public class FeatureClassDefinition : TableDefinition, System.IDisposable  

{
  await QueuedTask.Run(() =>
  {
    using (Geodatabase geodatabase = new Geodatabase(new DatabaseConnectionFile(new Uri("path\\to\\sde\\file\\sdefile.sde"))))
    {
      // Remember that for Enterprise databases you have to qualify your dataset names with the DatabaseName and UserName.
      TableDefinition enterpriseTableDefinition = geodatabase.GetDefinition<TableDefinition>("LocalGovernment.GDB.CitizenContactInfo");

      // It does not matter if the dataset is within a FeatureDataset or not.
      FeatureClassDefinition featureClassDefinition = geodatabase.GetDefinition<FeatureClassDefinition>("LocalGovernment.GDB.FireStation");

      // GetDefinition For a RelationshipClass.
      RelationshipClassDefinition relationshipClassDefinition = geodatabase.GetDefinition<RelationshipClassDefinition>(
          "LocalGovernment.GDB.AddressPointHasSiteAddresses");

      // GetDefinition For a FeatureDataset.
      FeatureDatasetDefinition featureDatasetDefinition = geodatabase.GetDefinition<FeatureDatasetDefinition>("LocalGovernment.GDB.Address");
    }
  });
}

{
  await QueuedTask.Run(() =>
  {
    using (Geodatabase geodatabase = new Geodatabase(new DatabaseConnectionFile(new Uri("path\\to\\sde\\file\\sdefile.sde"))))
    {
      IReadOnlyList<FeatureClassDefinition> enterpriseDefinitions = geodatabase.GetDefinitions<FeatureClassDefinition>();
      IEnumerable<Definition> featureClassesHavingGlobalID = enterpriseDefinitions.Where(definition => definition.HasGlobalID());

      IReadOnlyList<FeatureDatasetDefinition> featureDatasetDefinitions = geodatabase.GetDefinitions<FeatureDatasetDefinition>();
      bool electionRelatedFeatureDatasets = featureDatasetDefinitions.Any(definition => definition.GetName().Contains("Election"));

      IReadOnlyList<AttributedRelationshipClassDefinition> attributedRelationshipClassDefinitions = geodatabase.GetDefinitions<AttributedRelationshipClassDefinition>();

      IReadOnlyList<RelationshipClassDefinition> relationshipClassDefinitions = geodatabase.GetDefinitions<RelationshipClassDefinition>();
    }
  });
}

{
  //Url examples for (federated) feature services
  //(by "ref" online):
  var url =
      @"https://sampleserver6.arcgisonline.com/arcgis/rest/services/SF311/FeatureServer";
  //(federated by ref on portal)
  //https://portal.example.com/server/rest/services/FeatureServiceName/FeatureServer");
  //(federated by value - Hosted - on portal)
  //https://portal.example.com/server/rest/services/Hosted/FeatureServiceName/FeatureServer");

  await QueuedTask.Run(() =>
  {
    var uri = new Uri(url, UriKind.Absolute);
    using (var fs_db = new ArcGIS.Core.Data.Geodatabase(new ServiceConnectionProperties(uri)))
    {
      //Assuming that id 0 is a FeatureClass for the given service
      FeatureClassDefinition featureClassDefinition =
          fs_db.GetDefinition<FeatureClassDefinition>("0");
      string shapeField = featureClassDefinition.GetShapeField();
      IReadOnlyList<Field> fields = featureClassDefinition.GetFields();

      //Assuming that id 1 is a Table for the given service
      TableDefinition tableDefinition =
            fs_db.GetDefinition<TableDefinition>("1");
      string objectIDField = tableDefinition.GetObjectIDField();
    }
  });
}

{
  await QueuedTask.Run(() =>
  {
    using (Geodatabase geodatabase =
           new Geodatabase(new DatabaseConnectionFile(new Uri("path\\to\\sde\\file\\sdefile.sde"))))
    {
      // Remember the qualification of DatabaseName. for the RelationshipClass.

      RelationshipClassDefinition enterpriseDefinition = geodatabase.GetDefinition<RelationshipClassDefinition>("LocalGovernment.GDB.AddressPointHasSiteAddresses");
      IReadOnlyList<Definition> enterpriseDefinitions = geodatabase.GetRelatedDefinitions(enterpriseDefinition,
          DefinitionRelationshipType.DatasetsRelatedThrough);
      FeatureClassDefinition enterpriseAddressPointDefinition = enterpriseDefinitions.First(defn => defn.GetName().Equals("LocalGovernment.GDB.AddressPoint"))
          as FeatureClassDefinition;

      FeatureDatasetDefinition featureDatasetDefinition = geodatabase.GetDefinition<FeatureDatasetDefinition>("LocalGovernment.GDB.Address");
      IReadOnlyList<Definition> datasetsInAddressDataset = geodatabase.GetRelatedDefinitions(featureDatasetDefinition,
          DefinitionRelationshipType.DatasetInFeatureDataset);
      FeatureClassDefinition addressPointInAddressDataset = datasetsInAddressDataset.First(defn => defn.GetName().Equals("LocalGovernment.GDB.AddressPoint"))
          as FeatureClassDefinition;

      RelationshipClassDefinition addressPointHasSiteAddressInAddressDataset = datasetsInAddressDataset.First(defn =>
            defn.GetName().Equals("LocalGovernment.GDB.AddressPointHasSiteAddresses"))
          as RelationshipClassDefinition;
    }
  });
}

{
  //Must be called within QueuedTask.Run()
  RowCursor SortWorldCities(FeatureClass worldCitiesTable)
  {
    using (FeatureClassDefinition featureClassDefinition = worldCitiesTable.GetDefinition())
    {
      Field countryField = featureClassDefinition.GetFields()
        .First(x => x.Name.Equals("COUNTRY_NAME"));

      Field cityNameField = featureClassDefinition.GetFields()
        .First(x => x.Name.Equals("CITY_NAME"));

      // Create SortDescription for Country field
      SortDescription countrySortDescription = new SortDescription(countryField);
      countrySortDescription.CaseSensitivity = CaseSensitivity.Insensitive;
      countrySortDescription.SortOrder = SortOrder.Ascending;

      // Create SortDescription for City field
      SortDescription citySortDescription = new SortDescription(cityNameField);
      citySortDescription.CaseSensitivity = CaseSensitivity.Insensitive;
      citySortDescription.SortOrder = SortOrder.Ascending;

      // Create our TableSortDescription
      TableSortDescription tableSortDescription = new TableSortDescription(
        new List<SortDescription>() { countrySortDescription, citySortDescription });

      return worldCitiesTable.Sort(tableSortDescription);
    }
  }
}