In the last “car sale application” related post we have described the result grouping functionality. Today I would like to show you how easily we can determine the groups amount and how to sort documents within every group.
Requirements specification
I would like to be able to create a grouping query, that will show me the number of generated groups and provide only one result within every group – the one with the lowest price in its year group.
New functionality request parameters description
What we need is:
- group.ngroups – boolean type parameter that allows us to include the number of generated groups
- group.sort – parameter describing how to sort documents within a group
Let’s create query
Using the query example from the previous post, let’s add two new parameters:
?q=audi+a4&group=true&group.field=year_group&group.limit=1&fl=id,mileage,make,model,year,price&group.ngroups=true&group.sort=price+asc
As you see, we’ve also set the group.limit parameter to 1 (in order to have the only one result within every group) and extended the value of fl parameter by adding the price field. As a result we have the response:
<lst name="grouped"> <lst name="year_group"> <int name="matches">5</int> <int name="ngroups">3</int> <arr name="groups"> <lst> <str name="groupValue">2002</str> <result name="doclist" numFound="2" start="0"> <doc> <str name="id">3</str> <str name="make">Audi</str> <int name="mileage">125000</int> <str name="model">A4</str> <float name="price">21300.0</float> <int name="year">2002</int> </doc> </result> </lst> <lst> <str name="groupValue">2003</str> <result name="doclist" numFound="2" start="0"> <doc> <str name="id">2</str> <str name="make">Audi</str> <int name="mileage">220000</int> <str name="model">A4</str> <float name="price">27800.0</float> <int name="year">2003</int> </doc> </result> </lst> <lst> <str name="groupValue">2006</str> <result name="doclist" numFound="1" start="0"> <doc> <str name="id">5</str> <str name="make">Audi</str> <int name="mileage">9900</int> <str name="model">A4</str> <float name="price">32100.0</float> <int name="year">2006</int> </doc> </result> </lst> </arr> </lst> </lst>
As we see in the response, we have a new element that shows us how many groups are generated:
<int name="ngroups">3</int>
We also have only one document in each year group – the car with the lowest price in its year group. You don’t believe me ? Look at the query responses from the previous post and compare the prices 🙂
The end
It was a fast review of yet two another grouping parameters. Big thanks to David Martin who gave me the subject by asking some questions in the previous post 🙂