Implementing Repository Pattern with EF4 POCO support

About two years ago have written a post and an article in codeproject about the repository pattern implementation with EF V1. After that I got a lot of requests in my articles to make it compatible for EF4 POCO support. So here I am going to make that. In this implementation of repository, I am going to add some new methods which has helped me to regularly while working with EF4 POCO support. Hope it will be helpful to you.

Here BaseContext is inherited from ObjectContext and BaseDataContract is base class of all my entities as POCO. 

public enum State{Unchanged, Added, Modified, Deleted}


[DataContractAttribute(IsReference = true)]
public abstract class BaseDataContract
       {
           /// <summary>
           /// This string holds all the validation-error messages.
           /// </summary>
           ///
           public BaseDataContract()
           {
           }

           [DataMember]
           public State ObjectState { get; set; }
       }

Take a look Repository class first and I will explain these methods later :

public class Repository<E, C> : IRepository<E, C>, IDisposable
    where E : BaseDataContract 
    where C : BaseContext
{
    private C _ctx;

    private string _KeyProperty = "ID";

    public string KeyProperty
    {
        get
        {
            return _KeyProperty;
        }
        set
        {
            _KeyProperty = value;
        }
    }

    public C Session
    {
        get { return _ctx; }
        set { _ctx = value; }
    }

    public Repository(C session)
    {
        _ctx = session;
    }

    public Repository(C session, string keyProperty) : this(session)
    {
        _KeyProperty = keyProperty;
    }

    #region IRepository<E,C> Members

    public int Save()
    {
        return _ctx.SaveChanges();
    }
    /// <summary>
    /// A generic method to return ALL the entities
    /// of type TEntity. This overload will use the
    /// the parameter entitySetName in the resolution of mapping
    /// between the CSDL and SSDL. In Version
    /// 2.0 this pluralizing behaviour will change and this
    /// method overload should be used only if Developers
    /// change EntitySet names from the default name generated.
    /// </summary>
    /// <param name="entitySetName">
    /// The EntitySet name of the entity in the model.
    /// </param>
    /// <typeparam name="TEntity">
    /// The Entity to load from the database.
    /// </typeparam>
    /// <returns>Returns a set of TEntity.</returns>
    public ObjectQuery<E> DoQuery(string entitySetName)
    {
        _ctx.ContextOptions.LazyLoadingEnabled = true;
        return _ctx.CreateQuery<E>("[" + entitySetName + "]");
    }
    /// <summary>
    /// A generic method to return ALL the entities
    /// of type TEntity. This overload will use the
    /// typeof(TEntity).Name in the resolution of mapping
    /// between the CSDL and SSDL. This method is useful
    /// for Models that DO NOT have their pluralized names
    /// changed by the developer.
    /// </summary>
    /// <typeparam name="TEntity">
    /// The Entity to load from the database.
    /// </typeparam>
    /// <returns>Returns a set of TEntity.</returns>
    public ObjectQuery<E> DoQuery()
    {
        _ctx.ContextOptions.LazyLoadingEnabled = true;
        return _ctx.CreateQuery<E>("[" + typeof(E).Name + "]");
    }

    /// <summary>
    /// A generic method to return ALL the entities
    /// of type TEntity. This overload will use the
    /// the parameter entitySetName in the resolution of mapping
    /// between the CSDL and SSDL. This method is useful
    /// for Models that DO have their pluralized names
    /// changed by the developer.
    /// </summary>
    /// <param name="entitySetName">
    /// The EntitySet name of the entity in the model.
    /// </param>
    /// <typeparam name="TEntity">
    /// The Entity to load from the database.
    /// </typeparam>
    /// <returns>Returns a set of TEntity.</returns>
    public ObjectQuery<E> DoQuery(string entitySetName, ISpecification<E> where)
    {
        _ctx.ContextOptions.LazyLoadingEnabled = true;
        return
            (ObjectQuery<E>)_ctx.CreateQuery<E>("[" + entitySetName + "]")
            .Where(where.EvalPredicate);
    }

