1 files changed, 59 insertions, 0 deletions
diff --git a/product/database/transactions/IIdentityMap.cs b/product/database/transactions/IIdentityMap.cs
new file mode 100644
index 0000000..e2f25a0
--- /dev/null
+++ b/product/database/transactions/IIdentityMap.cs
@@ -0,0 +1,59 @@
+using System.Collections.Generic;
+
+namespace momoney.database.transactions
+{
+    public interface IIdentityMap<TKey, TValue>
+    {
+        IEnumerable<TValue> all();
+        void add(TKey key, TValue value);
+        void update_the_item_for(TKey key, TValue new_value);
+        bool contains_an_item_for(TKey key);
+        TValue item_that_belongs_to(TKey key);
+        void evict(TKey key);
+    }
+
+    public class IdentityMap<TKey, TValue> : IIdentityMap<TKey, TValue>
+    {
+        readonly IDictionary<TKey, TValue> items_in_map;
+
+        public IdentityMap() : this(new Dictionary<TKey, TValue>())
+        {
+        }
+
+        public IdentityMap(IDictionary<TKey, TValue> items_in_map)
+        {
+            this.items_in_map = items_in_map;
+        }
+
+        public IEnumerable<TValue> all()
+        {
+            return items_in_map.Values;
+        }
+
+        public void add(TKey key, TValue value)
+        {
+            items_in_map.Add(key, value);
+        }
+
+        public void update_the_item_for(TKey key, TValue new_value)
+        {
+            if (contains_an_item_for(key)) items_in_map[key] = new_value;
+            else add(key, new_value);
+        }
+
+        public bool contains_an_item_for(TKey key)
+        {
+            return items_in_map.ContainsKey(key);
+        }
+
+        public TValue item_that_belongs_to(TKey key)
+        {
+            return contains_an_item_for(key) ? items_in_map[key] : default(TValue);
+        }
+
+        public void evict(TKey key)
+        {
+            if (contains_an_item_for(key)) items_in_map.Remove(key);
+        }
+    }
+}
+\ No newline at end of file