The CData ADO.NET Provider for Elasticsearch implements two ADO.NET interfaces you can use to retrieve data from Elasticsearch: ElasticsearchDataAdapter and ElasticsearchDataReader objects. Whereas ElasticsearchDataAdapter objects retrieve a single result set of all the data that matches a query, ElasticsearchDataReader objects fetch data in subset increments as needed.

Using the ElasticsearchDataReader

The ElasticsearchDataReader retrieves data faster than the ElasticsearchDataAdapter because it can retrieve data in pages. As you read data from the ElasticsearchDataReader, it periodically requests the next page of results from the data source, if required. This causes results to be returned at a faster rate. The following example selects all the columns from the [CData].[Elasticsearch].Employee table:

C#

string connectionString = "Server=127.0.0.1;Port=9200;";

using (ElasticsearchConnection connection = new ElasticsearchConnection(connectionString)) {
  ElasticsearchCommand cmd = new ElasticsearchCommand("SELECT * FROM [CData].[Elasticsearch].Employee", connection);
  
  ElasticsearchDataReader rdr = cmd.ExecuteReader();

  while (rdr.Read()) {
    Console.WriteLine(String.Format("\t{0} --> \t\t{1}", rdr["Id"], rdr["Name"]));
  }
}

VB.NET

Dim connectionString As String = "Server=127.0.0.1;Port=9200;"

Using connection As New ElasticsearchConnection(connectionString)
  Dim cmd As New ElasticsearchCommand("SELECT * FROM [CData].[Elasticsearch].Employee", connection)

  Dim rdr As ElasticsearchDataReader = cmd.ExecuteReader()

  While rdr.Read()
    Console.WriteLine([String].Format(vbTab & "{0} --> " & vbTab & vbTab & "{1}", rdr("Id"), rdr("Name")))
  End While
End Using