The IndexColumns schema collection lists the indexes and their corresponding columns. By filtering on indexes, you can write more selective queries with faster query response times.

Retrieving Index Column Information

To retrieve this schema collection, call the GetSchema method of the FHIRConnection class. You can restrict the results by table name. The following example retrieves the column and sequence number for each index of the FHIR table Patient.

C#

String connectionString = "URL=http://test.fhir.org/r4b/;ConnectionType=Generic;ContentType=JSON;AuthScheme=None;";

using (FHIRConnection conn = new FHIRConnection(connectionString)) {
  conn.Open();
  DataTable databaseSchema = conn.GetSchema("IndexColumns", new string[] {"Patient"});
  foreach (DataRow row in databaseSchema.Rows) {
    Console.WriteLine(row["COLUMN_NAME"]);
    Console.WriteLine(row["ORDINAL_POSITION"]);
  }
}

VB.NET

Dim connectionString As String = "URL=http://test.fhir.org/r4b/;ConnectionType=Generic;ContentType=JSON;AuthScheme=None;"

Using conn As New FHIRConnection(connectionString)
  conn.Open()
  Dim databaseSchema As DataTable = conn.GetSchema("IndexColumns",  New String() {"Patient"})
  For Each row As DataRow In databaseSchema.Rows
    Console.WriteLine(row["COLUMN_NAME"])
    Console.WriteLine(row["ORDINAL_POSITION"])
  Next
End Using

Columns Returned

The IndexColumns schema collection returns the following columns: