CouchDB Map/Reduce view query from Ektorp

问题:

I'm trying to execute a query from java against a Map/Reduce view I have created on the CouchDB. My map function looks like the following:

function(doc) {
  if(doc.type == 'SPECIFIC_DOC_TYPE_NAME' && doc.userID){
    for(var g in doc.groupList){
        emit([doc.userID,doc.groupList[g].name],1);
    }
  }
}

and Reduce function:

  function (key, values, rereduce) {
        return sum(values); 
}

The view seems to be working when executed from the Futon interface (without keys specified though). What I'm trying to do is to count number of some doc types belonging to a single group. I want to query that view using 'userID' and name of the group as a keys.

I'm using Ektorp library for managing CouchDB data, if I execute this query without keys it returns the scalar value, otherwise it just prints an error saying that for reduce query group=true must be specified.

I have tried the following:

ViewQuery query = createQuery("some_doc_name");
        List<String> keys = new ArrayList<String>();
        keys.add(grupaName);
        keys.add(uzytkownikID);
        query.group(true);
        query.groupLevel(2);
        query.dbPath(db.path());
        query.designDocId(stdDesignDocumentId);
        query.keys(keys);
        ViewResult r = db.queryView(query);
        return r.getRows().get(0).getValueAsInt();

above example works without 'keys' specified. I have other queries working with ComplexKey like eg:

ComplexKey key = ComplexKey.of(userID);
return queryView("list_by_userID",key);

but this returns only a list of type T (List) - using CouchDbRepositorySupport of course - and cannot be used with reduce type queries (from what I know).

Is there any way to execute the query with reduce function specified and a complex key with 2 or more values using Ektorp library? Any examples highly appreciated.

回答1:

Addition to Kris's answer:

Note that ViewQuery.keys() is used when you want to query for documents matching a set of keys, not for finding document(s) with a complex key.

Like Kris's answer, the following samples will get document(s) matching the specified key (not "keys")

viewQuery.key("hello");                             // simple key
viewQuery.key(documentSlug);                        // simple key
viewQuery.key(new String[] { userID, groupName });  // complex key, using array
viewQuery.key(ComplexKey.of(userID, groupName));    // complex key, using ComplexKey

The following samples, on the other hand, will get document(s) matching the specified keys, where each key may be either a simple key or a complex key:

// simple key: in essence, same as using .key()
viewQuery.keys(ImmutableSet.of("hello"));
viewQuery.keys(ImmutableSet.of(documentSlug1));
// simple keys
viewQuery.keys(ImmutableSet.of("hello", "world"));
viewQuery.keys(ImmutableSet.of(documentSlug1, documentSlug2));
// complex key: in essence, same as using .key()
viewQuery.keys(ImmutableSet.of(
    new String[] { "hello", "world" } ));
viewQuery.keys(ImmutableSet.of(
    new String[] { userID1, groupName1 } ));
// complex keys
viewQuery.keys(ImmutableSet.of(
    new String[] { "hello", "world" },
    new String[] { "Mary", "Jane" } ));
viewQuery.keys(ImmutableSet.of(
    new String[] { userID1, groupName1 },
    new String[] { userID2, groupName2 } ));
// a simple key and a complex key. while technically possible,
// I don't think anybody actually does this
viewQuery.keys(ImmutableSet.of(
    "hello",
    new String[] { "Mary", "Jane" } ));

Note: ImmutableSet.of() is from guava library.

new Object[] { ... } seems to have same behavior as ComplexKey.of( ... )

Also, there are startKey() and endKey() for querying using partial key. To send an empty object {}, use ComplexKey.emptyObject(). (only useful for partial key querying)

回答2:

Ok, I've found the solution using trial and error approach:

public int getNumberOfDocsAssigned(String userID, String groupName) {
        ViewQuery query = createQuery("list_by_userID")
                .group(true)
                .dbPath(db.path())
                .designDocId(stdDesignDocumentId)
                .key(new String[]{userID,groupName});
        ViewResult r = db.queryView(query);
        return r.getRows().get(0).getValueAsInt();
    }

So, the point is to send the complex key (not keys) actually as a single (but complex) key containing the String array, for some reason method '.keys(...)' didn't work for me (it takes a Collection as an argument). (for explanation on difference between .key() and .keys() see Hendy's answer)

This method counts all documents assigned to the specific user (specified by 'userID') and specific group (specified by 'groupName').

Hope that helps anybody executing map/reduce queries for retrieving scalar values from CouchDB using Ektorp query.