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Very Lightweight Data Access Layer in C# and .NET 2.0

, 4 Apr 2007 CPOL
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Very Lightweight Data Access Layer in C# and .NET 2.0


In my spare time I write a lot of small applications for my friends and family. The common thing for all these small applications is that they grab some data from the database, display the data to the user and save the changes back to database.

When I design programs, I break them into tiers. Most of the time I have three logical tiers, which are User Interface Layer, Business Logic and Data Access Layer. I usually start with the class diagram, and only after I am happy with the class diagram then I build the tables and stored procedures to access the data from/to tables. User Interface is usually dictated by the user.

As I was building more and more of these small apps, I realized that I was spending a lot of time on my Data Access Layer, since I had to create mappings for populating the business objects from the tables in database, and since each application had a different business logic and business objects, I ended up writing Data Access Layer from scratch. So to make my life easier, I decided to build a generic data access helper class that could be reused on all my projects with little or no changes.

To be able to populate the object with the data from the database, the business object needs to have public properties with GET and SET methods. Then using reflection I could query the object for the public properties and if the property name matched the name of the field in the table, then the object would be populated with the data from that field.

There were times when the properties and the fields in the database were different or that the object could have more properties than the fields in database, so I decided to have two ways of populating the object with the data from the database:

  • Use a mapping class that would provide information of what property is mapped to what field, and
  • Decorate the properties with a custom attribute to show to what field the property is mapped.

The first step is to build a mapping class. This is a very simple class that holds a collection of a strings. The first string would be in the format property=field, where property is the name of the property of the object, and the field is the name of the field in database. So the mapping class, after implementation, looks like this:

/// <summary>
/// This class holds information about mapping a database field to a 
/// object property.
/// </summary>
public class Mapper
    private List<string> mMappingInfo;

    /// <summary>
    /// Default constructor
    /// </summary>
    public Mapper()
        mMappingInfo = new List<string>();

    /// <summary>
    /// Add mapping information. This method can be used to add more than 
    /// one mapping at a time.
    /// You could use it like: mapper.Add("property1=field1", 
    ///     "property2=field2", "property3=field3", ...)
    /// </summary>
    /// <param name="mappings">mapping information in format 
    //     "[property name]=[field name]"</param>
    public void Add(params string[] mappings)
        foreach (string map in mappings)

    /// <summary>
    /// Return mapping information held in this class as string array
    /// </summary>
    public string[] MappingInformation
            string[] mappings = new string[mMappingInfo.Count];

            return mappings;

    /// <summary>
    /// Indexer property. By providing the name it returns the mapping info
    /// for that property.
    /// If the mapping information for the provided property does not exist,
    /// the indexer 
    /// return null. 
    /// You could use it like: string mapInfo = mapper["property1"];
    /// </summary>
    /// <param name="propertyName">the name of the property to 

    /// mapping information</param>
    /// <returns>mapping information for the property 


The next thing to implement is the custom attribute that will be used to map properties with the fields in database. Again this is a very simple attribute that will be used to store the name of the field. The implementation looks like:

/// <summary>
/// Specifies the name of the field in the table that the property maps to 
/// </summary>
    public class DBFieldAttribute : Attribute
        private string mFieldName;

        /// <summary>
        /// constructor
        /// </summary>
        /// <param name="fieldName">name of the field that the 

property will
        /// be mapped to</param>
        public DBFieldAttribute(string fieldName)
            mFieldName = fieldName;

        public string FieldName
            get { return mFieldName; }

Since this attribute can only be used on properties, the class is decorated with AttributeUsage(AttributeTargets.Property) attribute.

And now finally the only thing left is the helper class that will be used to retrieve data from the database. The implemented class looks like:

public class DBHelper
    /// <summary>
    /// Generic method. Gets an object of type T from the data reader. It 
    /// uses mapping information provided to read a field from the reader, 
    /// and gets the property name and sets the value of the property with 
    /// the data which are held in database field
    /// </summary>
    /// <typeparam name="T>The type of object to be 


DBHelper is a static class which means that it does not need to be instantiated and all the methods are static as well. It is generic in a sense that you provide the type of the object to be loaded from the database, and the class creates the objects and populates its public properties (the ones that either are decorated with the DBField attribute or mapping information is provided) from the data read from the table.

