Fix Bulk set operation for entities

Author: SergeiPavlov

Extensions/Xtensive.Orm.BulkOperations/BulkExtensions.cs

@@ -81,7 +81,7 @@ public static IUpdatable<T> Set<T, TResult>(this IQueryable<T> query, Expression
         TResult value) where T: IEntity =>
       Set(query,
         field,
-        Expression.Lambda<Func<T, TResult>>(Expression.Constant(value), Expression.Parameter(typeof(T), "a"))   // Manually constructed expression is simpler than `a => value`
+        Expression.Lambda<Func<T, TResult>>(Expression.Constant(value, typeof(TResult)), Expression.Parameter(typeof(T), "a"))   // Manually constructed expression is simpler than `a => value`
       );
 
     /// <summary>

Extensions/Xtensive.Orm.BulkOperations/Internals/SetOperation.cs

@@ -227,7 +227,10 @@ private void AddEntityValue(AddValueContext addContext)
         }
       }
       i = -1;
-      var entity = (IEntity) FastExpression.Lambda(addContext.Lambda.Body).Compile().DynamicInvoke();
+      var entity = (IEntity) (addContext.Lambda.Body is ConstantExpression ce
+          ? ce.Value
+          : FastExpression.Lambda(addContext.Lambda.Body).Compile().DynamicInvoke());
+
       foreach (ColumnInfo column in addContext.Field.Columns) {
         i++;
         SqlExpression value;