Add support for HasValue

Author: bjornharrtell

src/PgKeyValueDB/SqlExpressionVisitor.cs

@@ -248,6 +248,36 @@ private string BuildJsonPath(MemberInfo member, string parentPath = "value")
 
     protected override Expression VisitMember(MemberExpression node)
     {
+        // Handle HasValue property on nullable types
+        if (node.Member.Name == "HasValue" && node.Expression is MemberExpression nullableMember)
+        {
+            // Check if this is accessing a closure field
+            if (nullableMember.Expression?.NodeType == ExpressionType.Constant)
+            {
+                var value = Expression.Lambda(node).Compile().DynamicInvoke();
+                AddParameter(value, node.Type);
+                return node;
+            }
+
+            // For nullable properties, HasValue means the JSON field is not null
+            if (nullableMember.Expression is MemberExpression nestedMember)
+            {
+                var parentPath = BuildNestedJsonPath(nestedMember);
+                var jsonPath = BuildJsonPath(nullableMember.Member, parentPath);
+                // Remove the cast since we're checking for null
+                var pathWithoutCast = jsonPath.Substring(1, jsonPath.LastIndexOf(')') - 1);
+                whereClause.Append($"({pathWithoutCast}) is not null");
+            }
+            else if (nullableMember.Expression?.NodeType == ExpressionType.Parameter)
+            {
+                var jsonPath = BuildJsonPath(nullableMember.Member);
+                // Remove the cast since we're checking for null
+                var pathWithoutCast = jsonPath.Substring(1, jsonPath.LastIndexOf(')') - 1);
+                whereClause.Append($"({pathWithoutCast}) is not null");
+            }
+            return node;
+        }
+
         // Handle closure/captured variables
         if (node.Expression?.NodeType == ExpressionType.Constant)
         {

test/PgKeyValueDB.Tests/PgKeyValueDBTest.cs

@@ -755,4 +755,50 @@ public async Task FilterByIsNullOrWhiteSpaceTest()
         Assert.AreEqual(1, usersWithValidDisplayName.Count);
         Assert.AreEqual("Alice", usersWithValidDisplayName[0].Name);
     }
+
+    [TestMethod]
+    public async Task FilterByHasValueTest()
+    {
+        var key1 = nameof(FilterByHasValueTest) + "1";
+        var key2 = nameof(FilterByHasValueTest) + "2";
+        var key3 = nameof(FilterByHasValueTest) + "3";
+        var pid = nameof(FilterByHasValueTest);
+
+        var user1 = new UserProfile
+        {
+            Name = "Alice",
+            IsVerified = true
+        };
+
+        var user2 = new UserProfile
+        {
+            Name = "Bob",
+            IsVerified = false
+        };
+
+        var user3 = new UserProfile
+        {
+            Name = "Charlie",
+            IsVerified = null // null value
+        };
+
+        await kv.UpsertAsync(key1, user1, pid);
+        await kv.UpsertAsync(key2, user2, pid);
+        await kv.UpsertAsync(key3, user3, pid);
+
+        // This query should filter users where IsVerified has a value (not null)
+        Expression<Func<UserProfile, bool>> expr = u => u.IsVerified.HasValue;
+        var usersWithVerificationStatus = await kv.GetListAsync(pid, expr).ToListAsync();
+
+        Assert.AreEqual(2, usersWithVerificationStatus.Count);
+        Assert.IsTrue(usersWithVerificationStatus.Any(u => u.Name == "Alice"));
+        Assert.IsTrue(usersWithVerificationStatus.Any(u => u.Name == "Bob"));
+
+        // Test the opposite - users where IsVerified is null
+        Expression<Func<UserProfile, bool>> exprNoValue = u => !u.IsVerified.HasValue;
+        var usersWithoutVerificationStatus = await kv.GetListAsync(pid, exprNoValue).ToListAsync();
+
+        Assert.AreEqual(1, usersWithoutVerificationStatus.Count);
+        Assert.AreEqual("Charlie", usersWithoutVerificationStatus[0].Name);
+    }
 }