Traversing an object Tree to the end in EF4

Posted on July 16, 2012. Filed under: C#, CodeProject, EF4, Entity Framework | Tags: , , |


Years ago, I read about Golden rule of Entity Framework from a blog post of Julia Lerman.As the Golden Rule says –

EF will not do anything that developer has not explicitly told you to do.

Some days ago I got an issue where I need to load a full object graph will all its relationship. It means I need to load the object with all children and also with grand children of the each child which means I need to traverse the full tree of the object through their relationship/navigation until I will reach to leaf.

For Example, The tree can be represent as:

<Customer>
    ...
    <Orders>
      <Order>
        ...
        <Order_Details>
          </Order_Detail>
          ... .. .. .. .. .. So on.. .. .. (continue)
          </Order_Detail>
          ...
        </Order_Details>
      </Order>
      ...
    </Orders>
  ...
  </Customer> 

Or can be represent as:

Customar

   |

   |

   -----Orders

          |

          |

          ------OrderDetails

|

|________.. .. .. .. So on .. ..(continue)

 

So I don’t know how much depth of the object-tree will be and that’s why I am going to avoid the LINQ way. You can also

do this by disabling the Lazy-loading but POCO entities do not have the same relationship requirements as objects that

inherit from EntityObject, a slightly different process is required to load related objects. Ok, it is a very simple matter

of Recursive solution by loading entity for the each navigation object. To load the navigation property I got

simple and useful method there-

 

ObjectContext.LoadProperty Method (Object, String)

public void LoadProperty(
    Object entity,
    string navigationProperty)
 

Before going into my recursive method, I would like to talk about my Entity. All of my entity is child of “BaseDataContract”

class. While traversing to the object you can set a list of data type also to ignore while traversing them. Here I check the

navigation property whether that is a one or many relationship with current entity. If it is one –then I simply call the

same method that it is currently in Recursive way; otherwise is call another Generic method which calls the Traverse method

for each entity in a collection for many relationship ends.

private ObjectContext _ctx;
private bool IsInheritFromType(Type childType, Type parentType)
        {
            var type = childType;
            while (type.BaseType != null)
            {
                if (type.BaseType.Equals(parentType))
                    return true;

                type = type.BaseType;
            }
            return false;
        }    
        /// <summary>
        /// Traverse to the end and load the related entity. 
        /// </summary>
        /// <param name="entity">Set the entity from which start traversing</param>
        /// <param name="parentType">Set the Parent to ignore the recurtion. For root entity, set it null</param>
        /// <param name="ignoreType">Some Type of entity I want to Ignore</param>
        /// <returns></returns>
        public void TraverseToTheEnd<T>(T entity, Type parentType =null ,Type[] ignoreType =null ) where T : BaseDataContract
        {
            if (null != entity)
            {
                var navigationProperties = _ctx.GetNavigationProperty<T>();
                if (null != navigationProperties)
                {
                    foreach (var navigationProperty in navigationProperties)
                    {
                        var info = entity.GetType().GetProperty(navigationProperty.Name);

                        if (null != info)
                        {
                            Type t = info.PropertyType;
                            if (null == ignoreType || !Array.Exists(ignoreType, i => i.Equals(t)))
                            {
                                if (((AssociationType) navigationProperty.RelationshipType).IsForeignKey)
                                {
                                    _ctx.LoadProperty(entity, navigationProperty.Name);

                                    var value = info.GetValue(entity, null);
                                    if (value != null)
                                    {
                                        Type baseType;
                                        if (!t.IsGenericType)
                                        {
                                            #region One to One or Zero

                                            baseType = t.BaseType;
                                            if (null != baseType && (parentType == null || !t.Equals(parentType))
                                                //avoid the recursion, dont back to parent 
                                                && baseType.BaseType != null
                                                && IsInheritFromType(baseType, typeof (BaseDataContract)))
                                            {
                                                //Traverse each child
                                                MethodInfo method = this.GetType().GetMethod("TraverseToTheEnd");
                                                MethodInfo generic = method.MakeGenericMethod(t);
                                                generic.Invoke(this, new object[] {value, typeof (T), ignoreType});
                                            }

