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Implementing Audit Trail using Entity Framework Part -1

, 27 Mar 2009
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Implementing Audit Trail using Entity Framework's caching entries

Introduction

Entity framework keeps track for those entire objects and relationships which have been deleted, added and modified in the container. EF keeps the state of the object and holds the necessary change-information and all these track information for each object or relationship resides as “objectStateEntry”. Using “ObjectStateManager” one can access all these change-information like object-state (added/modified/deleted), modified properties, original and current values and can easily do audit trail for those objects. To get the Rollback feature from that audit trail we have to consider some issues. We have to maintain the order of entity graph while insertion and deletion. That means root entity has been inserted before the children and during deletion we have to make it reverse. The most important issue is that we have to make sure that audit trail entry will be inserted according this order.

So now I am going to talk about audit trail implementation that’s capable to rollback to a certain period. To make such implementation I am going to use the Entity framework’s caching Management that is called as “ObjectStateManager”.Using this Manager I will be capable to find out the object that is currently changed or added or deleted and resides in EF cache as Object state entry. In part 1, I just going to talk about creating audit trail objects using the object state entry. In Second Part I will talk about roll back feature of this audit trial.

Using the Code

First I make table audit trail in database

DataBaseDbAudit.JPG

For this table, I am going to make an Entity set in my conceptual level as

dbAuditEF.JPG

In Entity Framework, to save my all changes into Db we have call “Context.SaveChanges()” and This Context is a container that has been inherited from “ObjectContext” Class.To create the Audit trail Objects for each “Modified/Added/Deleted”I am going to catch the event-

Context.SavingChanges +=new EventHandler(Context_SavingChanges);

In sample program I have done it with writing partial class -

public partial class AdventureWorksEntities
{ partial void OnContextCreated()
{
    this.SavingChanges += new EventHandler(AdventureWorksEntities_SavingChanges);
}

void AdventureWorksEntities_SavingChanges(object sender, EventArgs e)
{

So in my “AdventureWorksEntities_SavingChanges” method I am going to create all “dbaudit” objects those are going to save in DB.Here its takes each entry from EF cache of state- Added or Deleted or Modified and call a factory method to produce audit trail object.

public partial class AdventureWorksEntities
{
    public string UserName { get; set; }
    List<DBAudit> auditTrailList = new List<DBAudit>();

    public enum AuditActions
    {
        I,
        U,
        D
    }

    partial void OnContextCreated()
    {
        this.SavingChanges += new EventHandler(AdventureWorksEntities_SavingChanges);
    }

    void AdventureWorksEntities_SavingChanges(object sender, EventArgs e)
    {
        IEnumerable<ObjectStateEntry> changes = 
            this.ObjectStateManager.GetObjectStateEntries(
            EntityState.Added | EntityState.Deleted | EntityState.Modified);
        foreach (ObjectStateEntry stateEntryEntity in changes)
        {
            if (!stateEntryEntity.IsRelationship &&
            stateEntryEntity.Entity != null &&
            !(stateEntryEntity.Entity is DBAudit))
            {//is a normal entry, not a relationship
                DBAudit audit = this.AuditTrailFactory(stateEntryEntity, UserName);
                auditTrailList.Add(audit);
            }
        }

        if (auditTrailList.Count > 0)
        {
            foreach (var audit in auditTrailList)
            {//add all audits 
                this.AddToDBAudit(audit);
            }
        }
    }

And here “AuditTrailFactory” is Factory method to create dbaudit object.Specially for Modify state it keeps the modified properties and serialized as XML.So using these field you can easily show the changes of modified object with doing any comparison of old and new data.

private DBAudit AuditTrailFactory(ObjectStateEntry entry, string UserName)
{
    DBAudit audit = new DBAudit();
    audit.AuditId = Guid.NewGuid().ToString();
    audit.RevisionStamp = DateTime.Now;
    audit.TableName = entry.EntitySet.Name;
    audit.UserName = UserName;

    if (entry.State == EntityState.Added)
    {//entry is Added 
        audit.NewData = GetEntryValueInString(entry, false);
        audit.Actions = AuditActions.I.ToString();
    }
    else if (entry.State == EntityState.Deleted)
    {//entry in deleted
        audit.OldData = GetEntryValueInString(entry, true);
        audit.Actions = AuditActions.D.ToString();
    }
    else
    {//entry is modified
        audit.OldData = GetEntryValueInString(entry, true);
        audit.NewData = GetEntryValueInString(entry, false);
        audit.Actions = AuditActions.U.ToString();

        IEnumerable<string> modifiedProperties = entry.GetModifiedProperties();
        //assing collection of mismatched Columns name as serialized string 
        audit.ChangedColumns = XMLSerializationHelper.XmlSerialize(
            modifiedProperties.ToArray());
    }

    return audit;
}

Here “GetEntryValueInString” is for creating XML text of Previous or modified object. In Entity Framework each entry hold all change defination.First I make a clone the current object.Using entry.GetModifiedProperties() I can get only modified properties of an object and Using “OriginalValues” and “CurrentValues” I can build myself the old data and new data.Factory has told me what that wants – old or new. At the End I have done XML serialized and return back XML string .

