Added a new trait for aggregating items from a repository.

Author: johelvisguzman

src/DotNetToolkit.Repository/IRepository.cs

@@ -7,7 +7,7 @@
     /// </summary>
     /// <typeparam name="TEntity">The type of the entity.</typeparam>
     /// <typeparam name="TKey">The type of the primary key.</typeparam>
-    public interface IRepository<TEntity, in TKey> : ICanAdd<TEntity>, ICanUpdate<TEntity>, ICanDelete<TEntity, TKey>, ICanGet<TEntity, TKey>, ICanFind<TEntity>
+    public interface IRepository<TEntity, in TKey> : ICanAggregate<TEntity>, ICanAdd<TEntity>, ICanUpdate<TEntity>, ICanDelete<TEntity, TKey>, ICanGet<TEntity, TKey>, ICanFind<TEntity>
         where TEntity : class
     {
     }

src/DotNetToolkit.Repository/RepositoryBase.cs

@@ -85,7 +85,7 @@ protected virtual IQueryable<TEntity> GetQuery(Expression<Func<TEntity, bool>> p
 
             return GetQuery(new Specification<TEntity>(predicate));
         }
-        
+
         /// <summary>
         /// Returns a specification for getting an entity by it's primary key.
         /// </summary>
@@ -116,7 +116,40 @@ protected virtual ISpecification<TEntity> ByPrimaryKeySpecification(TKey key, IF
         }
 
         #endregion
-        
+
+        #region Implementation of ICanAggregate<TEntity>
+
+        /// <summary>
+        /// Returns the number of entities contained in the repository.
+        /// </summary>
+        /// <returns>The number of entities contained in the repository.</returns>
+        public int Count()
+        {
+            return Count((ISpecification<TEntity>)null);
+        }
+
+        /// <summary>
+        /// Returns the number of entities that satisfies the criteria specified by the <paramref name="criteria" /> in the repository.
+        /// </summary>
+        /// <param name="criteria">The specification criteria that is used for matching entities against.</param>
+        /// <returns>The number of entities that satisfied the criteria specified by the <paramref name="criteria" /> in the repository.</returns>
+        public int Count(ISpecification<TEntity> criteria)
+        {
+            return GetQuery(criteria).Count();
+        }
+
+        /// <summary>
+        /// Returns the number of entities that satisfies the criteria specified by the <paramref name="predicate" /> in the repository.
+        /// </summary>
+        /// <param name="predicate">A function to filter each entity.</param>
+        /// <returns>The number of entities that satisfied the criteria specified by the <paramref name="predicate" /> in the repository.</returns>
+        public int Count(Expression<Func<TEntity, bool>> predicate)
+        {
+            return GetQuery(predicate == null ? null : new Specification<TEntity>(predicate)).Count();
+        }
+
+        #endregion
+
         #region Implementation of ICanAdd<in TEntity>
 
         /// <summary>

src/DotNetToolkit.Repository/Traits/ICanAggregate.cs

@@ -0,0 +1,33 @@
+namespace DotNetToolkit.Repository.Traits
+{
+    using Specifications;
+    using System;
+    using System.Linq.Expressions;
+
+    /// <summary>
+    /// Represents a trait for aggregating items from a repository.
+    /// </summary>
+    /// <typeparam name="TEntity">The type of the entity.</typeparam>
+    public interface ICanAggregate<TEntity> where TEntity : class
+    {
+        /// <summary>
+        /// Returns the number of entities contained in the repository.
+        /// </summary>
+        /// <returns>The number of entities contained in the repository.</returns>
+        int Count();
+
+        /// <summary>
+        /// Returns the number of entities that satisfies the criteria specified by the <paramref name="criteria" /> in the repository.
+        /// </summary>
+        /// <param name="criteria">The specification criteria that is used for matching entities against.</param>
+        /// <returns>The number of entities that satisfied the criteria specified by the <paramref name="criteria" /> in the repository.</returns>
+        int Count(ISpecification<TEntity> criteria);
+
+        /// <summary>
+        /// Returns the number of entities that satisfies the criteria specified by the <paramref name="predicate" /> in the repository.
+        /// </summary>
+        /// <param name="predicate">A function to filter each entity.</param>
+        /// <returns>The number of entities that satisfied the criteria specified by the <paramref name="predicate" /> in the repository.</returns>
+        int Count(Expression<Func<TEntity, bool>> predicate);
+    }
+}