$select doesn't work on fields of type IList<string>

[anasik]

Assemblies affected
ASP.NET Core OData 8.x
ASP.NET Core OData 9.x

Describe the bug
EF Core 8 comes with support for primtive collections in models.

Naturally, OData should pick up on that support. As of now, if you create a List<string> field in your model and then fetch all the records for that model, it works flawlessly. You see an array of strings in the response.

However, if you try to $select that field, it fails with the following error:

Click to expand error

``` System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.CreateGetValueExpression(ParameterExpression dbDataReader, Int32 index, Boolean nullable, RelationalTypeMapping typeMapping, Type type, IPropertyBase property) at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.VisitExtension(Expression extensionExpression) at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.ProcessShaper(Expression shaperExpression, RelationalCommandCache& relationalCommandCache, IReadOnlyList`1& readerColumns, LambdaExpression& relatedDataLoaders, Int32& collectionId) at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.VisitExtension(Expression extensionExpression) at System.Linq.Expressions.ExpressionVisitor.VisitMemberAssignment(MemberAssignment node) at System.Linq.Expressions.ExpressionVisitor.VisitMemberBinding(MemberBinding node) at System.Linq.Expressions.ExpressionVisitor.Visit[T](ReadOnlyCollection`1 nodes, Func`2 elementVisitor) at System.Linq.Expressions.ExpressionVisitor.VisitMemberInit(MemberInitExpression node) at System.Linq.Expressions.ExpressionVisitor.VisitMemberAssignment(MemberAssignment node) at System.Linq.Expressions.ExpressionVisitor.VisitMemberBinding(MemberBinding node) at System.Linq.Expressions.ExpressionVisitor.Visit[T](ReadOnlyCollection`1 nodes, Func`2 elementVisitor) at System.Linq.Expressions.ExpressionVisitor.VisitMemberInit(MemberInitExpression node) at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.ProcessShaper(Expression shaperExpression, RelationalCommandCache& relationalCommandCache, IReadOnlyList`1& readerColumns, LambdaExpression& relatedDataLoaders, Int32& collectionId) at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitShapedQuery(ShapedQueryExpression shapedQueryExpression) at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.VisitExtension(Expression extensionExpression) at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitExtension(Expression extensionExpression) at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query) at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass12_0`1.b__0() at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.GetAsyncEnumerator(CancellationToken cancellationToken) at System.Text.Json.Serialization.Converters.IAsyncEnumerableOfTConverter`2.OnWriteResume(Utf8JsonWriter writer, TAsyncEnumerable value, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.Serialization.JsonCollectionConverter`2.OnTryWrite(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.Serialization.JsonConverter`1.WriteCore(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.SerializeAsync(Stream utf8Json, T rootValue, CancellationToken cancellationToken, Object rootValueBoxed) at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.SerializeAsync(Stream utf8Json, T rootValue, CancellationToken cancellationToken, Object rootValueBoxed) at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.SerializeAsync(Stream utf8Json, T rootValue, CancellationToken cancellationToken, Object rootValueBoxed) at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|30_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters() --- End of stack trace from previous location --- at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context) at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext) at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider) at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context) at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context) ```

Reproduce steps
Run a $select on any IList field.

Data Model

public class TestPrimitiveCollections
    {
        [Key]
        public string Key { get; set; }
        public ICollection<string>? ListTestString { get; set; }
        public IList<bool>? ListTestBool { get; set; }
        public IList<int>? ListTestInt { get; set; }
        public IList<double>? ListTestDouble { get; set; }
        public IList<float>? ListTestFloat { get; set; }
        public IList<DateTime>? ListTestDateTime { get; set; }
        public IList<DateOnly>? ListTestDateOnly { get; set; }
        public IList<Uri>? ListTestUri { get; set; }
        public uint[]? ListTestUint { get; set; }

    }

EDM (CSDL) Model

<?xml version="1.0" encoding="utf-8"?>
<edmx:Edmx Version="4.0" xmlns:edmx="http://docs.oasis-open.org/odata/ns/edmx">
    <edmx:DataServices>
        <Schema Namespace="Models.SRE" xmlns="http://docs.oasis-open.org/odata/ns/edm">
            <ComplexType Name="Property">
                <Property Name="Key" Type="Edm.String" Nullable="false" />
                <Property Name="ListTestString" Type="Collection(Edm.String)" />
                <Property Name="ListTestBool" Type="Collection(Edm.Boolean)" Nullable="false" />
                <Property Name="ListTestInt" Type="Collection(Edm.Int32)" Nullable="false" />
                <Property Name="ListTestDouble" Type="Collection(Edm.Double)" Nullable="false" />
                <Property Name="ListTestFloat" Type="Collection(Edm.Single)" Nullable="false" />
                <Property Name="ListTestDateTime" Type="Collection(Edm.DateTimeOffset)" Nullable="false" />
                <Property Name="ListTestDateOnly" Type="Collection(Edm.Date)" Nullable="false" />
                <Property Name="ListTestUri" Type="Collection(System.Uri)" />
                <Property Name="ListTestUint" Type="Collection(Edm.Int64)" Nullable="false" />
                <NavigationProperty Name="Member" Type="Models.SRE.Member" />
                <NavigationProperty Name="OpenHouses" Type="Collection(Models.SRE.OpenHouse)" />
            </ComplexType>
        </Schema>
    </edmx:DataServices>
</edmx:Edmx>

Request/Response
http://localhost:5270/odata/mls/Properties?select=ListTestString

Expected behavior
The following output:

[

    {
        "ListTestString": [
            "I",
            "Was",
            "Lost"
        ]
    },
    {
        "ListTestString": [
            "I",
            "Am",
            "Lost"
        ]
    },
    {
        "ListTestString": [
            "I",
            "Am",
            "sda"
        ]
    }
]

Screenshots

Additional context
his happens because in SelectExpandBinder.ProjectAsWrapper(), we check if it's a collection, and if yes, we wrap it as a collection rather than an element. This works perfectly fine for all collections except for strings.

In my model, I have collection fields for a number of primitive types out there. None of them crash. Uri doesn't fully work but I will report that separately.

That's because queries of the form: Entity().Select( d=> d.StringListProperty.Select(d=> d))) just inherently don't work. It appears to be a bug in EF Core that one can easily recreate without even needing to initialize OData.

Furthermore, I also upgraded my project to use the under-preview dotnet 9.0 with EF Core 9.0, hoping that the issue would have been fixed by now but had no luck.

[anasik]

I want to add that I have already submitted a PR that fixes this. Sadly, I'm not able to request a review from anyone. I thought maybe opening an issue would help with getting that kind of attention so here I am.

[julealgon]

@anasik

I want to add that I have already submitted a PR that fixes this.

Can you add a "Fixes" link from the PR to the issue then?

[anasik]

@WanjohiSammy , @xuzhg, @gathogojr

This issue is also present in 9.x I believe. I copied over my tests from 8.x to main and they were failing. I'm not sure what the way forward is? Do we fix them separately in 9.x in a new PR or do we do a partial merge of the release-8.x branch to main?