Wednesday, 9 December 2015

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!

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