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      Custom JavaScript Stages for Query Pipelines

      The JavaScript Query stage allows you to write a custom processing logic using JavaScript to manipulate search requests and responses. The first time that the pipeline is run, Fusion compiles the JavaScript program into Java bytecode using the JDK’s JavaScript engine.

      The JavaScript Query stage allows you to run JavaScript functions over search requests and responses by manipulating variables called "request" and "response" which are Request objects and Response objects, respectively.

      JavaScript Query Stage Global Variables

      JavaScript is a lightweight scripting language. The JavaScript in a JavaScript stage is standard ECMAScript. What a JavaScript program can do depends on the container in which it runs. For a JavaScript Query stage, the container is a Fusion query pipeline. The following global pipeline variables are available:

      Name Type Description

      request

      The Solr query information.

      response

      The Solr response information.

      collection

      String

      The name of the Fusion collection being indexed or queried.

      solrServer

      The Solr server instance that manages the pipeline’s default Fusion collection. All indexing and query requests are done by calls to methods on this object. See SolrClient for details.

      solrServerFactory

      The SolrCluster server used for lookups by collection name which returns a Solr server instance for a that collection, e.g.
      var productsSolr = solrServerFactory.getSolrServer("products");.

      QueryRequestAndResponse

      Used to create query pipeline requests and responses.

      JSONResponse

      Returns list of info as a string.

      The now-deprecated global variable _context refers to the same object as ctx.

      Syntax Variants

      JavaScript stages can be written using legacy syntax or function syntax. The key difference between these syntax variants is how the "global variables" are used and interpreted. While using legacy syntax, these variables are used as global variables. With function syntax, however, these variables are passed as function parameters.

      Legacy Syntax

      request.addParam("foo", "bar");

      Function Syntax

      function(request,response) {
         request.addParam("foo", "bar");
      }
      Function syntax is used for the examples in this document.

      Global variable logger

      The global variable named logger writes messages to the log file of the server running the pipeline. This variable is truly global and does not need to be declared as part of the function parameter list.

      Since Fusion’s API service does the query pipeline processing, these log messages go into the log file: {fusion_path}/var/log/api/api.log. There are 5 methods available, which each take either a single argument (the string message to log) or two arguments (the string message and an exception to log). The five methods are, "debug", "info", "warn", and "error".