The blog will explain “ How to trigger a plugin for many to many (N:N) relationship. For this blog, I have created a new N:N relationship between account and contact entity. I am displaying this relationship just in account entity. The following screen shot is displaying the properties of the relationship.
a1
To trigger a plugin on association of 2 entities in a n:n relationship, we will use associate plugin message. I am using the developer’s toolkit for writing code from last 6 months. The problem is developer’s toolkit does not support “Associate” message. To create a plugin in developer’s toolkit, you need to choose primary entity and to use “Associate” message primary entity and secondary entity has to be “none”. There is a workaround to register  plugin step on “Associate” message. Here are the steps.
  1. Follow the steps in this blog on how to create a plugin using developer’s toolkit.
  2. In the step 12th of above-mentioned blog, replace the function “ExecutePostAccountCreate” with the following code
    protected void ExecutePostAccount(LocalPluginContext localContext)
    {

    if (localContext == null)
    {
    throw new ArgumentNullException("localContext");
    }

    // TODO: Implement your custom Plug-in business logic.
    // Obtain the execution context from the service provider.
    IPluginExecutionContext context = localContext.PluginExecutionContext;
    IOrganizationService service = localContext.OrganizationService;
    ITracingService tracingService = localContext.TracingService;

    try{
    // The InputParameters collection contains all the data passed in the message request.
    if (!context.InputParameters.Contains("Target")) { return; }

    EntityReference ef = (EntityReference)context.InputParameters["Target"];
    if (ef.LogicalName != "account") { return; }

    Relationship relationship = (Relationship)context.InputParameters["Relationship"];
    if (relationship.SchemaName != "new_account_contact") { return; }

    // Get Related Entities
    EntityReferenceCollection re = (EntityReferenceCollection)context.InputParameters["RelatedEntities"];

    foreach (EntityReference rel in re)
    {

    Entity relatedEntity = service.Retrieve("contact", rel.Id, new ColumnSet("address1_city"));
    string city = (string)relatedEntity.Attributes["address1_city"];
    if (city=="Sydney")
    {
    //create a task
    Entity task = new Entity("task");
    task["subject"] = "A new contact from sydney is added to the account";
    task["regardingobjectid"] = ef;
    task["description"] = "A new contact from sydney is added to the account";
    // Create the task in Microsoft Dynamics CRM.
    service.Create(task);

    }
    }//endfor
    }
    catch (FaultException ex)
    {
    tracingService.Trace(ex.Message.ToString());
    throw new InvalidPluginExecutionException("An error occurred in the plug-in.", ex);
    }

    }//end function
  3. Add the following reference to your plugin class.
    using Microsoft.Xrm.Sdk.Query;
  4. The above code will create a task, when we add a contact with “address1_city” field equal to “Sydney” to an account. Just remember we are relating a contact to account using N:N relationship.
  5. Now change the RegisterFile.crmregister file  to register on an “Associate” message. Open the file and look for your plugin definition. It will look something like the following code.
    <Plugin Description="Plug-in to PostAccountCreate" FriendlyName="PostAccountCreate" Name="CRM2011PluginSeries.Plugins.PostAccountCreate" Id="420419bd-9fe7-404e-a5e3-afa582f21dd3" TypeName="CRM2011PluginSeries.Plugins.PostAccountCreate">
    <Steps>
    <clear />
    <Step CustomConfiguration="" Name="PostAccountCreate" Description="Post-Operation of Account Create" Id="b248f264-2b3f-e111-ab54-00155d32042e" MessageName="Create" Mode="Synchronous" PrimaryEntityName="account" Rank="1" SecureConfiguration="" Stage="PostOutsideTransaction" SupportedDeployment="ServerOnly">
    <Images />
    </Step>
    </Steps>
    </Plugin>
  6. Now change the MessageName="Create" to MessageName="Associate" and PrimaryEntityName="account" to PrimaryEntityName="".
  7. Save the changes and deploy the plugin.
  8. If you get any errors during deployment, just deploy the plugin using plugin registeration tool. Don't forget to leave the "PrimaryEntityName" = none.
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