{"action":"created","comment":{"url":"https://api.github.com/repos/caskdata/cdap/pulls/comments/55946214","id":55946214,"diff_hunk":"@@ -0,0 +1,222 @@\n+/*\n+ * Copyright © 2016 Cask Data, Inc.\n+ *\n+ * Licensed under the Apache License, Version 2.0 (the \"License\"); you may not\n+ * use this file except in compliance with the License. You may obtain a copy of\n+ * the License at\n+ *\n+ * http://www.apache.org/licenses/LICENSE-2.0\n+ *\n+ * Unless required by applicable law or agreed to in writing, software\n+ * distributed under the License is distributed on an \"AS IS\" BASIS, WITHOUT\n+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the\n+ * License for the specific language governing permissions and limitations under\n+ * the License.\n+ */\n+\n+package co.cask.cdap.api.data.batch;\n+\n+import co.cask.cdap.api.annotation.Beta;\n+import co.cask.cdap.api.common.RuntimeArguments;\n+import co.cask.cdap.api.data.format.FormatSpecification;\n+import co.cask.cdap.api.data.stream.StreamBatchReadable;\n+import co.cask.cdap.api.flow.flowlet.StreamEvent;\n+import co.cask.cdap.api.stream.StreamEventDecoder;\n+\n+import java.util.ArrayList;\n+import java.util.Collections;\n+import java.util.HashMap;\n+import java.util.List;\n+import java.util.Map;\n+import javax.annotation.Nullable;\n+\n+/**\n+ * Defines input to a program, such as MapReduce.\n+ */\n+public abstract class Input {\n+\n+  private final String name;\n+\n+  private Input(String name) {\n+    this.name = name;\n+  }\n+\n+  public String getName() {\n+    return name;\n+  }\n+\n+  /**\n+   * Returns an Input defined by a dataset.\n+   *\n+   * @param datasetName the name of the input dataset\n+   */\n+  public static Input.DatasetInput ofDataset(String datasetName) {","path":"cdap-api/src/main/java/co/cask/cdap/api/data/batch/Input.java","position":53,"original_position":53,"commit_id":"ded3a21d5262e7407312e2c080b1738409df312a","original_commit_id":"bf1429a4d3b01d5816bd6bad3d7f59f89161b54b","user":{"login":"anew","id":483004,"avatar_url":"https://avatars.githubusercontent.com/u/483004?v=3","gravatar_id":"","url":"https://api.github.com/users/anew","html_url":"https://github.com/anew","followers_url":"https://api.github.com/users/anew/followers","following_url":"https://api.github.com/users/anew/following{/other_user}","gists_url":"https://api.github.com/users/anew/gists{/gist_id}","starred_url":"https://api.github.com/users/anew/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/anew/subscriptions","organizations_url":"https://api.github.com/users/anew/orgs","repos_url":"https://api.github.com/users/anew/repos","events_url":"https://api.github.com/users/anew/events{/privacy}","received_events_url":"https://api.github.com/users/anew/received_events","type":"User","site_admin":false},"body":"I would still keep the API clean and let the factory methods return Input. That gives us flexibility to make changes later, whereas if they return the subclasses, then user's code may declare the return types as those exact subclasses, making backwards-compatible future changes very difficult. I think its ok to cast in the internal code. ","created_at":"2016-03-13T23:39:27Z","updated_at":"2016-03-13T23:39:27Z","html_url":"https://github.com/caskdata/cdap/pull/5276#discussion_r55946214","pull_request_url":"https://api.github.com/repos/caskdata/cdap/pulls/5276","_links":{"self":{"href":"https://api.github.com/repos/caskdata/cdap/pulls/comments/55946214"},"html":{"href":"https://github.com/caskdata/cdap/pull/5276#discussion_r55946214"},"pull_request":{"href":"https://api.github.com/repos/caskdata/cdap/pulls/5276"}}},"pull_request":{"url":"https://api.github.com/repos/caskdata/cdap/pulls/5276","id":62474697,"html_url":"https://github.com/caskdata/cdap/pull/5276","diff_url":"https://github.com/caskdata/cdap/pull/5276.diff","patch_url":"https://github.com/caskdata/cdap/pull/5276.patch","issue_url":"https://api.github.com/repos/caskdata/cdap/issues/5276","number":5276,"state":"open","locked":false,"title":"MultipleInputs for