Pascal (Lazarus/Delphi)

DynamoDB - DeleteItem

See more Amazon DynamoDB Examples

Deletes a single item in a table by primary key. You can perform a conditional delete operation that deletes the item if it exists, or if it has an expected attribute value. Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.AuthAws,
  Chilkat.Rest,
  Chilkat.JsonObject,
  Chilkat.StringBuilder;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  rest: TRest;
  authAws: TAuthAws;
  bTls: Boolean;
  port: Integer;
  bAutoReconnect: Boolean;
  json: TJsonObject;
  sbRequestBody: TStringBuilder;
  sbResponseBody: TStringBuilder;
  respStatusCode: Integer;
  jsonResponse: TJsonObject;
  strVal: string;
  AttributesLastPostedByS: string;
  AttributesForumNameS: string;
  AttributesLastPostDateTimeS: string;
  AttributesSubjectS: string;
  AttributesMessageS: string;
  i: Integer;
  count_i: Integer;

begin
  success := False;

  rest := TRest.Create;

  //  Implements the following CURL command:

  //  curl -X POST https://dynamodb.us-west-2.amazonaws.com/ \
  //    -H "Accept-Encoding: identity" \
  //    -H "Content-Type: application/x-amz-json-1.0" \
  //    -H "Authorization: AWS4-HMAC-SHA256 Credential=<Credential>, SignedHeaders=<Headers>, Signature=<Signature>" \
  //    -H "X-Amz-Date: <Date>" \
  //    -H "X-Amz-Target: DynamoDB_20120810.DeleteItem" \
  //    -d '{
  //      "TableName": "Thread",
  //      "Key": {
  //          "ForumName": {
  //              "S": "Amazon DynamoDB"
  //          },
  //          "Subject": {
  //              "S": "How do I update multiple items?"
  //          }
  //      },
  //      "ConditionExpression": "attribute_not_exists(Replies)",
  //      "ReturnValues": "ALL_OLD"
  //  }'

  //  Use the following online tool to generate REST code from a CURL command
  //  Convert a cURL Command to REST Source Code

  authAws := TAuthAws.Create;
  authAws.AccessKey := 'AWS_ACCESS_KEY';
  authAws.SecretKey := 'AWS_SECRET_KEY';
  //  Don't forget to change the region to your particular region. (Also make the same change in the call to Connect below.)
  authAws.Region := 'us-west-2';
  authAws.ServiceName := 'dynamodb';
  //  SetAuthAws causes Chilkat to automatically add the following headers: Authorization, X-Amz-Date
  rest.SetAuthAws(authAws);

  //  URL: https://dynamodb.us-west-2.amazonaws.com/
  bTls := True;
  port := 443;
  bAutoReconnect := True;
  success := rest.Connect('dynamodb.us-west-2.amazonaws.com',port,bTls,bAutoReconnect);
  if (success <> True) then
    begin
      WriteLn('ConnectFailReason: ' + rest.ConnectFailReason);
      WriteLn(rest.LastErrorText);
      Exit;
    end;

  //  Note: The above code does not need to be repeatedly called for each REST request.
  //  The rest object can be setup once, and then many requests can be sent.  Chilkat will automatically
  //  reconnect within a FullRequest* method as needed.  It is only the very first connection that is explicitly
  //  made via the Connect method.

  //  Use this online tool to generate code from sample JSON:
  //  Generate Code to Create JSON

  //  The following JSON is sent in the request body.

  //  {
  //    "TableName": "Thread",
  //    "Key": {
  //      "ForumName": {
  //        "S": "Amazon DynamoDB"
  //      },
  //      "Subject": {
  //        "S": "How do I update multiple items?"
  //      }
  //    },
  //    "ConditionExpression": "attribute_not_exists(Replies)",
  //    "ReturnValues": "ALL_OLD"
  //  }

  json := TJsonObject.Create;
  json.UpdateString('TableName','Thread');
  json.UpdateString('Key.ForumName.S','Amazon DynamoDB');
  json.UpdateString('Key.Subject.S','How do I update multiple items?');
  json.UpdateString('ConditionExpression','attribute_not_exists(Replies)');
  json.UpdateString('ReturnValues','ALL_OLD');

  rest.AddHeader('Content-Type','application/x-amz-json-1.0');
  rest.AddHeader('X-Amz-Target','DynamoDB_20120810.DeleteItem');
  rest.AddHeader('Accept-Encoding','identity');

  sbRequestBody := TStringBuilder.Create;
  json.EmitSb(sbRequestBody);
  sbResponseBody := TStringBuilder.Create;
  success := rest.FullRequestSb('POST','/',sbRequestBody,sbResponseBody);
  if (success <> True) then
    begin
      WriteLn(rest.LastErrorText);
      Exit;
    end;
  respStatusCode := rest.ResponseStatusCode;
  WriteLn('response status code = ' + respStatusCode);
  if (respStatusCode >= 400) then
    begin
      WriteLn('Response Status Code = ' + respStatusCode);
      WriteLn('Response Header:');
      WriteLn(rest.ResponseHeader);
      WriteLn('Response Body:');
      WriteLn(sbResponseBody.GetAsString());
      Exit;
    end;

  jsonResponse := TJsonObject.Create;
  jsonResponse.LoadSb(sbResponseBody);

  jsonResponse.EmitCompact := False;
  WriteLn(jsonResponse.Emit());

  //  Sample JSON response:
  //  (Sample code for parsing the JSON response is shown below)

  //  {
  //    "Attributes": {
  //      "LastPostedBy": {
  //        "S": "fred@example.com"
  //      },
  //      "ForumName": {
  //        "S": "Amazon DynamoDB"
  //      },
  //      "LastPostDateTime": {
  //        "S": "201303201023"
  //      },
  //      "Tags": {
  //        "SS": [
  //          "Update",
  //          "Multiple Items",
  //          "HelpMe"
  //        ]
  //      },
  //      "Subject": {
  //        "S": "How do I update multiple items?"
  //      },
  //      "Message": {
  //        "S": "I want to update multiple items in a single call. What's the best way to do that?"
  //      }
  //    }
  //  }

  //  Sample code for parsing the JSON response...
  //  Use the following online tool to generate parsing code from sample JSON:
  //  Generate Parsing Code from JSON

  AttributesLastPostedByS := jsonResponse.StringOf('Attributes.LastPostedBy.S');
  AttributesForumNameS := jsonResponse.StringOf('Attributes.ForumName.S');
  AttributesLastPostDateTimeS := jsonResponse.StringOf('Attributes.LastPostDateTime.S');
  AttributesSubjectS := jsonResponse.StringOf('Attributes.Subject.S');
  AttributesMessageS := jsonResponse.StringOf('Attributes.Message.S');
  i := 0;
  count_i := jsonResponse.SizeOfArray('Attributes.Tags.SS');
  while i < count_i do
    begin
      jsonResponse.I := i;
      strVal := jsonResponse.StringOf('Attributes.Tags.SS[i]');
      i := i + 1;
    end;



  rest.Free;
  authAws.Free;
  json.Free;
  sbRequestBody.Free;
  sbResponseBody.Free;
  jsonResponse.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.