fix duplicate join issues

[ElizabethOkerio]

This issue leads to duplicate joins being generated, like the one below, when we execute such a query RawIncidents?$expand=alerts

SELECT [t].[IncidentId], [t0].[Id], [t1].[AlertId]
FROM (
    SELECT TOP(@__TypedProperty_3) [r].[IncidentId]
    FROM [WcdTestCloudEusStg].[RawIncidents] AS [r]
) AS [t]
LEFT JOIN (
    SELECT [a].[AlertId] AS [Id], [a].[IncidentId]
    FROM [WcdTestCloudEusStg].[AlertsForPublicApi] AS [a]
) AS [t0] ON [t].[IncidentId] = [t0].[IncidentId]
LEFT JOIN (
    SELECT [t2].[AlertId], [t2].[IncidentId]
    FROM (
        SELECT [a0].[AlertId], [a0].[IncidentId], ROW_NUMBER() OVER(PARTITION BY [a0].[IncidentId] ORDER BY [a0].[AlertId]) AS [row]
        FROM [WcdTestCloudEusStg].[AlertsForPublicApi] AS [a0]
    ) AS [t2]
    WHERE [t2].[row] <= @__TypedProperty_1
) AS [t1] ON [t].[IncidentId] = [t1].[IncidentId]
ORDER BY [t].[IncidentId], [t0].[Id], [t1].[IncidentId], [t1].[AlertId]

SelectExpandWrapper uses the Instance property which contains all the properties of a type including the structural and navigation properties. We then again add the navigation properties to the Container property. So it's like the navigation properties get added twice and EF doesn't do deduplication of custom expressions (by design) which leads to duplicate joins being generated.

The solution here was to only write the structural properties to the Instance and leave out the navigation properties which get added to the Container property.

To the ProjectElement method in the SelectExpandBinder class, I have made some updates to ensure that the Instance that gets created is in this form:

{ Instance = new Customer() {Id = $it.Id, Name= $it.Name}}

That's, it only has structural properties.

Another change was to check that the QueryProvider is an EF query provider.. These changes are only done when we are dealing with an EF QueryProvider. If not, then the expression is built the way it has always been built.

[KenitoInc]

Add some unit tests here

[habbes]

I think it would be great to add a test that looks like the customer scenario described in the issue, i.e.: applying OData query options to an IQueryable that is the result of a .Select() mapping from one type to another, where the input comes from a DbSet with an Includes call on a navigation property.