Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web.Extensions/ui/WebControls/Expressions/CustomExpression.cs

@@ -0,0 +1,40 @@
+namespace System.Web.UI.WebControls.Expressions {
+    using System.Web.Query.Dynamic;
+    using System;
+    using System.Linq.Expressions;
+    using System.Security.Permissions;
+    using System.Text.RegularExpressions;    
+    using System.Web.UI;
+    using System.Web.UI.WebControls;
+    using System.Collections.Generic;
+    using System.Linq;
+
+    [
+    PersistChildren(false),
+    ParseChildren(true, "Parameters")
+    ]
+    public class CustomExpression : ParameterDataSourceExpression {
+        private EventHandler<CustomExpressionEventArgs> _querying;
+       
+        public event EventHandler<CustomExpressionEventArgs> Querying {
+            add {
+                _querying += value;
+            }
+            remove {
+                _querying -= value;
+            }
+        }
+
+        public override IQueryable GetQueryable(IQueryable source) {
+            CustomExpressionEventArgs e = new CustomExpressionEventArgs(source, GetValues());
+            OnQuerying(e);
+            return e.Query;
+        }
+
+        private void OnQuerying(CustomExpressionEventArgs e) {
+            if (_querying != null) {
+                _querying(this, e);
+            }
+        }
+    }
+}