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Posted 9 Apr 2007

Persistent Object Management in Less than 300 Lines of Code

, 8 Oct 2007
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Presenting a lightweight method to cut out most of the repetitive work of creating data classes.


There's a lot of repetitive work associated with the writing of data classes within the data access layer of an N-tiered architecture. Apart from adding a column to the relevant database table, adding a field to the class involves adding a private variable to hold the field value, a property to expose it to other classes, and several lines to make sure the field is included in insert, fetch, and update operations. If you're using stored procedures (very silly for CRUD queries) there are several more modifications to make. This is dull work, I'm sure you'll agree. Presented here is a lightweight method for taking away all this tedium, such that you only have to add a getter/setter property in order to add a field to a data class.

The technique involves abstracting SQL query writing and execution, and variable storage in data access classes to a base class. In the implementation presented here, I've named this base class "PersistentDataObject". The "less than 300 lines of code" referred to in the title of this post are the lines of code in this base class, the database access class it uses, and a couple of exception classes used as markers to add clarity to exception origins. The complete code is included at the end of the post.


I conceived this idea, before my .NET days, while working on a monolithic PHP project. After writing hundreds of simple CRUD queries that were all basically the same, I realized that it would be a simple matter to abstract all that query writing in such a way that I would never have to write such a simple query again. That was over a year ago. Now I'm a fully paid up ASP.NET developer, and I think the code has reached a level of refinement at which it is ready to be presented to the world. I use the code presented here in every system I build and I love it. Maybe you will too.

Using the Code

Here is a simple Person class created by extending PersistentDataObject:

using System;

public class Person : PersistentDataObject
 public Person() : base("Person", "PersonId") { }
 public Person(int id) : this() { Load(id); }

 public string FirstName
   get { return Get<string>("FirstName"); }
   set { Set("FirstName", value); }
 public string LastName
   get { return Get<string>("LastName"); }
   set { Set("LastName", value); }
 public DateTime DateOfBirth
   get { return Get<DateTime>("DateOfBirth"); }
   set { Set("DateOfBirth", value); }
 public int? LuckyNumber
   get { return Get<int?>("LuckyNumber"); }
   set { Set("LuckyNumber", value); }

Configuring the Data Object Class

The only configuration values necessary for the class are name of the table from which the data is to be retrieved, and the name of the unique id column within that table (assumed to be an integer column). These are passed to PersistentDataObject in the constructor.

public Person() : base("Person", "PersonId") { }

Fetching Data from the Database

The Person class shown above provides a constructor that accepts an integer identifier as an argument. This constructor delegates to the Load method of PersistentDataObject to fetch all data from the database for the row with the specified identifier.

public Person(int id) : this() { Load(id); }

An overload of the Load method is provided that takes a DataRow as an argument. This allows the object to be populated with data from a DataRow that has already been fetched from the database.

Exposing Column Values as Properties

Column Values are exposed by delegating to the Get and Set methods of PersistentDataObject. The Get method takes a string argument indicating the column from which the value should be retrieved. Similarly, the Set method takes a string argument to indicate for which column the value is to be set. This example shows a property exposing a DateTime column:

public DateTime DateOfBirth
get { return Get<DateTime>("DateOfBirth"); }
set { Set("DateOfBirth", value); }

Note that the Get method uses generics to identify the type of the value that should be returned. The type specified should be the appropriate type dependant on the type of the column.

Handling Null Values

Nullable value types come into play in order to handle columns that allow null values. This example shows an integer column for which null values are allowed exposed as a property:

public int? LuckyNumber
get { return Get<int?>("LuckyNumber"); }
set { Set("LuckyNumber", value); }

Note that as string is a reference type, it does not need to be specified as nullable to accept null values.