As you can see from the code above we are using constraints on generics, which basically means that the generic type T has to be an object (reference type) and can't be of value type (primitives like int, float, byte, and so on, or struct which is also of value type). The above class also uses reflection to check if the properties have the DBField set, and if yes then the code reads the attribute, gets the field name from the attribute and reads the data from the table.

Using the code

To use the class above is very easy, as you can see from the following example. Suppose we have a table that contains persons' details and its definition is like the below:

and a class Person that looks like the code below:

public class Person
    private int mID;
    private string mName;
    private string mSurname;
    private DateTime mDob;
    private string mProfession;

    public Person()

    public int ID
        get { return mID; }
        set { mID = value; }

    public string Name
        get { return mName; }
        set { mName = value; }

    public string Surname
        get { return mSurname; }
        set { mSurname = value; }

    public DateTime DateOfBirth
        get { return mDob; }
        set { mDob = value; }

    public string Profession
        get { return mProfession; }
        set { mProfession = value; }

    public int CalculateAge()
        int age = DateTime.Now.Year - mDob.Year;
        return age;

As you can see from the code of class Person, public properties are decorated with the attribute DBField. Each attribute corresponds with the field name in the table. Now to read the data from the table and return populated objects we would use the DBHelper class like this:

public List<Person> GetAllPersonsFromDB()
    using (SqlConnection connection = new SqlConnection(connectionString))
        SqlCommand command = new SqlCommand("Select * from Persons order 

            _Surname", connection);
        List<Person> persons = 

        return persons;

or, if you need to retrieve a particular object, you could use the code below:

public Person GetPersonByID(int id)
    using (SqlConnection connection = new SqlConnection(connectionString))
        SqlCommand command = new SqlCommand("Select * from Persons where 

            _= @ID", connection);
        SqlParameter param = command.Parameters.Add("@ID", 

        param.Value = id;

        Person person = DBHelper.ReadObject<Person>(command);
        return person;

If for some reason you need to get data from another table where the fields are named differently from the attributes, we need to provide mapping information by using Mapper class to the DBHelper.

Example: If we need to read data from another table and the table definition is as follows:

To read the data from the above table, we need to provide mapping information to DBHelper as follows:

public List<Person> GetAllPersonsFromDB()
    using (SqlConnection connection = new SqlConnection(connectionString))
        SqlCommand command = new SqlCommand("Select * from Persons order 

            _Surname", connection);
        Mapper mapper = new Mapper();
        // Provide the mapping information in format: "[Property Name]=
        // [Field Name]" for the appropriate fields 
        mapper.Add("ID=ID", "Name=FirstName", 



        List<Person> persons = 

        return persons;

As you can see from the examples above, the DBHelper class can be used easily on different projects to get the data from the database and convert them to objects in a convenient way. So the first step is to declare the appropriate class with default constructor (parameterless constructor) and provide public properties with get/set methods, then either use DBField attribute on properties to map them to database fields, or use Mapper class to provide mapping information.

This class could be extended to support storing object to the database as well.


I have changed the source code, so now the DBHelper class can be used to insert/update business objects to database. I have also created a small demo program (attached to source solution).


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


About the Author

Fitim Skenderi
Software Developer (Senior)
United Kingdom United Kingdom
No Biography provided

