LINQ-to-XPO throws InvalidOperationException when a query tries to expand a collection property

Hello Oleksandr.

I'm afraid the infromation you provided is insufficient to research the issue. It is unclear what you are doing and how. Would you please provide us with a small sample project demonstrating your sceanrio, describe your task in detail and explain how to replicate the issue?

It requires some time to do isolated example. I will try on next week.

Here example is. It uses Oracle and you will find SqlScripts.sql in root of the solution which creates tables and fulfill them. I guess you can use any DB because the problem looks DB independent. Connection string is located in WebApiConfig class. Example is built with VS 2013 Update 5. After running the service try next URLs:
http://localhost:52599/Products?$expand=Category
You should get:
HTTP/1.1 200 OK
{
 "@odata.context":"http://localhost:52599/$metadata#Products";,
 "value":
 [
   {
     "Id":1,
     "Name":"PROD1",
     "Category":{"Id":1,"Name":"CAT1"}
   },
   {
     "Id":2,
     "Name":"PROD2",
     "Category":{"Id":1,"Name":"CAT1"}
   }
 ]
}
So expanding of single entity is working. Try to expand a collection
http://localhost:52599/Categories?$expand=Products
comes to
HTTP/1.1 500 Internal Server Error
{
 "error":{
   "code":"",
   "message":"An error has occurred.",
   "innererror":{
     "message":"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; odata.metadata=minimal; odata.streaming=true'.",
     "type":"System.InvalidOperationException",
     "stacktrace":"",
     "internalexception":{
       "message":"No coercion operator is defined between types 'DevExpress.Xpo.XPCollection`1[XpoOdataTest.Models.Product]' and 'System.Boolean'.",
       "type":"System.InvalidOperationException",
       "stacktrace":"
           at System.Linq.Expressions.Expression.GetUserDefinedCoercionOrThrow(ExpressionType coercionType, Expression expression, Type convertToType)
           at System.Linq.Expressions.Expression.Convert(Expression expression, Type type, MethodInfo method)
           at System.Linq.Expressions.Expression.Convert(Expression expression, Type type)
           at DevExpress.Xpo.XPQueryBase.CreateSubItemCore(Type subType, ExpressionAccessOperator last, CriteriaTypeResolver resolver, ParameterExpression row, Int32& rowIndex)
           at DevExpress.Xpo.XPQueryBase.CreateSubItemCore(Type subType, ExpressionAccessOperator last, CriteriaTypeResolver resolver, ParameterExpression row, Int32& rowIndex)
           at DevExpress.Xpo.XPQueryBase.CreateSubItemCore(Type subType, ExpressionAccessOperator last, CriteriaTypeResolver resolver, ParameterExpression row, Int32& rowIndex)
           at DevExpress.Xpo.XPQueryBase.CreateSubItemCore(Type subType, MemberInitOperator last, CriteriaTypeResolver resolver, ParameterExpression row, Int32& rowIndex)
           at DevExpress.Xpo.XPQueryBase.CreateSubItemCore(Type subType, MemberInitOperator last, CriteriaTypeResolver resolver, ParameterExpression row, Int32& rowIndex)
           at DevExpress.Xpo.XPQueryBase.CreateItemCore(Type type, MemberInitOperator last)
           at DevExpress.Xpo.XPQueryBase.GetData(Type type)
           at DevExpress.Xpo.XPQueryBase.Enumerate(Type type)
           at DevExpress.Xpo.XPQuery`1.GetEnumerator()
           at DevExpress.Xpo.XPQuery`1.System.Collections.IEnumerable.GetEnumerator()
           at System.Web.OData.Formatter.Serialization.ODataFeedSerializer.WriteFeed(IEnumerable enumerable, IEdmTypeReference feedType, ODataWriter writer, ODataSerializerContext writeContext)
           at System.Web.OData.Formatter.Serialization.ODataFeedSerializer.WriteObjectInline(Object graph, IEdmTypeReference expectedType, ODataWriter writer, ODataSerializerContext writeContext)
           at System.Web.OData.Formatter.Serialization.ODataFeedSerializer.WriteObject(Object graph, Type type, ODataMessageWriter messageWriter, ODataSerializerContext writeContext)
           at System.Web.OData.Formatter.ODataMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content, HttpContentHeaders contentHeaders)
           at System.Web.OData.Formatter.ODataMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)
           --- End of stack trace from previous location where exception was thrown ---
           at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
           at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
           at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
           at System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__1b.MoveNext()"
     }
   }
 }
}
If you also can investigate why $select is not working on subentitties it would be highly appreciated:
http://localhost:52599/Categories(1)?$select=Products
HTTP/1.1 200 OK
{
 "@odata.context":"http://localhost:52599/$metadata#Categories(Products)/$entity";
}
http://localhost:52599/Products(1)?$select=Category
HTTP/1.1 200 OK
{
 "@odata.context":"http://localhost:52599/$metadata#Products(Category)/$entity";
}
It always returns empty result (selection of a primitive value works fine). If you grab everything it creates one empty entry for each parent record:
http://localhost:52599/Products?$select=Category
{
 "@odata.context":"http://localhost:52599/$metadata#Products(Category)";,"value":[
   {

},{

}
 ]
}
The same for collection:
http://localhost:52599/Categories?$select=Products
{
 "@odata.context":"http://localhost:52599/$metadata#Categories(Products)";,"value":[
   {

},{

}
 ]
}
Thanks!