Generic base class supporting ObjectContext CRUD operations

In Entity Framework it is interesting to see if it is possible to create a base class that support CRUD operations with ObjectContext. I want to create a basic scenario where you can either insert, update (insert many) and delete rows into tables. The matching between entities and datacontracts will be matched upon the same kind of name of properties and data type. First off, let us define an interface for such a base class. Note that I have tested the code with Entity Framework 6.1.3.

using System.Collections.Generic;
using System.Data.Entity.Core.Objects.DataClasses;

namespace BaseClassObjectContext
{

    public interface IDefaultDbCrudOperation<TEntity, TDataContract>
        where TEntity : EntityObject
        where TDataContract : class
    {

        List<TDataContract> GetAll();

        TDataContract InsertOrUpdate(TDataContract dataContract);

        bool Delete(TDataContract entity);

        List<TDataContract> InsertOrUpdateMany(List<TDataContract> dataContracts);

    }

}

We will also need the help of Linq Expression trees, so here is a class QueryableExtensions that helps with that:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace BaseClassObjectContext
{


    /// <summary>
    /// Enables auto mapping features in Entity Framework
    /// </summary>
    /// <remarks>More information here: http://toreaurstad.blogspot.no/2015/02/automatic-mapping-for-deep-object.html </remarks>
    public static class QueryableExtensions
    {
        public static ProjectionExpression<TSource> Project<TSource>(this IQueryable<TSource> source)
        {
            return new ProjectionExpression<TSource>(source);
        }
    }

    public class ProjectionExpression<TSource>
    {
        private static readonly Dictionary<string, Expression> _expressionCache = new Dictionary<string, Expression>();

        private readonly IQueryable<TSource> _source;

        public ProjectionExpression(IQueryable<TSource> source)
        {
            _source = source;
        }

        public IQueryable<TDest> To<TDest>()
        {
            var queryExpression = GetCachedExpression<TDest>() ?? BuildExpression<TDest>();

            return _source.Select(queryExpression);
        }

        private static Expression<Func<TSource, TDest>> GetCachedExpression<TDest>()
        {
            var key = GetCacheKey<TDest>();

            return _expressionCache.ContainsKey(key) ? _expressionCache[key] as Expression<Func<TSource, TDest>> : null;
        }

        public static Expression<Func<TSource, TDest>> BuildExpression<TDest>()
        {
            var sourceProperties = typeof(TSource).GetProperties();
            var destinationProperties = typeof(TDest).GetProperties().Where(dest => dest.CanWrite);
            var parameterExpression = Expression.Parameter(typeof(TSource), "src");

            var bindings = destinationProperties
                                .Select(destinationProperty => BuildBinding(parameterExpression, destinationProperty, sourceProperties))
                                .Where(binding => binding != null);

            var expression = Expression.Lambda<Func<TSource, TDest>>(Expression.MemberInit(Expression.New(typeof(TDest)), bindings), parameterExpression);

            var key = GetCacheKey<TDest>();

            _expressionCache.Add(key, expression);

            return expression;
        }       

        private static MemberAssignment BuildBinding(Expression parameterExpression, MemberInfo destinationProperty, IEnumerable<PropertyInfo> sourceProperties)
        {
            var sourceProperty = sourceProperties.FirstOrDefault(src => src.Name == destinationProperty.Name);

            if (sourceProperty != null)
            {
                return Expression.Bind(destinationProperty, Expression.Property(parameterExpression, sourceProperty));
            }

            var propertyNameComponents = SplitCamelCase(destinationProperty.Name);

            if (propertyNameComponents.Length >= 2)
            {
                sourceProperty = sourceProperties.FirstOrDefault(src => src.Name == propertyNameComponents[0]);
                if (sourceProperty == null)
                    return null;

                var propertyPath = new List<PropertyInfo> { sourceProperty };
                TraversePropertyPath(propertyPath, propertyNameComponents, sourceProperty);

                if (propertyPath.Count != propertyNameComponents.Length)
                    return null; //must be able to identify the path 

