Add example of optional input fields (#52)

* Add example of optional input fields

* Add example of reusing same object for input and output fields

Author: dariuszkuc

example/src/main/kotlin/com.expedia.graphql.sample/model/Widget.kt

@@ -6,7 +6,7 @@ import com.expedia.graphql.annotations.GraphQLIgnore
 @GraphQLDescription("A useful widget")
 data class Widget(
     @property:GraphQLDescription("The widget's value that can be null")
-    val value: Int?,
+    var value: Int? = null,
     @property:Deprecated(message = "This field is deprecated", replaceWith = ReplaceWith("value"))
     @property:GraphQLDescription("The widget's deprecated value that shouldn't be used")
     val deprecatedValue: Int? = value,

example/src/main/kotlin/com.expedia.graphql.sample/mutation/WidgetMutation.kt

@@ -0,0 +1,20 @@
+package com.expedia.graphql.sample.mutation
+
+import com.expedia.graphql.annotations.GraphQLDescription
+import com.expedia.graphql.sample.model.Widget
+import org.springframework.stereotype.Component
+
+/**
+ * Simple widget mutation that shows that same objects can be used for input and output GraphQL types.
+ */
+@Component
+class WidgetMutation : Mutation {
+
+    @GraphQLDescription("modifies passed in widget so it doesn't have null value")
+    fun processWidget(@GraphQLDescription("widget to be modified") widget: Widget): Widget {
+        if (null == widget.value) {
+            widget.value = 42
+        }
+        return widget
+    }
+}

example/src/main/kotlin/com.expedia.graphql.sample/query/SimpleQuery.kt

@@ -46,4 +46,10 @@ class SimpleQuery: Query {
         val random = Random()
         return (1..10).map { random.nextInt(100) }.toList()
     }
+
+    @GraphQLDescription("query with optional input")
+    fun doSomethingWithOptionalInput(
+            @GraphQLDescription("this field is required") requiredValue: Int,
+            @GraphQLDescription("this field is optional") optionalValue: Int? = null)
+            = "required value=$requiredValue, optional value=$optionalValue"
 }