[GitHub] [flink] wuchong commented on a change in pull request #9916: [FLINK-14408][Table-Planner]UDF's open method is invoked to initialize when sql is optimized in oldPlanner

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wuchong commented on a change in pull request #9916: [FLINK-14408][Table-Planner]UDF's open method is invoked to initialize when sql is optimized in oldPlanner
URL: https://github.com/apache/flink/pull/9916#discussion_r338355369
 
 

 ##########
 File path: flink-table/flink-table-planner/src/main/scala/org/apache/flink/table/codegen/ExpressionReducer.scala
 ##########
 @@ -164,3 +180,96 @@ class ExpressionReducer(config: TableConfig)
     }
   }
 }
+
+/**
+  * A [[ConstantFunctionContext]] allows to obtain user-defined configuration information set
+  * in [[TableConfig]].
+  *
+  * @param parameters User-defined configuration set in [[TableConfig]].
+  */
+class ConstantFunctionContext(parameters: Configuration) extends FunctionContext(null) {
+
+  override def getMetricGroup: MetricGroup = {
+    throw new UnsupportedOperationException("getMetricGroup is not supported when optimizing")
+  }
+
+  override def getCachedFile(name: String): File = {
+    throw new UnsupportedOperationException("getCachedFile is not supported when optimizing")
+  }
+
+  /**
+    * Gets the user-defined configuration value associated with the given key as a string.
+    *
+    * @param key          key pointing to the associated value
+    * @param defaultValue default value which is returned in case user-defined configuration
+    *                     value is null or there is no value associated with the given key
+    * @return (default) value associated with the given key
+    */
+  override def getJobParameter(key: String, defaultValue: String): String = {
+    parameters.getString(key, defaultValue)
+  }
+}
+
+/**
+  * A [[ConstantFunctionCodeGenerator]] used for constant expression code generator
+  * @param config configuration that determines runtime behavior
+  * @param nullableInput input(s) can be null.
+  * @param input1 type information about the first input of the Function
+  * @param functionContext functionContext that used for code generator
+  * @param parameters parameters that accessed by openFunction
+  */
+class ConstantFunctionCodeGenerator(config: TableConfig,
+                                    nullableInput: Boolean,
+                                    input1: TypeInformation[_ <: Any],
+                                    functionContext: FunctionContext,
+                                    parameters: String = null)
+  extends FunctionCodeGenerator(config, nullableInput, input1) {
+
+  override def addReusableFunction(function: UserDefinedFunction,
 
 Review comment:
   Codes of this method are duplicate with the super class. Could we use the similar way as blink planner? Add a `functionContextClass: Class[_ <: FunctionContext] = classOf[FunctionContext],` optional parameter. 

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