How to group records and retrieve only the first group with the top N records

Question

I have the following recordset

ID          BatchID     ClientName           CreatedDateTime
----------- -------------- --------------- -----------------------
1           NULL           B             2018-02-16 19:07:46.320
2           NULL           B             2018-02-16 19:07:46.320
3           NULL           B             2018-02-16 19:07:46.597
4           NULL           B             2018-02-16 19:07:46.597
5           NULL           B             2018-02-16 19:10:10.260
6           NULL           B             2018-02-16 19:10:10.260
7           NULL           B             2018-02-16 19:21:34.303
8           NULL           B             2018-02-16 19:21:34.303
9           NULL           B             2018-02-16 19:21:44.780
10          NULL           B             2018-02-16 19:21:44.780
11          NULL           A             2018-02-16 19:24:35.623
12          NULL           A             2018-02-16 19:24:35.623
13          NULL           A             2018-02-16 19:24:42.867
14          NULL           A             2018-02-16 19:24:42.867

I am using LINQ to SQL in EF Core.

I want to filter the records where they BatchIDare NULL, and then sort the filtered records by CreatedDateTime, and then group them by ClientName, and then the first 5 records from the first Group.

Based on the above record set, it should return records with identifiers 1,2,3,4,5 for ClientName B

So here is my request

 var result = await _DBContext.BatchRequests
                .Where(x => x.BatchID.HasValue == false)
                .OrderBy(x => x.CreatedDateTime)
                .GroupBy(x => x.ClientName)
                .FirstAsync();

Issue
1> Request returns Client A
2> How to make only the top 5 entries

Update 1

Sql Profiler shows the following: it is not even grouped in SQL

SELECT [x].[ID], [x].[BatchID], [x].[ClientName], [x].[CreatedDateTime]
FROM [BatchRequests] AS [x]
WHERE CASE
    WHEN [x].[BatchID] IS NULL
    THEN CAST(1 AS BIT) ELSE CAST(0 AS BIT)
END <> 0
ORDER BY [x].[ClientName]

Answer 1

-, OrderBy (), GroupBy Queryable, LINQ SQL.

-, EF Core GroupBy SQL, ( ) . - , ClientName , - :

var baseQuery = _DBContext.BatchRequests
    .Where(x => x.BatchId == null)
    .OrderBy(x => x.CreatedDateTime);

var clientName = await baseQuery
    .Select(x => x.ClientName)
    .FirstOrDefaultAsync();

var result = await baseQuery
    .Where(x => x.ClientName == clientName)
    .Take(5)
    .ToListAsync();

, , ( , ):

var baseQuery = _DBContext.BatchRequests
    .Where(x => x.BatchId == null)
    .OrderBy(x => x.CreatedDateTime);

var result = await baseQuery
    .Where(x => x.ClientName == baseQuery.Select(y => y.ClientName).FirstOrDefault())
    .Take(5)
    .ToListAsync();

Answer 2

, :

result = await _DBContext.BatchRequests
            .Where(x => x.BatchID.HasValue == false)
            .OrderBy(x => x.CreatedDateTime)
            .ThenBy(x => x.ClientName)
            .GroupBy(x => x.ClientName)
            .Select( x => new { ClientName= x.ClientName,
                                 TopFive = x.Take(5)
                         })
            .FirstAsync();