xDataService/Mongo/XMongoReadPreferenceResolver.cs

using MongoDB.Driver;

namespace xDataService.Mongo {
    public static class XMongoReadPreferenceResolver {
        public static ReadPreference GetEffectiveReadPreference (
            IClientSessionHandle session,
            ReadPreference explicitReadPreference,
            ReadPreference defaultReadPreference) {
            if (explicitReadPreference != null) {
                return explicitReadPreference;
            }

            if (session.IsInTransaction) {
                var transactionReadPreference = session.WrappedCoreSession.CurrentTransaction.TransactionOptions.ReadPreference;
                if (transactionReadPreference != null) {
                    return transactionReadPreference;
                }
            }

            return defaultReadPreference ?? ReadPreference.Primary;
        }
    }
}