| //// |
| Licensed to the Apache Software Foundation (ASF) under one |
| or more contributor license agreements. See the NOTICE file |
| distributed with this work for additional information |
| regarding copyright ownership. The ASF licenses this file |
| to you under the Apache License, Version 2.0 (the |
| "License"); you may not use this file except in compliance |
| with the License. You may obtain a copy of the License at |
| http://www.apache.org/licenses/LICENSE-2.0 |
| Unless required by applicable law or agreed to in writing, |
| software distributed under the License is distributed on an |
| "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| KIND, either express or implied. See the License for the |
| specific language governing permissions and limitations |
| under the License. |
| //// |
| :documentationPath: /plugins/transforms/ |
| :language: en_US |
| :page-alternativeEditUrl: https://github.com/apache/incubator-hop/edit/master/plugins/transforms/streamlookup/src/main/doc/streamlookup.adoc |
| |
| = Stream Lookup |
| |
| == Description |
| |
| The Stream lookup transform type allows you to look up data using information coming from other transforms in the pipeline. The data coming from the Source transform is first read into memory and is then used to look up data from the main stream. |
| |
| == Options |
| |
| [width="90%", options="header"] |
| |=== |
| |Option|Description |
| |Transform name|Name of the transform this name has to be unique in a single pipeline |
| |Lookup Transform|The Transform name where the lookup data is coming from |
| |The keys to lookup...|Allows you to specify the names of the fields that are used to look up values. Values are always searched using the "equal" comparison |
| |Fields to retrieve|You can specify the names of the fields to retrieve here, as well as the default value in case the value was not found or a new field name in case you didn't like the old one. |
| |Preserve memory|Encodes rows of data to preserve memory while sorting. (Technical background: Hop will store the lookup data as raw bytes in a custom storage object that uses a hashcode of the bytes as the key. More CPU cost related to calculating the hashcode, less memory needed.) |
| |Key and value are exactly one integer field|Preserves memory while executing a sort by . Note: Works only when "Preserve memory" is checked. Cannot be combined with the "Use sorted list" option. |
| |Use sorted list|Enable to store values using a sorted list; this provides better memory usage when working with data sets containing wide row. Note: Works only when "Preserve memory" is checked. Cannot be combined with the "Key and value are exactly one integer field" option. |
| |Get fields|Automatically fills in the names of all the available fields on the source side (A); you can then delete all the fields you don't want to use for lookup. |
| |Get lookup fields|Automatically inserts the names of all the available fields on the lookup side (B). You can then delete the fields you don't want to retrieve |
| |=== |
| |
| == Metadata Injection Support |
| |
| All fields of this transform support metadata injection. You can use this transform with ETL Metadata Injection to pass metadata to your pipeline at runtime. |
