Introduction and Goal
This is a pretty simple tutorial dedicated to LINQ newbie's who want to learn how to do CRUD operations using LINQ entities. I am sure many experienced LINQ players would criticize me for such a mild article. One of the biggest catch which I found is the in-memory update service by LINQ, which I think for any newbie for LINQ is a must to understand.
So we will start with an understanding of the differences between in-memory updates and physical commits and then we will deep in to the code for each database operation. Again this article is one of those small sprints which I need to run so that I can complete the huge LINQ FAQ project.
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Screen shot of what we are going to talk about
LINQ In-memory commits and physical commits
Entity objects forms the base of LINQ technologies. So when any data is submitted to database it goes through the LINQ objects. Database operations are done through 'DataContext' class. As said previously entities form the base of LINQ, so all the data is sent to these entities first and then its routed to the actual physical database. Due to this nature of working database commits is a two step process, the first step is in-memory and final step is physical commits.
In order to do in-memory operation 'DataContext' has provided 'DeleteOnSubmit' and 'InsertOnSubmit' methods. When we call these methods from the 'DataContext' class they add and update data in the entity objects memory. Please note these methods do not change / add new data in the actual database.
Once we are done with the in-memory operations and we want to send all the updates to the database for that we need to call 'SubmitChanges()' method. This method finally commits data in to the physical database.
So let's consider a customer table (customerid, customercode and customername) and see how we can do the in-memory and physical commit operations.
Step 1 :- Create the entity customer class
So as a first step we create the entity of customer class as shown in the below code snippet.
[Table(Name = "Customer")]
public class clsCustomerEntity
{
private int _CustomerId;
private string _CustomerCode;
private string _CustomerName; [Column(DbType = "nvarchar(50)")]
public string CustomerCode
{
set
{
_CustomerCode = value;
}
get
{
return _CustomerCode;
}
}
[Column(DbType = "nvarchar(50)")]
public string CustomerName
{
set
{
_CustomerName = value;
}
get
{
return _CustomerName;
}
}
[Column(DbType = "int", IsPrimaryKey = true, IsDbGenerated = true)]
public int CustomerId
{
set
{
_CustomerId = value;
}
get
{
return _CustomerId;
}
}
}
Create data context
So the first thing is to create a 'datacontext' object using the connection string.
DataContext objContext = new DataContext(strConnectionString);
Set the data for insert
Once you create the connection using the 'DataContext' object the next step is to create the customer entity object and set the data to the object property.
clsCustomerEntity objCustomerData = new clsCustomerEntity();
objCustomerData.CustomerCode = txtCustomerCode.Text;
objCustomerData.CustomerName = txtCustomerName.Text;
Do an in-memory update
We then do an in-memory update in entity objects itself using 'InsertOnSubmit' method.
objContext.GetTable<clsCustomerEntity>().InsertOnSubmit(objCustomerData);
Do the final physical commit
Finally we do a physical commit to the actual database. Please note until we do not call 'SubmitChanges()' data is not finally committed to the database.
objContext.SubmitChanges();
The final create LINQ code
Below is the final LINQ code put together.
DataContext objContext = new DataContext(strConnectionString);
clsCustomerEntity objCustomerData = new clsCustomerEntity();
objCustomerData.CustomerCode = txtCustomerCode.Text;
objCustomerData.CustomerName = txtCustomerName.Text;
objContext.GetTable<clsCustomerEntity>().InsertOnSubmit(objCustomerData);
objContext.SubmitChanges();
Step 3:- Update using LINQ
So let's take the next database operation i.e. update.
Create data Context
As usual we first need to create a 'datacontext' object using the connection string as discussed in the create step.
DataContext objContext = new DataContext(strConnectionString);
Select the customer LINQ object which we want to update
Get the LINQ object using LINQ query which we want to update
var MyQuery = from objCustomer in objContext.GetTable<clsCustomerEntity>()
where objCustomer.CustomerId == Convert.ToInt16(txtCustomerId.Text)
select objCustomer;
Finally set new values and update data to physical database
Do the updates and call 'SubmitChanges()' to do the final update.
clsCustomerEntity objCustomerData = (clsCustomerEntity)MyQuery.First<clsCustomerEntity>();
objCustomerData.CustomerCode = txtCustomerCode.Text;
objCustomerData.CustomerName = txtCustomerName.Text;
objContext.SubmitChanges();
The final code of LINQ update
Below is how the final LINQ update query looks like.
DataContext objContext = new DataContext(strConnectionString);
var MyQuery = from objCustomer in objContext.GetTable<clsCustomerEntity>()
where objCustomer.CustomerId == Convert.ToInt16(txtCustomerId.Text)
select objCustomer; clsCustomerEntity objCustomerData = (clsCustomerEntity)MyQuery.First<clsCustomerEntity>();
objCustomerData.CustomerCode = txtCustomerCode.Text;
objCustomerData.CustomerName = txtCustomerName.Text;
objContext.SubmitChanges();
Step 4:- Delete using LINQ
Let's take the next database operation delete.
DeleteOnSubmit
We will not be going through the previous steps like creating data context and selecting LINQ object , both of them are explained in the previous section. To delete the object from in-memory we need to call 'DeleteOnSubmit()' and to delete from final database we need use 'SubmitChanges()'.
objContext.GetTable<clsCustomerEntity>().DeleteOnSubmit(objCustomerData);
objContext.SubmitChanges();
Step 5 :- Self explanatory LINQ select and read
Now on the final step selecting and reading the LINQ object by criteria. Below is the code snippet which shows how to fire the LINQ query and set the object value to the ASP.NET UI.
DataContext objContext = new DataContext(strConnectionString);
var MyQuery = from objCustomer in objContext.GetTable<clsCustomerEntity>()
where objCustomer.CustomerId == Convert.ToInt16(txtCustomerId.Text)
select objCustomer; clsCustomerEntity objCustomerData = (clsCustomerEntity)MyQuery.First<clsCustomerEntity>();
txtCustomerCode.Text = objCustomerData.CustomerCode;
txtCustomerName.Text = objCustomerData.CustomerName;
The LINQ CRUD code
You can download the complete CRUD source code top of this article