How do I limit the columns in a dbcontext query?

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I have a dbcontext query to a MySql database using EF Core 2 fetching from my usermaster table.

My usermaster inherits from IdentityUser so that I can take advantage of .NET Core's user security features.

But I do not implement all columns in my child class. e.g. Email which is on PersonMaster because while all users are people not all people will be users.

The autogenerated select statement arising from this snippet is pulling in columns from both the parent and child classes

CUserMasterLocal dbEntry = context.UserMaster
          .FirstOrDefault(u => u.p_Username == user.p_Username);

How do I restrict it to just pull from the child class?

What I have tried:

I have tried implementing one of the columns that is not required in the child class with the

[NotMapped]

attribute. It had no effect.

Later today I will try something like this:[^] to see if it delivers for me.

Regardless of this issue it looks like good practice, because if my Oracle days taught me anything all those years ago, surplus columns in a select kill performance.

Posted 18-Sep-18 21:50pm

Ger Hayden

Updated 18-Sep-18 22:10pm

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Comments

Maciej Los 19-Sep-18 3:58am

Is there any problem to write custom select statement?

var myData = context.UserMaster
          .Where(u => u.p_Username == user.p_Username)
          .Select(x => new {whatever_you_want});

Ger Hayden 19-Sep-18 4:15am

Hi Maciej, I will be trying that this evening (once I get the day job out of the way). I have only just learned that this is possible.

ZurdoDev 19-Sep-18 8:58am

Looks like a solution to me.

Maciej Los 19-Sep-18 9:10am

Let's find out ;)

Ger Hayden 19-Sep-18 13:02pm

Its a solution! Put it in the Solution box so that I can accept and rate it.

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How do I limit the columns in a dbcontext query?

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