Sql – Using LINQ to delete child records automatically

linqlinq-to-sql

I am somewhat new to LINQ and have a quick question regarding deleting.

Say, for example I have 2 tables, Orders and OrderItems. Using LINQ, I can easily create a new child record by using

order.Items.Add(new OrderItem());

and this will create the child record in the database and update its foreign key to the orderId. This is great, I like it! However when I want to remove a child record

order.Items.Remove(orderItem);

I get an error when I sumbit the changes (because its not actually deleting the child row (order item), just removing the foreign keyId). Is it possible to do this the way I would like to? I don't want to have to create a whole bunch of repositories and if ladders to delete all child rows for a large database.

Thanks in advance.

Best Answer

You can achieve that in the DB itself by configuring the Foreign key relationship to delete child records on deletion of the parent's key.

Note that this is transparent to Linq2SQL and it will not be aware of it, so it's best to make sure you do not keep the datacontexts around after that, since the OrderItem objects will still be present.

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LINQ to SQL only supports 1 to 1 mapping of database tables, views, sprocs and functions available in Microsoft SQL Server. It's a great API to use for quick data access construction to relatively well designed SQL Server databases. LINQ2SQL was first released with C# 3.0 and .Net Framework 3.5.

LINQ to Entities (ADO.Net Entity Framework) is an ORM (Object Relational Mapper) API which allows for a broad definition of object domain models and their relationships to many different ADO.Net data providers. As such, you can mix and match a number of different database vendors, application servers or protocols to design an aggregated mash-up of objects which are constructed from a variety of tables, sources, services, etc. ADO.Net Framework was released with the .Net Framework 3.5 SP1.

This is a good introductory article on MSDN: Introducing LINQ to Relational Data

C# – LINQ query on a DataTable

You can't query against the DataTable's Rows collection, since DataRowCollection doesn't implement IEnumerable<T>. You need to use the AsEnumerable() extension for DataTable. Like so:

var results = from myRow in myDataTable.AsEnumerable()
where myRow.Field<int>("RowNo") == 1
select myRow;

And as @Keith says, you'll need to add a reference to System.Data.DataSetExtensions

AsEnumerable() returns IEnumerable<DataRow>. If you need to convert IEnumerable<DataRow> to a DataTable, use the CopyToDataTable() extension.

Below is query with Lambda Expression,

var result = myDataTable
    .AsEnumerable()
    .Where(myRow => myRow.Field<int>("RowNo") == 1);

Best Answer

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