    /// <summary>
    /// A generic method to return ALL the entities
    /// of type TEntity. This overload will use the
    /// typeof(TEntity).Name in the resolution of mapping
    /// between the CSDL and SSDL. This method is useful
    /// for Models that DO NOT have their pluralized names
    /// changed by the developer. 
    /// </summary>
    /// <typeparam name="TEntity">
    /// The Entity to load from the database.
    /// </typeparam>
    /// <returns>Returns a set of TEntity.</returns>
    public ObjectQuery<E> DoQuery(ISpecification<E> where)
    {
        _ctx.ContextOptions.LazyLoadingEnabled = true;
        return
            (ObjectQuery<E>)_ctx.CreateQuery<E>("[" + typeof(E).Name + "]")
            .Where(where.EvalPredicate);
    }
    /// <summary>
    /// Query Entity with Paging 
    /// </summary>
    /// <param name="maximumRows">Max no of row to Fetch</param>
    /// <param name="startRowIndex">Start Index</param>
    /// <returns>Collection of Entities</returns>
    public ObjectQuery<E> DoQuery(int maximumRows, int startRowIndex)
    {
        _ctx.ContextOptions.LazyLoadingEnabled = true;
        return (ObjectQuery<E>)_ctx.CreateQuery<E>("[" + 
              typeof(E).Name + "]").Skip<E>(startRowIndex).Take(maximumRows);
    }
    /// <summary>
    /// Query Entity in sorted Order
    /// </summary>
    /// <param name="sortExpression">Sort Expression/condition</param>
    /// <param name="ErrorCode">custom Error Message</param> 
    /// <returns>Collection of Entities</returns>
    public ObjectQuery<E> DoQuery(Expression<Func<E, object>> sortExpression)
    {
        if (null == sortExpression)
        {
            return ((IRepository<E, C>)this).DoQuery();
        }
        return (ObjectQuery<E>)((IRepository<E, C>)this).DoQuery().OrderBy<E, object>(sortExpression);
    }
    /// <summary>
    /// Query All Entity in sorted Order with Paging support
    /// </summary>
    /// <param name="sortExpression">Sort Expression/condition</param>
    /// <param name="maximumRows">Max no of row to Fetch</param>
    /// <param name="startRowIndex">Start Index</param>
    /// <returns>Collection Of entites</returns>
    public ObjectQuery<E> DoQuery(Expression<Func<E, object>> sortExpression, int maximumRows, int startRowIndex)
    {
        if (sortExpression == null)
        {
            return ((IRepository<E, C>)this).DoQuery(maximumRows, startRowIndex);
        }
        return (ObjectQuery<E>)((IRepository<E, C>)this).DoQuery(sortExpression).Skip<E>(startRowIndex).Take(maximumRows);
    }
    /// <summary>
    /// A generic method to return ALL the entities
    /// of type TEntity. This overload will use the
    /// the parameter entitySetName in the resolution of mapping
    /// between the CSDL and SSDL. In Version
    /// 2.0 this pluralizing behaviour will change and this
    /// method overload should be used only if Developers
    /// change EntitySet names from the default name generated.
    /// </summary>
    /// <param name="entitySetName">
    /// The EntitySet name of the entity in the model.
    /// </param>
    /// <typeparam name="TEntity">
    /// The Entity to load from the database.
    /// </typeparam>
    /// <returns>Returns a set of TEntity.</returns>
    public ObjectQuery<E> SelectAll(string entitySetName)
    {
        return DoQuery(entitySetName);
    }
    /// <summary>
    /// A generic method to return ALL the entities
    /// of type TEntity. This overload will use the
    /// typeof(TEntity).Name in the resolution of mapping
    /// between the CSDL and SSDL. This method is useful
    /// for Models that DO NOT have their pluralized names
    /// changed by the developer.
    /// </summary>
    /// <typeparam name="TEntity">
    /// The Entity to load from the database.
    /// </typeparam>
    /// <returns>Returns a set of TEntity.</returns>
    public ObjectQuery<E> SelectAll()
    {
        try
        {
            return DoQuery(); //_ctx.CreateQuery<E>("[" + typeof(E).Name + "]");
        }
        catch (Exception)
        {
            throw;
        }
    }

