs(DataTable dtSource, 
                       string IDColumnName, string Condition)
{
    List<string> arUniqueId = new List<string>();
    foreach (DataRow dr in dtSource.Select(Condition))
    {
        if(dr[IDColumnName] == DBNull.Value || 
           arUniqueId.Contains(dr[IDColumnName].ToString()))
        {
            continue;
        }
        arUniqueId.Add(dr[IDColumnName].ToString());
    }
    return arUniqueId;
}


/// <summary>
/// Gives the unique value rows from the rows
/// of the table which satisfy the given condition.
/// </summary>
/// <param name="dtSource">The source table
/// from which rows will be selected.</param>
/// <param name="IDColumnName">The ID column
/// name which will be created as list.</param>
/// <param name="ValueColumnName">The Value column name which
/// will be created as Value in Hashtable.</param>
/// <param name="Condition">The condition based
/// upon which rows will be selected. 
/// If one wants to select all rows pass Condition as ""
/// </param>
/// <returns>A Hashtable Containing unique keys
/// as Ids and Value corresponds to them.</returns>
public Hashtable GetDistinctValues(DataTable dtSource, string IDColumnName, 
                                   string ValueColumnName, string Condition)
{
    Hashtable ht = new Hashtable();
    foreach (DataRow dr in dtSource.Select(Condition))
    {
        if (dr[IDColumnName] == DBNull.Value || 
            ht.ContainsKey(dr[IDColumnName]))
        {
            continue;
        }
        ht.Add(dr[IDColumnName],dr[ValueColumnName]);
    }
    return ht;
}

关注点

您可以使用此代码片段进行多种用途。哈希表是一种实现方式。如果您想实现多列值，那么您可能可以创建一个简单的表，而不是 Hashtable，并添加行并在 DataTable 中填充值。

历史

• 1.0 版，作者：Mahendra。