1 、什麼是Faceted Search

Facet['fæsɪt]很難翻譯，只能靠例子來理解了。Solr作者Yonik Seeley也給出更為直接的名字：導航（Guided Navigation）、引數化查詢（Paramatic Search）。

上面是比較直接的Faceted Search例子，品牌、產品特徵、賣家，均是 Facet 。而Apple、Lenovo等品牌，就是 Facet values 或者說 Constraints ，而Facet values所帶的統計值就是 Facet count/Constraint count 。

2 、Facet 使用

q = 超級本 
facet = true 
facet.field = 產品特性 
facet.field = 品牌 
facet.field = 賣家

http://…/select?q=超級本&facet=true&wt=json

&facet.field=品牌&facet.field=產品特性&facet.field=賣家

也可以提交查詢條件，設定fq(filter query)。

q = 電腦 
facet = true 
fq = 價格:[8000 TO *] 
facet.mincount = 1 // fq將不符合的欄位過濾後，會顯示count為0 
facet.field = 產品特性 
facet.field = 品牌 
facet.field = 賣家

http://…/select?q=超級本&facet=true&wt=json

&fq=價格:[8000 TO *]&facet.mincount=1

&facet.field=品牌&facet.field=產品特性&facet.field=賣家

"facet_counts": {
"facet_fields": {
  "品牌": [
    "Apple", 4,
    "Lenovo", 39
      …]
  "產品特性": [
    "顯示卡", 42,
    "酷睿", 38
      …]
 
  …}}

如果使用者選擇了Apple這個分類，查詢條件中需要新增另外一個fq查詢條件，並移除Apple所在的facet.field。

http://…/select?q=超級本&facet=true&wt=json

&fq=價格:[8000 TO *]&fq=品牌:Apple&facet.mincount=1

&facet.field= 品牌 &facet.field=產品特性&facet.field=賣家

3 、Facet 引數

facet.prefix  –  限制constaints的字首

facet.mincount=0 –  限制constants count的最小返回值，預設為0

facet.sort=count –  排序的方式，根據count或者index

facet.offset=0  –  表示在當前排序情況下的偏移，可以做分頁

facet.limit=100 –  constraints返回的數目

facet.missing=false –  是否返回沒有值的field

facet.date –  Deprecated, use facet.range

facet.query

指定一個查詢字串作為Facet Constraint

facet.query = rank:[* TO 20]

facet.query = rank:[21 TO *]

"facet_counts": {
"facet_fields": {
  "品牌": [
    "Apple", 4,
    "Lenovo", 10
      …]
  "產品特性": [
    "顯示卡", 11,
    "酷睿", 20
      …]
 
  …}}

facet.range

http://…/select?&facet=true

&facet.range=price

&facet.range.start=5000

&facet.range.end=8000

&facet.range.gap=1000

<result numFound="27" ... />
 ...
 <lst name="facet_counts">
 <lst name="facet_queries">
   <int name="rank:[* TO 20]">2</int>
   <int name="rank:[21 TO *]">15</int>
 </lst>
...

WARNING:  range範圍是左閉右開，[start, end)

facet.pivot

這個是Solr 4.0的新特性，pivot和facet一樣難理解，還是用例子來講吧。

Syntax:  facet.pivot=field1,field2,field3...

e.g.  facet.pivot=comment_user, grade

"facet_counts":{
"facet_pivot":{
 "comment_user, grade ":[{
   "field":"comment_user",
   "value":"1",
   "count":10,
   "pivot":[{
     "field":"grade",
     "value":"好",
     "count":8}, {
     "field":"grade",
     "value":"中",
     "count":1}, {
     "field":"grade",
     "value":"差",
     "count":1}]
   }, {
     "field":" comment_user ",
     "value":"2",
     "count":20,
     "pivot":[{
      …

沒有pivot機制的話，要做到上面那點可能需要多次查詢：

http://...q= comment&fq= grade:好&facet=true&facet.field=comment_user

http://...q=comment&fq=grade:中&facet=true&facet.field=comment_user

http://...q=comment&fq=grade:差&facet=true&facet.field=comment_user

Facet.pivot -  Computes a Matrix of Constraint Counts across multiple Facet Fields. by Yonik Seeley.

上面那個解釋很不錯，只能理解不能翻譯。