                MemberExpression compoundExpression = null;

                for (int i = 0; i < propertyPath.Count; i++)
                {
                    compoundExpression = i == 0 ? Expression.Property(parameterExpression, propertyPath[0]) :
                        Expression.Property(compoundExpression, propertyPath[i]);
                }

                return compoundExpression != null ? Expression.Bind(destinationProperty, compoundExpression) : null;
            }

            return null;
        }

        private static List<PropertyInfo> TraversePropertyPath(List<PropertyInfo> propertyPath, string[] propertyNames,
            PropertyInfo currentPropertyInfo, int currentDepth = 1)
        {
            if (currentDepth >= propertyNames.Count() || currentPropertyInfo == null)
                return propertyPath; //do not go deeper into the object graph

            PropertyInfo subPropertyInfo = currentPropertyInfo.PropertyType.GetProperties().FirstOrDefault(src => src.Name == propertyNames[currentDepth]);
            if (subPropertyInfo == null)
                return null; //The property to look for was not found at a given depth 

            propertyPath.Add(subPropertyInfo);

            return TraversePropertyPath(propertyPath, propertyNames, subPropertyInfo, ++currentDepth);
        }

        private static string GetCacheKey<TDest>()
        {
            return string.Concat(typeof(TSource).FullName, typeof(TDest).FullName);
        }

        private static string[] SplitCamelCase(string input)
        {
            return Regex.Replace(input, "([A-Z])", " $1", RegexOptions.Compiled).Trim().Split(' ');
        }

    }

}

Next off we need a utility method for reflection:

using System;
using System.ComponentModel;
using System.Linq; 

namespace BaseClassObjectContext
{
    
    public static class ReflectionExtensions
    {


        public static bool HasAttribute<TAttribute>(this PropertyDescriptor pr)
        {
            return pr.Attributes.OfType<TAttribute>().Any(); 
        }

    }
}

The base class for handling all this is then is the following:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Data.Entity.Core;
using System.Data.Entity.Core.Mapping;
using System.Data.Entity.Core.Metadata.Edm;
using System.Data.Entity.Core.Objects;
using System.Data.Entity.Core.Objects.DataClasses;
using System.Data.Entity.Infrastructure;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace BaseClassObjectContext
{


    public class BaseDataManager<TEntity, TDataContract> : IDefaultDbCrudOperation<TEntity, TDataContract>
        where TEntity : EntityObject
        where TDataContract : class
    {

        public bool Delete(TDataContract dataContract)
        {
            using (var ctx = new BooksEntities())
            {
                var primaryKey = GetPrimaryKey(dataContract);
                var entityFound = FindEntityByKey(primaryKey, ctx);
                if (entityFound == null)
                    return false;
                ctx.CreateObjectSet<TEntity>().DeleteObject(entityFound);
                ctx.SaveChanges();
                return true;
            }
        }

        private TEntity FindEntityByKey(object primaryKey, ObjectContext ctx)
        {
            return ctx.CreateObjectSet<TEntity>().SingleOrDefault(GetEqualityExpression(primaryKey));
        }

        /// <summary>
        /// Builds up an equality expression using LINQ Expression trees
        /// </summary>
        /// <param name="primaryKey"></param>
        /// <remarks>Source: http://dotnetspeak.com/2013/09/use-reflection-and-expression-to-find-an-entity-by-primary-key </remarks>
        private static Expression<Func<TEntity, bool>> GetEqualityExpression(object primaryKey)
        {
            var primaryKeyProperty = typeof(TEntity).GetProperties()
                .First(p => p.GetCustomAttributes(typeof(EdmScalarPropertyAttribute), true)
                .Any(pc => ((EdmScalarPropertyAttribute)pc).EntityKeyProperty));

            //Create entity => portion of lambda expression 
            ParameterExpression parameter = Expression.Parameter(typeof(TEntity), "entity");

            //Create entity.Id portion of lambda expression 
            MemberExpression property = Expression.Property(parameter, primaryKeyProperty.Name);

            //Create 'id' portion of lambda expression 
            var equalsTo = Expression.Constant(primaryKey);

