Fix decimal equality comparison for Sqlite

src/NHibernate.Test/Async/Linq/OperatorTests.cs

@@ -35,6 +35,20 @@ public async Task UnaryMinusAsync()
 			Assert.AreEqual(1, await (session.Query<TimesheetEntry>().CountAsync(a => -a.NumberOfHours == -7)));
 		}
 
+		[Test]
+		public async Task DecimalAddAsync()
+		{
+			decimal offset = 5.5m;
+			decimal test = 10248 + offset;
+			var result = await (session.Query<Order>().Where(e => offset + e.OrderId == test).ToListAsync());
+			Assert.That(result, Has.Count.EqualTo(1));
+
+			offset = 5.5m;
+			test = 32.38m + offset;
+			result = await (session.Query<Order>().Where(e => offset + e.Freight == test).ToListAsync());
+			Assert.That(result, Has.Count.EqualTo(1));
+		}
+
 		[Test]
 		public async Task UnaryPlusAsync()
 		{

src/NHibernate.Test/Async/Linq/ParameterTests.cs

@@ -320,7 +320,7 @@ public async Task CompareFloatingPointParametersAndColumnsAsync()
 					totalParameters,
 					sql =>
 					{
-						Assert.That(sql, Does.Not.Contain("cast"));
+						Assert.That(sql, pair.Value == "Decimal" && Dialect.IsDecimalStoredAsFloatingPointNumber ? Does.Contain("cast") : Does.Not.Contain("cast"));
 						Assert.That(GetTotalOccurrences(sql, $"Type: {pair.Value}"), Is.EqualTo(totalParameters));
 					}));
 			}

src/NHibernate.Test/Linq/OperatorTests.cs

@@ -24,6 +24,20 @@ public void UnaryMinus()
 			Assert.AreEqual(1, session.Query<TimesheetEntry>().Count(a => -a.NumberOfHours == -7));
 		}
 
+		[Test]
+		public void DecimalAdd()
+		{
+			decimal offset = 5.5m;
+			decimal test = 10248 + offset;
+			var result = session.Query<Order>().Where(e => offset + e.OrderId == test).ToList();
+			Assert.That(result, Has.Count.EqualTo(1));
+
+			offset = 5.5m;
+			test = 32.38m + offset;
+			result = session.Query<Order>().Where(e => offset + e.Freight == test).ToList();
+			Assert.That(result, Has.Count.EqualTo(1));
+		}
+
 		[Test]
 		public void UnaryPlus()
 		{

src/NHibernate.Test/Linq/ParameterTests.cs

@@ -308,7 +308,7 @@ public void CompareFloatingPointParametersAndColumns()
 					totalParameters,
 					sql =>
 					{
-						Assert.That(sql, Does.Not.Contain("cast"));
+						Assert.That(sql, pair.Value == "Decimal" && Dialect.IsDecimalStoredAsFloatingPointNumber ? Does.Contain("cast") : Does.Not.Contain("cast"));
 						Assert.That(GetTotalOccurrences(sql, $"Type: {pair.Value}"), Is.EqualTo(totalParameters));
 					});
 			}

src/NHibernate.Test/TestCase.cs

@@ -17,6 +17,7 @@
 using NHibernate.Dialect;
 using NHibernate.Driver;
 using NHibernate.Engine.Query;
+using NHibernate.SqlTypes;
 using NHibernate.Util;
 using NSubstitute;
 
@@ -525,6 +526,8 @@ protected void ClearQueryPlanCache()
 			var forPartsOfMethod = ReflectHelper.GetMethodDefinition(() => Substitute.ForPartsOf<object>());
 			var substitute = (Dialect.Dialect) forPartsOfMethod.MakeGenericMethod(origDialect.GetType())
 																.Invoke(null, new object[] { new object[0] });
+			substitute.GetCastTypeName(Arg.Any<SqlType>())
+			          .ReturnsForAnyArgs(x => origDialect.GetCastTypeName(x.ArgAt<SqlType>(0)));
 
 			dialectProperty.SetValue(Sfi.Settings, substitute);
 

src/NHibernate/Dialect/Dialect.cs

@@ -2611,6 +2611,11 @@ public virtual bool SupportsSqlBatches
 			get { return false; }
 		}
 
+		/// <summary>
+		/// Whether <see cref="decimal"/> is stored as a floating point number.
+		/// </summary>
+		public virtual bool IsDecimalStoredAsFloatingPointNumber => false;
+
 		public virtual bool IsKnownToken(string currentToken, string nextToken)
 		{
 			return false;

src/NHibernate/Dialect/SQLiteDialect.cs

@@ -362,6 +362,9 @@ public override bool GenerateTablePrimaryKeyConstraintForIdentityColumn
 			get { return false; }
 		}
 
+		/// <inheritdoc />
+		public override bool IsDecimalStoredAsFloatingPointNumber => true;
+
 		public override string Qualify(string catalog, string schema, string table)
 		{
 			StringBuilder qualifiedName = new StringBuilder();

src/NHibernate/Linq/Visitors/HqlGeneratorExpressionVisitor.cs

@@ -579,8 +579,12 @@ protected HqlTreeNode VisitConstantExpression(ConstantExpression expression)
 			if (_parameters.ConstantToParameterMap.TryGetValue(expression, out namedParameter))
 			{
 				_parameters.RequiredHqlParameters.Add(new NamedParameterDescriptor(namedParameter.Name, null, false));
+				var parameter = _hqlTreeBuilder.Parameter(namedParameter.Name).AsExpression();
 
-				return _hqlTreeBuilder.Parameter(namedParameter.Name).AsExpression();
+				// SQLite driver binds decimal parameters to text, which can cause unexpected results in arithmetic operations.
+				return _parameters.SessionFactory.Dialect.IsDecimalStoredAsFloatingPointNumber && expression.Type.UnwrapIfNullable() == typeof(decimal)
+					? _hqlTreeBuilder.TransparentCast(parameter, expression.Type)
+					: parameter;
 			}
 
 			return _hqlTreeBuilder.Constant(expression.Value);