How to delete a single row from database using linq query?

Question

This is my table ts_grp_perm_mapping

grp_permid     grp_id      perm_id
22              4           1
23              2           2

This is my code to delete row. usr_groupId below is grp_id in above table. usr_doctypeids below is perm_id in above table.

public int saveNewUser(int usr_groupId, int usr_doctypeids)
{
     ts_grp_perm_mapping tm = db.ts_grp_perm_mapping.Find(usr_groupId);
     db.ts_grp_perm_mapping.Remove(tm);
     int rowiseffected=db.SaveChanges();
     return rowiseffected;
}

When I trace my tm shows null, and error pops up like values cannot be null. So where I am going wrong?

grp_id is forein key. grp_permid is primary. I am trying to delete based on grp_id. — LUTHFI ABDUL KADER
– LUTHFI ABDUL KADER, Commented Feb 3, 2016 at 10:00

Krishna shidnekoppa · Accepted Answer · 2016-02-04 10:20:20Z

If grp_id is Primary Key

 public int saveNewUser(int usr_groupId, int usr_doctypeids)
    {
         ts_grp_perm_mapping tm = db.ts_grp_perm_mapping.SingleOrDefault(ts => ts.grp_id == usr_groupId);
         if(tm != null)
             {
         db.ts_grp_perm_mapping.Remove(tm);
         int rowiseffected=db.SaveChanges();
         return rowiseffected;
    }
    else
    {
    return 0;
    }
    }

If grp_id is not a primary key

public int saveNewUser(int usr_groupId, int usr_doctypeids)
        {
             ts_grp_perm_mapping tm = db.ts_grp_perm_mapping.FirstOrDefault(ts => ts.grp_id == usr_groupId);
             if(tm != null)
                 {
             db.ts_grp_perm_mapping.Remove(tm);
             int rowiseffected=db.SaveChanges();
             return rowiseffected;
        }
        else
        {
        return 0;
        }
        }

wertzui · Accepted Answer · 2016-02-03 09:15:31Z

1

Find only works for the Primary Key. Use Linq Single or SingleOrDefault for other properties.

public int saveNewUser(int usr_groupId, int usr_doctypeids)
{
     ts_grp_perm_mapping tm = db.ts_grp_perm_mapping.SingleOrDefault(ts => ts.grp_id == usr_groupId);
     if(tm == null)
         throw new Exception($"The grp_id {usr_groupId} was not found");
     db.ts_grp_perm_mapping.Remove(tm);
     int rowiseffected=db.SaveChanges();
     return rowiseffected;
}

And if possible make your method async and use

ts_grp_perm_mapping tm = await db.ts_grp_perm_mapping.SingleOrDefaultAsync(ts => ts.grp_id == usr_groupId).ConfigureAwait(false);
//...
int rowiseffected = await db.SaveChangesAsync().ConfigureAwait(false);

answered Feb 3, 2016 at 9:15

wertzui

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2 Comments

LUTHFI ABDUL KADER Over a year ago

The above method worked for me. Thanks, Also can i know the usage if savechangesasync()?

wertzui Over a year ago

If you don't know how async and await work, i suggest you read the MSDN article at msdn.microsoft.com/en-us/library/…

Zippy · Accepted Answer · 2016-02-03 09:51:44Z

-1

Try

        public int saveNewUser(int usr_groupId, int usr_doctypeids) 
    { 
      var tm = db.ts_grp_perm_mapping.Where(a => a.grp_id == usr_groupId); 
      db.ts_grp_perm_mapping.Remove(tm); 
      int rowiseffected=db.SaveChanges();
      return rowiseffected;
    }

edited Feb 3, 2016 at 9:51

Zippy

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answered Feb 3, 2016 at 9:15

NubbyMcNuberson

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4 Comments

Zippy Over a year ago

why should OP try this? Could you elaborate more on your answer?

wertzui Over a year ago

This won't work, Where returns IQueryable<ts_grp_perm_mapping> and Remove expects ts_grp_perm_mapping you need to use RemoveRange

NubbyMcNuberson Over a year ago

.Find is looking for the primary key. grp_id isn't the primary key, but OP is feeding in the grp_id

LUTHFI ABDUL KADER Over a year ago

Thanks for everyone whoever helped me.

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