    /// <summary>
    /// A generic method to return ALL the entities
    /// of type TEntity. This overload will use the
    /// the parameter entitySetName in the resolution of mapping
    /// between the CSDL and SSDL. This method is useful
    /// for Models that DO have their pluralized names
    /// changed by the developer.
    /// </summary>
    /// <param name="entitySetName">
    /// The EntitySet name of the entity in the model.
    /// </param>
    /// <typeparam name="TEntity">
    /// The Entity to load from the database.
    /// </typeparam>
    /// <returns>Returns a set of TEntity.</returns>
    public ObjectQuery<E> SelectAll(string entitySetName, ISpecification<E> where)
    {
        return DoQuery(entitySetName, where);
    }

    /// <summary>
    /// A generic method to return ALL the entities
    /// of type TEntity. This overload will use the
    /// typeof(TEntity).Name in the resolution of mapping
    /// between the CSDL and SSDL. This method is useful
    /// for Models that DO NOT have their pluralized names
    /// changed by the developer. 
    /// </summary>
    /// <typeparam name="TEntity">
    /// The Entity to load from the database.
    /// </typeparam>
    /// <returns>Returns a set of TEntity.</returns>
    public ObjectQuery<E> SelectAll(ISpecification<E> where)
    {
        return DoQuery(where);
    }
    /// <summary>
    /// Select All Entity with Paging 
    /// </summary>
    /// <param name="maximumRows">Max no of row to Fetch</param>
    /// <param name="startRowIndex">Start Index</param>
    /// <returns>Collection of Entities</returns>
    public ObjectQuery<E> SelectAll(int maximumRows, int startRowIndex)
    {
        return DoQuery(maximumRows, startRowIndex);
    }
    /// <summary>
    /// Select All Entity in sorted Order
    /// </summary>
    /// <param name="sortExpression">Sort Expression/condition</param>
    /// <param name="ErrorCode">custom Error Message</param> 
    /// <returns>Collection of Entities</returns>
    public ObjectQuery<E> SelectAll(Expression<Func<E, object>> sortExpression)
    {
        if (null == sortExpression)
        {
            return DoQuery(sortExpression);
        }
        return DoQuery(sortExpression);
    }
    /// <summary>
    /// Select All Entity in sorted Order with Paging support
    /// </summary>
    /// <param name="sortExpression">Sort Expression/condition</param>
    /// <param name="maximumRows">Max no of row to Fetch</param>
    /// <param name="startRowIndex">Start Index</param>
    /// <returns>Collection Of entites</returns>
    public ObjectQuery<E> SelectAll(Expression<Func<E, 
               object>> sortExpression, int maximumRows, int startRowIndex)
    {
        if (sortExpression == null)
        {
            return DoQuery(maximumRows, startRowIndex);
        }
        return DoQuery(sortExpression, maximumRows, startRowIndex);
    }
    /// <summary>
    /// Get Entity By Primary Key
    /// </summary>
    /// <typeparam name="E">Entity Type</typeparam>
    /// <param name="Key">Primary Key Value</param>
    /// <returns>return entity</returns>
    public E SelectByKey(string Key)
    {
        _ctx.ContextOptions.LazyLoadingEnabled = true;
        // First we define the parameter that we are going to use the clause. 
        var xParam = Expression.Parameter(typeof(E), typeof(E).Name);
        MemberExpression leftExpr = MemberExpression.Property(xParam, this._KeyProperty);
        Expression rightExpr = Expression.Constant(Key);
        BinaryExpression binaryExpr = MemberExpression.Equal(leftExpr, rightExpr);
        //Create Lambda Expression for the selection 
        Expression<Func<E, bool>> lambdaExpr = Expression.Lambda<Func<E, 
                 bool>>(binaryExpr, new ParameterExpression[] { xParam });
        //Searching ....
        ObjectQuery<E> resultCollection = ((IRepository<E, C>)this).SelectAll(new Specification<E>(lambdaExpr));
        if (null != resultCollection && resultCollection.Count() > 0)
        {
            //return valid single result
            return resultCollection.First<E>();
        }//end if 
        return null;
    }
    /// <summary>
    /// Check if value of specific field is already exist
    /// </summary>
    /// <typeparam name="E"></typeparam>
    /// <param name="fieldName">name of the Field</param>
    /// <param name="fieldValue">Field value</param>
    /// <param name="key">Primary key value</param>
    /// <returns>True or False</returns>
    public bool TrySameValueExist(string fieldName, object fieldValue, string key)
    {
        // First we define the parameter that we are going to use the clause. 
        var xParam = Expression.Parameter(typeof(E), typeof(E).Name);
        MemberExpression leftExprFieldCheck = MemberExpression.Property(xParam, fieldName);
        Expression rightExprFieldCheck = Expression.Constant(fieldValue);
        BinaryExpression binaryExprFieldCheck = MemberExpression.Equal(leftExprFieldCheck, rightExprFieldCheck);

