Add NHibernate unit of work implementation

src/ContractImplementations.NHibernate/ContractImplementations.NHibernate.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+    <Import Project="../MSBuild/Base.props"/>
+    <Import Project="../MSBuild/Packable.props"/>
+
+    <ItemGroup Label="Package references">
+        <PackageReference Include="Dapper" Version="2.1.35" />
+        <PackageReference Include="NHibernate" Version="5.5.*"/>
+    </ItemGroup>
+
+    <ItemGroup Label="Project dependencies">
+        <ProjectReference Include="..\Bootstrapping\Bootstrapping.csproj" />
+        <ProjectReference Include="..\Foundation\Foundation.csproj"/>
+    </ItemGroup>
+</Project>

src/ContractImplementations.NHibernate/EntitySet.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using IOKode.OpinionatedFramework.Persistence.QueryBuilder;
+using IOKode.OpinionatedFramework.Persistence.QueryBuilder.Exceptions;
+using IOKode.OpinionatedFramework.Persistence.QueryBuilder.Filters;
+using IOKode.OpinionatedFramework.Persistence.UnitOfWork;
+using NHibernate;
+using NHibernate.Criterion;
+using NHNonUniqueResultException = NHibernate.NonUniqueResultException;
+using NonUniqueResultException = IOKode.OpinionatedFramework.Persistence.QueryBuilder.Exceptions.NonUniqueResultException;
+
+namespace IOKode.OpinionatedFramework.ContractImplementations.NHibernate;
+
+public class EntitySet<T> : IEntitySet<T> where T : Entity
+{
+    private readonly ISession _session;
+
+    public EntitySet(ISession session)
+    {
+        _session = session;
+    }
+
+    public async Task<T> GetByIdAsync(object id, CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            return await _session.LoadAsync<T>(id, cancellationToken);
+        }
+        catch (ObjectNotFoundException ex)
+        {
+            throw new EntityNotFoundException(id, ex);
+        }
+    }
+
+    public async Task<T> GetByIdOrDefaultAsync(object id, CancellationToken cancellationToken = default)
+    {
+        return await _session.GetAsync<T>(id, cancellationToken);
+    }
+
+    public async Task<T> SingleAsync(Filter? filter, CancellationToken cancellationToken = default)
+    {
+        var criteria = _session.CreateCriteria<T>();
+        ApplyFilter(criteria, filter);
+
+        try
+        {
+            var result = await criteria.UniqueResultAsync<T>(cancellationToken);
+            if (result == null)
+            {
+                throw new EmptyResultException();
+            }
+
+            return result;
+        }
+        catch(NHNonUniqueResultException ex)
+        {
+            throw new NonUniqueResultException(ex);
+        }
+    }
+
+    public async Task<T?> SingleOrDefaultAsync(Filter? filter, CancellationToken cancellationToken = default)
+    {
+        var criteria = _session.CreateCriteria<T>();
+        ApplyFilter(criteria, filter);
+
+        try
+        {
+            return await criteria.UniqueResultAsync<T>(cancellationToken);
+        }
+        catch(NHNonUniqueResultException ex)
+        {
+            throw new NonUniqueResultException(ex);
+        }
+    }
+
+    public async Task<T> FirstAsync(Filter? filter, CancellationToken cancellationToken = default)
+    {
+        var criteria = _session.CreateCriteria<T>();
+        ApplyFilter(criteria, filter);
+        criteria.SetMaxResults(1);
+
+        var list = await criteria.ListAsync<T>(cancellationToken);
+        if (list.Count == 0)
+        {
+            throw new EmptyResultException();
+        }
+
+        return list[0];
+    }
+
+    public async Task<T?> FirstOrDefaultAsync(Filter? filter, CancellationToken cancellationToken = default)
+    {
+        var criteria = _session.CreateCriteria<T>();
+        ApplyFilter(criteria, filter);
+        criteria.SetMaxResults(1);
+
+        var list = await criteria.ListAsync<T>(cancellationToken);
+        return list.Count == 0 ? null : list[0];
+    }
+
+    public async Task<IReadOnlyCollection<T>> ManyAsync(Filter? filter, CancellationToken cancellationToken = default)
+    {
+        var criteria = _session.CreateCriteria<T>();
