Add support for json params object (#28)

* Add support for json params object
* Add test and README example for json params object

Author: takanuva15

README.md

@@ -55,6 +55,9 @@ query := solr.NewQuery(solr.NewDisMaxQueryParser().
         solr.NewQueryFacet("high_popularity").
             Query("popularity:[8 TO 10]"),
     ).
+    Params(solr.M{
+        "spellcheck.q": "solr rocks",
+    }).
     Sort("score").
     Offset(1).
     Limit(10).

query.go

@@ -16,11 +16,13 @@ type Query struct {
 	// responseWriter        string // wt
 
 	// supported params in json request api
+	// https://solr.apache.org/guide/8_7/json-request-api.html#supported-properties-and-syntax
 	sort    string
 	offset  int      // start
 	limit   int      // rows
 	filters []string // fq
 	fields  []string // fl
+	params  M        // additional params to add verbatim to request query params
 
 	// query is the main query
 	query string
@@ -68,6 +70,10 @@ func (q *Query) BuildQuery() M {
 		qm["fields"] = q.fields
 	}
 
+	if len(q.params) > 0 {
+		qm["params"] = q.params
+	}
+
 	if len(q.facets) > 0 {
 		facets := M{}
 		for _, facet := range q.facets {
@@ -110,6 +116,12 @@ func (q *Query) Fields(fields ...string) *Query {
 	return q
 }
 
+// Params sets the params param
+func (q *Query) Params(params M) *Query {
+	q.params = params
+	return q
+}
+
 // Facets sets the facet query
 func (q *Query) Facets(facets ...Faceter) *Query {
 	q.facets = facets

query_test.go

@@ -43,6 +43,9 @@ func TestQuery(t *testing.T) {
 		Limit(10).
 		Filters("inStock:true").
 		Fields("name", "price").
+		Params(solr.M{
+			"spellcheck.q": "sports",
+		}).
 		BuildQuery()
 
 	expect := solr.M{
@@ -54,6 +57,9 @@ func TestQuery(t *testing.T) {
 		"filter": []string{"inStock:true"},
 		"limit":  10,
 		"offset": 1,
+		"params": solr.M{
+			"spellcheck.q": "sports",
+		},
 		"queries": solr.M{
 			"query_filters": []solr.M{
 				{"#size_tag": solr.M{"field": solr.M{"f": "size", "query": "XL"}}},
@@ -66,3 +72,24 @@ func TestQuery(t *testing.T) {
 
 	a.Equal(expect, got)
 }
+
+// Ensure params can handle arbitrary arguments (like those used in parameter dereferencing)
+// https://solr.apache.org/guide/solr/9_7/query-guide/local-params.html#parameter-dereferencing
+func TestQueryParamsArbitraryArgs(t *testing.T) {
+	a := assert.New(t)
+	got := solr.NewQuery(solr.NewDisMaxQueryParser().
+		Query("$customQueryArg").BuildParser()).
+		Params(solr.M{
+			"customQueryArg": "solr rocks",
+		}).
+		BuildQuery()
+
+	expect := solr.M{
+		"params": solr.M{
+			"customQueryArg": "solr rocks",
+		},
+		"query": "{!dismax v=$customQueryArg}",
+	}
+
+	a.Equal(expect, got)
+}