Chained select clauses, last one disregarded

We have reproduced this issue in EF Core 2.2 and 3.1, on both MSSQL and Oracle (Devart provider) I am not sure whether we are doing something wrong, or have something configured incorrectly or whether it’s an EF Core bug. We have the following IQueryable:

var query = _context.EntityDbSet
    .OrderBy(nameof(Entity.StartDate))
    .Select(e => new Entity 
       { 
            Id = e.Id, 
            RelatedItemId = e.RelatedItemId, 
            StartDate = e.StartDate, 
            EndDate = e.EndDate ... 
        })
    .Skip(0).Take(10)

We then proceed to use this query in several other queries. The Id field is the Key in this table. The issue I have is as follows:

var relatedItems = query.Select(e => e.RelatedItemId).ToList();

Generates the following SQL:

SELECT [e].[RELATED_ITEM_ID]
FROM [ENTITY] AS [e]
ORDER BY [e].[START_DATE]
OFFSET @__p_0 ROWS FETCH NEXT @__p_1 ROWS ONLY

This works as expected. But the following doesn’t:

var ids = query.Select(e => e.Id).ToList();

Generates the following SQL:

SELECT [e].[ID], [e].[RELATED_ITEM_ID], [e].[START_DATE], [e].[END_DATE] ... 
FROM [ENTITY] AS [e]
ORDER BY [e].[START_DATE]
OFFSET @__p_0 ROWS FETCH NEXT @__p_1 ROWS ONLY

I use ids.Contains in a different query. Obviously this fails, because you must only select a single field to use this query in an IN SQL clause.

I tried putting the original Select cause at the end of the var query = … part of the code. If I completely remove this original select, then it works as expected, selecting only the Id field.

Not sure if this has anything to do with it, but we use a custom value generator for the Id column,

Further technical details

EF Core version: Database provider: Microsoft.EntityFrameworkCore.SqlServer Target framework: .NET Core 2.2, 3.1) Operating system: IDE: Visual Studio 2019 16.3

[roji]

@arthur-liberman unfortunately our daily builds feed isn’t in a great state at the moment… You want to use the latest packages with version 5.0.0-alpha.1.* (note the dot after the alpha!). Your nuget.config should look something like the following:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <clear />
    <add key="aspnet-extensions" value="https://dotnetfeed.blob.core.windows.net/aspnet-extensions/index.json" />
    <add key="efcore" value="https://dotnetfeed.blob.core.windows.net/aspnet-entityframeworkcore/index.json" />
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
  </packageSources>
</configuration>

[maumar]

@arthur-liberman we discussed it within the team, but unfortunately this doesn’t meet our bar for 3.1.x patch - it only seems to affect the dynamic expression generation, which is quite niche/advanced scenario. So the issue will only be officially fixed in the 5.0 timeframe.