Xojo Plugin
DynamoDB - UpdateItem

Edits an existing item's attributes, or adds a new item to the table if it does not already exist. You can put, delete, or add attribute values. You can also perform a conditional update on an existing item (insert a new attribute name-value pair if it doesn't exist, or replace an existing name-value pair if it has certain expected attribute values).
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Xojo Plugin
Dim success As Boolean
success = False

Dim rest As New Chilkat.Rest

// 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.UpdateItem" \
//   -d '{
//     "TableName": "Thread",
//     "Key": {
//         "ForumName": {
//             "S": "Amazon DynamoDB"
//         },
//         "Subject": {
//             "S": "Maximum number of items?"
//         }
//     },
//     "UpdateExpression": "set LastPostedBy = :val1",
//     "ConditionExpression": "LastPostedBy = :val2",
//     "ExpressionAttributeValues": {
//         ":val1": {"S": "alice@example.com"},
//         ":val2": {"S": "fred@example.com"}
//     },
//     "ReturnValues": "ALL_NEW"
// }'

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

Dim authAws As New Chilkat.AuthAws
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
success = rest.SetAuthAws(authAws)

// URL: https://dynamodb.us-west-2.amazonaws.com/
Dim bTls As Boolean
bTls = True
Dim port As Int32
port = 443
Dim bAutoReconnect As Boolean
bAutoReconnect = True
success = rest.Connect("dynamodb.us-west-2.amazonaws.com",port,bTls,bAutoReconnect)
If (success <> True) Then
    System.DebugLog("ConnectFailReason: " + Str(rest.ConnectFailReason))
    System.DebugLog(rest.LastErrorText)
    Return
End If

// 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": "Maximum number of items?"
//     }
//   },
//   "UpdateExpression": "set LastPostedBy = :val1",
//   "ConditionExpression": "LastPostedBy = :val2",
//   "ExpressionAttributeValues": {
//     ":val1": {
//       "S": "alice@example.com"
//     },
//     ":val2": {
//       "S": "fred@example.com"
//     }
//   },
//   "ReturnValues": "ALL_NEW"
// }

Dim json As New Chilkat.JsonObject
success = json.UpdateString("TableName","Thread")
success = json.UpdateString("Key.ForumName.S","Amazon DynamoDB")
success = json.UpdateString("Key.Subject.S","Maximum number of items?")
success = json.UpdateString("UpdateExpression","set LastPostedBy = :val1")
success = json.UpdateString("ConditionExpression","LastPostedBy = :val2")
success = json.UpdateString("ExpressionAttributeValues.:val1.S","alice@example.com")
success = json.UpdateString("ExpressionAttributeValues.:val2.S","fred@example.com")
success = json.UpdateString("ReturnValues","ALL_NEW")

success = rest.AddHeader("Content-Type","application/x-amz-json-1.0")
success = rest.AddHeader("X-Amz-Target","DynamoDB_20120810.UpdateItem")
success = rest.AddHeader("Accept-Encoding","identity")

Dim sbRequestBody As New Chilkat.StringBuilder
success = json.EmitSb(sbRequestBody)
Dim sbResponseBody As New Chilkat.StringBuilder
success = rest.FullRequestSb("POST","/",sbRequestBody,sbResponseBody)
If (success <> True) Then
    System.DebugLog(rest.LastErrorText)
    Return
End If

Dim respStatusCode As Int32
respStatusCode = rest.ResponseStatusCode
System.DebugLog("response status code = " + Str(respStatusCode))
If (respStatusCode >= 400) Then
    System.DebugLog("Response Status Code = " + Str(respStatusCode))
    System.DebugLog("Response Header:")
    System.DebugLog(rest.ResponseHeader)
    System.DebugLog("Response Body:")
    System.DebugLog(sbResponseBody.GetAsString())
    Return
End If

Dim jsonResponse As New Chilkat.JsonObject
success = jsonResponse.LoadSb(sbResponseBody)

jsonResponse.EmitCompact = False
System.DebugLog(jsonResponse.Emit())

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

// {
//   "Attributes": {
//     "LastPostedBy": {
//       "S": "alice@example.com"
//     },
//     "ForumName": {
//       "S": "Amazon DynamoDB"
//     },
//     "LastPostDateTime": {
//       "S": "20130320010350"
//     },
//     "Tags": {
//       "SS": [
//         "Update",
//         "Multiple Items",
//         "HelpMe"
//       ]
//     },
//     "Subject": {
//       "S": "Maximum number of items?"
//     },
//     "Views": {
//       "N": "5"
//     },
//     "Message": {
//       "S": "I want to put 10 million data items to an Amazon DynamoDB table.  Is there an upper limit?"
//     }
//   }
// }

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

Dim strVal As String

Dim AttributesLastPostedByS As String
AttributesLastPostedByS = jsonResponse.StringOf("Attributes.LastPostedBy.S")
Dim AttributesForumNameS As String
AttributesForumNameS = jsonResponse.StringOf("Attributes.ForumName.S")
Dim AttributesLastPostDateTimeS As String
AttributesLastPostDateTimeS = jsonResponse.StringOf("Attributes.LastPostDateTime.S")
Dim AttributesSubjectS As String
AttributesSubjectS = jsonResponse.StringOf("Attributes.Subject.S")
Dim AttributesViewsN As String
AttributesViewsN = jsonResponse.StringOf("Attributes.Views.N")
Dim AttributesMessageS As String
AttributesMessageS = jsonResponse.StringOf("Attributes.Message.S")
Dim i As Int32
i = 0
Dim count_i As Int32
count_i = jsonResponse.SizeOfArray("Attributes.Tags.SS")
While i < count_i
    jsonResponse.I = i
    strVal = jsonResponse.StringOf("Attributes.Tags.SS[i]")
    i = i + 1
Wend