            //Create entity.Id == 'id' portion of lambda expression 
            var equality = Expression.Equal(property, equalsTo);

            //finally create the entire expression: entity => entity.Id = 'id' 
            Expression<Func<TEntity, bool>> retVal = Expression.Lambda<Func<TEntity, bool>>(equality,
                new[] { parameter });

            return retVal;
        }

        private TEntity FindEntityByKeys(object[] primaryKeys, ObjectContext ctx)
        {
            foreach (var keyValues in ctx.CreateObjectSet<TEntity>().Select(t =>
                new { Key = t.EntityKey, Values = t.EntityKey.EntityKeyValues }))
            {
                if (keyValues.Values.ToArray().SequenceEqual(primaryKeys))
                    return ctx.GetObjectByKey(keyValues.Key) as TEntity;
            }
            return null;
        }

        public List<TDataContract> GetAll()
        {
            using (var ctx = new BooksEntities())
            {
                return ctx.CreateObjectSet<TEntity>().Project().To<TDataContract>().ToList();
            }
        }

        public TDataContract InsertOrUpdate(TDataContract dataContract)
        {
            using (var ctx = new BooksEntities())
            {
                var primaryKey = GetPrimaryKey(dataContract);
                var entityToInsertOrUpdate = FindEntityByKey(primaryKey, ctx);
                bool isNew = entityToInsertOrUpdate == null;

                entityToInsertOrUpdate = Queryable.AsQueryable(new[] { dataContract }).Project().To<TEntity>().First();

                if (isNew)
                    ctx.CreateObjectSet<TEntity>().AddObject(entityToInsertOrUpdate);
                else
                {
                    var existingEntity = FindEntityByKey(primaryKey, ctx);
                    ctx.CreateObjectSet<TEntity>().Detach(existingEntity);
                    ctx.CreateObjectSet<TEntity>().Attach(entityToInsertOrUpdate);
                    ctx.ObjectStateManager.ChangeObjectState(entityToInsertOrUpdate, System.Data.Entity.EntityState.Modified);
                }

                ctx.SaveChanges();

                return Queryable.AsQueryable(new[] { entityToInsertOrUpdate }).Project().To<TDataContract>().First();
            }
        }  


        public List<TDataContract> InsertOrUpdateMany(List<TDataContract> dataContracts)
        {
            if (dataContracts == null)
                throw new ArgumentNullException("An empty list was provided!");
            var changesMade = new List<TDataContract>();
            foreach (var dc in dataContracts)
                changesMade.Add(InsertOrUpdate(dc)); //Simple logic in this case 
            return changesMade;
        }

        private object GetPrimaryKey(TDataContract entity)
        {
            PropertyDescriptor pDesc = TypeDescriptor.GetProperties(entity)
                .Cast<PropertyDescriptor>().FirstOrDefault(p => p.HasAttribute<KeyAttribute>());
            if (pDesc == null)
                throw new InvalidOperationException("Provided datacontract must have one column with Key attribute!");

            var primaryKey = pDesc.GetValue(entity);
            return primaryKey;
        }

        private string GetPrimaryKeyName(TDataContract entity)
        {

            var primaryKeyProperty = typeof(TEntity).GetProperties()
              .First(p => p.GetCustomAttributes(typeof(EdmScalarPropertyAttribute), true)
              .Any(pc => ((EdmScalarPropertyAttribute)pc).EntityKeyProperty));
            return primaryKeyProperty.Name;
        }

        private static MetadataWorkspace _metaDataWorkSpace;

        public static string GetTableName(Type type, ObjectContext context)
        {
            if (_metaDataWorkSpace == null)
                _metaDataWorkSpace = context.MetadataWorkspace;

            // Get the part of the model that contains info about the actual CLR types
            var objectItemCollection = ((ObjectItemCollection)_metaDataWorkSpace.GetItemCollection(DataSpace.OSpace));