+        ApplyFilter(criteria, filter);
+
+        var list = await criteria.ListAsync<T>(cancellationToken);
+        return (IReadOnlyCollection<T>)list;
+    }
+
+    private void ApplyFilter(ICriteria criteria, Filter? filter)
+    {
+        if (filter == null)
+        {
+            return;
+        }
+
+        var criterion = BuildCriterion(filter);
+        criteria.Add(criterion);
+    }
+
+    private ICriterion BuildCriterion(Filter filter)
+    {
+        return filter switch
+        {
+            EqualsFilter eq => Restrictions.Eq(eq.FieldName, eq.Value),
+            LikeFilter like => Restrictions.Like(like.FieldName, like.Pattern, MatchMode.Anywhere),
+            InFilter inFilter => Restrictions.In(inFilter.FieldName, inFilter.Values),
+            BetweenFilter betweenFilter => Restrictions.Between(betweenFilter.FieldName, betweenFilter.Low, betweenFilter.High),
+            GreaterThanFilter greaterThanFilter => Restrictions.Gt(greaterThanFilter.FieldName, greaterThanFilter.Value),
+            LessThanFilter lessThanFilter => Restrictions.Lt(lessThanFilter.FieldName, lessThanFilter.Value),
+            AndFilter andFilter => BuildJunction(andFilter.Filters, isAnd: true),
+            OrFilter orFilter => BuildJunction(orFilter.Filters, isAnd: false),
+            NotFilter notFilter => Restrictions.Not(BuildCriterion(notFilter.Filter)),
+            NotEqualsFilter notEqualsFilter => Restrictions.Not(Restrictions.Eq(notEqualsFilter.FieldName, notEqualsFilter.Value)),
+            _ => throw new NotSupportedException($"Filter type '{filter.GetType().Name}' is not supported.")
+        };
+    }
+
+    private Junction BuildJunction(Filter[] conditions, bool isAnd)
+    {
+        Junction junction = isAnd ? Restrictions.Conjunction() : Restrictions.Disjunction();
+        foreach (var cond in conditions)
+        {
+            junction.Add(BuildCriterion(cond));
+        }
+
+        return junction;
+    }
+}

src/ContractImplementations.NHibernate/UnitOfWork.cs

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+using System;
+using System.Collections.Generic;
+using System.Data;
+using System.Diagnostics;
+using System.Linq;
+using System.Reflection;
+using System.Threading;
+using System.Threading.Tasks;
+using Dapper;
+using IOKode.OpinionatedFramework.Persistence.QueryBuilder;
+using IOKode.OpinionatedFramework.Persistence.UnitOfWork;
+using IOKode.OpinionatedFramework.Persistence.UnitOfWork.Exceptions;
+using NHibernate;
+
+namespace IOKode.OpinionatedFramework.ContractImplementations.NHibernate;
+
+public class UnitOfWork : IUnitOfWork, IAsyncDisposable
+{
+    private readonly Dictionary<Type, Repository> repositories = new();
+    private readonly ISession session;
+    private ITransaction? transaction;
+    private bool isRollbacked;
+
+    public UnitOfWork(ISessionFactory sessionFactory)
+    {
+        this.session = sessionFactory.OpenSession();
+    }
+
+    public bool IsRolledBack => this.isRollbacked;
+
+    public Task BeginTransactionAsync(CancellationToken cancellationToken = default)
+    {
+        ThrowsIfRolledBack();
+
+        this.transaction = this.session.BeginTransaction();
+        return Task.CompletedTask;
+    }
+
+    public async Task CommitTransactionAsync(CancellationToken cancellationToken = default)
+    {
+        ThrowsIfRolledBack();
+
+        if (this.transaction is null)
+        {
+            throw new InvalidOperationException("No transaction is active.");
+        }
+
+        await this.transaction.CommitAsync(cancellationToken);
+        this.transaction.Dispose();
+        this.transaction = null;
+    }
+
+    public async Task RollbackTransactionAsync(CancellationToken cancellationToken = default)
+    {
+        ThrowsIfRolledBack();
+
+        if (this.transaction is null)
+        {
+            throw new InvalidOperationException("No transaction is active.");
+        }
+
+        await this.transaction.RollbackAsync(cancellationToken);
+        this.transaction.Dispose();
+        this.transaction = null;
+        this.session.Clear();
