How to write an LINQ for entities for joining empty tables

Question

0.00/5 (No votes)

See more:

Hi,

I have two tables :

Category(categ) 
Sub Category (scat)

I want to perform the following query on the above tables.

select a.code, a.name, a.type, b.category as category from categ a left join scat b on a.code=b.code

The above sql when executed on SQL Server this is the result.

code     name      type    category
1001     abc       F       NULL
1002     def       F       NULL
1003     ghi       B       NULL

I tried this LINQ for the above query :
Please note : The scats context table is an empty table.

List<categscat> lstcateg = (from categrow in Context.categs.AsEnumerable()
                            join scatrow in Context.scats
                            on categrow.code equals scatrow.code                             
                            select new categscat(categrow.code, categrow.name, 
                            categrow.type, categrow.cate, 
                            joinedrow.category)).ToList();

This returns a NullReferenceException.

What I have tried:

tried using the DefaultIfEmpty() as per suggestions in the link below :

https://www.codeproject.com/articles/169590/linq-to-sql-left-join-with-null-values

lstcateg = (from categrow in dlsmain.odlsContext.categs.AsEnumerable()
                            join scatrow in dlsmain.odlsContext.scats.AsEnumerable()
                            on categrow.code equals scatrow.code into jointable
                            from joinedrow in jointable.DefaultIfEmpty()
                            select new categscat(categrow.code, categrow.name, categrow.type, categrow.cate, joinedrow.category)).ToList();

Still I'm getting the same error. What is my mistake? How to get this right ? Please suggest.

Posted 12-Feb-19 20:39pm

Priya-Kiko

Updated 12-Feb-19 20:53pm

v2

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Priya-Kiko · Accepted Answer · 2019-02-12T20:53:00

Revised the query to include a null check and it was fine.

Referred : 101 LINQ Samples in C#[^]

Revised LINQ query with the change highlighted :

lstcateg = (from categrow in dlsmain.odlsContext.categs.AsEnumerable()
                           join scatrow in dlsmain.odlsContext.scats.AsEnumerable()
                           on categrow.code equals scatrow.code into jointable
                           from joinedrow in jointable.DefaultIfEmpty()
                           select new categscat(categrow.code, categrow.name, categrow.type, categrow.cate, joinedrow == null ? "" : joinedrow.category)).ToList();