            // Get the entity type from the model that maps to the CLR type
            var entityType = _metaDataWorkSpace
                    .GetItems<EntityType>(DataSpace.OSpace)
                    .Single(e => objectItemCollection.GetClrType(e) == type);

            // Get the entity set that uses this entity type
            var entitySet = _metaDataWorkSpace
                .GetItems<EntityContainer>(DataSpace.CSpace)
                .Single()
                .EntitySets
                .Single(s => s.ElementType.Name == entityType.Name);

            // Find the mapping between conceptual and storage model for this entity set
            var mapping = _metaDataWorkSpace.GetItems<EntityContainerMapping>(DataSpace.CSSpace)
                    .Single()
                    .EntitySetMappings
                    .Single(s => s.EntitySet == entitySet);

            // Find the storage entity set (table) that the entity is mapped
            var table = mapping
                .EntityTypeMappings.Single()
                .Fragments.Single()
                .StoreEntitySet;

            // Return the table name from the storage entity set
            return (string)table.MetadataProperties["Table"].Value ?? table.Name;
        }
    }

}

The following to compact DAL-layer managers can then be defined in a sample database:

namespace BaseClassObjectContext
{

    public class AuthorManager : BaseDataManager<Author, AuthorDataContract>
    {

    }

}

namespace BaseClassObjectContext
{
    
    public class BookManager : BaseDataManager<Book, BookDataContract>
    {

    }

}

See how little code we need to write to work against a table with Entity Framework now and support easy methods such as GetAll, InsertOrUpdate, InsertOrUpdateMany and Delete? This may seem overly complex, but by developing a sturdy generic code that can handle different mapping scenarios, it would be possible to end up with a Data Access Layer (DAL) that is more easy to maintain than a regular one with the same kind of tedious mapping that you end up with the default path chosen. I have also created some default integration tests:

using System;
using NUnit.Framework;

namespace BaseClassObjectContext.Test
{
  
    [TestFixture]
    public class BookAuthorCrudTests
    {

        [Test]
        public void InsertAuthorAndBookAndDeleteAfterwardsTest()
        {

            var authorManager = new AuthorManager();
            var savedAuthor = authorManager.InsertOrUpdate(new AuthorDataContract
            {
                Name = "Anne B. Ragde",
                Age = 58
            });
            var bookManager = new BookManager();
            var savedBook = bookManager.InsertOrUpdate(new BookDataContract
            {
                PageCount = 302,
                Title = "Eremittkrepsene",
                ISBN = " 9788252560930",
                AuthorId = savedAuthor.AuthorId
            });
            Assert.IsTrue(savedAuthor.AuthorId > 0);
            Assert.IsTrue(savedBook.BookId > 0);

            var authors = authorManager.GetAll();
            var books = authorManager.GetAll();

            CollectionAssert.IsNotEmpty(authors);
            CollectionAssert.IsNotEmpty(books);

            bool bookDeleted = bookManager.Delete(savedBook);
            bool authorDeleted = authorManager.Delete(savedAuthor);

            Assert.IsTrue(authorDeleted);
            Assert.IsTrue(bookDeleted);
        }

        [Test]
        public void InsertAuthorAndBookAndGetAllTest()
        {
            var authorManager = new AuthorManager();
            var savedAuthor = authorManager.InsertOrUpdate(new AuthorDataContract
            {
                Name = "Anne B. Ragde",
                Age = 58              
            });
            var bookManager = new BookManager();
            var savedBook = bookManager.InsertOrUpdate(new BookDataContract
            {
                PageCount = 313,
                Title = "Berlinerpopplene",
                ISBN = " 9788249509584",
                AuthorId = savedAuthor.AuthorId
            });
            Assert.IsTrue(savedAuthor.AuthorId > 0); 
            Assert.IsTrue(savedBook.BookId > 0);

            var authors = authorManager.GetAll();
            var books = authorManager.GetAll();

            CollectionAssert.IsNotEmpty(authors);
            CollectionAssert.IsNotEmpty(books);

            savedBook.Title = "Berlinerpoplene";
            var savedBookAgain = bookManager.InsertOrUpdate(savedBook);
            Assert.AreEqual(savedBook.Title, savedBookAgain.Title); 
        }



    }
}

Note that the code works, but needs further refinement and cleanup to support more scenarios. What would be nice would be to device a way to handle navigation properties, lazy loading and lists within the entities. I have not tested this. Some support for navigation properties should be present with the QueryableExtensions class.

