Bring back AddAsync

src/Microsoft.EntityFrameworkCore.SqlServer/ValueGeneration/Internal/SqlServerSequenceHiLoValueGenerator.cs

@@ -3,6 +3,8 @@
 
 using System;
 using System.Globalization;
+using System.Threading;
+using System.Threading.Tasks;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Metadata;
 using Microsoft.EntityFrameworkCore.Storage;
@@ -56,6 +58,18 @@ protected override long GetNewLowValue()
                 typeof(long),
                 CultureInfo.InvariantCulture);
 
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        protected override async Task<long> GetNewLowValueAsync(CancellationToken cancellationToken = default(CancellationToken))
+            => (long)Convert.ChangeType(
+                await _rawSqlCommandBuilder
+                    .Build(_sqlGenerator.GenerateNextSequenceValueOperation(_sequence.Name, _sequence.Schema))
+                    .ExecuteScalarAsync(_connection, cancellationToken: cancellationToken),
+                typeof(long),
+                CultureInfo.InvariantCulture);
+
         /// <summary>
         ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
         ///     directly from your code. This API may change or be removed in future releases.

src/Microsoft.EntityFrameworkCore/ChangeTracking/Internal/IKeyPropagator.cs

@@ -1,6 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System.Threading;
+using System.Threading.Tasks;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Metadata;
 
@@ -17,5 +19,14 @@ public interface IKeyPropagator
         ///     directly from your code. This API may change or be removed in future releases.
         /// </summary>
         void PropagateValue([NotNull] InternalEntityEntry entry, [NotNull] IProperty property);
+
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used 
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        Task PropagateValueAsync(
+            [NotNull] InternalEntityEntry entry, 
+            [NotNull] IProperty property,
+            CancellationToken cancellationToken = default(CancellationToken));
     }
 }

src/Microsoft.EntityFrameworkCore/ChangeTracking/Internal/IValueGenerationManager.cs

@@ -1,6 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System.Threading;
+using System.Threading.Tasks;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Metadata;
 
@@ -18,6 +20,14 @@ public interface IValueGenerationManager
         /// </summary>
         void Generate([NotNull] InternalEntityEntry entry);
 
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used 
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        Task GenerateAsync(
+            [NotNull] InternalEntityEntry entry, 
+            CancellationToken cancellationToken = default(CancellationToken));
+
         /// <summary>
         ///     This API supports the Entity Framework Core infrastructure and is not intended to be used 
         ///     directly from your code. This API may change or be removed in future releases.

src/Microsoft.EntityFrameworkCore/ChangeTracking/Internal/InternalEntityEntry.cs

@@ -8,6 +8,8 @@
 using System.Diagnostics;
 using System.Linq;
 using System.Reflection;
+using System.Threading;
+using System.Threading.Tasks;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Internal;
 using Microsoft.EntityFrameworkCore.Metadata;
@@ -74,6 +76,25 @@ public virtual void SetEntityState(EntityState entityState, bool acceptChanges =
             SetEntityState(oldState, entityState, acceptChanges);
         }
 
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used 
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        public virtual async Task SetEntityStateAsync(
+            EntityState entityState, 
+            bool acceptChanges,
+            CancellationToken cancellationToken = default(CancellationToken))
+        {
+            var oldState = _stateData.EntityState;
+
+            if (PrepareForAdd(entityState))
+            {
+                await StateManager.ValueGeneration.GenerateAsync(this, cancellationToken);
+            }
+
+            SetEntityState(oldState, entityState, acceptChanges);
+        }
+
         private bool PrepareForAdd(EntityState newState)
         {
             if (newState != EntityState.Added

src/Microsoft.EntityFrameworkCore/ChangeTracking/Internal/KeyPropagator.cs

@@ -2,6 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Diagnostics;
+using System.Threading;
+using System.Threading.Tasks;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Internal;
 using Microsoft.EntityFrameworkCore.Metadata;
@@ -48,6 +50,29 @@ public virtual void PropagateValue(InternalEntityEntry entry, IProperty property
             }
         }
 
