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c# Linq statement needed to delete records from 2 tables

Posted on 2010-11-16
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Last Modified: 2013-12-17


Say I have to tables that are related by and ID (int) in a one to many join.   I want a linq statement to delete the one row with a certain ID in the “masterTable” and all the child records with the same ID in the “ChildTable”

MasterTable
ID int
Name varchar(100)

ChildTable
ID int
Region varchar(100)



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Question by:ToString1
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10 Comments
 
LVL 52

Assisted Solution

by:Carl Tawn
Carl Tawn earned 142 total points
ID: 34144322
Can you modify the table schema? Because this sort of thing would be better implemented as a cascade delete rule on your tables.
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LVL 5

Assisted Solution

by:roxviper
roxviper earned 215 total points
ID: 34144386
Hi,

Here is an example of mine:

            
InvoicerDataContext db = new InvoicerDataContext();
            var costCenter = db.CostCenters.SingleOrDefault(q => q.CostCentersID == CostCenterID);
            if (costCenter != null)
            {
                var invoices = db.Invoices.Where(q => q.CostCenterID == CostCenterID);
                db.Invoices.DeleteAllOnSubmit(invoices);
                db.SubmitChanges();

                db.CostCenters.DeleteOnSubmit(costCenter);
                db.SubmitChanges();
            }

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Author Comment

by:ToString1
ID: 34144407
OK thanks

Yes I already have a cascade delete rule in my database schema but have not written any code yet
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LVL 52

Assisted Solution

by:Carl Tawn
Carl Tawn earned 142 total points
ID: 34144431
If you have a cascade rule then you only need to delete the header record, the cascade will take the related child records with it.
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Author Comment

by:ToString1
ID: 34144482
I have tried the code above but get the error

Cannot remove an entity that has not been attached

It appears to remove child records but not master record
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LVL 10

Assisted Solution

by:Mathiyazhagan
Mathiyazhagan earned 143 total points
ID: 34144483
hi, have attached comprehensive linq query to delete master and child records. but, LINQ needs each table should have primary key to Delete operation.that is , assumption of my query is, ID is primary key of Master table and child table has ChildID field as primary key field.


hope this helps.
int MasterIDToDelete =2;
//select and delete all child records
var ChildsToDelete = from  child  in db.Childtable  
          join master in db.Mastertable on child.ID equals master.ID
		  where master.ID == MasterIDToDelete
		  select child ;
db.Childtable.DeleteAllOnSubmit(ChildsToDelete);
db.SubmitChanges();
// select single master record and delete
var MasterToDelete = (from master in db.Mastertable  
				where master.ID == MasterIDToDelete 
				select master).Single();
db.Mastertable.DeleteOnSubmit(MasterToDelete);
db.SubmitChanges();

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Accepted Solution

by:
roxviper earned 215 total points
ID: 34144501
try to let only the code for deleting a single record and see if gives error
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Author Comment

by:ToString1
ID: 34144673
Hi the code posted by roxviper does delete the "many" table records but not the master.

It is to do with being attached to two different data contexts
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LVL 5

Assisted Solution

by:roxviper
roxviper earned 215 total points
ID: 34144698
use one datacontext
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LVL 10

Assisted Solution

by:Mathiyazhagan
Mathiyazhagan earned 143 total points
ID: 34152324
you can also directly delete child records filtered by child.ID = MasterIDToDelete and no need of join also...
int MasterIDToDelete =2;
//select and delete all child records
var ChildsToDelete = from  child  in db.Childtable  
          	  where child.ID == MasterIDToDelete
		  select child ;
db.Childtable.DeleteAllOnSubmit(ChildsToDelete);
db.SubmitChanges();
// select single master record and delete
var MasterToDelete = (from master in db.Mastertable  
				where master.ID == MasterIDToDelete 
				select master).Single();
db.Mastertable.DeleteOnSubmit(MasterToDelete);
db.SubmitChanges();

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