Download sample Visual Studio Solution:

[GenericObjectContextCrudSampleSolution.zip | 14.6 MB | (.Zip) file]
The sample database contains two simple tables: Authors and Books, where a Book has an Author. To test out all the code above, you can download a Zip file below with the source code. I have used Visual Studio 2013. Enjoy and happy Entity Framework coding!

Generic Entity Framework CRUD Baseclass

Often a lot of time is done in Entity Framework by doing the same tedious mapping procedure to and from the database to POCO entities that are returned to the consumers, such as data contracts. Let us investigate a way to do this is in a more generic way. First, we create an interface for the CRUD operations we will support.

using System.Collections.Generic;

namespace SomeAcme.Data.EntityFramework
{

    public interface IDefaultDbCrudOperation<TEntity, TDataContract>
        where TEntity : class
        where TDataContract : class
    {

        List<TDataContract> GetAll();

        TDataContract InsertOrUpdate(TDataContract dataContract);

        bool Delete(TDataContract entity);

        List<TDataContract> InsertOrUpdateMany(List<TDataContract> dataContracts); 

    }

}

Next off, we need to provide the implementation itself, I choose here to support DbContext and not ObjectContext in EF:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using SomeAcme.Common;
using System.ComponentModel.DataAnnotations;

namespace Nonline.Data.EntityFramework
{

    public class BaseDataManager<TEntity, TDataContract> : IDefaultDbCrudOperation<TEntity, TDataContract> 
        where TEntity : class, new()
        where TDataContract : class
    {

        public bool Delete(TDataContract dataContract)
        {
            using (var ctx = new SvarrapportEntities())
            {
                var primaryKey = GetPrimaryKey(dataContract); 
                var entityFound = ctx.Set<TEntity>().Find(primaryKey);
                if (entityFound == null)
                    return false; 
                ctx.Set<TEntity>().Remove(entityFound);
                ctx.SaveChanges(); 
                return true;
            }
        }

        public List<TDataContract> GetAll()
        {
            using (var ctx = new SvarrapportEntities())
            {
                return ctx.Set<TEntity>().Project().To<TDataContract>().ToList();
            }
        }

        public TDataContract InsertOrUpdate(TDataContract dataContract)
        {
            using (var ctx = new SvarrapportEntities())
            {
                var primaryKey = GetPrimaryKey(dataContract);
                var foundEntity = ctx.Set<TEntity>().Find(primaryKey);
                bool isNew = foundEntity == null;

                foundEntity = Queryable.AsQueryable(new[] { dataContract }).Project().To<TEntity>().First();

                if (isNew)
                    ctx.Set<TEntity>().Add(foundEntity);

                ctx.SaveChanges();

                return Queryable.AsQueryable(new[] { foundEntity }).Project().To<TDataContract>().First();
            }
        }

        public List<TDataContract> InsertOrUpdateMany(List<TDataContract> dataContracts)
        {
            if (dataContracts == null)
                throw new ArgumentNullException("An empty list was provided!");
            var changesMade = new List<TDataContract>();
            foreach (var dc in dataContracts)
                changesMade.Add(InsertOrUpdate(dc)); //Simple logic in this case 
            return changesMade; 
        }

        private object GetPrimaryKey(TDataContract entity) 
        {
            PropertyDescriptor pDesc = TypeDescriptor.GetProperties(entity).Cast<PropertyDescriptor>().FirstOrDefault(p => p.HasAttribute<KeyAttribute>());
            if (pDesc == null)
                throw new InvalidOperationException("Provided datacontract must have one column with Key attribute!");

            var primaryKey = pDesc.GetValue(entity);
            return primaryKey; 
        }