        MemberExpression leftExprKeyCheck = MemberExpression.Property(xParam, this._KeyProperty);
        Expression rightExprKeyCheck = Expression.Constant(key);
        BinaryExpression binaryExprKeyCheck = MemberExpression.NotEqual(leftExprKeyCheck, rightExprKeyCheck);
        BinaryExpression finalBinaryExpr = Expression.And(binaryExprFieldCheck, binaryExprKeyCheck);

        //Create Lambda Expression for the selection 
        Expression<Func<E, bool>> lambdaExpr = Expression.Lambda<Func<E, 
                  bool>>(finalBinaryExpr, new ParameterExpression[] { xParam });
        //Searching ....            
        return ((IRepository<E, C>)this).TryEntity(new Specification<E>(lambdaExpr));
    }
    /// <summary>
    /// Check if Entities exist with Condition
    /// </summary>
    /// <param name="selectExpression">Selection Condition</param>
    /// <returns>True or False</returns>
    public bool TryEntity(ISpecification<E> selectSpec)
    {
        return _ctx.CreateQuery<E>("[" + typeof(E).Name + "]").Any<E>(selectSpec.EvalPredicate);
    }
    /// <summary>
    /// Get Count of all records
    /// </summary>
    /// <typeparam name="E"></typeparam>
    /// <returns>count of all records</returns>
    public int GetCount()
    {
        return _ctx.CreateQuery<E>("[" + typeof(E).Name + "]").Count();
    }
    /// <summary>
    /// Get count of selection
    /// </summary>
    /// <typeparam name="E">Selection Condition</typeparam>
    /// <returns>count of selection</returns>
    public int GetCount(ISpecification<E> selectSpec)
    {
        return _ctx.CreateQuery<E>("[" + typeof(E).Name + "]")
            .Where(selectSpec.EvalPredicate).Count();
    }
    /// <summary>
    /// Delete data from context
    /// </summary>
    /// <typeparam name="E"></typeparam>
    /// <param name="entity"></param>
    public void Delete(E entity)
    {
        //object deletedObject;
        //_ctx.TryGetObjectByKey(entity.EntityKey, out deletedObject);
        _ctx.DeleteObject(entity);
    }
    /// <summary>
    /// Delete data from context
    /// </summary>
    /// <typeparam name="E"></typeparam>
    /// <param name="entity"></param>
    public void Delete(object entity)
    {
        //object deletedObject;
        //_ctx.TryGetObjectByKey(((EntityObject)entity).EntityKey, out deletedObject);
        _ctx.DeleteObject(entity);
    }
    /// <summary>
    /// Insert new data into context
    /// </summary>
    /// <typeparam name="E"></typeparam>
    /// <param name="entity"></param>
    public void Add(E entity)
    {
        _ctx.AddObject(entity.GetType().Name, entity);
    }
    /// <summary>
    /// Insert if new otherwise attach data into context. Plus, 
    /// returns a list of changed property name and value (in 
    /// this format--> "propName|originalValue|newValue")- if any.
    /// </summary>
    /// <param name="entity"></param>
    public List<String> AddOrAttach(E entity, EntityKey key = null)
    {
        try
        {
            _ctx.ContextOptions.LazyLoadingEnabled = false;

