Enterprise Integration Patterns Part-3 – Resequencer


At times ordered delivery of multiple messages are required and these messages are received in a non-sequential order. This problem is solved by the resequencer enterprise integration pattern. The resequencer integration pattern implies the following.

  • All the incoming messages must have the BatchID, their sequence and the last message of the sequence must be determined.
  • All the incoming messages are stored in a correct order in a temporary cache and when all of the messages are received the messages are sent in order.
  • You can read more about resequencer pattern here.

    In the example shown the incoming messages have a BatchID which works as a correlation set. The property is promoted to the message context and the correlation type is configured. The correlation is initialized by the first receive shape and the orchestration is started when the first message arrives. The message is saved in the SortedList of type System.Xml.XmlDocument so that we can save the message as a key value pair.

    The sequence of the message is determined from the message payload and each message has the field for its sequence. To receive all the messages a listen shape with a receive which follows the correlation based on the batchID is placed and on the other branch a delay of 20 secs is configured. The loop terminates when all the messages in the message stream are received. Each message has a field of TotalMsgs which determines the total messages. A loop variable is incremented when each message arrives.

    resequencer_1

    In the next loop all of the messages are returned to the send port in the right sequence.

    resequencer_2

    Note
    :
    Resequencing pattern must have a cache where the messages should be stored temporarily and when all the messages are received they must be sorted and sent in a sequence. However in this simple example we have used memory for storing messages whereas this approach is not good if the message size are very large. Another approach to store messages would be in a Database or on the Disk as a file. Storing on disk would involve efforts to retreive the files again. However storing in a database would also require connection to database, involving SQLServer/Oracle Ports and handling failure exceptions. I haven’t still found the best approach to cache messages, though I think storing the messages in the database would be best considering the performance factor.

    You can download the sample here.

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    Enterprise Integration Patterns Part-2 – Recipient List


    In the recipient list enterprise pattern a message is sent to multiple recipients in the list through different channels. The recipient list inspects the incoming message determines the list of recipients based on the incoming message and forwards the message to all the recipients through different channels. You can read more about recipient list pattern here.

    Determining Recipient List

    From the impletation point of view in the first round the incoming message is inspected and then depending on the data the recipient list is determined. For this we create a parent orchestration who receives an order message and if the order amount is greater that 10,000 it forwards the message to its different suppliers for quote otherwise buys it from its favourite supplier. I have also applied the filter for recipients in the child orchestration. In the parent orchestration we have a variable amount which is passed as a parameter to the child orchestration. This variable determines the recipient of the message. The value of this variable is extracted from the incoming message.

    RecipientListChildOrchestration


    Forwarding the message to recipients through different  channels

    In the first part we use the parent orchestration in which a loop is started to call the child orchestration asynchronously using a Start Orchestration shape. A self-correlating port, the request message and the filter variable is passed to the child orchestration as a parameter. You can read more about self correlating ports in my previous post about Scatter and Gather Enterprise pattern. In the second iteration all the response messages are collected back using the self correlating port. Remember to set the child orchestration long-running scope timeout so that if the orchestration fails to return the message the parent orchestration does not waits for it. Then the response messages can be processed and a response can be returned back from the orchestration.

    RecipientListParentOrchestratio
    You can download the sample from here.

    Enterprise Integration Patterns Part-1 – Scatter and Gather using Self Correlating Port


    Scatter and Gather Integration pattern implies that a message is sent to the Scatter-Garther Operation and the message is either debatched and sent to multiple recepients or is sent as it is depending upon the requirements. The recepients process the message request and when the processing is completed a response is sent back to Scatter-Gather where all the responses are collected from all the recepients and then processed and aggregated into a single message. You can read more about Scatter-Gather Enterprise pattern here.

    There can be many approaches for building this pattern but I would suggest to follow a loosely coupled design where you can add more systems. I have used Self correlating ports where the parent orchestration calls the partner orchestrations.

    Self Correlating ports – Response messsage returned by Start Orchestration shape:

    Self correlating ports are used by orchestrations where it calls another orchestration by passing a port instance as a parameter to the child orchestration. The child orchestration sends the message back to this port instance. In the parent orchestration you can create a new one-way send communication port and use direct binding and select “self correlating” in the port configuration wizard. In the child orchestration drag a port shape and select use existing port type and select the self correlating port you created in the partent orchestration. Use one way communication and send in the port configuration wizard. The self correlating port is part as a port parameter to the child orchestration and the orchestration is called by Start Orchestration shape. In this way a response message is returned by Start orchestration shape.

     self_correlating_parent

    The diagram below shows the design of the parent orchestration where the parent orchestration calls the partner orchestrations using Start Orchestration shape within the parallel shape. Remember that the Start Orchestration shape executes asynchronously and it does not returns a message.  So we use self correlating ports to return the message back to the parent orchestration. The advantage in this approach is that it is an asynchronous operation and the child orchestration are called concurrently and their responses are also collected independently irrespective of the order of response messages are received. With looping the parent orchestration has to wait for the first child orchestration to complete before calling the next orchestration.

     Scatter_And_Gather_Parent_Orch

    At the end you must apply the business logic to aggregate all the responses into one consolidated response message. I have used a simple transformation map that outputs a response message. In the partner 1 orchestration I have placed a delay shape with delay of 10 seconds and the partner1 orchestration is started in the first branch of the parallel shape. Therefore the response is received after the execution and response of the other two orchestrations.

     

    Partner orchestrations cannot be invoked by start orchestration shape

    However if the child/partner orchestrations cannot have a self-correlating port as a parameter or you cannot start orchestrations (if the orchestration has receive shape activate property value “True”) then you have to place send shapes in place of start orchestration shapes while the rest of the design will remain the same. When sending the message you have to ensure that the child or partner orchestration is invoked and also you have to use correlation in this design. The send shape will initialize the correlation set while the receive shape will follow the correlation.

     

    Web Services as partners for Scatter-Gather

    If the partner is a web service then the calling and receiving of the message will be a synchronous operation therefore the send and receive shape will be in the parallel shape branches. The self correlating ports or correlation will not be required for this design.

    You can download the Scatter and gather integration pattern sample from here.

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