[EventGrid] Generate switch expressions instead of dictionary lookups (#49426)

* Generate switch expression

* Ordinal version

* Simplified if version for comparison

---------

Co-authored-by: Daniel Marbach <[email protected]>

Author: danielmarbach

sdk/eventgrid/Azure.Messaging.EventGrid/EventGridSourceGenerator/src/EventGridSourceGenerator.cs

@@ -109,28 +109,21 @@ internal class SystemEventExtensions
     {{
         public static object AsSystemEventData(string eventType, JsonElement data)
         {{
-            if (s_systemEventDeserializers.TryGetValue(eventType, out Func<JsonElement,{(_isSystemEventsLibrary ? " ModelReaderWriterOptions," : string.Empty)} object> systemDeserializationFunction))
-            {{
-                return systemDeserializationFunction(data{(_isSystemEventsLibrary ? ", null" : string.Empty)});
-            }}
-            else
-            {{
-                return null;
-            }}
-        }}
-
-        internal static readonly IReadOnlyDictionary<string, Func<JsonElement,{(_isSystemEventsLibrary ? " ModelReaderWriterOptions," : string.Empty)} object>> s_systemEventDeserializers = new Dictionary<string, Func<JsonElement,{(_isSystemEventsLibrary ? " ModelReaderWriterOptions," : string.Empty)} object>>(StringComparer.OrdinalIgnoreCase)
-        {{
+            var eventTypeSpan = eventType.AsSpan();
 ");
             foreach (SystemEventNode sysEvent in _visitor.SystemEvents)
             {
                 // Add each an entry for each system event to the dictionary containing a mapping from constant name to deserialization method.
                 sourceBuilder.AppendLine(
-                    $"{Indent}{Indent}{Indent}{{ SystemEventNames.{sysEvent.EventConstantName}, {sysEvent.EventName}.{sysEvent.DeserializeMethod} }},");
+                    $"{Indent}{Indent}{Indent}if (eventTypeSpan.Equals(SystemEventNames.{sysEvent.EventConstantName}.AsSpan(), StringComparison.OrdinalIgnoreCase))");
+                sourceBuilder.AppendLine(
+                    $"{Indent}{Indent}{Indent}{Indent}return {sysEvent.EventName}.{sysEvent.DeserializeMethod}(data{(_isSystemEventsLibrary ? ", null" : string.Empty)});");
             }
-            sourceBuilder.Append($@"{Indent}{Indent}}};
-{Indent}}}
-}}");
+            sourceBuilder.AppendLine($"{Indent}{Indent}{Indent}return null;");
+            sourceBuilder.AppendLine($"{Indent}{Indent}}}");
+            sourceBuilder.AppendLine($"{Indent}}}");
+            sourceBuilder.AppendLine("}");
+
             return sourceBuilder.ToString();
         }
     }

sdk/eventgrid/Azure.Messaging.EventGrid/tests/SystemEventTests.cs

@@ -6,6 +6,7 @@
 using System.ComponentModel;
 using System.Linq;
 using System.Reflection;
+using System.Text.Json;
 using Azure.Messaging.EventGrid.SystemEvents;
 using NUnit.Framework;
 
@@ -39,10 +40,9 @@ public void MappingContainsAllSystemEvents()
                 }
 
                 ValidateName(systemEvent.Name);
-                Assert.IsTrue(
-                    SystemEventExtensions.s_systemEventDeserializers.Values.Any(
-                        f => f.Method.ReturnType == systemEvent), systemEvent.Name);
+                Assert.IsNotNull(SystemEventExtensions.AsSystemEventData(systemEvent.Name, JsonDocument.Parse("{}").RootElement));
             }
+            Assert.IsNull(SystemEventExtensions.AsSystemEventData("DoesNotExist", JsonDocument.Parse("{}").RootElement));
         }
 
         [Test]