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Comments and Discussions

QuestionWhy not just use an object database? Pin
Ramon Smits4-Apr-07 12:20
memberRamon Smits4-Apr-07 12:20 
AnswerRe: Why not just use an object database? Pin
Marc Leger4-Apr-07 14:02
memberMarc Leger4-Apr-07 14:02 
GeneralRe: Why not just use an object database? Pin
Ramon Smits4-Apr-07 22:15
memberRamon Smits4-Apr-07 22:15 
GeneralRe: Why not just use an object database? Pin
Craig G. Wilson5-Apr-07 2:53
memberCraig G. Wilson5-Apr-07 2:53 
GeneralNice idea, but.... Pin
C Jones19-Mar-07 0:04
memberC Jones19-Mar-07 0:04 
GeneralRe: Nice idea, but.... Pin
li_robert19-Mar-07 2:42
memberli_robert19-Mar-07 2:42 
GeneralRe: Nice idea, but.... Pin
C Jones19-Mar-07 2:57
memberC Jones19-Mar-07 2:57 
GeneralRe: Nice idea, but.... Pin
Fitim Skenderi19-Mar-07 11:34
memberFitim Skenderi19-Mar-07 11:34 
You have some valid points. However, it depends on the application that you are writting. and the environment that your application will reside. I will try to discuss your points in order.

First point is changing the column names in the database. Well here it depends on your application, and also on the ownership of the database. If you are changing the database schema, then in a sense you are creating a new release (new version), since you need to deploy your new database schema to your customers, which means that your release should include the changes necessary to the application as well as database.

The second point is adding new column to a table. Again, even if you use ORM or any other DAL, you still need to extend the business logic of your application to acommodate the new column. The way I understand it is: since the user requirements have changed which have resulted with a new column added to the table, that means your business object has changed (a new property needs to be added) and as a matter of fact your business logic has changed as well, so you still will need to make the necessary changes to your objects anyway regardless of what methodology/pattern/framework you use.

The third point is the use of stored procedures to overcome the changes to database schema. There are a lot of people that put a lot of business logic in database for performance purposes. I personally think that the database should only be for persisting data, and the stored procedures should only be for CRUD operations to tables, and the business logic should be on the application itself. But again, this is my preference and there are a lot articles and debate of whether the database should be free of any business logic, or if it should contain some business logic.

And the final point is ORM layer with XML/XSD schema. I have two comments here. The first one is, as article suggests this is very lightweight ORM which works for small applications. The second comment is that you can always change/enhance the Mapper class to use XML/XSD schema instead, or event update the DBHelper class as well.
GeneralRe: Nice idea, but.... [modified] Pin
C Jones19-Mar-07 23:35
memberC Jones19-Mar-07 23:35 
GeneralRe: Nice idea, but.... Pin
paulkatherine13-Apr-07 21:37
memberpaulkatherine13-Apr-07 21:37 
GeneralPerformance Pin
ITEK13-Mar-07 4:20
memberITEK13-Mar-07 4:20 
GeneralRe: Performance Pin
Fitim Skenderi13-Mar-07 5:28
memberFitim Skenderi13-Mar-07 5:28 
GeneralRe: Performance Pin
Craig G. Wilson5-Apr-07 2:50
memberCraig G. Wilson5-Apr-07 2:50 
GeneralRe: Performance Pin
technicaltitch7-Oct-08 6:52
membertechnicaltitch7-Oct-08 6:52 
QuestionWhy use a List for the mapping? Pin
ChicagoNovice13-Mar-07 3:25
memberChicagoNovice13-Mar-07 3:25 
AnswerRe: Why use a List for the mapping? Pin
Fitim Skenderi13-Mar-07 5:19
memberFitim Skenderi13-Mar-07 5:19 
QuestionDB fields and NULL Value Pin
df49412-Mar-07 11:49
memberdf49412-Mar-07 11:49 
AnswerRe: DB fields and NULL Value Pin
Fitim Skenderi12-Mar-07 23:12
memberFitim Skenderi12-Mar-07 23:12 
GeneralVB.Net Pin
Sanju.Net11-Mar-07 0:22
memberSanju.Net11-Mar-07 0:22 
QuestionCould you extend DBHelper class for updating business object? Pin
li_robert9-Mar-07 14:54
memberli_robert9-Mar-07 14:54 
AnswerRe: Could you extend DBHelper class for updating business object? Pin
Fitim Skenderi10-Mar-07 11:36
memberFitim Skenderi10-Mar-07 11:36 

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