RSS

Repository and Unit of Work that is Fully Generic Part 3

04 Sep

So now for the last part the extensions to DBContext

using System;
using System.Data;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Data.Metadata.Edm;
using System.Linq;
using System.Reflection;

namespace MyCompany.Repo.Generic.Extensions
{
    ///
/// Code First extensions.
    ///
    public static class DbContextExtensions
    {
        ///
/// Adds an entity (if newly created) or update (if has non-default Id).
        ///
        ///
        ///The db context.
        ///The entity.
        ///
        ///
        /// Will not work for HasDatabaseGeneratedOption(DatabaseGeneratedOption.None).
        /// Will not work for composite keys.
        ///
        public static T AddOrUpdate(this DbContext context, T entity)
            where T : class
        {
            if (context == null) throw new ArgumentNullException("context");
            if (entity == null) throw new ArgumentNullException("entity");

            if (IsTransient(context, entity))
            {
                context.Set().Add(entity);
            }
            else
            {
                context.Set().Attach(entity);
                context.Entry(entity).State = EntityState.Modified;
            }
            return entity;
        }

        ///
/// Determines whether the specified entity is newly created (Id not specified).
        ///
        ///
        ///The context.
        ///The entity.
        ///
        ///   true if the specified entity is transient; otherwise, false.
        ///
        ///
        /// Will not work for HasDatabaseGeneratedOption(DatabaseGeneratedOption.None).
        /// Will not work for composite keys.
        ///
        public static bool IsTransient(this DbContext context, T entity)
            where T : class
        {
            if (context == null) throw new ArgumentNullException("context");
            if (entity == null) throw new ArgumentNullException("entity");

            var propertyInfo = FindPrimaryKeyProperty(context);
            var propertyType = propertyInfo.PropertyType;
            //what's the default value for the type?
            var transientValue = propertyType.IsValueType ?
                Activator.CreateInstance(propertyType) : null;
            //is the pk the same as the default value (int == 0, string == null ...)
            return Equals(propertyInfo.GetValue(entity, null), transientValue);
        }

        ///
/// Loads a stub entity (or actual entity if already loaded).
        ///
        ///
        ///The context.
        ///The id.
        ///
        ///
        /// Will not work for composite keys.
        ///
        public static T Load(this DbContext context, object id)
             where T : class
        {
            if (context == null) throw new ArgumentNullException("context");
            if (id == null) throw new ArgumentNullException("id");

            var property = FindPrimaryKeyProperty(context);
            //check to see if it's already loaded (slow if large numbers loaded)
            var entity = context.Set().Local
                .FirstOrDefault(x => id.Equals(property.GetValue(x, null)));
            if (entity == null)
            {
                //it's not loaded, just create a stub with only primary key set
                entity = CreateEntity(id, property);

                context.Set().Attach(entity);
            }
            return entity;
        }

        ///
/// Determines whether the specified entity is loaded from the database.
        ///
        ///
        ///The context.
        ///The id.
        ///
        ///   true if the specified entity is loaded; otherwise, false.
        ///
        ///
        /// Will not work for composite keys.
        ///
        public static bool IsLoaded(this DbContext context, object id)
            where T : class
        {
            if (context == null) throw new ArgumentNullException("context");
            if (id == null) throw new ArgumentNullException("id");

            var property = FindPrimaryKeyProperty(context);
            //check to see if it's already loaded (slow if large numbers loaded)
            var entity = context.Set().Local
                .FirstOrDefault(x => id.Equals(property.GetValue(x, null)));
            return entity != null;
        }

        ///
/// Marks the reference navigation properties unchanged.
        /// Use when adding a new entity whose references are known to be unchanged.
        ///
        ///
        ///The context.
        ///The entity.
        public static void MarkReferencesUnchanged(DbContext context, T entity)
            where T : class
        {
            var objectContext = ((IObjectContextAdapter)context).ObjectContext;
            var objectSet = objectContext.CreateObjectSet();
            var elementType = objectSet.EntitySet.ElementType;
            var navigationProperties = elementType.NavigationProperties;
            //the references
            var references = from navigationProperty in navigationProperties
                             let end = navigationProperty.ToEndMember
                             where end.RelationshipMultiplicity == RelationshipMultiplicity.ZeroOrOne ||
                             end.RelationshipMultiplicity == RelationshipMultiplicity.One
                             select navigationProperty.Name;
            //Note: We don't check Collections. EF wants to handle the object graph so we let it.

            var parentEntityState = context.Entry(entity).State;
            foreach (var navigationProperty in references)
            {
                //if it's modified but not loaded, don't need to touch it
                if (parentEntityState == EntityState.Modified &&
                    !context.Entry(entity).Reference(navigationProperty).IsLoaded)
                    continue;
                var propertyInfo = typeof(T).GetProperty(navigationProperty);
                var value = propertyInfo.GetValue(entity, null);
                context.Entry(value).State = EntityState.Unchanged;
            }
        }

        private static PropertyInfo FindPrimaryKeyProperty(IObjectContextAdapter context)
            where T : class
        {
            //find the primary key
            var objectContext = context.ObjectContext;
            //this will error if it's not a mapped entity
            var objectSet = objectContext.CreateObjectSet();
            var elementType = objectSet.EntitySet.ElementType;
            var pk = elementType.KeyMembers.First();
            //look it up on the entity
            var propertyInfo = typeof(T).GetProperty(pk.Name);
            return propertyInfo;
        }

        private static T CreateEntity(object id, PropertyInfo property)
            where T : class
        {
            // consider IoC here
            var entity = (T)Activator.CreateInstance(typeof(T));
            //set the value of the primary key (may error if wrong type)
            property.SetValue(entity, id, null);
            return entity;
        }
    }
}

  1. Create an Entity project
  2. Add EF 5 from nugget
  3. Add an ADO.Net Entity Data Model of your database
  4. Right click on the designer and click “Add Code Generation Item”
  5. If you do not have the EF 5.x DbContect Generator installed already click online templates select the EF 5.x DbContect Generator, name it appropriately, and click add.
  6. If they do not generat off the bat open the .tt and put in the correct .edmx file name and your db context and poco classes will generate
  7. Add the connection string into the consuming app and add your entity project and the generic repo to your consuming app. Then do something like this in you BLL J
            NPM_EXTEntities context = new NPM_EXTEntities();
            IUnitOfWork efu = new UoWFactory(context).getUoW();

            IGenericRepository<Application>; 
            applications = efu.GetRepository<Application>;
Advertisements
 
Leave a comment

Posted by on September 4, 2013 in C#, Entity Framework, Repository, SQL, Unit Of Work

 

Tags: , , , , , ,

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

 
%d bloggers like this: