job candidate should be unique by for pair of "jobId" and "userId"

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For create the job candidate - User can have many jobid assigned. But, same uid and job id combination should not be allowed.

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@nkumar-topcoder after the second though I guess we could skip this for now.

As I understand the same user could have multiple ResourceBooking records for the same job. For example, some user did some work for a particular job for 2 days. And after customer wants that users again and assign the same user to the same job for 3 more days using new ResourceBooking record.

So I guess this could be implemented by creating multiple JobCandidates records for the same job and user, so the whole process might look like this:

• We create JobCandidate for user1/job1
• Customer approves it and we create ResourceBooking user1/job1
• After some time contract for user1/job1 finished but customer wants to continue job
• We create another JobCandidate for the same user1/job1 so cusomter can choose some users again
• Customer choose the same user again
• We create another ResourceBooking for the same user user1/job1

At the end we have 2 JobCandidate and 2 ResourceBooking records for the same user and job.

@nkumar-topcoder what do you think? In general, I think it would be good to keep less validations in the API on the current early stage, when not all the requirements are fully clear. And only implement such validations when requirements are stabilized.