LIBLINEAR model lacks weight(s) when training for SolrFeatures in LTR

[Zheng Lin Edwin Yeo]

Hi,

I am using Solr 7.4.0, and using LIBLINEAR to do the training for the LTR
model based on this example:
https://github.com/bloomberg/lucene-solr/blob/master-ltr/solr/contrib/ltr/example/README.md

However, I found that when I wanted to train for solr filter query with the
class SolrFeature, I will get the following error saying that the model
lacks weight(s):

Exception: Status: 400 Bad Request
Response: {
  "responseHeader":{
    "status":400,
    "QTime":1},
  "error":{
    "metadata":[
      "error-class","org.apache.solr.common.SolrException",
      "root-error-class","org.apache.solr.ltr.model.ModelException"],
    "msg":"org.apache.solr.ltr.model.ModelException: Model myModel lacks
weight(s) for [category]",

This is how I define it in my feature JSON file:

  {
    "store" : "myFeatures",
    "name" : "category",
    "class" : "org.apache.solr.ltr.feature.SolrFeature",
    "params" : {
"fq": ["{!terms f=category}book"]
}
  }

What could be the reason that causes this, and how can we resolve this
issue?

Regards,
Edwin