    }

}

Note here that I use code from another article of mine, Automatic Mapping for Deep Objects in EF, where you see the Project() and To() methods. Here is that code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text.RegularExpressions;

namespace SomeAcme.Data.EntityFramework
{

    /// <summary>
    /// Enables auto mapping features in Entity Framework
    /// </summary>
    /// <remarks>More information here: http://toreaurstad.blogspot.no/2015/02/automatic-mapping-for-deep-object.html </remarks>
    public static class QueryableExtensions
    {
        public static ProjectionExpression<TSource> Project<TSource>(this IQueryable<TSource> source)
        {
            return new ProjectionExpression<TSource>(source);
        }
    }

    public class ProjectionExpression<TSource>
    {
        private static readonly Dictionary<string, Expression> _expressionCache = new Dictionary<string, Expression>();

        private readonly IQueryable<TSource> _source;

        public ProjectionExpression(IQueryable<TSource> source)
        {
            _source = source;
        }

        public IQueryable<TDest> To<TDest>()
        {
            var queryExpression = GetCachedExpression<TDest>() ?? BuildExpression<TDest>();

            return _source.Select(queryExpression);
        }

        private static Expression<Func<TSource, TDest>> GetCachedExpression<TDest>()
        {
            var key = GetCacheKey<TDest>();

            return _expressionCache.ContainsKey(key) ? _expressionCache[key] as Expression<Func<TSource, TDest>> : null;
        }

        private static Expression<Func<TSource, TDest>> BuildExpression<TDest>()
        {
            var sourceProperties = typeof(TSource).GetProperties();
            var destinationProperties = typeof(TDest).GetProperties().Where(dest => dest.CanWrite);
            var parameterExpression = Expression.Parameter(typeof(TSource), "src");

            var bindings = destinationProperties
                                .Select(destinationProperty => BuildBinding(parameterExpression, destinationProperty, sourceProperties))
                                .Where(binding => binding != null);

            var expression = Expression.Lambda<Func<TSource, TDest>>(Expression.MemberInit(Expression.New(typeof(TDest)), bindings), parameterExpression);

            var key = GetCacheKey<TDest>();

            _expressionCache.Add(key, expression);

            return expression;
        }

        private static MemberAssignment BuildBinding(Expression parameterExpression, MemberInfo destinationProperty, IEnumerable<PropertyInfo> sourceProperties)
        {
            var sourceProperty = sourceProperties.FirstOrDefault(src => src.Name == destinationProperty.Name);

            if (sourceProperty != null)
            {
                return Expression.Bind(destinationProperty, Expression.Property(parameterExpression, sourceProperty));
            }

            var propertyNameComponents = SplitCamelCase(destinationProperty.Name);

            if (propertyNameComponents.Length >= 2)
            {
                sourceProperty = sourceProperties.FirstOrDefault(src => src.Name == propertyNameComponents[0]);
                if (sourceProperty == null)
                    return null;

                var propertyPath = new List<PropertyInfo> { sourceProperty };
                TraversePropertyPath(propertyPath, propertyNameComponents, sourceProperty);

                if (propertyPath.Count != propertyNameComponents.Length)
                    return null; //must be able to identify the path 

                MemberExpression compoundExpression = null;

                for (int i = 0; i < propertyPath.Count; i++)
                {
                    compoundExpression = i == 0 ? Expression.Property(parameterExpression, propertyPath[0]) :
                        Expression.Property(compoundExpression, propertyPath[i]);
                }

                return compoundExpression != null ? Expression.Bind(destinationProperty, compoundExpression) : null;
            }

            return null;
        }

        private static List<PropertyInfo> TraversePropertyPath(List<PropertyInfo> propertyPath, string[] propertyNames,
            PropertyInfo currentPropertyInfo, int currentDepth = 1)
        {
            if (currentDepth >= propertyNames.Count() || currentPropertyInfo == null)
                return propertyPath; //do not go deeper into the object graph

