Hi I want to fetch data from couchdb-view by applying reduce and pagination.
My view gives reduce function result as complex key as follows
{"rows":[
{"key":{"attribute":"Attribute1"},"value":20},
{"key":{"attribute":"Attribute2"},"value":1}
{"key":{"attribute":"Attribute3"},"value":1}
]}
I am trying to fetch data from couchdb using ektorp, check following code
PageRequest pageRequest = PageRequest.firstPage(10);
ViewQuery query = new ViewQuery()
.designDocId("_design/medesign")
.viewName("viewname")
.includeDocs(false)
.reduce(true)
.group(true);
Page<ViewResult> rs1 = db.queryForPage(query, pageRequest, ViewResult.class);
rs1.forEach(v -> {
System.out.println(v.getSize());
});
I am getting following error
org.ektorp.DbAccessException: com.fasterxml.jackson.databind.JsonMappingException:
Can not construct instance of org.ektorp.ViewResult:
no int/Int-argument constructor/factory method to deserialize from Number value (20)
at [Source: N/A; line: -1, column: -1]
CouchDB doesn't Give paginated details if you want paginated reduced data.
Request with paginated include docs
group=false & reduce=false & include_docs=true
URL : http://localhost:5984/dn_anme/_design/design_name/_view/viewname?include_docs=true&reduce=false&skip=0&group=false&limit=2
Response :
{
"total_rows":81,
"offset":0,
"rows":[
{
"id":"906a74b8019716f1240a7117580ec172",
"key":{
"attribute":"BuildArea"
},
"value":1,
"doc":{
"_id":"906a74b8019716f1240a7117580ec172",
"_rev":"3-7e0a1da0c2260040f8a9787636385785",
"country":"POL",
"recordStatus":"MATCHED"
}
},
{
"id":"906a74b8019716f1240a7117580eaefb",
"key":{
"attribute":"Area",
},
"value":1,
"doc":{
"_id":"906a74b8019716f1240a7117580eaefb",
"_rev":"3-165ea3a3ed07ad8cce1f3e095cd476b5",
"country":"POL",
"recordStatus":"MATCHED"
}
}
]
}
Request with Reduce
group=true& reduce=true& include_docs=false
URL : http://localhost:5984/dn_anme/_design/design_name/_view/viewname?include_docs=false&reduce=true&group=true&limit=2
Resoonse :
{
"rows":[
{
"key":[
"BuildArea"
],
"value":1
},
{
"key":[
"Area"
],
"value":1
}
]
}
Difference in between both Request:
Request with paginated include docs gives page data {"total_rows":81, "offset":0, rows":[{...},{...}]}
AND
Request with reduce give {"rows":[{...},{..}]}
How you can get paginated reduce data:
Step 1: Request rows_per_page + 1 rows from the view
Step 2: if in response one extra records than page_size then there are more records
Step 3: calculate and update skip value and got to step 1 for next page
Note: adding skip is not good option for lots of records instead of that find start key and add start key, its good for better perforamance