How to reference other documents in a couchDB view (joining like functionality)

Question

We have a CouchDB representation of an XML database which we use to power a javascript based front-end for manipulating the XML documents. The basic structure is a simple 3 level hierarchy. i.e.

A -> B -> C

• A: Parent document (type A)
• B: any number of child documents of parent type A
• C: any number of child documents of parent type B

We represent these 3 document types in CouchDB with a type attribute:

e.g.

{
"_id":"llgc-id:433",
"_rev":"1-3760f3e01d7752a7508b047e0d094301",
"type":"A",
"label":"Top Level A document",
"logicalMap":{
    "issues":{
        "1":{
            "URL":"http://hdl.handle.net/10107/434-0",
            "FILE":"llgc-id:434"
        },
        "2":{
            "URL":"http://hdl.handle.net/10107/467-0",
            "FILE":"llgc-id:467" 
        etc...
        }
    }
}
}


{
"_id":"llgc-id:433",
"_rev":"1-3760f3e01d7752a7508b047e0d094301",
"type":"B",
"label":"a B document",
}

What I want to do is produce a view which returns documents just like the A type but includes the label attribute from the B document within the logicalMap list e.g.

{
"_id":"llgc-id:433",
"_rev":"1-3760f3e01d7752a7508b047e0d094301",
"type":"A",
"label":"Top Level A document",
"logicalMap":{
    "issues":{
        "1":{
            "URL":"http://hdl.handle.net/10107/434-0",
            "FILE":"llgc-id:434",
            "LABEL":"a B document"
        },
        "2":{
            "URL":"http://hdl.handle.net/10107/467-0",
            "FILE":"llgc-id:467",
            "LABEL":"another B document" 
        etc...
        }
    }
}
}

I'm struggling to get my head around the best way to perform this. It looks like it should be fairly simple though!

Answer 1

Have a look at the "Linked Document' Section in http://wiki.apache.org/couchdb/Introduction_to_CouchDB_views#Linked_documents

function(doc) {
    //....
    if (doc.logicalMap.issues) {
        for (var i in doc.logicalMap.issues) {
            emit([doc._id,doc.logicalMap.issues[i]['FILE']], 
                                 {_id: doc.logicalMap.issues[i]['FILE']});
        }
    }
}

(untested)

Then query with include_docs=true