Facet['fæsɪt]很难翻译，只能靠例子来理解了。Solr作者Yonik Seeley也给出更为直接的名字：导航（Guided Navigation）、参数化查询（Paramatic Search）。

facet-1

上面是比较直接的Faceted Search例子，品牌、产品特征、卖家，均是Facet。而Apple、Lenovo等品牌，就是Facet values或者说Constraints，而Facet values所带的统计值就是Facet count/Constraint count。

2、Facet使用

q = 超级本
facet = true
facet.field = 产品特性
facet.field = 品牌
facet.field = 卖家
http://.../select?q=超级本&facet=true&wt=json&facet.field=品牌&facet.field=产品特性&facet.field=卖家

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"facet_counts": {
"facet_fields": {
  "品牌": [
    "Apple", 4,
    "Lenovo", 39
      …]
  "产品特性": [
    "显卡", 42,
    "酷睿", 38
      …]

  …}}

也可以提交查询条件，设置fq(filter query)。

q = 电脑
facet = true
fq = 价格:[8000 TO *]
facet.mincount = 1 // fq将不符合的字段过滤后，会显示count为0
facet.field = 产品特性
facet.field = 品牌
facet.field = 卖家


`http://.../select?q=超级本&facet=true&wt=json&fq=价格:[8000 TO *]&facet.mincount=1&facet.field=品牌&facet.field=产品特性&facet.field=卖家

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"facet_counts": {
"facet_fields": {
  "品牌": [
    "Apple", 4,
    "Lenovo", 10
      …]
  "产品特性": [
    "显卡", 11,
    "酷睿", 20
      …]

  …}}

如果用户选择了Apple这个分类，查询条件中需要添加另外一个fq查询条件，并移除Apple所在的facet.field。

http://.../select?q=超级本&facet=true&wt=json&fq=价格:[8000 TO *]&fq=品牌:Apple&facet.mincount=1 &facet.field=产品特性&facet.field=卖家

3、Facet参数

  • facet.prefix: 限制constaints的前缀
  • facet.mincount=0: 限制constants count的最小返回值，默认为0
  • facet.sort=count: 排序的方式，根据count或者index
  • facet.offset=0: 表示在当前排序情况下的偏移，可以做分页
  • facet.limit=100: constraints返回的数目
  • facet.missing=false: 是否返回没有值的field
  • facet.date: Deprecated, use facet.range
  • facet.query: 指定一个查询字符串作为Facet Constraint
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facet.query = rank:[* TO 20]
facet.query = rank:[21 TO *]
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 <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>
...
  • **facet.range:

http://.../select?&facet=true&facet.range=price&facet.range.start=5000&facet.range.end=8000&facet.range.gap=1000

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"facet_counts":{
 "facet_ranges":{
   "price":{
     "counts”:[
       "5000.0”,5,
       "6000.0”,2,
       "7000.0”,3,],
     "gap":1000.0,
     "start":5000.0,
     "end":8000.0}}}}

WARNING:

range范围是左闭右开，[start, end)

  • facet.pivot

这个是Solr 4.0的新特性，pivot和facet一样难理解，还是用例子来讲吧。

Syntax: facet.pivot=field1,field2,field3…
e.g.: facet.pivot=comment_user, grade

#docs #docs grade:好 #docs 等级:中 #docs 等级:差
comment_user:1 10 8 1 1
comment_user:2 20 18 2 0
comment_user:3 15 12 2 1
comment_user:4 18 15 2 1 
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"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":[{
     ...

没有pivot机制的话，要做到上面那点可能需要多次查询：

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.
上面那个解释很不错，只能理解不能翻译。

参考资料：