[GitHub] incubator-flink pull request: SemanticProperties for Projections

[StephanEwen <gi...@git.apache.org>]

Github user StephanEwen commented on a diff in the pull request:

    https://github.com/apache/incubator-flink/pull/29#discussion_r14508478
  
    --- Diff: stratosphere-java/src/main/java/eu/stratosphere/api/java/operators/JoinOperator.java ---
    @@ -510,6 +522,16 @@ protected ProjectJoin(DataSet<I1> input1, DataSet<I2> input2, Keys<I1> keys1, Ke
     					new ProjectJoinFunction<I1, I2, OUT>(fields, isFromFirst, returnType.createSerializer().createInstance()), 
     					returnType, hint);
     		}
    +
    +		@Override
    +		public JoinOperator<I1, I2, OUT> withConstantSetFirst(String... constantSetFirst) {
    +			throw new RuntimeException("Please do not use ConstantFields on ProjectJoins. The Fields are automatically calculated.");
    --- End diff --
    
    You can skip the "please". No need for the API to kindly ask for something. Use something like "The Semantic properties (constant and forwarded fields) are automatically calculated on projection joins."


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