private string GetEntryValueInString(ObjectStateEntry entry, bool isOrginal)
{
    if (entry.Entity is EntityObject)
    {
        object target = CloneEntity((EntityObject)entry.Entity);
        foreach (string propName in entry.GetModifiedProperties())
        {
            object setterValue = null;
            if (isOrginal)
            {
                //Get orginal value 
                setterValue = entry.OriginalValues[propName];
            }
            else
            {
                //Get orginal value 
                setterValue = entry.CurrentValues[propName];
            }
            //Find property to update 
            PropertyInfo propInfo = target.GetType().GetProperty(propName);
            //update property with orgibal value 
            if (setterValue == DBNull.Value)
            {//
                setterValue = null;
            }
            propInfo.SetValue(target, setterValue, null);
        }//end foreach

        XmlSerializer formatter = new XmlSerializer(target.GetType());
        XDocument document = new XDocument();

        using (XmlWriter xmlWriter = document.CreateWriter())
        {
            formatter.Serialize(xmlWriter, target);
        }
        return document.Root.ToString();
    }
    return null;
}

To clone the entity I have used the method which I have found in MSDN forum Post (Thanx toPatrick Magee )-

public EntityObject CloneEntity(EntityObject obj)
{
    DataContractSerializer dcSer = new DataContractSerializer(obj.GetType());
    MemoryStream memoryStream = new MemoryStream();

    dcSer.WriteObject(memoryStream, obj);
    memoryStream.Position = 0;

    EntityObject newObject = (EntityObject)dcSer.ReadObject(memoryStream);
    return newObject;
}

That is all for Part-1 where I just create the Audit trail objects for each CUD operation.

License

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

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About the Author

Morshed Anwar
Team Leader Adaptive Enterprise Limited (www.ael-bd.com)
Bangladesh Bangladesh
No Biography provided

Comments and Discussions

 
GeneralRe: CloneEntity throwing Out-of-memory error PinmemberLee Keel21-Nov-12 11:01 
GeneralRe: CloneEntity throwing Out-of-memory error PinmemberMorshed Anwar21-Nov-12 11:11 
QuestionProblem with self-tracking entities PinmemberMember 950081122-Oct-12 4:09 
AnswerRe: Problem with self-tracking entities PinmemberMorshed Anwar22-Oct-12 4:30 
GeneralRe: Problem with self-tracking entities PinmemberMember 950081123-Oct-12 2:30 
GeneralRe: Problem with self-tracking entities PinmemberMorshed Anwar23-Oct-12 4:20 
QuestionRegarding master detail audit trail PinmemberTridip Bhattacharjee17-Oct-12 4:11 
AnswerRe: Regarding master detail audit trail PinmemberMorshed Anwar17-Oct-12 9:35 
Hey Tridip, First of all thanks to you for give me a chance to think on a scenario. In my current implementation, Off-course it will audit each changes separately. From my early thinking , I can tell you similar kind of master-detail idea while working one of my projects where I did master and detail table for Audit. There I have created a audit session by inserting a user information with time during user logged-in and after that all my audits(this article implementation) by that specific user will go into details table of Audit with reference of that master key .In my scenario One user can be logged in one workstation at a time. I know it is different from your scenario but you can apply this kind of master-detail audit idea while doing a request workflow...which means when you request product changes...you can insert in master table with some screen information or something like that and get a unique id to identify your request workflow ...and after that rest of the procedure will be same. It will help you to grouping you changes. In achieve this, You need to create and dispose your context(ObjectContext/Dbcontext) while handling a request...Which mean A Context will be created when request come to business layer end and Context will be alive till to save changes and after dispose on finish of request. Hope it helps Smile | :)
Md. Morshed Anwar | Senior Software Engineer
Adaptive Enterprise Limited
Blog: http://morshedanwar.wordpress.com/

GeneralRe: Regarding master detail audit trail PinmemberTridip Bhattacharjee17-Oct-12 20:10 
SuggestionAudit trail for Entity Framework Code-first (DbContext) PinmemberMorshed Anwar3-Oct-12 21:48 
QuestionGreat works, but it is not working with EntityDataSource. Pinmembercoderdest1-Aug-12 21:11 
AnswerRe: Great works, but it is not working with EntityDataSource. PinmemberMorshed Anwar1-Aug-12 23:30 
QuestionDbContext Pinmembermohammed926-Jul-12 23:30 
GeneralRe: DbContext [modified] PinmemberMorshed Anwar27-Jul-12 6:53 
AnswerRe: DbContext PinmemberMorshed Anwar3-Oct-12 21:51 
GeneralMy vote of 5 PinmemberYugan_SA5-Jul-12 0:36 
QuestionOriginal Values not available for Self Tracking Entities [modified] PinmemberBrett Dalldorf21-May-12 0:48 
AnswerRe: Original Values not available for Self Tracking Entities PinmemberLipi Hardjono27-May-12 15:47 
GeneralRe: Original Values not available for Self Tracking Entities Pinmembermark.deraeve13-Jun-12 20:20 
GeneralRe: Original Values not available for Self Tracking Entities PinmemberMorshed Anwar23-Oct-12 4:31 
QuestionHow to preserve Old data in Audit Trail implementation via Entity Framework Pinmembermittarah7-May-12 2:40 
AnswerRe: How to preserve Old data in Audit Trail implementation via Entity Framework PinmemberMorshed Anwar8-May-12 23:15 
SuggestionBrilliant Article! Just needs a bit of editing for a Context Template (See this post) PinmemberBrett Dalldorf26-Apr-12 1:03 
QuestionPrimary key still zero on added objects Pinmemberangelo carlt18-Nov-11 5:00 
AnswerRe: Primary key still zero on added objects Pinmembermark.deraeve11-Apr-12 23:12 

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