Connection Class

global with sharing class SampleDataSourceConnection extends DataSource.Connection {
    global SampleDataSourceConnection(DataSource.ConnectionParams connectionParams) {
    }
    
    override global List<DataSource.Table> sync() {
        List<DataSource.Table> tables = new List<DataSource.Table>();        
        List<DataSource.Column> columns;
        columns = new List<DataSource.Column>();
        columns.add(DataSource.Column.text('Name', 255));
        columns.add(DataSource.Column.text('ExternalId', 255));
        columns.add(DataSource.Column.url('DisplayUrl'));
        tables.add(DataSource.Table.get('Sample', 'Title', columns));
        return tables;
    }
    
    override global DataSource.TableResult query(DataSource.QueryContext c) {
        return DataSource.TableResult.get(c, DataSource.QueryUtils.process(c, getRows()));
    }
    
    override global List<DataSource.TableResult> search(DataSource.SearchContext c) {        
        List<DataSource.TableResult> results = new List<DataSource.TableResult>();
        for (DataSource.TableSelection tableSelection : c.tableSelections) {
            results.add(DataSource.TableResult.get(tableSelection, getRows()));
        }
        return results;
    }

    // Helper method to get record values from the external system for the Sample table.
    private List<Map<String, Object>> getRows () {
        // Get row field values for the Sample table from the external system via a callout.
        HttpResponse response = makeGetCallout();
        // Parse the JSON response and populate the rows.
        Map<String, Object> m = (Map<String, Object>)JSON.deserializeUntyped(
                response.getBody());
        Map<String, Object> error = (Map<String, Object>)m.get('error');
        if (error != null) {
            throwException(string.valueOf(error.get('message')));
        }
        List<Map<String,Object>> rows = new List<Map<String,Object>>();
        List<Object> jsonRows = (List<Object>)m.get('value');
        if (jsonRows == null) {
            rows.add(foundRow(m));
        } else {
            for (Object jsonRow : jsonRows) {
                Map<String,Object> row = (Map<String,Object>)jsonRow;
                rows.add(foundRow(row));
            }
        }
        return rows;
    }
    
    global override List<DataSource.UpsertResult> upsertRows(DataSource.UpsertContext
            context) {
       if (context.tableSelected == 'Sample') {
           List<DataSource.UpsertResult> results = new List<DataSource.UpsertResult>();
           List<Map<String, Object>> rows = context.rows;
           
           for (Map<String, Object> row : rows){
              // Make a callout to insert or update records in the external system.
              HttpResponse response;
              // Determine whether to insert or update a record.
              if (row.get('ExternalId') == null){
                 // Send a POST HTTP request to insert new external record.
                 // Make an Apex callout and get HttpResponse.
                 response = makePostCallout(
                     '{"name":"' + row.get('Name') + '","ExternalId":"' + 
                     row.get('ExternalId') + '"');
              }
              else {
                 // Send a PUT HTTP request to update an existing external record.
                 // Make an Apex callout and get HttpResponse.
                 response = makePutCallout(
                     '{"name":"' + row.get('Name') + '","ExternalId":"' + 
                     row.get('ExternalId') + '"',
                     String.valueOf(row.get('ExternalId')));
              }
         
              // Check the returned response.
              // First, deserialize it.
              Map<String, Object> m = (Map<String, Object>)JSON.deserializeUntyped(
                      response.getBody());
              if (response.getStatusCode() == 200){
                  results.add(DataSource.UpsertResult.success(
                          String.valueOf(m.get('id'))));
              } 
              else {
                 results.add(DataSource.UpsertResult.failure(
                                 String.valueOf(m.get('id')), 
                     'The callout resulted in an error: ' + 
                     response.getStatusCode()));
              }
           } 
           return results;
       } 
       return null;
    }
         
    global override List<DataSource.DeleteResult> deleteRows(DataSource.DeleteContext 
            context) {
       if (context.tableSelected == 'Sample'){
           List<DataSource.DeleteResult> results = new List<DataSource.DeleteResult>();
           for (String externalId : context.externalIds){
              HttpResponse response = makeDeleteCallout(externalId);
              if (response.getStatusCode() == 200){
                 results.add(DataSource.DeleteResult.success(externalId));
              } 
              else {
                 results.add(DataSource.DeleteResult.failure(externalId, 
                             'Callout delete error:' 
                             + response.getBody()));
              }
           }
           return results;
       }
       return null;
     }
     
    // Helper methods
        
    // Make a GET callout
     private static HttpResponse makeGetCallout() {
         HttpResponse response;
         // Make callout
         // ...
         return response;
     }
     
     // Populate a row based on values from the external system.
     private Map<String,Object> foundRow(Map<String,Object> foundRow) {
        Map<String,Object> row = new Map<String,Object>();
        row.put('ExternalId', string.valueOf(foundRow.get('Id')));
        row.put('DisplayUrl', string.valueOf(foundRow.get('DisplayUrl')));
        row.put('Name', string.valueOf(foundRow.get('Name')));        
        return row;
    }

     // Make a POST callout
     private static HttpResponse makePostCallout(String jsonBody) {
         HttpResponse response;
         // Make callout
         // ...
         return response;
     }
     
     // Make a PUT callout
     private static HttpResponse makePutCallout(String jsonBody, String externalID) {
         HttpResponse response;
         // Make callout
         // ...
         return response;
     }
     
     // Make a DELETE callout
     private static HttpResponse makeDeleteCallout(String externalID) {
         HttpResponse response;
         // Make callout
         // ...
         return response;
     }
}