public void SetConfiguration(string configuration)
{
    XmlDocument xmlDoc = new XmlDocument();
    xmlDoc.LoadXml(configuration);
    string ConfigFilePath = AppDomain.CurrentDomain.SetupInformation.ApplicationBase + xmlDoc.ChildNodes[0].Attributes["configSource"].InnerText;
    ExeConfigurationFileMap file = new ExeConfigurationFileMap();
    file.ExeConfigFilename = ConfigFilePath;
    Configuration config = ConfigurationManager.OpenMappedExeConfiguration(file, ConfigurationUserLevel.None);
    foreach (ConnectionStringSettings cf in config.ConnectionStrings.ConnectionStrings)
    {
        connectionStrings.Add(cf.Name, cf.ToString());
    }
}

public SqlConnection GetConnectionByParameter(IDataParameterCollection parameters)
{
    var connString = connectionStrings["CentralDBConnString"];

    foreach (DBParameter param in parameters)
    {
        if (param.ParameterName.Equals("ClinicCode"))
        {
            //Using the first value if the ClinicCode were selected for more than 1 option.
            if (param.Values != null && param.Values.Length > 1)
            {
                param.Value = http://www.mamicode.com/param.Values[0];>

public IDataReader ExecuteReader(CommandBehavior behavior)
{
    Debug.WriteLine("IDBCommand.ExecuteReader with CommandBehavior." + behavior);

    // get connection based on parameters
    using (SqlConnection conn = m_connection.GetConnectionByParameter(this.Parameters))
    {
        conn.Open();

        SqlCommand cmd = new SqlCommand(CommandText, conn);
        cmd.CommandType = (System.Data.CommandType)this.CommandType;
        foreach (DBParameter param in this.Parameters)
        {
            if (param.Value != null)
                cmd.Parameters.Add(new SqlParameter(param.ParameterName, param.Value));
            else
                cmd.Parameters.Add(new SqlParameter(param.ParameterName, DBNull.Value));
        }

        SqlDataAdapter sqlDA = new SqlDataAdapter(cmd);
        System.Data.DataSet dsResult = new System.Data.DataSet();
        sqlDA.Fill(dsResult);
        m_dataTable = dsResult.Tables[0];

        conn.Close();
        return new DBDataReader(this);
    }
}

1. Open the project "ProjectName" and rebuild it ;
2. Copy the file "ProjectName.dll" and "ProjectName.pdb" inside folder "ProjectName\ProjectName\bin\Debug" to path "C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\PrivateAssemblies\";
3. Copy file "ProjectName.config" inside project root directory to path "C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\PrivateAssemblies\";
4. Open the file "RSReportDesigner.config" inside folder "C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\PrivateAssemblies\"(The exactly path base on the Visio Studio version you installed in your local);
   4.1. Find the node <Data> inside node <Extensions>, add node "<Extension Name="XXXX DataSource Extension" Type="ProjectName.DBConnection, ProjectName" />" inside node <Data>;
   4.2  Find the node <Desinger> inside node <Extensions>, add node "<Extension Name="XXXX DataSource Extension" Type="Microsoft.ReportingServices.QueryDesigners.GenericQueryDesigner,Microsoft.ReportingServices.QueryDesigners"/>" inside node <Desinger>;

5. Open the file "RSPreviewPolicy.config" inside folder "C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\PrivateAssemblies\"(The exactly path base on the Visio Studio version you installed in your local);
   5.1  Find the node <Data> inside node <Extensions>, add node below content inside node <CodeGroup>;
    <CodeGroup
         class="UnionCodeGroup"
         version="1"
         PermissionSetName="FullTrust"
         Name="XXXX DataSource Extension"
         Description="Code group for my Custom DataSource for data processing extension">
             <IMembershipCondition
             class="UrlMembershipCondition"
             version="1"
             Url="C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\PrivateAssemblies\ProjectName.dll"
             />
    </CodeGroup>

6. Open your DataSource of SSRS report ,select the Embedded connections and choice the DPE named "XXXX DataSource Extension" from the dropdownlist of Type;
7. Click OK button to use the DPE.

PS.
1. Please close and open your Visio Studio again, if you can not find the DPE named "XXXX DataSource Extension" after you finished above steps;

Using the DEP in Report Server(After deploy to Reporting Server):
***********************************************************************************************************
1. Open the project "ProjectName" and rebuild it ;
2. Copy the file "ProjectName.dll" and "ProjectName.pdb" inside folder "ProjectName\ProjectName\bin\Debug" to path "C:\Program Files\Microsoft SQL Server\MSRS12.MSSQLSERVER\Reporting Services\ReportServer\bin\";
3. Copy file "ProjectName.config" inside project root directory to path "C:\Program Files\Microsoft SQL Server\MSRS12.MSSQLSERVER\Reporting Services\ReportServer\bin\";
4. Open the file "rsreportserver.config" inside folder "C:\Program Files\Microsoft SQL Server\MSRS12.MSSQLSERVER\Reporting Services\ReportServer\"(The exactly path base on the Visio Studio version you installed in your local);
   4.1. Find the node <Data> inside node <Extensions>, add below content inside node <Data>;
        <Extension Name="DPEName" Type="ProjectName.DBConnection,ProjectName">
            <Configuration>
                <connectionStrings configSource="\bin\ProjectName.config" />
            </Configuration>
        </Extension>
   4.2  Find the node <Desinger> inside node <Extensions>, add below  inside node <Desinger>;

5. Open your DataSource of SSRS report in Reporting Server,then open the report through right click it and select "Manage";
6. Click "Data Source" from the menu located left side of the new page;
7. Select "A Custom Data Source" in the right side of the page,followed by selecting DPE named "XXXX DataSource Extension" as the Data source type;
8. Click Apply button to use the DPE.

PS.
1. Please restart the Reporting Services if you still can not find the DataSource manage page after you finished above steps;