How to except entity in C#?

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If you have the difference in the following query, I want to look at these queries and print them with the message box. But if there is a difference, I cannot find the value as integer and I cannot print.

STUDENT TABLE

ALEX

JOHN

MARY

CLASS INFORMATION

ALEX

EXCEPT RESULT:
JOHN

MARY

I WANT TO:

MessageBox write JOHN,MARY IS NOT FOUND CLASS INFORMATION TABLE.

How to select and print a query in entity?

What I have tried:

C#

using Name=new HashSet<string>(studententities.Student.Select(x=>x.ID);
using Name2=new HashSet<string>(studententities.ClassInformation.Select(x=>x.ID));
var except=ID.Except(Name).ToList();

MessageBox.Show(except + "is not found class ınformation table");

Posted 24-Aug-19 10:25am

Member 14169626

Updated 26-Aug-19 9:29am

v5

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Maciej Los 25-Aug-19 14:47pm

Sorry, i don't get you... Does ID is a string field? Does ID means Name?

Member 14169626 25-Aug-19 15:03pm

to summarize, I want to find the differences of the name fields in the two tables and print the differences with the message box

2 solutions

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RickZeeland · Answer 1 · 2019-08-24T20:05:00

Solution 1

You are defining Name twice, so only the last statement is used.
See examples here: EXCEPT (Entity SQL) | Microsoft Docs[^]
c# - Get All Except from SQL database using Entity Framework - Stack Overflow[^]

For more information about the using statement, see: c# - using statement with multiple variables - Stack Overflow[^]

Posted 24-Aug-19 20:05pm

RickZeeland

Updated 24-Aug-19 20:08pm

v2

Comments

Member 14169626 25-Aug-19 2:17am

Hello there.Incorrectly defined.I corrected name2.I want to compare two names with the same values from a different table.

RickZeeland 25-Aug-19 2:39am

That's a step in the right direction :)
But I'm afraid I can't be of much help any further as I don't use Entity Framework myself, so hopefully some EF expert will help you further.

Member 14169626 25-Aug-19 5:42am

Thank you for your help.

Maciej Los · Answer 2 · 2019-08-26T09:29:00

I'm not sure i understand you well, but...
Assuming that you want to find students which are not in ClassInformation table.

C#

var result = studententities.Student
    .Where(s => s.ID==some_id)
    .Select(s => s.Name)
    .Except(studententities.ClassInformation
        .Select(ci => ci.Name)
    .ToList();
//display names of unregistered students
foreach(string sname in result)
{
    Console.WriteLine(sname);
}