            ObjectStateEntry entry = null;
            //Add the object graph into the context
            if (null == key )
            {
                var entitySet = _ctx.GetEntitySet(entity.GetType());
                key = _ctx.CreateEntityKey(entitySet.Name, entity);
            }
        
            if( null != key )
                _ctx.ObjectStateManager.TryGetObjectStateEntry(key, out entry);
            if (entry == null)
            {
                _ctx.AddObject(typeof(E).Name, entity);
                _ctx.ObjectStateManager.ChangeObjectState(entity, StateHelpers.GetEquivelantEntityState(entity.ObjectState));                
            }
            else
            {
                _ctx.ApplyCurrentValues(typeof(E).Name, entity);
            }           
            //get the changed column values (needed for audit trail)
            List<String> changedCols = new List<string>();
            var ose = (entry != null)? entry : _ctx.ObjectStateManager.GetObjectStateEntry(entity);
            foreach (var propName in ose.GetModifiedProperties())
            {
                string pNameValue = propName;
                pNameValue += "|" + ose.OriginalValues[propName] + "|" + ose.CurrentValues[propName];
                changedCols.Add(pNameValue);
            }

            return changedCols;
        }
        catch (Exception)
        {                    
            throw;
        }
    }
    /// <summary>
    /// Start Transaction
    /// </summary>
    /// <returns></returns>
    public DbTransaction BeginTransaction()
    {
        if (_ctx.Connection.State != ConnectionState.Open)
        {
            _ctx.Connection.Open();
        }
        return _ctx.Connection.BeginTransaction();
    }
    /// <summary>
    /// Change state of Navigation Object(s)
    /// </summary>
    /// <typeparam name="E"></typeparam>
    /// <typeparam name="T"></typeparam>
    /// <param name="context"></param>
    /// <param name="entity"></param>
    /// <param name="state"></param>
    public void ChangeStateOfNavigationObject(E entity, State state)
    {
        if (null != entity)
        {
            var navigationProperties = _ctx.GetNavigationProperty<C, E>();
            if (null != navigationProperties)
            {
                foreach (var navigationProperty in navigationProperties)
                {
                    var info = entity.GetType().GetProperty(navigationProperty.Name);
                    var value = info.GetValue(entity, null);

                    if (value != null)
                    {

                        if (((AssociationType)navigationProperty.RelationshipType).IsForeignKey
                            &&
                            navigationProperty.FromEndMember.RelationshipMultiplicity !=
                            RelationshipMultiplicity.Many)
                        {
                            Type t = value.GetType();
                            Type baseType;
                            if (!t.IsGenericType)
                            {
                                baseType = t.BaseType;

                                if (baseType.BaseType.Equals(typeof(BaseDataContract)))
                                {
                                    MethodInfo method = this.GetType().GetMethod("ChangeObjectStatetoAttach");
                                    MethodInfo generic = method.MakeGenericMethod(baseType);
                                    generic.Invoke(this, new object[] { value, state });
                                }
                            }
                            else
                            {
                                Type[] genericBases = t.GetGenericArguments();
                                // Q&D: pick the first one
                                baseType = genericBases[0];

                                if (baseType.BaseType.Equals(typeof(BaseDataContract)))
                                {
                                    MethodInfo method =
                                        this.GetType().GetMethod("ChangeCollectionObjectStatetoAttach");
                                    MethodInfo generic = method.MakeGenericMethod(baseType);
                                    generic.Invoke(this, new object[] { value, state });
                                }
                            }
                        }
                        else
                        {
                            info.SetValue(entity, null, null);
                        }
                    }//end if
                }
            }
        }
    }
    /// <summary>
    /// change state of an single object
    /// </summary>
    /// <param name="entity"></param>
    /// <param name="state"></param>
    public void ChangeObjectStatetoAttach<T>(T entity, State state) where T : BaseDataContract 
    {
        if (null != entity)
        {
            var dataContract = entity as BaseDataContract;
            dataContract.ObjectState = state;
            EntityKey entityKey = _ctx.CreateEntityKey(
                _ctx.GetEntitySet(dataContract.GetType()).Name, dataContract);
            ObjectStateEntry storeEntity;
            if (_ctx.ObjectStateManager.TryGetObjectStateEntry(entityKey, out storeEntity))
            {
                _ctx.ApplyCurrentValues(_ctx.GetEntitySet(typeof(T)).Name, entity);
                //(storeEntity as T).ObjectState = State.Unchanged;
            }
            else
            {
                _ctx.AddObject(_ctx.GetEntitySet(dataContract.GetType()).Name, dataContract);
            }
            _ctx.ObjectStateManager.ChangeObjectState(dataContract,
                                                         StateHelpers.
                                                             GetEquivelantEntityState
                                                             (dataContract.ObjectState));
        }
    }
    /// <summary>
    /// 
    /// </summary>
    /// <param name="entities"></param>
    /// <param name="state"></param>
    public void ChangeCollectionObjectStatetoAttach<T>(FixupCollection<T> entities, State state)
       where T : BaseDataContract
    {
        if (null != entities)
        {
            for (int i = 0; i < entities.Count; i++)
            {
                ChangeObjectStatetoAttach<T>(entities[i], state);
            }
        }
    }

