Migration strategy for simple .NET classes to LINQ classes

Introduction and Goal

When new technologies are introduced one of the biggest business challenges faces is migrating the current projects to new technologies with least effort. I am sure scratch development is not always a preferred option from business investment point of view. One of the new technologies which is talked most is 'LINQ'. This article will focus on how we can convert simple existing .NET classes in to LINQ enabled classes.

LINQ is a uniform programming language which basically takes the old .NET classes to a much improvised level. It brings down the complexity of the business classes by using LINQ queries. In this article we will touch base how can we leverage and migrate our old .NET classes to make them LINQ enabled. LINQ has much more benefits than what I just talked in case you are not aware of basics you can read the basics from http://www.c-sharpcorner.com/UploadFile/shivprasadk/654654607132009040318AM/6546546.aspx?ArticleID=e51427a9-7f26-4db9-8b84-f6a3a6a698a6

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Disclaimer: - Do not blast me....

The conclusion which I have drawn here is based on a project which was migrated. The project had hardly 15 classes and they where well written. I am really not sure how this will work for projects having huge number of classes. I will be working on this migration project for more 6 months so any more challenges or issues I will be updating in this article.

So please do your home work before you start implementing.

Simple .NET class

So here's a simple .NET customer class which basically has 3 properties Id , CustomerName and Customercode. We will look in to how we can migrate this .NET class in to LINQ class without touching the core logic.

public class clsCustomer
{
    private int _intCustomerId;
    private string _strCustomerName;
    private string _strCustomerCode;

    public int CustomerId
    {
        set
        {
            _intCustomerId = value;
        }
        get
        {
            return _intCustomerId;
        }
    }

    public string CustomerName
    {
        set
        {
            _strCustomerName = value;
        }
        get
        {
            return _strCustomerName;
        }
    }

    public string CustomerCode
    {
        set
        {
            _strCustomerCode = value;
        }
        get
        {
            return _strCustomerCode;
        }
    }                       
}

The core of the approach: - XML mapping

LINQ had provided attribute based XML mapping. So you can have your pure .NET classes and you can define the LINQ mapping in a XML file. LINQ engine can then read the mapping from a XML file and apply the same to your simple .NET classes.



The XML file

Below is my XML file where I have define my mappings of table columns with class properties, database names, table name and class types.

<?xml version="1.0" encoding="utf-8"?>
<Database Name="TstServer"  xmlns="http://schemas.microsoft.com/linqtosql/mapping/2007">
  <Table Name="dbo.Customer" Member="WebAppMappingXML.clsCustomer">
    <Type Name="WebAppMappingXML.clsCustomer">
      <Column Name="CustomerId" Member="CustomerId" />
      <Column Name="CustomerName" Member="CustomerName"  />
      <Column Name="CustomerCode" Member="CustomerCode"  />
    </Type>
  </Table>
</Database>

To bind the XML mapping with the simple .NET class we need to first create the XMLMappingSource object as shown in the below code snippet.

XmlMappingSource xms = XmlMappingSource.FromUrl(physicalPath + "Mapping.xml");

We need to pass the XMLMappingSource object to the datacontext class shown in the below code snippet.

DataContext objContext = new DataContext(strConn, xms);

Finally we can get the table and loop through the entity objects.

var query = from customer in objContext.GetTable<clsCustomer>()
            select customer;
foreach (var item in query)
{
    Response.Write(item.CustomerCode + "<br>");
}

Applying Stored procedure

In case you have stored procedures in your project you can use 'Function' XML element to define your stored procedure name in the XML file. The client code does not change for binding the datacontext and XMLMappingsource object.

<?xml version="1.0" encoding="utf-8"?>
<Database Name="TstServer"  xmlns="http://schemas.microsoft.com/linqtosql/mapping/2007">
  <Table Name="dbo.Customer" Member="WebAppMappingXML.clsCustomer">
    <Type Name="WebAppMappingXML.clsCustomer">
      <Column Name="CustomerId" Member="CustomerId" />
      <Column Name="CustomerName" Member="CustomerName"  />
      <Column Name="CustomerCode" Member="CustomerCode"  />
    </Type>
  </Table>
  <Function Name="dbo.sp_getCustomerCode" Method="getCustomerByCode">
    <Parameter Name="CustomerCode" Parameter="" />
    <ElementType Name="clsCustomer" />
  </Function>
</Database>

Advantages and disadvantages of the approach

First let's start with all goodies

• You do not need to change your core .NET classes. There is a complete XML isolation between your core .NET classes and LINQ engines.
• You can exploit the LINQ Query and minimize your business object logic complexity.
• Your database classes are completely removed and replaced by LINQ data context. This minimizes lot of coding in the DAL classes.

Bad things:-

• Sometimes effort of this migration can be more than building from scratch.
• You need to write those complicated XML files by hand. We did not try SQLMETAL or other tools. Probably you guys can try it out to remove this disadvantage.
• Classes having relationships need to replaced by 'EntitySet' and 'EntityRef'. It's a bit tricky and can change your collection interfaces.

Source code

You can download the source code from top of this article.