Fix compiled queries with IsOneOf and array parameters

src/LinqTests/Bugs/compiled_query_problem_with_search_by_string_and_string_collections.cs

@@ -0,0 +1,53 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Threading.Tasks;
+using Marten;
+using Marten.Linq;
+using Marten.Testing.Documents;
+using Marten.Testing.Harness;
+using Shouldly;
+
+namespace LinqTests.Bugs;
+
+public class compiled_query_problem_with_search_by_string_and_string_collections(DefaultStoreFixture fixture): IntegrationContext(fixture)
+{
+    protected override async Task fixtureSetup()
+    {
+        await theStore.Advanced.ResetAllData();
+    }
+
+    public class IssuesByTitles: ICompiledListQuery<Issue>, IQueryPlanning
+    {
+        public required string[] Titles { get; set; }
+        public required string Status { get; set; }
+
+        public Expression<Func<IMartenQueryable<Issue>, IEnumerable<Issue>>> QueryIs()
+        {
+            return query => query.Where(x => x.Status == Status && x.Title.IsOneOf(Titles));
+        }
+        void IQueryPlanning.SetUniqueValuesForQueryPlanning()
+        {
+            Status = "status";
+            Titles = ["title"];
+        }
+    }
+
+    [Fact]
+    public async Task can_search_isOneOf_strings_with_compiled_queries_and_query_planning()
+    {
+        var issue1 = new Issue { Title = "Issue1", Status = "Open" };
+        var issue2 = new Issue { Title = "Issue2", Status = "Open"};
+        var issue3 = new Issue { Title = "Issue3", Status = "Open" };
+
+        theSession.Store(issue1, issue2, issue3);
+        await theSession.SaveChangesAsync();
+
+        await using var session = theStore.QuerySession();
+        var query = new IssuesByTitles { Titles = [issue1.Title, issue2.Title], Status = issue1.Status };
+        var issues = await session.QueryAsync(query);
+
+        issues.Count().ShouldBe(2);
+    }
+}

src/Marten/Internal/CompiledQueries/ArrayParameterFinder.cs

@@ -0,0 +1,76 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Marten.Internal.CompiledQueries;
+
+/// <summary>
+/// Parameter finder for array-typed query members (string[], Guid[], int[], etc.)
+/// used in compiled queries with operators like IsOneOf().
+/// </summary>
+internal class ArrayParameterFinder<TElement> : IParameterFinder
+{
+    private readonly Func<int, TElement[]> _uniqueElementValues;
+
+    public ArrayParameterFinder(Func<int, TElement[]> uniqueElementValues)
+    {
+        _uniqueElementValues = uniqueElementValues;
+    }
+
+    public Type DotNetType => typeof(TElement[]);
+
+    public Queue<object> UniqueValueQueue(Type type)
+    {
+        // Each unique value is itself a TElement[] with unique content
+        var queue = new Queue<object>();
+        for (var i = 0; i < 20; i++)
+        {
+            queue.Enqueue(_uniqueElementValues(i + 1));
+        }
+        return queue;
+    }
+
+    public bool Matches(Type memberType)
+    {
+        return memberType == typeof(TElement[]);
+    }
+
+    public bool AreValuesUnique(object query, CompiledQueryPlan plan)
+    {
+        var members = plan.QueryMembers.OfType<IQueryMember<TElement[]>>().ToArray();
+
+        if (members.Length == 0)
+        {
+            return true;
+        }
+
+        // For arrays, check that each member has a distinct array (by reference or content)
+        return members.Select(x => x.GetValue(query))
+            .Distinct(new ArrayContentComparer<TElement>())
+            .Count() == members.Length;
+    }
+}
+
+internal class ArrayContentComparer<T> : IEqualityComparer<T[]?>
+{
+    public bool Equals(T[]? x, T[]? y)
+    {
+        if (ReferenceEquals(x, y)) return true;
+        if (x == null || y == null) return false;
+        return x.SequenceEqual(y);
+    }
+
+    public int GetHashCode(T[]? obj)
+    {
+        if (obj == null) return 0;
+        unchecked
+        {
+            var hash = 17;
+            foreach (var item in obj)
+            {
+                hash = hash * 31 + (item?.GetHashCode() ?? 0);
+            }
+            return hash;
+        }
+    }
+}

