How to perform this EF Core nested date comparison query in SQL

asp.net-core c# entity-framework-core linq sql-server

Question

Using .Net Core 2.1 and EF Core 2.1.1 and SQL Server

I am trying to pull a list of Organizations and their list of Communications
I then want to limit it to those that have not had any Communications in the last 6 months

Here are my skimmed down ViewModels:

public class OrganizationViewModel
{
    public Guid Id { get; set; }
    public IEnumerable<CommunicationViewModel> CommunicationViewModels { get; set;
}

public class CommunicationViewModel
{
    public Guid Id { get; set; }
    public DateTime Date { get; set; }

    public Guid OrganizationViewModelId { get; set; }
    public OrganizationViewModel OrganizationViewModel { get; set; }
}

And here is my query:

DateTime sixMonthsAgo = DateTime.Today.AddMonths(-6);
int pageIndex = 1; // Would be passed in
int pageSize = 3;

IQueryable<OrganizationViewModel> query = _context.Organizations
    .AsNoTracking()
    .Select(organization => new OrganizationViewModel
    {
        CommunicationViewModels = organization.Communications.Select(communication => new CommunicationViewModel
        {
            Date = communication.Date
        })              
        .OrderByDescending(communication => communication.Date)
        .Take(1)
        .ToList()
    })
    .Where(organization => 
        (!searchViewModel.LimitToLastSixMonths || 
            organization.CommunicationViewModels.Any(communication => communication.Date <= sixMonthsAgo)));

int totalAmount = await query.CountAsync();
List<OrganizationViewModel> items = await query
            .Skip((pageIndex - 1) * pageSize)
            .Take(pageSize)
            .ToListAsync();

This gets me the expected results, but I can see in my logs that I'm performing this query on every record when I hit .CountAsync() and .Skip(..).Take(..):

SELECT CASE
    WHEN EXISTS (
        SELECT 1
        FROM (
            SELECT TOP(1) [comm].[Date]
            FROM [Communications] AS [comm]
            WHERE @_outer_Id = [comm].[OrganizationId]
            ORDER BY [comm].[Date] DESC
        ) AS [t]
        WHERE [t].[Date] <= @__sixMonthsAgo_0)
    THEN CAST(1 AS BIT) ELSE CAST(0 AS BIT)
END

I'm also seeing these warnings when .CountAsync() is called (slightly edited):

Microsoft.EntityFrameworkCore.Query:Warning: The LINQ expression
'where (False OrElse {from CommunicationViewModel cvm in {from Communication comm in value(..EntityQueryable'1[..Models.Communication]) orderby [comm].Date desc where ?= (Property([o], "Id") == Property([comm], "OrganizationId")) =? select new CommunicationViewModel() {Date = [comm].Date} => Take(1) => AsQueryable()} where ([cvm].Date <= __sixMonthsAgo_0) select [cvm] => Any()})' could not be translated and will be evaluated locally.
Microsoft.EntityFrameworkCore.Query:Warning: The LINQ expression 'Count()' could not be translated and will be evaluated locally.

And similar errors when the .Take(..).Skip(..) is called:

Microsoft.EntityFrameworkCore.Query:Warning: The LINQ expression
same as above could not be translated and will be evaluated locally. Microsoft.EntityFrameworkCore.Query:Warning: The LINQ expression 'Skip(__p_1)' could not be translated and will be evaluated locally.
Microsoft.EntityFrameworkCore.Query:Warning: The LINQ expression 'Take(__p_2)' could not be translated and will be evaluated locally.

This does not happen when searchViewModel.LimitToLastSixMonths is false

Any suggestions on how I can rewrite my query to not perform that query locally on each record?

1
0
10/1/2018 5:03:08 PM

Accepted Answer

I figured it out!

This is my new query:

DateTime sixMonthsAgo = DateTime.Today.AddMonths(-6);
int pageIndex = 1; // Would be passed in
int pageSize = 3;

IQueryable<OrganizationViewModel> query = _context.Organizations
    .AsNoTracking()
    .Select(organization => new OrganizationViewModel
    {
        CommunicationViewModels = organization.Communications.Select(communication  => 
            new CommunicationViewModel
            {
                Id = communication.Id,
                Date = communication.Date
            })
            .OrderByDescending(communicationViewModel => communicationViewModel.Date)
            .Take(1)
            .Where(communicationViewModel => communicationViewModel.Date <= sixMonthsAgo)
            .AsQueryable()
    })
    .Where(organizationViewModel =>
        (!searchViewModel.LimitToLastSixMonths || organizationViewModel.CommunicationViewModels.Any()));

int totalAmount = await query.CountAsync();
List<OrganizationViewModel> items = await query
            .Skip((pageIndex - 1) * pageSize)
            .Take(pageSize)
            .ToListAsync();

Which now produces these two queries when searchViewModel.LimitToLastSizeMonths is true:

SELECT COUNT(*)
FROM [Organizations] AS [organization]
WHERE EXISTS (
    SELECT 1
    FROM (
        SELECT [t].[Id], [t].[Date]
        FROM (
            SELECT TOP(1) [communication].[Id], [communication].[Date]
            FROM [Communications] AS [communication]
            WHERE [organization].[Id] = [communication].[OrganizationId]
            ORDER BY [communication].[Date] DESC
        ) AS [t]
        WHERE [t].[Date] <= @__sixMonthsAgo_0
    ) AS [t0])


SELECT [organization].[Id]
FROM [Organizations] AS [organization]
WHERE EXISTS (
    SELECT 1
    FROM (
        SELECT [t].[Id], [t].[Date]
        FROM (
            SELECT TOP(1) [communication].[Id], [communication].[Date]
            FROM [Communications] AS [communication]
            WHERE [organization].[Id] = [communication].[OrganizationId]
            ORDER BY [communication].[Date] DESC
        ) AS [t]
        WHERE [t].[Date] <= @__sixMonthsAgo_0
    ) AS [t0])
ORDER BY (SELECT 1)
OFFSET @__p_1 ROWS FETCH NEXT @__p_2 ROWS ONLY

Without the .AsQueryable() it goes back to checking each record and performing the count and ski/take locally.

0
10/1/2018 6:01:23 PM

Popular Answer

What if you try to include the navigation property into the select:

IQueryable<OrganizationViewModel> query = _context.Organizations
    .Include(o => o.CommunicationViewModels)
...


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