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copied!<p>If you were to put the Business Rule Check (ie limit check) inside a transaction, it will be fine. That is</p> <ol> <li>User Clicks button that fires the Add Proposal Command</li> <li>Code starts a new transaction. See <a href="https://stackoverflow.com/questions/646318/nhibernate-with-transactionscope/4085328#4085328">here for how I suggest you use transactions</a> </li> <li>Load the RequestForProposal object from the db, or Refresh it. I suggest you use an upgrade lock.</li> <li>Add the new proposals to the root. Check the limit constraint, throw an exception it fails.</li> <li>Commit the transaction</li> </ol> <p>Doing it this way you are using the databases <a href="http://en.wikipedia.org/wiki/Concurrency_control" rel="nofollow noreferrer">concurrency controls</a>. I don't think there is any other way of doing it. </p> <p>This will create some contention, but you can take a few steps to minimize that. Namely make sure in Step 3 that the db column you select by has an index on it. This will cause a row lock, instead of a page lock.</p> <p>If you use an Upgrade lock in step 3, this will avoid deadlocks. Basically when the second users submits a proposal for the same Aggregate Root the db will not let you read it until the first transaction has committed.</p> <p>You should also consider adding a db index on Proposal.RequestForProposalId, it will help performance as that is the column the Proposal's are loaded on. I'm not 100% if it helps minimize the scope of any locks on that table, but it might ...</p>

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