Fixed the != querying against nullable booleans. Closes GH-3953

Author: jeremydmiller

src/LinqTests/Acceptance/nullable_types.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Linq;
 using System.Threading.Tasks;
+using Marten;
 using Marten.Testing.Documents;
 using Marten.Testing.Harness;
 using Shouldly;
@@ -70,6 +71,50 @@ public async Task query_against_null_3()
             .ShouldBe(1);
     }
 
+    [Fact]
+    public async Task query_against_nullable_bool_not_true()
+    {
+        var target1 = new Target { NullableBoolean = null };
+        theSession.Store(target1);
+
+        var target2 = new Target { NullableBoolean = true };
+        theSession.Store(target2);
+
+        var target3 = new Target { NullableBoolean = false };
+        theSession.Store(target3);
+
+        await theSession.SaveChangesAsync();
+
+        theSession.Logger = new TestOutputMartenLogger(_output);
+
+        var list = await theSession.Query<Target>().Where(x => x.NullableBoolean != true).ToListAsync();
+        list.Count.ShouldBe(2);
+        list.Any(x => x.Id == target1.Id).ShouldBeTrue();
+        list.Any(x => x.Id == target3.Id).ShouldBeTrue();
+    }
+
+    [Fact]
+    public async Task query_against_nullable_bool_not_false()
+    {
+        var target1 = new Target { NullableBoolean = null };
+        theSession.Store(target1);
+
+        var target2 = new Target { NullableBoolean = true };
+        theSession.Store(target2);
+
+        var target3 = new Target { NullableBoolean = false };
+        theSession.Store(target3);
+
+        await theSession.SaveChangesAsync();
+
+        theSession.Logger = new TestOutputMartenLogger(_output);
+
+        var list = await theSession.Query<Target>().Where(x => x.NullableBoolean != false).ToListAsync();
+        list.Count.ShouldBe(2);
+        list.Any(x => x.Id == target1.Id).ShouldBeTrue();
+        list.Any(x => x.Id == target2.Id).ShouldBeTrue();
+    }
+
     [Fact]
     public async Task query_against_null_4()
     {

src/Marten/Linq/Members/BooleanMember.cs

@@ -1,20 +1,49 @@
 #nullable enable
+using System;
+using System.Linq.Expressions;
 using System.Reflection;
+using JasperFx.Core.Reflection;
 using Marten.Linq.SqlGeneration.Filters;
 using Weasel.Postgresql.SqlGeneration;
 
 namespace Marten.Linq.Members;
 
 internal class BooleanMember: QueryableMember, IComparableMember, IBooleanMember
 {
+    private readonly bool _isNullable;
+
     public BooleanMember(IQueryableMember parent, Casing casing, MemberInfo member, string pgType): base(parent,
         casing, member)
     {
         TypedLocator = $"CAST({RawLocator} as {pgType})";
+
+        _isNullable = member.GetRawMemberType().IsNullable();
     }
 
     public ISqlFragment BuildIsTrueFragment()
     {
         return new BooleanFieldIsTrue(this);
     }
+
+    public override ISqlFragment CreateComparison(string op, ConstantExpression constant)
+    {
+        if (constant.Value == null)
+        {
+            return op == "=" ? new IsNullFilter(this) : new IsNotNullFilter(this);
+        }
+
+        if (_isNullable && op == "!=")
+        {
+            if (constant.Value.Equals(true))
+            {
+                return CompoundWhereFragment.Or(new IsNullFilter(this), base.CreateComparison(op, constant));
+            }
+            else
+            {
+                return CompoundWhereFragment.Or(new IsNullFilter(this), base.CreateComparison(op, constant));
+            }
+        }
+
+        return base.CreateComparison(op, constant);
+    }
 }