Update C# docs for connect/disconnect (#9)

Update after the change in clockworklabs/SpacetimeDB#309.

Author: RReverser

docs/Server Module Languages/C#/ModuleReference.md

@@ -289,6 +289,9 @@ These are two special kinds of reducers that can be used to respond to module li
 
 - `ReducerKind.Init` - this reducer will be invoked when the module is first published.
 - `ReducerKind.Update` - this reducer will be invoked when the module is updated.
+- `ReducerKind.Connect` - this reducer will be invoked when a client connects to the database.
+- `ReducerKind.Disconnect` - this reducer will be invoked when a client disconnects from the database.
+
 
 Example:
 
@@ -299,16 +302,3 @@ public static void Init()
     Log("...and we're live!");
 }
 ```
-
-### Connection events
-
-`OnConnect` and `OnDisconnect` `SpacetimeDB.Runtime` events are triggered when a client connects or disconnects from the database. They can be used to initialize per-client state or to clean up after the client disconnects. They get passed an instance of the earlier mentioned `DbEventArgs` which can be used to distinguish clients via its `Sender` field.
-
-```csharp
-[SpacetimeDB.Reducer(ReducerKind.Init)]
-public static void Init()
-{
-    OnConnect += (e) => Log($"Client {e.Sender} connected!");
-    OnDisconnect += (e) => Log($"Client {e.Sender} disconnected!");
-}
-```

docs/Server Module Languages/C#/index.md

@@ -182,64 +182,62 @@ You could extend the validation in `ValidateMessage` in similar ways to `Validat
 
 ## Set users' online status
 
-In C# modules, you can register for OnConnect and OnDisconnect events in a special initializer function that uses the attribute `ModuleInitializer`. We'll use the `OnConnect` event to create a `User` record for the client if it doesn't yet exist, and to set its online status.
+In C# modules, you can register for `Connect` and `Disconnect` events by using a special `ReducerKind`. We'll use the `Connect` event to create a `User` record for the client if it doesn't yet exist, and to set its online status.
 
 We'll use `User.FilterByIdentity` to look up a `User` row for `dbEvent.Sender`, if one exists. If we find one, we'll use `User.UpdateByIdentity` to overwrite it with a row that has `Online: true`. If not, we'll use `User.Insert` to insert a new row for our new user. All three of these methods are generated by the `[SpacetimeDB.Table]` attribute, with rows and behavior based on the row attributes. `FilterByIdentity` returns a nullable `User`, because the unique constraint from the `[SpacetimeDB.Column(ColumnAttrs.PrimaryKey)]` attribute means there will be either zero or one matching rows. `Insert` will throw an exception if the insert violates this constraint; if we want to overwrite a `User` row, we need to do so explicitly using `UpdateByIdentity`.
 
 In `server/Lib.cs`, add the definition of the connect reducer to the `Module` class:
 
 ```C#
-    [ModuleInitializer]
-    public static void Init()
+    [SpacetimeDB.Reducer(ReducerKind.Connect)]
+    public static void OnConnect(DbEventArgs dbEventArgs)
     {
-        OnConnect += (dbEventArgs) =>
-        {
-            Log($"Connect {dbEventArgs.Sender}");
-            var user = User.FindByIdentity(dbEventArgs.Sender);
+        Log($"Connect {dbEventArgs.Sender}");
+        var user = User.FindByIdentity(dbEventArgs.Sender);
 
-            if (user is not null)
-            {
-                // If this is a returning user, i.e., we already have a `User` with this `Identity`,
-                // set `Online: true`, but leave `Name` and `Identity` unchanged.
-                user.Online = true;
-                User.UpdateByIdentity(dbEventArgs.Sender, user);
-            }
-            else
+        if (user is not null)
+        {
+            // If this is a returning user, i.e., we already have a `User` with this `Identity`,
+            // set `Online: true`, but leave `Name` and `Identity` unchanged.
+            user.Online = true;
+            User.UpdateByIdentity(dbEventArgs.Sender, user);
+        }
+        else
+        {
+            // If this is a new user, create a `User` object for the `Identity`,
+            // which is online, but hasn't set a name.
+            new User
             {
-                // If this is a new user, create a `User` object for the `Identity`,
-                // which is online, but hasn't set a name.
-                new User
-                {
-                    Name = null,
-                    Identity = dbEventArgs.Sender,
-                    Online = true,
-                }.Insert();
-            }
-        };
+                Name = null,
+                Identity = dbEventArgs.Sender,
+                Online = true,
+            }.Insert();
+        }
     }
 ```
 
-Similarly, whenever a client disconnects, the module will execute the `OnDisconnect` event if it's registered. We'll use it to un-set the `Online` status of the `User` for the disconnected client.
+Similarly, whenever a client disconnects, the module will execute the `OnDisconnect` event if it's registered with `ReducerKind.Disconnect`. We'll use it to un-set the `Online` status of the `User` for the disconnected client.
 
 Add the following code after the `OnConnect` lambda:
 
 ```C#
-        OnDisconnect += (dbEventArgs) =>
-        {
-            var user = User.FindByIdentity(dbEventArgs.Sender);
+    [SpacetimeDB.Reducer(ReducerKind.Disconnect)]
+    public static void OnDisconnect(DbEventArgs dbEventArgs)
+    {
+        var user = User.FindByIdentity(dbEventArgs.Sender);
 
-            if (user is not null)
-            {
-                // This user should exist, so set `Online: false`.
-                user.Online = false;
-                User.UpdateByIdentity(dbEventArgs.Sender, user);
-            }
-            else
-            {
-                // User does not exist, log warning
-                Log($"Warning: No user found for disconnected client.");
-            }
-        };
+        if (user is not null)
+        {
+            // This user should exist, so set `Online: false`.
+            user.Online = false;
+            User.UpdateByIdentity(dbEventArgs.Sender, user);
+        }
+        else
+        {
+            // User does not exist, log warning
+            Log($"Warning: No user found for disconnected client.");
+        }
+    }
 ```
 
 ## Publish the module