MapReduce","user":{"login":"anwar6953","id":2440977,"avatar_url":"https://avatars.githubusercontent.com/u/2440977?v=3","gravatar_id":"","url":"https://api.github.com/users/anwar6953","html_url":"https://github.com/anwar6953","followers_url":"https://api.github.com/users/anwar6953/followers","following_url":"https://api.github.com/users/anwar6953/following{/other_user}","gists_url":"https://api.github.com/users/anwar6953/gists{/gist_id}","starred_url":"https://api.github.com/users/anwar6953/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/anwar6953/subscriptions","organizations_url":"https://api.github.com/users/anwar6953/orgs","repos_url":"https://api.github.com/users/anwar6953/repos","events_url":"https://api.github.com/users/anwar6953/events{/privacy}","received_events_url":"https://api.github.com/users/anwar6953/received_events","type":"User","site_admin":false},"body":"This implementation supports multiple inputs for a MapReduce job. I have updated `PurchaseHistoryBuilder` to show case one of the use cases (using two datasets as source, each with different format). I have also added a test case to showcase another use case (joining two datasets), using `AppWithMapReduceUsingMultipleInputs`.\r\n\r\nAt the core of it, there is a DelegatingMapper, which has an implementation of `getSplits()` which will call `getSplits()` to each of the delegate input formats, and return the concatenated list. Each of these returned splits is tagged with information specific to that particular input, for use by the Mapper that processes that split. The hadoop framework is then responsible for creating separate mapper instances for each of these lists.\r\n\r\n\r\nhttps://issues.cask.co/browse/CDAP-3980\r\nhttp://builds.cask.co/browse/CDAP-DUT3616","created_at":"2016-03-10T23:32:38Z","updated_at":"2016-03-13T23:39:27Z","closed_at":null,"merged_at":null,"merge_commit_sha":"ebd5d246f4952a069302e16723d4dc05bba17491","assignee":null,"milestone":null,"commits_url":"https://api.github.com/repos/caskdata/cdap/pulls/5276/commits","review_comments_url":"https://api.github.com/repos/caskdata/cdap/pulls/5276/comments","review_comment_url":"https://api.github.com/repos/caskdata/cdap/pulls/comments{/number}","comments_url":"https://api.github.com/repos/caskdata/cdap/issues/5276/comments","statuses_url":"https://api.github.com/repos/caskdata/cdap/statuses/ded3a21d5262e7407312e2c080b1738409df312a","head":{"label":"caskdata:feature/CDAP-3980-mapreduce-multiple-input-datasets","ref":"feature/CDAP-3980-mapreduce-multiple-input-datasets","sha":"ded3a21d5262e7407312e2c080b1738409df312a","user":{"login":"caskdata","id":8123023,"avatar_url":"https://avatars.githubusercontent.com/u/8123023?v=3","gravatar_id":"","url":"https://api.github.com/users/caskdata","html_url":"https://github.com/caskdata","followers_url":"https://api.github.com/users/caskdata/followers","following_url":"https://api.github.com/users/caskdata/following{/other_user}","gists_url":"https://api.github.com/users/caskdata/gists{/gist_id}","starred_url":"https://api.github.com/users/caskdata/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/caskdata/subscriptions","organizations_url":"https://api.github.com/users/caskdata/orgs","repos_url":"https://api.github.com/users/caskdata/repos","events_url":"https://api.github.com/users/caskdata/events{/privacy}","received_events_url":"https://api.github.com/users/caskdata/received_events","type":"Organization","site_admin":false},"repo":{"id":22542759,"name":"cdap","full_name":"caskdata/cdap","owner":{"login":"caskdata","id":8123023,"avatar_url":"https://avatars.githubusercontent.com/u/8123023?v=3","gravatar_id":"","url":"https://api.github.com/users/caskdata","html_url":"https://github.com/caskdata","followers_url":"https://api.github.com/users/caskdata/followers","following_url":"https://api.github.com/users/caskdata/following{/other_user}","gists_url":"https://api.github.com/users/caskdata/gists{/gist_id}","starred_url":"https://api.github.com/users/caskdata/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/caskdata/subscriptions","organizations_url":"https://api.github.com/users/caskdata/orgs","repos_url":"https://api.github.com/users/caskdata/repos","events_url":"https://api.github.com/users/caskdata/events{/privacy}","received_events_url":"https://api.github.com/users/caskdata/received_events","type":"Organization","site_admin":false},"private":false,"html_url":"https://github.com/caskdata/cdap","description":"Cask 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