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.netcore EF linq - this is a BUG? Very strange behavior

I have two table in sql. Document and User. Document have relation to User and I want to get users that I sent document recently.
I need to sort by the date document was sent and get unique (distinct) user with relation to this document
This is my linq queries
var recentClients = documentCaseRepository.Entities
.Where(docCase => docCase.AssignedByAgentId == WC.UserContext.UserId)
.OrderByDescending(userWithDate => userWithDate.LastUpdateDate)
.Take(1000) // I need this because if I comment this line then EF generate completely different sql query.
.Select(doc => new { doc.AssignedToClient.Id, doc.AssignedToClient.FirstName, doc.AssignedToClient.LastName })
.Distinct()
.Take(configuration.MaxRecentClientsResults)
.ToList();
and generated sql query is:
SELECT DISTINCT TOP(5) [t].*
FROM (
SELECT TOP(1000) [docCase.AssignedToClient].[Id]
FROM [DocumentCase] AS [docCase]
INNER JOIN [User] AS [docCase.AssignedToClient]
ON ([docCase].[AssignedToClientId] = [docCase.AssignedToClient].[Id])
WHERE [docCase].[AssignedByAgentId] = 3
ORDER BY [docCase].[LastUpdateDate] DESC
)
AS [t]
Every thing is correct for now. But if I delete this line
.Take(1000) // I need this because...
EF generated completely different query such as:
SELECT DISTINCT TOP(5)
[docCase.AssignedToClient].[Id]
FROM [DocumentCase] AS [docCase]
INNER JOIN [User] AS [docCase.AssignedToClient]
ON ([docCase].[AssignedToClientId] = [docCase.AssignedToClient].[Id])
WHERE [docCase].[AssignedByAgentId] = 3
My question is: why EF not generated orderby clause and subquery with distinct?
This is a BUG EF or I'm doing something wrong? And what I must do to generate in linq this sql query ()
SELECT DISTINCT TOP 5 [t].*
FROM ( SELECT [docCase.AssignedToClient].[Id]
FROM [DocumentCase] AS [docCase]
INNER JOIN [User] AS [docCase.AssignedToClient]
ON [docCase].[AssignedToClientId] = [docCase.AssignedToClient].[Id]
WHERE [docCase].[AssignedByAgentId] = 1
ORDER BY [docCase].[LastUpdateDate] DESC
) AS [t]

OrderBy information not always retained across other operators such as Distinct. Entity Framework does not document (to my knowledge) how exactly OrderBy is propagated.
This kind of makes sense because some operators have undefined output order. The fact that ordering is retained in many situations is a convenience for the developer.
Move the OrderBy to the end of the query (or at least past the Distinct).

The reason for the difference in queries is that Distinct messes up result order. So when you first execute OrderBy and then Distinct, you can just es well not execute OrderBy, because this order is lost anyway. So EF can just optimize it away.
Calling Take in between causes the result set to be semantically different: You first order the items, take the first 1000 items of that order and then call Distinct on them.
What you can change in your query depends mainly on the result you want to achieve. Maybe you want to first make the result set distinct then order by date and finally take the amount of items. Other options are also thinkable based on your requirements.

Joining two tables actually runs two Selects in SQL profiler

var query = from organization in _context.Organizations
join location in
(
from location in _context.Locations
orderby location.Name
select new
{
location.Id,
location.Name,
location.OrganizationId,
}
) on organization.Id equals location.OrganizationId into
locations
orderby organization.Name
select new
{
organization.Id,
organization.Name,
locations
};
I am using Entity Framework Core 1.1 . Here I am joining Organizations & Locations table in LINQ. But when I run the above LINQ query i get two separate select statements in SQL Profiler,
I see:
SELECT [organization].[Id], [organization].[Name]
FROM [Organization] AS [organization]
ORDER BY [organization].[Name]
SELECT [location].[Id], [location].[Name]
FROM [Location] AS [location]
ORDER BY [location].[LoName]
My expectation was a single query joining two tables in SQL Profiler. But what I am missing so this runs as a single join query in SQL?

EF Core 1.x cannot translate complex LINQ query to optimized TSQL query like EF 6. in such cases EF Core only generates query for fetching data from database and rest of operations like group by or complex where clause, will happen in memory. in your case generated tsql queries are for fetching data and join, order by and projection will happen in memory, so be careful if you have large data in those tables or write raw sql query instead of linq query.

Using the SQL "IsNull()" command in NHibernate criteria in C#

I need to be able to use with NHibernate criteria, the SQL's IsNull() function in C#.NET. I don't need to use it with LINQ.
Meaning that Table1 has the following columns:
Name | Description
Table2 has the following columns:
OriginalDescription | TranslatedDescription
And Table1.Description = Table2.OriginalDescription.
How would I write the following SQL statement with NHibernate criteria:
SELECT Table1.Model, IsNull(Table2.TranslatedDescription, Table1.Description)
FROM Table1
LEFT JOIN Table2 ON Table2.OriginalDescription = Table1.Description
The SQL statement above will give me the Names, and TranslatedDescriptions if the TranslatedDescriptions exist, otherwise it will return the Descriptions, for the records.
There cannot be duplicates of OriginalDescription in the Table2.

