Added Find method to DbSet

src/MongoFramework/IMongoDbSet.cs

@@ -17,6 +17,7 @@ public interface IMongoDbSet
 	public interface IMongoDbSet<TEntity> : IMongoDbSet, IQueryable<TEntity> where TEntity : class
 	{
 		IMongoDbContext Context { get; }
+		TEntity Find(object id);
 		TEntity Create();
 		void Add(TEntity entity);
 		void AddRange(IEnumerable<TEntity> entities);

src/MongoFramework/Infrastructure/EntityEntryContainer.cs

@@ -66,8 +66,28 @@ public EntityEntry GetEntry<TCollectionBase>(TCollectionBase entity)
 			}
 
 			return null;
-		}
+		}
+
+		public EntityEntry GetEntryById<TCollectionBase>(object id)
+		{		
+			var collectionType = typeof(TCollectionBase);
+
+			if (EntryLookupByType.TryGetValue(collectionType, out var entries))
+			{
+				var entityDefinition = EntityMapping.GetOrCreateDefinition(collectionType);
+
+				foreach (var entry in entries)
+				{
+					var entryEntityId = entityDefinition.GetIdValue(entry.Entity);
+					if (entryEntityId.Equals(id))
+					{
+						return entry;
+					}
+				}
+			}
 
+			return null;
+		}
 		public EntityEntry SetEntityState<TCollectionBase>(TCollectionBase entity, EntityEntryState state) where TCollectionBase : class
 		{
 			if (entity is null)

src/MongoFramework/MongoDbSet.cs

@@ -1,7 +1,9 @@
-using MongoFramework.Infrastructure;
+using MongoDB.Driver;
+using MongoFramework.Infrastructure;
 using MongoFramework.Infrastructure.Commands;
 using MongoFramework.Infrastructure.Linq;
 using MongoFramework.Infrastructure.Linq.Processors;
+using MongoFramework.Infrastructure.Mapping;
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -30,8 +32,44 @@ public virtual TEntity Create()
 			var entity = Activator.CreateInstance<TEntity>();
 			Add(entity);
 			return entity;
-		}
-
+		}
+
+		/// <summary>
+		///     Finds an entity with the given primary key value. If an entity with the given primary key value
+		///     is being tracked by the context, then it is returned immediately without making a request to the
+		///     database. Otherwise, a query is made to the database for an entity with the given primary key value
+		///     and this entity, if found, is attached to the context and returned. If no entity is found, then
+		///     null is returned.
+		/// </summary>
+		/// <param name="id">The value of the primary key for the entity to be found.</param>
+		/// <returns>The entity found, or null.</returns>
+		public virtual TEntity Find(object id) 
+		{
+			if (id == null)
+				throw new ArgumentNullException(nameof(id));
+
+			var tracked = Context.ChangeTracker.GetEntryById<TEntity>(id);
+
+			if (tracked != null)
+			{
+				return tracked.Entity as TEntity;
+			}
+
+			var entityDefinition = EntityMapping.GetOrCreateDefinition(typeof(TEntity));
+			var filter = entityDefinition.CreateIdFilter<TEntity>(id);
+
+			var collection = Context.Connection.GetDatabase().GetCollection<TEntity>(entityDefinition.CollectionName);
+			var cursor = collection.Find(filter);
+			var entity = cursor.FirstOrDefault();
+
+			if (entity != null)
+			{
+				Context.ChangeTracker.SetEntityState(entity, EntityEntryState.NoChanges);
+			}
+
+			return entity;
+		}
+
 		/// <summary>
 		/// Marks the entity for insertion into the database.
 		/// </summary>

tests/MongoFramework.Tests/Infrastructure/EntityEntryContainerTests.cs

@@ -119,6 +119,28 @@ public void EntryDoesntMatchOnEqualityOverride()
 			Assert.AreEqual(2, entryContainer.Entries().Count());
 		}
 
+		[TestMethod]
+		public void GetExistingEntryIdMatch()
+		{
+			var entryContainer = new EntityEntryContainer();
+			var entity = new EntityEntryContainerModel
+			{
+				Id = "123",
+				Title = "EntityEntryContainerTests.UpdateExistingEntryWithoutId"
+			};
+			entryContainer.SetEntityState(entity, EntityEntryState.Added);
+
+			var entry = entryContainer.GetEntryById<EntityEntryContainerModel>("123");
+			Assert.AreEqual(entity, entry.Entity);
+			Assert.AreEqual(EntityEntryState.Added, entry.State);
+
+			entryContainer.SetEntityState(entity, EntityEntryState.NoChanges);
+
+			entry = entryContainer.GetEntryById<EntityEntryContainerModel>("123");
+			Assert.AreEqual(entity, entry.Entity);
+			Assert.AreEqual(EntityEntryState.NoChanges, entry.State);
+		}
+
 		[TestMethod]
 		public void RemoveRange()
 		{

tests/MongoFramework.Tests/MongoDbSetTests.cs

@@ -50,6 +50,67 @@ public async Task SuccessfulInsertAndQueryBackAsync()
 			Assert.IsTrue(dbSet.Any(m => m.Description == "ValueAsync"));
 		}
 
+		[TestMethod]
+		public void SuccessfulInsertAndFind()
+		{
+			var connection = TestConfiguration.GetConnection();
+			var context = new MongoDbContext(connection);
+			var dbSet = new MongoDbSet<TestModel>(context);
+
+			var model = new TestModel
+			{
+				Description = "ValueSync"
+			};
+
+			dbSet.Add(model);
+
+			context.SaveChanges();
+
+			context = new MongoDbContext(connection);
+			dbSet = new MongoDbSet<TestModel>(context);
+			Assert.IsTrue(dbSet.Find(model.Id).Description == "ValueSync");
+			Assert.IsTrue(context.ChangeTracker.GetEntry(model).State == MongoFramework.Infrastructure.EntityEntryState.NoChanges);			
+		}
+
+		[TestMethod]
+		public void SuccessfulNullFind()
+		{
+			var connection = TestConfiguration.GetConnection();
+			var context = new MongoDbContext(connection);
+			var dbSet = new MongoDbSet<TestModel>(context);
+
+			var model = new TestModel
+			{
+				Description = "ValueSync"
+			};
+
+			dbSet.Add(model);
+
+			context.SaveChanges();
+
+			Assert.IsNull(dbSet.Find("abcd"));
+		}
+
+		[TestMethod]
+		public void SuccessfullyFindTracked()
+		{
+			var connection = TestConfiguration.GetConnection();
+			var context = new MongoDbContext(connection);
+			var dbSet = new MongoDbSet<TestModel>(context);
+
+			var model = new TestModel
+			{
+				Id = "abcd",
+				Description = "ValueSync"
+			};
+
+			dbSet.Add(model);
+
+			//Note: not saving, but still should be found as tracked
+			Assert.IsTrue(dbSet.Find(model.Id).Description == "ValueSync");
+			Assert.IsTrue(context.ChangeTracker.GetEntry(model).State == MongoFramework.Infrastructure.EntityEntryState.Added);
+		}
+
 		[TestMethod]
 		public void SuccessfullyUpdateEntity()
 		{