            PropertyInfo subPropertyInfo = currentPropertyInfo.PropertyType.GetProperties().FirstOrDefault(src => src.Name == propertyNames[currentDepth]);
            if (subPropertyInfo == null)
                return null; //The property to look for was not found at a given depth 

            propertyPath.Add(subPropertyInfo);

            return TraversePropertyPath(propertyPath, propertyNames, subPropertyInfo, ++currentDepth);
        }

        private static string GetCacheKey<TDest>()
        {
            return string.Concat(typeof(TSource).FullName, typeof(TDest).FullName);
        }

        private static string[] SplitCamelCase(string input)
        {
            return Regex.Replace(input, "([A-Z])", " $1", RegexOptions.Compiled).Trim().Split(' ');
        }

    }

}

Now, all you have to do create a basic CRUD-supporting Entity Framework Manager is to inherit from the base class above and specify which entity and data contract type you will support. Note that the mapping utilitizes demands that you match your property names of the data contract with the columns in the database (e.g. entity properties), in addition to their types. Also, note that you can map deep objects by using a camel case convention, see the previously mentioned article for the details. I have added four methods:

• GetAll()
• InsertOrUpdate()
• Delete()
• InsertOrUpdateMany()

Note that you have to decorate ONE property of your data contracts with the System.ComponentModel.DataAnnotations.KeyAttribute! The attribute is found in the System.ComponentModel.DataAnnotations DLL. Some additional code:

 public class Singleton<T> where T : new()
    {
        private static readonly T instance;

        static Singleton()
        {
            instance = new T();
        }

        public static T Instance
        {
            get { return instance; }
        }

        private Singleton()
        {

        }

    } //class Singleton<T> 


using System.Configuration;
using System.Diagnostics;

namespace SomeAcme.Common.Logging
{

    /// <summary>
    /// Facade class to log information, warnings and exceptions to the event log
    /// </summary>
    /// <remarks>Based upon Microsoft Prism Logger Facade </remarks>
    public class EventLogFacade : ILoggerFacade
    {

        public const int MaxLogMessageLength = 32765;

        public string EventLogSourceName;

        public EventLogFacade()
        {
            EventLogSourceName = ConfigurationManager.AppSettings[Constants.EventLogSourceNameKey];
         
            if (!EventLog.SourceExists(EventLogSourceName))
            {
                EventLog.CreateEventSource(EventLogSourceName, Constants.Application);
            }
        }

        private void WriteEntry(string message, Category category, Priority priority)
        {
            int eventID = 0;
            if (!string.IsNullOrEmpty(message) && message.Length >= (MaxLogMessageLength))
                message = message.Substring(0, MaxLogMessageLength - 1); //Limit in how large Event Log Items can be 

            EventLog.WriteEntry(EventLogSourceName, message, GetEventLogEntryType(category), eventID, GetPriorityId(priority));
        }

        private static EventLogEntryType GetEventLogEntryType(Category category)
        {
            switch (category)
            {
                case Category.Debug:
                    return EventLogEntryType.Information;
                case Category.Exception:
                    return EventLogEntryType.Error;
                case Category.Info:
                    return EventLogEntryType.Information;
                case Category.Warn:
                    return EventLogEntryType.Warning;
                default:
                    return EventLogEntryType.Error;
            }
        }

        private static short GetPriorityId(Priority priority)
        {
            switch (priority)
            {
                case Priority.None:
                    return 0;
                case Priority.High:
                    return 1;
                case Priority.Medium:
                    return 2;
                case Priority.Low:
                    return 3;
                default:
                    return 0;
            }
        }

        public void Log(string message, Category category = Category.Exception, Priority priority = Priority.High)
        {
            WriteEntry(message, category, priority);
        }

    }

}

Sadly, lists inside data contracts are not being auto mapped for now. Otherwise, the code above should in theory make mapping back and forth between those data contracts and entities in EF way easier now! Good luck!