+        await DisposeAsync();
+        this.isRollbacked = true;
+    }
+
+    public bool IsTransactionActive
+    {
+        get
+        {
+            ThrowsIfRolledBack();
+            return this.transaction is {IsActive: true};
+        }
+    }
+
+    public async Task AddAsync<T>(T entity, CancellationToken cancellationToken = default) where T : Entity
+    {
+        ThrowsIfRolledBack();
+        await this.session.PersistAsync(entity, cancellationToken);
+    }
+
+    public Task<bool> IsTrackedAsync<T>(T entity, CancellationToken cancellationToken = default) where T : Entity
+    {
+        ThrowsIfRolledBack();
+        return Task.FromResult(session.Contains(entity));
+    }
+
+    public async Task StopTrackingAsync<T>(T entity, CancellationToken cancellationToken = default) where T : Entity
+    {
+        ThrowsIfRolledBack();
+        await this.session.EvictAsync(entity, cancellationToken);
+    }
+
+    public async Task<bool> HasChangesAsync(CancellationToken cancellationToken)
+    {
+        ThrowsIfRolledBack();
+        return await this.session.IsDirtyAsync(cancellationToken);
+    }
+
+    public IEntitySet<T> GetEntitySet<T>() where T : Entity
+    {
+        ThrowsIfRolledBack();
+        return new EntitySet<T>(this.session);
+    }
+
+    public async Task<ICollection<T>> RawProjection<T>(string query, IList<object>? parameters = null, CancellationToken cancellationToken = default)
+    {
+        ThrowsIfRolledBack();
+
+        if (parameters != null && !parameters.Any())
+        {
+            parameters = null!;
+        }
+
+        var transaction = GetTransaction();
+        return (await this.session.Connection.QueryAsync<T>(query, parameters, transaction)).ToArray();
+    }
+
+    public Repository GetRepository(Type repositoryType)
+    {
+        ThrowsIfRolledBack();
+        IUnitOfWork.EnsureTypeIsRepository(repositoryType);
+
+        if (this.repositories.TryGetValue(repositoryType, out var repo))
+        {
+            return repo;
+        }
+
+        // Create an instance of the repository. This assumes the repository has
+        // a parameterless constructor or a constructor we can access non-publicly.
+        repo = (Repository)Activator.CreateInstance(repositoryType, nonPublic: true)!;
+
+        // Use reflection to set the UnitOfWork property.
+        // The property is defined on the Repository base class, so we reflect on typeof(Repository).
+        // The compiler generates a backing field named `<UnitOfWork>k__BackingField` for auto-properties.
+        var field = typeof(Repository).GetField("unitOfWork", BindingFlags.Instance | BindingFlags.NonPublic);
+
+        if (field is null)
+        {
+            throw new UnreachableException("Could not find the 'unitOfWork' field.");
+        }
+
+        // Set the field value to the current IUnitOfWork instance
+        field.SetValue(repo, this);
+
+        this.repositories[repositoryType] = repo;
+        return repo;
+    }
+
+    public async Task SaveChangesAsync(CancellationToken cancellationToken)
+    {
+        ThrowsIfRolledBack();
+        bool isTransaction = IsTransactionActive;
+
+        if (!isTransaction)
+        {
+            await BeginTransactionAsync(cancellationToken);
+        }
+
+        await this.session.FlushAsync(cancellationToken);
+
+        if (!isTransaction)
+        {
+            await CommitTransactionAsync(cancellationToken);
+        }
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        if (this.IsTransactionActive)
+        {
+            await this.transaction!.RollbackAsync();
+        }
+        this.transaction?.Dispose();
+        this.session.Dispose();
+    }
+
+    private void ThrowsIfRolledBack()
+    {
+        if (IsRolledBack)
+        {
+            throw new UnitOfWorkRolledBackException();
+        }
+    }
+
+    private IDbTransaction GetTransaction()
+    {
+        using(var command = this.session.Connection.CreateCommand())
+        {
+            this.session.Transaction.Enlist(command);
+            return command.Transaction;
+        }
+    }
+}