如何实现 IDataReader？

Question

我的 XML 看起来像这样：

<resultset>
    <datarow>
        <datacol>Row 1 - Col 1</datacol>
        <datacol>Row 1 - Col 2</datacol>
        <datacol>Row 1 - Col 3</datacol>
        ...
    </datarow>
    ...
</resultset>
...

我的问题是，如何使用这个 XML 实现 IDataReader 接口？我迷路了……

我已经开发了这个：

public sealed class SybaseDataReader : IDataReader
{
    private DataSet _dataSet = new DataSet();

    #region IDataReader methods implementation
    // ...
}

我走的很好？

感谢您提供建设性且解释清楚的帖子。

Answer 1

我写了一个简单的文件阅读器实现。您可以轻松地调整它以读取 xml 文件：

public class MyFileDataReader : IDataReader
{
    protected StreamReader Stream { get; set; }
    protected object[] Values;
    protected bool Eof { get; set; }
    protected string CurrentRecord { get; set; }
    protected int CurrentIndex { get; set; }

    public MyFileDataReader(string fileName)
    {
        Stream = new StreamReader(fileName);
        Values = new object[this.FieldCount];
    }  

请记住，IDataReader 有几种方法，您不需要根据您的场景实现这些方法。但可能有一些方法实现是你无法避免的：

 public void Close()
    {
        Array.Clear(Values, 0, Values.Length);
        Stream.Close();
        Stream.Dispose();
    }

    public int Depth
    {
        get { return 0; }
    }

    public DataTable GetSchemaTable()
    {
        // avoid to implement several methods if your scenario do not demand it
        throw new NotImplementedException();
    }

    public bool IsClosed
    {
        get { return Eof; }
    }

    public bool NextResult()
    {
        return false;
    }

    public bool Read()
    {
        CurrentRecord = Stream.ReadLine();            
        Eof = CurrentRecord == null;

        if (!Eof)
        {
            Fill(Values);
            CurrentIndex++;
        }

        return !Eof;
    }

    private void Fill(object[] values)
    { 
       //To simplify the implementation, lets assume here that the table have just 3         
       //columns: the primary key, and 2 string columns. And the file is fixed column formatted 
      //and have 2 columns: the first with width 12 and the second with width 40. Said that, we can do as follows

        values[0] = null;
        values[1] = CurrentRecord.Substring(0, 12).Trim();
        values[2] = CurrentRecord.Substring(12, 40).Trim();

       // by default, the first position of the array hold the value that will be  
       // inserted at the first column of the table, and so on
       // lets assume here that the primary key is auto-generated
        // if the file is xml we could parse the nodes instead of Substring operations
    } 

    public int RecordsAffected
    {
        get { return -1; }
    } 

要实现 IDataReader，还必须实现 IDisposable 和 IDataRecord 接口。

IDisposable 很简单，但 IDataRecord 可能很痛苦。同样，在这种情况下，我们无法避免一些方法实现：

 public int FieldCount
    {
        get { return 3;//assuming the table has 3 columns }
    }

    public IDataReader GetData(int i)
    {
        if (i == 0)
            return this;

        return null;
    }

    public string GetDataTypeName(int i)
    {
        return "String";
    }

    public string GetName(int i)
    {
        return Values[i].ToString();
    }

    public string GetString(int i)
    {
        return Values[i].ToString();
    }

    public object GetValue(int i)
    {
        return Values[i];
    }

    public int GetValues(object[] values)
    {
        Fill(values);

        Array.Copy(values, Values, this.FieldCount);

        return this.FieldCount;
    }

    public object this[int i]
    {
        get { return Values[i]; }
    }  

希望对你有帮助。

Answer 2

将 DataSet 作为 System.Data.IDataReader 的成员是不合逻辑的。

最好考虑 XmlDocumnet、XDocument 或 XmlReader。

Answer 3

这可能会有所帮助...

 //1. Create dataset
        var ds = new DataSet("A Dataset");
        var table = ds.Tables.Add("A Table");
        table.Columns.Add("Id", typeof(int));
        table.Columns.Add("Description", typeof(string));

        //2. Serialize as xml
        ds.WriteXml(@"C:\temp\dataset.xml");

        //3. Go look at the xml file's contents.
        //Your xml needs to be translated into this schema. 
        //You will have to write this. (Boring transform work...)
        //Dataset deserialization does not work with arbitrary xml documuents.


        //4. Loading the xml file
        var ds2 = new DataSet();
        ds2.ReadXml(@"C:\temp\dataset.xml");

        //Suggestion. Investigate using LINQ-to-xml. It would be easier to 
        //read the data from your xml schema. You could also load the Dataset tables row by row
        //using this type of approach 

        //1. Load xml data into an XElement.
        var element = XElement.Parse(@"<resultset>
            <datarow>
                <datacol>Row 1 - Col 1</datacol>
                <datacol>Row 1 - Col 2</datacol>
                <datacol>Row 1 - Col 3</datacol>
            </datarow>
        </resultset>
        ");

        //2. Create a dataset
        ds = new DataSet("A Dataset");
        table = ds.Tables.Add("A Table");
        table.Columns.Add("Col1", typeof(string));
        table.Columns.Add("Col2", typeof(string));
        table.Columns.Add("Col3", typeof(string));

        //3. Walk XElements and add rows to tables
        foreach (var row in element.Elements("datarow"))
        {
            var r = table.NewRow();                
            table.Rows.Add(r);
            int i = 0;
            foreach (var columnValue in row.Elements("datacol"))
            {
                r[i++] = columnValue.Value;
            }
        }