Add Criteria.ConditionalsProjection for "switch-case" expressions with multiple Criterias/Projections (when/thens)

Author: Paul H

src/NHibernate.Test/Criteria/ProjectionsTest.cs

@@ -1,6 +1,6 @@
 using System;
-using System.Collections;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text.RegularExpressions;
 using NHibernate.Criterion;
 using NHibernate.Dialect;
@@ -78,7 +78,7 @@ public void UsingSqlFunctions_Concat()
 		[Test]
 		public void UsingSqlFunctions_Concat_WithCast()
 		{
-			if(Dialect is Oracle8iDialect)
+			if (Dialect is Oracle8iDialect)
 			{
 				Assert.Ignore("Not supported by the active dialect:{0}.", Dialect);
 			}
@@ -198,6 +198,84 @@ public void UsingConditionals()
 			}
 		}
 
+		[Test]
+		public void UsingMultiConditionals()
+		{
+			if (TestDialect.HasBrokenTypeInferenceOnSelectedParameters)
+				Assert.Ignore("Current dialect does not support this test");
+
+			var students = new[]
+			{
+				new Student() { StudentNumber = 6L, Name = "testa", },
+				new Student() { StudentNumber = 5L, Name = "testz", },
+				new Student() { StudentNumber = 4L, Name = "test1", },
+				new Student() { StudentNumber = 3L, Name = "test2", },
+				new Student() { StudentNumber = 2L, Name = "test998", },
+				new Student() { StudentNumber = 1L, Name = "test999", },
+			};
+
+			var expecteds = new[]
+			{
+				students[0],
+				students[1],
+				students[2],
+				students[3],
+			};
+
+			// student, sortingindex
+			var testData = new Tuple<Student, string>[]
+			{
+				System.Tuple.Create(expecteds[0], "1"),
+				System.Tuple.Create(expecteds[1], "2"),
+				System.Tuple.Create(expecteds[2], "3"),
+				System.Tuple.Create(expecteds[3], "4"),
+			};
+
+			using (ISession session = this.Sfi.OpenSession())
+			{
+				using (ITransaction transaction = session.BeginTransaction())
+				{
+					session.Save<Student>(students);
+					transaction.Commit();
+				}
+
+				using (ITransaction transaction = session.BeginTransaction())
+				{
+					// when Name = "testa" then 1 ...
+					var criterionProjections = testData
+						.Select(x => new ConditionalCriterionProjectionPair(Expression.Eq(nameof(Student.Name), x.Item1.Name), Projections.Constant(x.Item2)))
+						.ToArray();
+
+					// ... else 99
+					var elseProjection = Projections.Constant("99");
+
+					var conditionalsProjection = Projections.Conditionals(criterionProjections, elseProjection);
+
+					var order = Order.Asc(conditionalsProjection);
+
+					var criteria = session.CreateCriteria(typeof(Student))
+						.AddOrder(order);
+
+					var actuals = criteria.List<Student>();
+
+					Assert.GreaterOrEqual(actuals.Count, expecteds.Length);
+					for (int i = 0; i < expecteds.Length; i++)
+					{
+						var expected = expecteds[i];
+						var actual = actuals[i];
+
+						Assert.AreEqual(expected.Name, actual.Name);
+					}
+				}
+
+				using (ITransaction transaction = session.BeginTransaction())
+				{
+					session.Delete<Student>(students);
+					transaction.Commit();
+				}
+			}
+		}
+
 		[Test]
 		public void UseInWithProjection()
 		{

src/NHibernate.Test/Criteria/SessionExtender.cs

@@ -0,0 +1,32 @@
+namespace NHibernate.Test.Criteria
+{
+	internal static class SessionExtender
+	{
+		public static void SaveOrUpdate<T>(this ISession session, params T[] models)
+		{
+			for (int i = 0; i < models.Length; i++)
+			{
+				var model = models[i];
+				session.SaveOrUpdate(model);
+			}
+		}
+
+		public static void Save<T>(this ISession session, params T[] models)
+		{
+			for (int i = 0; i < models.Length; i++)
+			{
+				var model = models[i];
+				session.Save(model);
+			}
+		}
+
+		public static void Delete<T>(this ISession session, params T[] models)
+		{
+			for (int i = 0; i < models.Length; i++)
+			{
+				var model = models[i];
+				session.Delete(model);
+			}
+		}
+	}
+}

src/NHibernate/Criterion/ConditionalCriterionProjectionPair.cs

@@ -0,0 +1,29 @@
+namespace NHibernate.Criterion
+{
+	/// <summary>
+	/// Defines a pair of <see cref="ConditionalCriterionProjectionPair.Criterion"/> and <see cref="ConditionalCriterionProjectionPair.Projection"/>.
+	/// </summary>
+	public class ConditionalCriterionProjectionPair
+	{
+		/// <summary>
+		/// Initializes a new instance of the <see cref="ConditionalCriterionProjectionPair"/> class.
+		/// </summary>
+		/// <param name="criterion">The <see cref="ConditionalCriterionProjectionPair.Criterion"/>.</param>
+		/// <param name="projection">The <see cref="ConditionalCriterionProjectionPair.Projection"/>.</param>
+		public ConditionalCriterionProjectionPair(ICriterion criterion, IProjection projection)
+		{
+			this.Criterion = criterion;
+			this.Projection = projection;
+		}
+
+		/// <summary>
+		/// Gets the <see cref="ICriterion"/>.
+		/// </summary>
+		public ICriterion Criterion { get; }
+
+		/// <summary>
+		/// Gets the <see cref="IProjection"/>.
+		/// </summary>
+		public IProjection Projection { get; }
+	}
+}