src/Marten/Internal/CompiledQueries/CompiledQueryPlan.cs

@@ -67,6 +67,22 @@ private void sortMembers()
             {
                 IncludeMembers.Add(member);
             }
+            else if (memberType.IsArray && QueryCompiler.Finders.Any(x => x.Matches(memberType.GetElementType()!)))
+            {
+                // Arrays like string[], int[], Guid[] etc. whose element type has a registered
+                // parameter finder should be treated as query parameters, NOT as include members.
+                // This check must come before the IList<> check since arrays implement IList<T>.
+                if (member is PropertyInfo)
+                {
+                    var queryMember = typeof(PropertyQueryMember<>).CloseAndBuildAs<IQueryMember>(member, memberType);
+                    QueryMembers.Add(queryMember);
+                }
+                else if (member is FieldInfo)
+                {
+                    var queryMember = typeof(FieldQueryMember<>).CloseAndBuildAs<IQueryMember>(member, memberType);
+                    QueryMembers.Add(queryMember);
+                }
+            }
             else if (memberType.Closes(typeof(IList<>)))
             {
                 IncludeMembers.Add(member);

src/Marten/Internal/CompiledQueries/ParameterUsage.cs

@@ -87,10 +87,47 @@ private static string npgsqlDataTypeInCodeFor(NpgsqlParameter parameter)
     private void generateSimpleCode(GeneratedMethod method, MemberInfo member, Type memberType,
         string parametersVariableName)
     {
-        method.Frames.Code($@"
+        // Array types like string[], Guid[], int[] need composite NpgsqlDbType (Array | ElementType)
+        // which can't be passed as a single enum value to the code generation template
+        if (memberType.IsArray)
+        {
+            var dbTypeCode = npgsqlArrayDbTypeCodeFor(memberType);
+            method.Frames.Code(
+                $"{parametersVariableName}[{Index}].NpgsqlDbType = {dbTypeCode};\n" +
+                $"{parametersVariableName}[{Index}].Value = _query.{member.Name};");
+        }
+        else
+        {
+            method.Frames.Code($@"
 {parametersVariableName}[{Index}].NpgsqlDbType = {{0}};
 {parametersVariableName}[{Index}].Value = _query.{member.Name};
 ", PostgresqlProvider.Instance.ToParameterType(memberType));
+        }
+    }
+
+    private static string npgsqlArrayDbTypeCodeFor(Type arrayType)
+    {
+        var elementType = arrayType.GetElementType()!;
+        var npgsqlTypeName = typeof(NpgsqlDbType).FullNameInCode();
+
+        if (elementType == typeof(string))
+            return $"{npgsqlTypeName}.{NpgsqlDbType.Array} | {npgsqlTypeName}.{NpgsqlDbType.Varchar}";
+        if (elementType == typeof(Guid))
+            return $"{npgsqlTypeName}.{NpgsqlDbType.Array} | {npgsqlTypeName}.{NpgsqlDbType.Uuid}";
+        if (elementType == typeof(int))
+            return $"{npgsqlTypeName}.{NpgsqlDbType.Array} | {npgsqlTypeName}.{NpgsqlDbType.Integer}";
+        if (elementType == typeof(long))
+            return $"{npgsqlTypeName}.{NpgsqlDbType.Array} | {npgsqlTypeName}.{NpgsqlDbType.Bigint}";
+        if (elementType == typeof(float))
+            return $"{npgsqlTypeName}.{NpgsqlDbType.Array} | {npgsqlTypeName}.{NpgsqlDbType.Real}";
+        if (elementType == typeof(decimal))
+            return $"{npgsqlTypeName}.{NpgsqlDbType.Array} | {npgsqlTypeName}.{NpgsqlDbType.Numeric}";
+        if (elementType == typeof(DateTime))
+            return $"{npgsqlTypeName}.{NpgsqlDbType.Array} | {npgsqlTypeName}.{NpgsqlDbType.Timestamp}";
+        if (elementType == typeof(DateTimeOffset))
+            return $"{npgsqlTypeName}.{NpgsqlDbType.Array} | {npgsqlTypeName}.{NpgsqlDbType.TimestampTz}";
+
+        throw new NotSupportedException($"Array type {arrayType.FullNameInCode()} is not supported for compiled query parameters");
     }
 
