NHibernate projection: How to create AliasToBean projection?

Question

I am trying to convert this inefficient query into one that projects into a dto. Original query looks like this:

var flatFeePolicies = _session.QueryOver<FlatChargeAccessFee>(() => flatChargeAccessFeeAlias)
                                .JoinAlias(x => x.AgreementAccessFee, () => agreementAccessFeeAlias)
                                .JoinQueryOver(x => x.ClientPolicy, () => clientPolicyAlias)
                                .Where(y => agreementAccessFeeAlias.Agreement.Id == request.AgreementId)
                                .List()
                                .Select(x => new FlatChargeAccessFeeInfo()
                                    {
                                        FlatChargeAccessFeeId = x.Id,
                                        ClientName = x.ClientPolicy.Bid.Client.Name,
                                        PolicyNumber = x.ClientPolicy.PolicyNumber,
                                        ClientPolicyId = x.ClientPolicy.Id,
                                        AgreementAccessFeeId = x.AgreementAccessFee.Id,
                                        ShouldCheckBeGenerated = x.ShouldCheckBeGenerated,
                                        MonthlyFee = x.MontlyFeeAmount.Amount.ToString(),
                                        PolicyYear = x.ClientPolicy.PolicyNumber.Year
                                    })
                                .ToList();

I tried it like this:

var flatFeePolicies = _session.QueryOver<FlatChargeAccessFee>(() => flatChargeAccessFeeAlias)
                              .JoinAlias(x => x.AgreementAccessFee, () => agreementAccessFeeAlias)
                              .JoinQueryOver(x => x.ClientPolicy, () => clientPolicyAlias)
                              .Where(y => agreementAccessFeeAlias.Agreement.Id == request.AgreementId)
                              .SelectList(list => list
                                                      .Select(x => x.Id).WithAlias(() => feeInfo.FlatChargeAccessFeeId)
                                                      .Select(x => x.ClientPolicy.Bid.Client.Name).WithAlias(() => feeInfo.ClientName)
                                                      .Select(x => x.ClientPolicy.PolicyNumber).WithAlias(() => feeInfo.PolicyNumber)
                                                      .Select(x => x.ClientPolicy.Id).WithAlias(() => feeInfo.ClientPolicyId)
                                                      .Select(x => x.AgreementAccessFee.Id).WithAlias(() => feeInfo.AgreementAccessFeeId)
                                                      .Select(x => x.ShouldCheckBeGenerated).WithAlias(() => feeInfo.ShouldCheckBeGenerated)
                                                      .Select(x => x.MontlyFeeAmount.Amount.ToString()).WithAlias(() => feeInfo.MonthlyFee)
                                                      .Select(x => x.ClientPolicy.PolicyNumber.Year).WithAlias(() => feeInfo.PolicyYear)
                               )
                               .TransformUsing(Transformers.AliasToBean<FlatChargeAccessFeeInfo>())
                               .List<FlatChargeAccessFeeInfo>();

and I am getting an error that variable "x" has been referenced in scope but was not defined. What is the proper syntax to convert this?

After help from Andrew, here is the correct version that works

ClientPolicy clientPolicyAlias = null;
Client clientAlias = null;
Bid bidAlias = null;
AgreementAccessFee agreementAccessFeeAlias = null;
FlatChargeAccessFee flatChargeAccessFeeAlias = null;
FlatChargeAccessFeeInfo feeInfo = null;


var flatFeePolicies = _session.QueryOver<FlatChargeAccessFee>(() => flatChargeAccessFeeAlias)
                              .JoinAlias(a => a.AgreementAccessFee, () => agreementAccessFeeAlias)
                              .JoinQueryOver(b => b.ClientPolicy, () => clientPolicyAlias)
                              .JoinAlias(b=>b.Bid,()=>bidAlias)
                              .JoinAlias(b=>b.Client, ()=>clientAlias)
                              .Where(c => agreementAccessFeeAlias.Agreement.Id == request.AgreementId)

                              .SelectList(list => list
                                                      .Select(d => d.Id).WithAlias(() => feeInfo.FlatChargeAccessFeeId)
                                                      .Select(e => clientAlias.Name).WithAlias(() => feeInfo.ClientName)
                                                      .Select(e => clientAlias.Number).WithAlias(() => feeInfo.ClientNumber)
                                                      .Select(f => bidAlias.OptionNumber).WithAlias(() => feeInfo.BidOptionNumber)
                                                      .Select(f => bidAlias.Year).WithAlias(()=>feeInfo.PolicyYear)
                                                      .Select(g => clientPolicyAlias.Id).WithAlias(() => feeInfo.ClientPolicyId)
                                                      .Select(h => agreementAccessFeeAlias.Id).WithAlias(() => feeInfo.AgreementAccessFeeId)
                                                      .Select(j => j.ShouldCheckBeGenerated).WithAlias(() => feeInfo.ShouldCheckBeGenerated)
                                                      .Select(k => k.MontlyFeeAmount.Amount).WithAlias(()=>feeInfo.MonthlyFee)

                               )
                               .TransformUsing(Transformers.AliasToBean<FlatChargeAccessFeeInfo>())
                               .List<FlatChargeAccessFeeInfo>();

Answer 1

You're close, a few things though:

• This select:

  .Select(x => x.MontlyFeeAmount.Amount.ToString()).WithAlias(() => feeInfo.MonthlyFee)
  

  will not work. QueryOver attempts to turn your code directly into SQL. If the property does not exist as a column in the database, the query won't work properly (unless you're using a mapped custom type, QueryOver can handle those)

• Nested property access won't work either:

  .Select(x => x.ClientPolicy.Bid.Client.Name).WithAlias(() => feeInfo.ClientName)
  

  for a similar reason listed above. QueryOver will attempt to turn your property access directly into SQL. You'll need to explicitly join from ClientPolicy to Bid to Client.

In general, remember that you're writing code that's going to be turned into SQL. In fact, I normally write the SQL I want to generate first and then write the QueryOver that corresponds to that. Hope that helps!