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used 
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        public virtual async Task PropagateValueAsync(
+            InternalEntityEntry entry, 
+            IProperty property,
+            CancellationToken cancellationToken = default(CancellationToken))
+        {
+            Debug.Assert(property.IsForeignKey());
+
+            if (!TryPropagateValue(entry, property)
+                && property.IsKey())
+            {
+                var valueGenerator = TryGetValueGenerator(property);
+
+                if (valueGenerator != null)
+                {
+                    entry[property] = await valueGenerator.NextAsync(new EntityEntry(entry), cancellationToken);
+                }
+            }
+        }
+
         private bool TryPropagateValue(InternalEntityEntry entry, IProperty property)
         {
             var entityType = entry.EntityType;

src/Microsoft.EntityFrameworkCore/ChangeTracking/Internal/ValueGenerationManager.cs

@@ -1,7 +1,10 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System.Diagnostics;
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Internal;
 using Microsoft.EntityFrameworkCore.Metadata;
@@ -10,7 +13,7 @@
 namespace Microsoft.EntityFrameworkCore.ChangeTracking.Internal
 {
     /// <summary>
-    ///     This API supports the Entity Framework Core infrastructure and is not intended to be used 
+    ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
     ///     directly from your code. This API may change or be removed in future releases.
     /// </summary>
     public class ValueGenerationManager : IValueGenerationManager
@@ -19,7 +22,7 @@ public class ValueGenerationManager : IValueGenerationManager
         private readonly IKeyPropagator _keyPropagator;
 
         /// <summary>
-        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used 
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
         ///     directly from your code. This API may change or be removed in future releases.
         /// </summary>
         public ValueGenerationManager(
@@ -31,40 +34,86 @@ public ValueGenerationManager(
         }
 
         /// <summary>
-        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used 
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
         ///     directly from your code. This API may change or be removed in future releases.
         /// </summary>
         public virtual void Generate(InternalEntityEntry entry)
         {
             var entityEntry = new EntityEntry(entry);
 
+            foreach (var propertyTuple in FindProperties(entry))
+            {
+                var property = propertyTuple.Item1;
+
+                if (propertyTuple.Item2)
+                {
+                    _keyPropagator.PropagateValue(entry, property);
+                }
+                else
+                {
+                    var valueGenerator = GetValueGenerator(entry, property);
+
+                    SetGeneratedValue(
+                        entry, 
+                        property, 
+                        valueGenerator.Next(entityEntry), 
+                        valueGenerator.GeneratesTemporaryValues);
+                }
+            }
+        }
+
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        public virtual async Task GenerateAsync(
+            InternalEntityEntry entry, 
+            CancellationToken cancellationToken = default(CancellationToken))
+        {
+            var entityEntry = new EntityEntry(entry);
+
+            foreach (var propertyTuple in FindProperties(entry))
+            {
+                var property = propertyTuple.Item1;
+
+                if (propertyTuple.Item2)
+                {
+                    _keyPropagator.PropagateValue(entry, property);
+                }
+                else
+                {
+                    var valueGenerator = GetValueGenerator(entry, property);
+
+                    SetGeneratedValue(
+                        entry, 
+                        property, 
+                        await valueGenerator.NextAsync(entityEntry, cancellationToken), 
+                        valueGenerator.GeneratesTemporaryValues);
+                }
+            }
+        }
+
+        private IEnumerable<Tuple<IProperty, bool>> FindProperties(InternalEntityEntry entry)
+        {
             foreach (var property in entry.EntityType.GetProperties())
             {
                 var isForeignKey = property.IsForeignKey();
 
                 if ((property.RequiresValueGenerator || isForeignKey)
                     && property.ClrType.IsDefaultValue(entry[property]))
                 {
-                    if (isForeignKey)
-                    {
-                        _keyPropagator.PropagateValue(entry, property);
-                    }
-                    else
-                    {
-                        var valueGenerator = _valueGeneratorSelector.Select(property, property.IsKey()
-                            ? property.DeclaringEntityType
-                            : entry.EntityType);
-
-                        Debug.Assert(valueGenerator != null);
-
-                        SetGeneratedValue(entry, property, valueGenerator.Next(entityEntry), valueGenerator.GeneratesTemporaryValues);
-                    }
+                    yield return Tuple.Create(property, isForeignKey);
                 }
             }
         }
 
+        private ValueGenerator GetValueGenerator(InternalEntityEntry entry, IProperty property)
+            => _valueGeneratorSelector.Select(property, property.IsKey()
+                ? property.DeclaringEntityType
+                : entry.EntityType);
+
         /// <summary>
-        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used 
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
         ///     directly from your code. This API may change or be removed in future releases.
         /// </summary>
         public virtual bool MayGetTemporaryValue(IProperty property, IEntityType entityType)