Locking and unlocking specific bytes of a file in C#

The following code shows a program that can lock and unlock specific bytes of file in C# using FileStream::Lock and FileStream::Unlock in System.IO. To test out that locking can protect designated bytes of a file, start up multiple instances of the program and try writing to the file after it has been locked. This will protect the file to be modified by other processes, which is handy if you want to ensure data integrity of files your system or application uses and expect to have a given contents and format. FileStream class allows us to work on files on a byte level and do detailed I/O operations on files in .NET.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TestOutFileLocking
{

    class FStreamLock
    {

        static void Main(string[] args)
        {
            var uniEncoding = new UnicodeEncoding();
            string lastRecordText = "The last processed record number was: ";
            int textLength = uniEncoding.GetByteCount(lastRecordText);
            int recordNumber = 13;
            int byteCount = uniEncoding.GetByteCount(recordNumber.ToString());
            string tempString;

            using (var fileStream = new FileStream("Test#@@#.dat", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite))
            {
                //Write the original file data. 
                if (fileStream.Length == 0)
                {
                    tempString = lastRecordText + recordNumber.ToString(); 
                    fileStream.Write(uniEncoding.GetBytes(tempString), 0, uniEncoding.GetByteCount(tempString));
                }

                //Allow the user to choose the operation. 
                char consoleInput = 'R'; 
                byte[] readText = new byte[fileStream.Length];
                while (consoleInput != 'X')
                {
                    Console.Write("\nEnter 'R' to read, 'W' to write, 'L' to " + "lock, 'U' to unlock, anything else to exit: ");

                    if ((tempString = Console.ReadLine()).Length == 0)
                    {
                        break;
                    }
                    consoleInput = char.ToUpper(tempString[0]);

                    switch (consoleInput)
                    {
                        //Read data from the file and 
                        //write it to the console 
                        case 'R':
                            try
                            {
                                fileStream.Seek(0, SeekOrigin.Begin);
                                fileStream.Read(readText, 0, (int) fileStream.Length);
                                tempString = new string(uniEncoding.GetChars(readText, 0, readText.Length));
                                Console.WriteLine(tempString);
                                recordNumber = int.Parse(tempString.Substring(tempString.IndexOf(':') + 2)); 

                            }
                            //Catch the IOException generated if the 
                            //specified part of the file is locked. 
                            catch (IOException e)
                            {
                                Console.WriteLine("{0}: The read " +
                                 "operation could not be performed " +
                                 "because the specified part of the " +
                                 "file is locked.",
                                 e.GetType().Name);
                                
                            }

                            break;

                            //Update the file. 
                        case 'W':

                            try
                            {
                                fileStream.Seek(textLength, SeekOrigin.Begin);
                                fileStream.Read(readText, textLength - 1, byteCount);
                                tempString = new string(uniEncoding.GetChars(readText, textLength - 1, byteCount));
                                recordNumber = int.Parse(tempString) + 1;
                                fileStream.Seek(textLength, SeekOrigin.Begin);
                                fileStream.Write(uniEncoding.GetBytes(recordNumber.ToString()), 0, byteCount);
                                fileStream.Flush(); 
                                Console.WriteLine("Record has een updated.");
                            }
                            catch (IOException e)
                            {
                                Console.WriteLine(
                                    "{0}: The write operation could not " +
                                    "be performed because the specified " +
                                    "part of the file is locked.",
                                    e.GetType().Name);
                            } //try-catch 
                            break;

                            //Lock the specified part of the file. 
                        case 'L':

                            try
                            {
                                fileStream.Lock(textLength - 1, byteCount);
                                Console.WriteLine("The specified part " + "of file has been locked.");
                            }
                            catch (IOException err)
                            {
                                Console.WriteLine("{0}: The specified part of file is" + " already locked.", err.GetType().Name);
                            } //try-catch 
                            break; 

                        case 'U':
                            try
                            {
                                fileStream.Unlock(textLength - 1, byteCount);
                                Console.WriteLine("The specified part of file has been unlocked.");

                            }
                            catch (IOException err)
                            {
                                Console.WriteLine("{0}: The specified part of file is " + "not locked by the current prcess.", err.GetType().Name);
                            }
                            break; 

                        default:
                            consoleInput = 'X';
                            break; 

                    } //switch 

                }

            } //using 



        }

    }

}