Inserting, Updating, and Deleting

A Save method is provided that handles both the inserting into, and the updating of objects in the database. If the Save method is called on an object that does not yet exist in the database, then an insertion is performed. If the object does already exist in the database, an update is performed. This code snippet shows an instance of Person being created and a record for it being inserted into the database:

Person person = new Person();
person.FirstName = "Nick";
person.LastName = "Higgs";
person.DateOfBirth = new DateTime(1983, 2, 7);

A Delete method is provided to allow the object to be deleted from the database. This code shows an object for an existing person record being instantiated and then deleted from the database:

Person person = new Person(51);

Closing Remarks

That completes the explanation. I've found that this technique not only takes most of the repetitive work out of writing data objects, but provides a solid foundation to a data access layer, regardless of the complexity of the system.


Modified from an article posted on my (now discontinued) blog


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Nick Higgs
Web Developer
United Kingdom United Kingdom
Since graduating from the University of Sheffield with a Masters degree in Software Engineering in 2005 I have been woking as a professional web developer for a Sheffield new media company.
ASP.Net is currently my primary technology, but I also have substantial experience with PHP and Flex and various Java technologies.

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Comments and Discussions

QuestionMultiple object Pin
suraj Chhetry9-Oct-07 21:56
membersuraj Chhetry9-Oct-07 21:56 
AnswerRe: Multiple object Pin
Nick Higgs10-Oct-07 3:25
memberNick Higgs10-Oct-07 3:25 
GeneralInitiative way! Pin
M.Khadem7-Jun-07 5:31
memberM.Khadem7-Jun-07 5:31 
QuestionHow to bind the Person object to a view object Pin
Aliasncnu7-May-07 17:43
memberAliasncnu7-May-07 17:43 
AnswerRe: How to bind the Person object to a view object Pin
Nick Higgs9-May-07 13:12
memberNick Higgs9-May-07 13:12 
GeneralQuestions and suggestions Pin
felipedr19-Apr-07 7:16
memberfelipedr19-Apr-07 7:16 
GeneralRe: Questions and suggestions Pin
Nick Higgs19-Apr-07 14:25
memberNick Higgs19-Apr-07 14:25 
Hi felipedr, thanks for the feedback.

felipedr wrote:
Person person = new Person();
person.FirstName = "Nick";

Whats the people.ID in this context? After insert a record, I need to save a picture, per example. How save the file as "ID + _picture.jpg"?

If an instance of a PersistentDataObject has not yet been inserted into the database, as in your example, the Id property contains the value -1. However, when Save is called the Id is automatically set to the primary key value of the object in the database. So, the Id is available immediately after the Save method is called.

felipedr wrote:
In my persistence object, I create a method to reload the record after the Insert, reloading the last record inserted as:

Select(String.Format("{0} in (select ident_current('{1}'))", primaryKeyFields[0], nameTable));

Think about this, ok?!

I was using @@IDENTITY to retrieve the Id, but after seeing your example and looking up IDENT_CURRENT and SCOPE_IDENTITY I see that that SCOPE_IDENTITY is a better method, and I’ll be changing my code to use that instead.

Note that you can do the INSERT query and the SELECT query in a single command, so you don’t have to do an extra round trip to the database server, like in this snippet from PersistentDataObject:

string sql = "SET NOCOUNT ON;"
           + "INSERT "+tableName+" ("+fieldList+")"
           + " VALUES ("+valueList+");"
           + " SELECT SCOPE_IDENTITY()"
           + " AS InsertionId;";
sc.CommandText = sql;
idValue = Convert.ToInt16(DatabaseAccessor.ExecuteScalar(sc));

felipedr wrote:
And, you can create new "LOAD" methods to increase you class and create a code more fast, adding:

public void Select(string where)
public void Select(string where, string orderby)
public void Select(string campos, string where, string orderby)

I agree that a quick intuitive way to get collections of data objects is the next logical step up, and I appreciate the suggestion. I will be doing some work on this in the future and if I come up with something worth sharing I'll post it up.


GeneralTransactions Pin
probe5319-Apr-07 0:05
memberprobe5319-Apr-07 0:05 
GeneralRe: Transactions Pin
Nick Higgs19-Apr-07 10:30
memberNick Higgs19-Apr-07 10:30 
GeneralExcellent Article Pin
Dewey9-Apr-07 21:02
memberDewey9-Apr-07 21:02 

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