    #endregion

    #region IDisposable Members

    public void Dispose()
    {
        if (null != _ctx)
        {
            if (_ctx.Connection.State == ConnectionState.Open)
                _ctx.Connection.Close();
            _ctx.Dispose();
        }
    }

    #endregion
}

Here those methods responsible to do queries, return the result in <a href="http://msdn.microsoft.com/en-us/library/bb345303.aspx">ObjectQuery</a> which have been used for a special reason and that is - ObjectQuery.EnablePlanCaching Property -indicates whether the query plan should be cached. Plan-caching caches information which is computed as part of putting together the query itself. By caching this, a subsequent execution of the same query (even if you change parameter values) will run much faster than the first one. This information is cached per app-domain so you will generally benefit from the query cache across multiple client requests to the same web app and the like. Here all DoQuery methods are responsible to queries and other query method like SelectAll or Select methods internally use these DoQuery methods with various parameters.

SelectByKey is creating a LINQ expression using Expression tree for Primary key and During creating the repository on an entity you can supply this Primary Key property as string. While using the POCO as you entity you can set attribute programming to serve this kind of job.

TrySameValueExist is doing the same job by allow you to set customize field and value comparison there. What will do is create the Expression for you and also add the PrimaryKey comparison so that it excludes the object that you are querying for (and where PrimaryKey != currentObjectPrimaryKey).

Add and Delete method simply respectively call the AddObject and DeleteObject Method of ObjectContext. AddOrAttach method is for special situation where you don’t know whether object is already added or not. It is expensive since it will do query to database to check the existence.This method uses a class called StateHelpers have been used for Retrieving the Object State that compatible with Entity Framework.

 public static class StateHelpers
    {
        public static EntityState GetEquivelantEntityState(State state)
        {
            //this handy method comes from Rowan Miller on the EF team!
            switch (state)
            {
                case State.Added:
                    return EntityState.Added;
                case State.Modified:
                    return EntityState.Modified;
                case State.Deleted:
                    return EntityState.Deleted;
                default:
                    return EntityState.Unchanged;
            }
        }
    }

In ChangeObjectStatetoAttach is a method which update the state of an entity and also go for all its navigation/related child object to change their state in object-tree traversing way. To find out the navigation object I need to add extension method of ObjectContext.

public static List<NavigationProperty> GetNavigationProperty<TObjectContext, T>(
this ObjectContext context)
where TObjectContext : ObjectContext
 {
     var containerName = context.DefaultContainerName;
     var model = DataSpace.CSpace;
     var workspace = context.MetadataWorkspace;
     var container = workspace.GetEntityContainer(containerName, model);
     EntitySetBase entitySet = context.GetEntitySet(typeof (T));

     if (entitySet == null)
         return null;

     //materialize nav props for testing
     var navigationProps = entitySet.ElementType.Members
         .Where(m => m.BuiltInTypeKind == BuiltInTypeKind.NavigationProperty
         )
         .Cast<NavigationProperty>()
         .ToList();

    return navigationProps;
 }
  
public static EntitySetBase GetEntitySet(this ObjectContext context, Type entityType)
{
    if (context == null)
    {
        throw new ArgumentNullException("context");
    }
    if (entityType == null)
    {
        throw new ArgumentNullException("entityType");
    }
    EntityContainer container = context.MetadataWorkspace.GetEntityContainer(context.DefaultContainerName, DataSpace.CSpace);
    if (container == null)
    {
        return null;
    }
    EntitySetBase entitySet = container.BaseEntitySets.Where(item => item.ElementType.Name.Equals(entityType.Name))
                                                      .FirstOrDefault();
    return entitySet;
} 

MethodInfo method = this.GetType().GetMethod("ChangeObjectStatetoAttach");
MethodInfo generic = method.MakeGenericMethod(baseType);
generic.Invoke(this, new object[] { value, state });