                                            #endregion
                                        }
                                        else
                                        {
                                            #region One to Many

                                            Type[] genericBases = t.GetGenericArguments();
                                            // Q&D: pick the first one
                                            baseType = genericBases[0];
                                            if (null != baseType && (parentType == null || !baseType.Equals(parentType))
                                                //avoid the recursion, dont back to parent
                                                && baseType.BaseType != null &&
                                                IsInheritFromType(baseType, typeof (BaseDataContract)))
                                            {
                                                //Traverse each child
                                                MethodInfo method =
                                                    this.GetType().GetMethod("TraverseToTheEndForCollection");
                                                MethodInfo generic = method.MakeGenericMethod(baseType);
                                                generic.Invoke(this, new object[] {value, typeof (T), ignoreType});
                                            }

                                            #endregion
                                        }

                                    } //end if 
                                } //end if
                            }//end if                            
                        }
                    }//end foreach
                }//end if
            }//end if 
        }
        /// <summary>
        /// Traverse each entity of a collection to their end and load the related entity. 
        /// </summary>
        /// <param name="entities">Set the collection of entity for traversing each entity</param>
        /// <param name="parentType">Set the Parent to ignore the recurtion. For root entity, set it null</param>
        /// <param name="ignoreType">Some Type of entity I want to Ignore</param>
        /// <returns></returns>
        public void TraverseToTheEndForCollection<T>(FixupCollection<T> entities, Type parentType =null ,Type[] ignoreType =null )
           where T : BaseDataContract
        {
            if (null != entities)
            {
                for (int i = 0; i < entities.Count; i++)
                {
                    TraverseToTheEnd(entities[i], parentType, ignoreType);
                }
            }
        }

To load the navigation property value I just call the above method –loadProperty which is provided by the ObjectContext 

_ctx.LoadProperty(entity, navigationProperty.Name);

var value = info.GetValue(entity, null);

 

After that , Check the navigation property type whether that is generic type or not. in EF , Generic navigation type is

used for Collection of entity in case of Many End and on the other hand normal property type for One or Zero End.

Here, The method –IsInheritFromType is nothing but check for BaseType to some desired parent Type.This has been checked

to determine whether it is database object or not. To call a Generic method -

 

MethodInfo method = this.GetType().GetMethod("TraverseToTheEnd");

MethodInfo generic = method.MakeGenericMethod(t);

generic.Invoke(this, new object[] {value, typeof (T), ignoreType});

 

And TraverseToTheEndForCollection method has been called in the same way with the parameter of child/navigation property value

parent type and other paramters.

 

Here I need to create some extension of ObjectContext to get all navigation properties of an entity by manipulating

the metadata information. In GetNavigationProperty method we need to retrieve the entity set name (that’s why we need the

GetEntitySet method) and from its type members it check for nevigationProperty as BuiltInTypeKind.

 

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);
          EntitySetBase entitySet = container.BaseEntitySets.Where(item => item.ElementType.Name.Equals(entityType.Name))
                                                            .FirstOrDefault();
          return entitySet;
      }

      public static List<NavigationProperty> GetNavigationProperty<T>(
      this ObjectContext context)
      {
          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;
      }

Ok that is it.

Yes you can ask me why I am going to such great length. Answer is-  because I want to backup the object tree into a backup file and later on it will be attached to database that might be the same database or another one with same schema. It will not override any entity if that any data of this object-tree already exist, if not then it will insert the object with related object as it is currently in its own. But that’s a different story. This method gives an object tree with all its related objects to the leaf and I can do whatever I want. For now I would like to serialize this object in a file and on the next post I will try to re-attach the object to database. Thanks for reading and Hope you like it Smile.

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