How to set up SOLR parameter substitution in solrconfig.xml - solr

Question

This is my first question at stackoverflow so apologies in advance if I break any rules but I did study them and also made sure this isn't a duplicate question.
So, according to this http://yonik.com/solr-query-parameter-substitution/ one can set up a search handler in solrconfig in a way that the
request handler defaults, appends, and invariants configured for the
handler may reference request parameters
I have the following query which works just fine with curl
curl http://localhost:7997/solr/vb_popbio/select -d 'q=*:*&fq=bundle:pop_sample_phenotype AND phenotype_type_s:"insecticide%20resistance"
&rows=0&wt=json&json.nl=map&indent=true
&fq=phenotype_value_type_s:${PFIELD}&
&PGAP=5&PSTART=0&PEND=101&PFIELD="mortality rate"&
json.facet = {
pmean: "avg(phenotype_value_f)",
pperc: "percentile(phenotype_value_f,5,25,50,75,95)",
pmin: "min(phenotype_value_f)",
pmax: "max(phenotype_value_f)",
denplot : {
type : range,
field : phenotype_value_f,
gap : ${PGAP:0.1},
start: ${PSTART:0},
end: ${PEND:1}
}
}'
I have translated this query to a search handler configuration in solrconfig.xml so a user only has to provide the PFIELD, PGAP, PSTART and PEND parameters. Here's how the configuration for the handler looks
<!--A request handler to serve data for violin plots (limited to IR assays)-->
<requestHandler name="/irViolin" class="solr.SearchHandler">
<!-- default values for query parameters can be specified, these
will be overridden by parameters in the request
-->
<lst name="defaults">
<str name="echoParams">explicit</str>
<int name="rows">0</int>
<str name="df">text</str>
<str name="wt">json</str>
<str name="json.nl">map</str>
<str name="json.facet">{
pmean: "avg(phenotype_value_f)",
pperc: "percentile(phenotype_value_f,5,25,50,75,95)",
pmin: "min(phenotype_value_f)",
pmax: "max(phenotype_value_f)",
denplot : {
type : range,
field : phenotype_value_f,
gap: ${PGAP:0.1},
start: ${PSTART:0},
end: ${PEND:1}
}
}
</str>
</lst>
<lst name="appends">
<str name="fq">bundle:pop_sample_phenotype</str>
<str name="fq">phenotype_type_s:"insecticide resistance"</str>
<str name="fq">has_geodata:true</str>
<str name="fq">phenotype_value_type_s:${PFIELD:"mortality rate"}</str>
</lst>
<lst name="invariants">
</lst>
</requestHandler>
Notice that I provided default values for all the parameters otherwise SOLR will fail to load the configuration. The problem is that using a query like this
curl http://localhost:7997/solr/vb_popbio/irViolin?q=*:*&
&PGAP=5&PSTART=0&PEND=101&PFIELD="mortality rate"
is not working. SOLR will read the request parameters fine (I can see them on the debug output) but will ignore them and use the default values in the configuration instead.
SOLR version is 5.2.1.
I tried moving the configuration parameters to either defaults, appends or invariants but nothing is working. After researching this for the past 2 days I'm almost ready to give up and just build the whole query on-the-fly instead.
Any help will be greatly appreciated.
Many thanks

Answer 1

I think (the post) is too old, but using a search engine I arrived at this page. A simple solution was to escape the dollar symbol. After that, you should achieve your desired result.
Example:
<str name="json.facet">{
pmean: "avg(phenotype_value_f)",
pperc: "percentile(phenotype_value_f,5,25,50,75,95)",
pmin: "min(phenotype_value_f)",
pmax: "max(phenotype_value_f)",
denplot : {
type : range,
field : phenotype_value_f,
gap: $${PGAP:0.1},
start: $${PSTART:0},
end: $${PEND:1}
}
}
</str>

Answer 2

I'm not sure when the Config API came to Solr but if query parameter substitution does work when added to configoverlay.json
{
"requestHandler": {
"/myHandler": {
"name": "/myHandler",
"class": "solr.SearchHandler",
"defaults": {
"fl": "id,name,color,size",
},
"invariants": {
"rows": 10,
},
"appends": {
"json": "{filter:[\"color:${color:red}\",\"size:${size:M}\"]}"
}
}
}
}
Now you can pass URL parameters &color=green&size=XXL to the /MyHandler query.