Add IsEmpty / NotEmpty overloads to CountEx (#250)

reactivemarbles · Apr 28, 2020 · 533d41a · 533d41a
1 parent 225c64f
commit 533d41a
Showing 1 changed file with 63 additions and 0 deletions.
diff --git a/src/DynamicData/Aggregation/CountEx.cs b/src/DynamicData/Aggregation/CountEx.cs
@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for full license information.
 
 using System;
+using System.Reactive.Linq;
 
 namespace DynamicData.Aggregation
 {
@@ -57,5 +58,67 @@ public static IObservable<int> Count<TObject>(this IObservable<IDistinctChangeSe
         {
             return source.ForAggregation().Count();
         }
+
+        /// <summary>
+        /// Counts the total number of items in the underlying data source
+        /// and return true if the number of items == 0
+        /// </summary>
+        /// <typeparam name="TObject">The type of the object.</typeparam>
+        /// <typeparam name="TKey">The type of the key.</typeparam>
+        /// <param name="source">The source.</param>
+        /// <returns></returns>
+        public static IObservable<bool> IsEmpty<TObject, TKey>(this IObservable<IChangeSet<TObject, TKey>> source)
+        {
+            return source.ForAggregation()
+                .Count()
+                .StartWith(0)
+                .Select(count => count == 0);
+        }
+
+        /// <summary>
+        /// Counts the total number of items in the underlying data source
+        /// and returns true if the number of items is greater than 0
+        /// </summary>
+        /// <typeparam name="TObject">The type of the object.</typeparam>
+        /// <typeparam name="TKey">The type of the key.</typeparam>
+        /// <param name="source">The source.</param>
+        /// <returns></returns>
+        public static IObservable<bool> NotEmpty<TObject, TKey>(this IObservable<IChangeSet<TObject, TKey>> source)
+        {
+            return source.ForAggregation()
+                .Count()
+                .StartWith(0)
+                .Select(count => count > 0);
+        }
+
+        /// <summary>
+        /// Counts the total number of items in the underlying data source
+        /// and return true if the number of items == 0
+        /// </summary>
+        /// <typeparam name="TObject">The type of the object.</typeparam>
+        /// <param name="source">The source.</param>
+        /// <returns></returns>
+        public static IObservable<bool> IsEmpty<TObject>(this IObservable<IChangeSet<TObject>> source)
+        {
+            return source.ForAggregation()
+                .Count()
+                .StartWith(0)
+                .Select(count => count == 0);
+        }
+
+        /// <summary>
+        /// Counts the total number of items in the underlying data source
+        /// and returns true if the number of items is greater than 0
+        /// </summary>
+        /// <typeparam name="TObject">The type of the object.</typeparam>
+        /// <param name="source">The source.</param>
+        /// <returns></returns>
+        public static IObservable<bool> NotEmpty<TObject>(this IObservable<IChangeSet<TObject>> source)
+        {
+            return source.ForAggregation()
+                .Count()
+                .StartWith(0)
+                .Select(count => count > 0);
+        }
     }
 }