     private void generateEnumCode(GeneratedMethod method, StoreOptions storeOptions, MemberInfo member,

src/Marten/Internal/CompiledQueries/QueryCompiler.cs

@@ -111,6 +111,32 @@ static QueryCompiler()
 
             return values;
         });
+
+        // Register array-type finders for compiled query members used with IsOneOf() etc.
+        forArrayType<string>(count =>
+        {
+            var values = new string[count];
+            for (var i = 0; i < count; i++) values[i] = $"_plan_{Guid.NewGuid():N}";
+            return values;
+        });
+        forArrayType<Guid>(count =>
+        {
+            var values = new Guid[count];
+            for (var i = 0; i < count; i++) values[i] = Guid.NewGuid();
+            return values;
+        });
+        forArrayType<int>(count =>
+        {
+            var values = new int[count];
+            for (var i = 0; i < count; i++) values[i] = -(500000 + i);
+            return values;
+        });
+        forArrayType<long>(count =>
+        {
+            var values = new long[count];
+            for (var i = 0; i < count; i++) values[i] = -(600000L + i);
+            return values;
+        });
     }
 
     private static void forType<T>(Func<int, T[]> uniqueValues)
@@ -119,6 +145,12 @@ private static void forType<T>(Func<int, T[]> uniqueValues)
         Finders.Add(finder);
     }
 
+    private static void forArrayType<T>(Func<int, T[]> uniqueElementValues)
+    {
+        var finder = new ArrayParameterFinder<T>(uniqueElementValues);
+        Finders.Add(finder);
+    }
+
     public static CompiledQueryPlan BuildQueryPlan(QuerySession session, Type queryType, StoreOptions storeOptions)
     {
         var querySignature = queryType.FindInterfaceThatCloses(typeof(ICompiledQuery<,>));

src/Marten/Internal/CompiledQueries/QueryMember.cs

@@ -72,10 +72,29 @@ public void TryWriteValue(UniqueValueSource valueSource, object query)
 
     public MemberInfo Member { get; }
 
+    private static bool valuesAreEqual(object value, object? parameterValue)
+    {
+        if (value.Equals(parameterValue)) return true;
+
+        // For array types (string[], Guid[], int[], etc.), Equals() does reference comparison.
+        // We need structural comparison to match array parameter values from compiled query planning.
+        if (value is Array valueArray && parameterValue is Array paramArray)
+        {
+            if (valueArray.Length != paramArray.Length) return false;
+            for (var i = 0; i < valueArray.Length; i++)
+            {
+                if (!Equals(valueArray.GetValue(i), paramArray.GetValue(i))) return false;
+            }
+            return true;
+        }
+
+        return false;
+    }
+
     private bool tryToFind(NpgsqlParameter parameter, ICompiledQueryAwareFilter[] filters,
         object value, out ICompiledQueryAwareFilter? filterUsed)
     {
-        if (filters.All(x => x.ParameterName != parameter.ParameterName) && value.Equals(parameter.Value))
+        if (filters.All(x => x.ParameterName != parameter.ParameterName) && valuesAreEqual(value, parameter.Value))
         {
             filterUsed = null;
             return true;