Implementing a two-way communication between Microsoft Dynamics CRM and 3rd party app

I need to implement a bi-directional communication between Microsoft Dynamics CRM and a 3rd party server. The ideal scenario is as follows:

1. User tries to create an entity in CRM
2. In pre-create hook a 3rd party library function is calle开发者_运维百科d (or web service or whatever), filled with relevant info, which tries to create the respective entity on the server
3. If the call fails, creation fails in CRM
4. If the call succeeds, the entity is created in the CRM AND additional fields are filled with return values from the call

More specifically, I want to do something like this when user tries to create a new entity instance:

try {
    ExternalWebService.CreateTrade(ref TradeInfo info)
    //this was initialized on the external server
    myCRM_Trade_Entity.SerialNo = info.SerialNo; 
    CreateNew(myCRM_Trade_Entity);

} catch (whatever) {
    fail;
}

What would be the suggested way to do this? I am new to Dynamics, have read about Workflows and Plugins but am not sure how should I do this properly.

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The way to do that is obviously a plugin, except if the process called by the web service is very long and could timeout.

The only way to avoid creating an entity, is to create a plugin and hook it on the pre-create event, like you are saying.

When using a workflow, the entity must be saved before the workflow is executed.

I think you are on the good way. I would, however, avoid including a library, the webservice solution should be better, because it does not required to register other libraries before registering the plugin assembly.