The solution of the ISNULL could be expressed like this:
// here is the criteria of the "Entity1" and the join to the "Entity2"
var criteria = session.CreateCriteria("Entity1", "table1");
criteria.CreateAlias("Entity2", "table2");
// here we drive the SELECT clause
criteria.SetProjection(
Projections.ProjectionList()
.Add(Projections.Property("Model"))
.Add(Projections.SqlFunction("COALESCE", NHibernateUtil.String
, Projections.Property("table2.TranslatedDescription")
, Projections.Property("table1.Description")
))
);
// just a list of object arrays
var list = criteria.List<object[]>();
So, what we do here, is a call of the SqlFunction. In this case one of the out-of-the-box mapped in many Dialects coming with NHibernate (but we can even extend the dialect with custom ones, an example how to: Nhibernate count distinct (based on multiple columns))
Must note, that the JOIN Clause is coming from the mapping. So this Table2.OriginalDescription = Table1.Description must come from a mapped relation many-to-one

Basic LINQ query to SQL C#

I have this LINQ query in C# for querying a db4o database.
IEnumerable<internetRecord> searchResult = from internetRecord ie in database
where ie.GSrecordID.Contains(txtSearchString.Text)
select ie;
What would be the equivalent query in SQL? (needed for comparison purposes) I have not worked with SQL much in the past and looking at it after using LINQ for a while it seems confusing.

SELECT *
FROM MyTable
WHERE GSRecordID LIKE '%txtSearchString%'

Select * from internetrecord where GSrecordID like '%your comparison string%'
Provided internetrecord is your SQL table GSrecordID is the column of your table.

I don't know much about db40 but in standard SQL it would be:
SELECT * FROM internetRecord
WHERE GSrecordID LIKE '%txtSearchString%'

YOu can do something like this
var result = database.Where(x => x.GSrecordID.Contains(txtSearchString.Text));

Joining Lists using Linq returns different result than corresponding SQL query?

I have 2 tables
TableA:
TableAID int,
Col1 varchar(8)
TableB:
TableBID int
Col1 char(8),
Col2 varchar(40)
When I run a SQL query on the 2 tables it returns the following number of rows
SELECT * FROM tableA (7200 rows)
select * FROM tableB (28030 rows)
When joined on col1 and selects the data it returns the following number of rows
select DISTINCT a.Col1,b.Col2 FROM tableA a
join tableB b on a.Col1=b.Col1 (6578 rows)
The above 2 tables on different databases so I created 2 EF models and retried the data separately and tried to join them in the code using linq with the following function. Surprisingly it returns 2886 records instead of 6578 records. Am I doing something wrong?
The individual lists seems to return the correct data but when I join them SQL query and linq query differs in the number of records.
Any help on this greatly appreciated.
// This function is returning 2886 records
public List<tableC_POCO_Object> Get_TableC()
{
IEnumerable<tableC_POCO_Object> result = null;
List<TableA> tableA_POCO_Object = Get_TableA(); // Returns 7200 records
List<TableB> tableB_POCO_Object = Get_TableB(); // Returns 28030 records
result = from tbla in tableA_POCO_Object
join tblb in tableB_POCO_Object on tbla.Col1 equals tblb.Col1
select new tableC_POCO_Object
{
Col1 = tblb.Col1,
Col2 = tbla.Col2
};
return result.Distinct().ToList();
}

The problem lies in the fact that in your POCO world, you're trying to compare two strings using a straight comparison (meaning it's case-sensitive). That might work in the SQL world (unless of course you've enabled case-sensitivity), but doesn't quite work so well when you have "stringA" == "StringA". What you should do is normalize the join columns to be all upper or lower case:
join tblb in tableB_POCO_Object on tbla.Col1.ToUpper() equals tblb.Col1.ToUpper()
Join operator creates a lookup using the specified keys (starts with second collection) and joins the original table/collection back by checking the generated lookup, so if the hashes ever differ they will not join.
Point being, joining OBJECT collections on string data/properties is bad unless you normalize to the same cAsE. For LINQ to some DB provider, if the database is case-insensitive, then this won't matter, but it always matters in the CLR/L2O world.
Edit: Ahh, didn't realize it was CHAR(8) instead of VARCHAR(8), meaning it pads to 8 characters no matter what. In that case, tblb.Col1.Trim() will fix your issue. However, still keep this in mind when dealing with LINQ to Objects queries.

This might happen because you compare a VARCHAR and a CHAR column. In SQL, this depends on the settings of ANSI_PADDING on the sql server, while in C# the string values are read using the DataReader and compared using standard string functions.
Try tblb.Col1.Trim() in your LINQ statement.

As SPFiredrake correctly pointed out this can be caused by case sensitivity, but I also have to ask you why did you write your code in such a way, why not this way:
// This function is returning 2886 records
public List<tableC_POCO_Object> Get_TableC()
{
return from tbla in Get_TableA()
join tblb in Get_TableB() on tbla.Col1 equals tblb.Col1
select new tableC_POCO_Object
{
Col1 = tblb.Col1,
Col2 = tbla.Col2
}.Distinct().ToList();
}
where Get_TableA() and Get_TableB() return IEnumerable instead of List. You have to watch out for that, because when you convert to list the query will be executed instantly. You want to send a single query to the database server.